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@incollection{maia_collagen_2024, address = {Cham}, title = {Collagen fibril reinforcement in connective tissue extracellular matrices}, isbn = {978-3-030-92090-6}, url = {https://link.springer.com/10.1007/978-3-031-56363-8_6}, abstract = {The connective tissues such as tendons contain an extracellular matrix (ECM) comprising collagen fibrils scattered within the ground substance. These fibrils are instrumental in lending mechanical stability to tissues. Unfortunately, our understanding of how collagen fibrils reinforce the ECM remains limited, with no direct experimental evidence substantiating current theories. Earlier theoretical studies on collagen fibril reinforcement in the ECM have relied predominantly on the assumption of uniform cylindrical fibers, which is inadequate for modelling collagen fibrils, which possessed tapered ends. Recently, Topçu and colleagues published a paper in the International Journal of Solids and Structures, presenting a generalized shear-lag theory for the transfer of elastic stress between the matrix and fibers with tapered ends. This paper is a positive step towards comprehending the mechanics of the ECM and makes a valuable contribution to formulating a complete theory of collagen fibril reinforcement in the ECM.}, language = {en}, urldate = {2023-07-19}, booktitle = {Handbook of the {Extracellular} {Matrix}: {Biologically}-{Derived} {Materials}}, publisher = {Springer International Publishing}, author = {Goh, Kheng Lim and Topçu, Murat and Madabhushi, Gopal S. P. and Staat, Manfred}, editor = {Maia, Fatima Raquel Azevedo and Oliveira, J. Miguel and Reis, Rui L.}, month = jul, year = {2024}, doi = {10.1007/978-3-031-56363-8_6}, pages = {89--108}, }
@article{zheng_discontinuous_2024, title = {Discontinuous fracture behaviors and constitutive model of sandstone specimens containing non-parallel prefabricated fissures under uniaxial compression}, volume = {131}, issn = {01678442}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0167844224001228}, doi = {10.1016/j.tafmec.2024.104373}, language = {en}, urldate = {2024-03-18}, journal = {Theoretical and Applied Fracture Mechanics}, author = {Zheng, Menghao and Liang, Yunpei and Staat, Manfred and Li, Quangui and Li, Jianbo}, month = jun, year = {2024}, pages = {104373}, }
@book{digel_4th_2024, address = {Duisburg, Germany}, series = {{YRA} {MedTech} {Symposium}}, title = {4th {YRA} {MedTech} {Symposium} 2024: {February} 1 / 2024 / {FH} {Aachen}}, copyright = {Creative Commons Attribution Non Commercial No Derivatives 4.0 International}, isbn = {978-3-940402-65-3}, shorttitle = {4th {YRA} {MedTech} {Symposium} 2024}, url = {https://duepublico2.uni-due.de/receive/duepublico_mods_00081475}, abstract = {The 4th YRA MedTech Symposium is jointly organized by the FH Aachen, the University of Duisburg-Essen, the Hochschule Hamm Lippstadt and the Westfälische Hochschule.}, language = {en}, number = {4}, urldate = {2024-01-28}, publisher = {University of Duisburg-Essen, Germany}, collaborator = {Digel, Ilya and Staat, Manfred and Trzewik, Jürgen and Sielemann, Stefanie and Erni, Daniel and Zylka, Waldemar}, year = {2024}, note = {Publisher: DuEPublico: Duisburg-Essen Publications online, University of Duisburg-Essen, Germany}, keywords = {610}, }
@article{lin_comparative_2023, title = {Comparative analysis of various hyperelastic models and element types for finite element analysis}, volume = {7}, issn = {2411-9660}, url = {https://www.mdpi.com/2411-9660/7/6/135}, doi = {10.3390/designs7060135}, abstract = {This study aims to evaluate the precision of nine distinct hyperelastic models using experimental data sourced from the existing literature. These models rely on parameters obtained through curve-fitting functions. The complexity in finite element models of elastomers arises due to their nonlinear, incompressible behaviour. To achieve accurate representations, it is imperative to employ sophisticated hyperelastic models and appropriate element types and formulations. Prior published work has primarily focused on the comparison between the fitting models and the experimental data. Instead, in this study, the results obtained from finite element analysis are compared against the original data to assess the impact of element formulation, strain range, and mesh type on the ability to accurately predict the response of elastomers over a wide range of strain values. This comparison confirms that the element formulation and strain range can significantly influence result accuracy, yielding different responses in various strain ranges also because of the limitation with the curve fitting tools.}, language = {en}, number = {6}, urldate = {2024-03-20}, journal = {Designs}, author = {Lin, Po-Sen and Le Roux De Bretagne, Olivier and Grasso, Marzio and Brighton, James and StLeger-Harris, Chris and Carless, Owen}, month = nov, year = {2023}, pages = {135}, }
@article{defosse_dental_2022, title = {Dental strain on maxillary incisors during tracheal intubation with double-lumen tubes and different laryngoscopy techniques - a blinded manikin study}, volume = {36}, issn = {1053-0770}, url = {https://www.sciencedirect.com/science/article/abs/pii/S1053-0770(22)00126-4 https://linkinghub.elsevier.com/retrieve/pii/S1053077022001264}, doi = {10.1053/j.jvca.2022.02.017}, abstract = {Objectives : To quantify dental forces during double-lumen tube intubations with different laryngoscopy techniques. Design : Experimental biomechanical manikin study. Setting : Two German university hospitals. Participants : 104 anaesthetists with varying levels of experience. Interventions : Participants performed a sequence of intubations on a manikin equipped with hidden forces sensors in the maxillary incisors. Different laryngoscopy techniques were evaluated under normal and difficult airway conditions. Direct laryngoscopy was compared to different videolaryngoscopy techniques: the C-MAC with a Macintosh blade, the GlideScope and the KingVision with hyperangulated blades. Measurements and Main Results : A total of 624 intubations were evaluated. In normal airway conditions, the median (IQR [range]) peak forces were significantly lower when the GlideScope (15.7 (11.3-22.0[2.1-110.5]) N) was used compared to direct laryngoscopy (21.0 (14.1-28.5[4.7-168.6]) N) (p=0.007). In difficult airways, resulting forces were reduced using hyperangulated videolaryngoscopes (GlideScope -13.7 N (p{\textless}0.001); KingVision -11.9 N (p{\textless}0.001)) compared to direct laryngoscopy, respectively. The time to intubation was prolonged with the use of the KingVision (25.5 (17.1-41.9[9.2-275.0])) s (p{\textless}0.001)) in comparison to direct laryngoscopy (20.8 (15.9-27.4[8.7-198.6]) s). The C-MAC demonstrated the shortest time to intubation. Conclusions : While hyperangulated videolaryngoscopes improve dental strain, clinicians should also consider the time to intubation, which is shortest with non-hyperangulated videoblades, when choosing a laryngoscopy technique on an individual patient basis.}, number = {8}, journal = {Journal of Cardiothoracic and Vascular Anesthesia}, author = {Defosse, Jerome and Kleinschmidt, Joris and Schmutz, Axel and Torsten, Loop and Staat, Manfred and Gatzweiler, Karl-Heinz and Wappler, Frank and Schieren, Mark}, month = aug, year = {2022}, note = {PIMD: 35339355}, pages = {3021--3027}, }
@inproceedings{tran_limit_2022, address = {Hanoi}, title = {Limit and shakedown analysis of structures underrandom strength}, volume = {1}, url = {https://www.researchgate.net/publication/366053333_Shakedown_analysis_of_structures_under_random_strength_by_chance_constrained_programming}, abstract = {Direct methods comprising limit and shakedown analysis is a branch of computational mechanics. It plays a significant role in mechanical and civil engineering design. The concept of direct method aims to determinate the ultimate load bearing capacity of structures beyond the elastic range. For practical problems, the direct methods lead to nonlinear convex optimization problems with a large number of variables and constraints. If strength and loading are random quantities, the problem of shakedown analysis is considered as stochastic programming. This paper presents a method so called chance constrained programming, an effective method of stochastic programming, to solve shakedown analysis problem under random condition of strength. In this our investigation, the loading is deterministic, the strength is distributed as normal or lognormal variables}, language = {Englisch}, booktitle = {Solid {Mechanics}, {Rock} {Mechanics}, {Artificial} {Intelligence}, {Teaching} and {Training}}, publisher = {Nhà xuất bản Khoa học Tự nhiên và Công nghệ, Hà Nội}, author = {Trần, Ngọc Trình and Trịnh, Tự Lực and Ngọc, Tiến Đào and Khuyến, Trương Mạnh and Văn, Tấn Giáp and Đinh, Thuý Hà and Staat, Manfred}, year = {2022}, pages = {510--518}, }
@inproceedings{staat_strain_2022, address = {Hanoi, Vietnam}, title = {Strain based failure criteria for rocks}, volume = {1}, url = {https://www.researchgate.net/publication/366053178_Strain_based_failure_criteria_for_rocks}, abstract = {When confining pressure is low or absent, extensional fractures are typical, with fractures occurring on unloaded planes in rock. These “paradox” fractures can be explained by a phenomenological extension strain failure criterion. In the past, a simple empirical criterion for fracture initiation in brittle rock has been developed. But this criterion makes unrealistic strength predictions in biaxial compression and tension. A new extension strain criterion overcomes this limitation by adding a weighted principal shear component. The weight is chosen, such that the enriched extension strain criterion represents the same failure surface as the Mohr–Coulomb (MC) criterion. Thus, the MC criterion has been derived as an extension strain criterion predicting failure modes, which are unexpected in the understanding of the failure of cohesive-frictional materials. In progressive damage of rock, the most likely fracture direction is orthogonal to the maximum extension strain. The enriched extension strain criterion is proposed as a threshold surface for crack initiation CI and crack damage CD and as a failure surface at peak P. Examples show that the enriched extension strain criterion predicts much lower volumes of damaged rock mass compared to the simple extension strain criterion.}, language = {Englisch}, booktitle = {Solid {Mechanics}, {Rock} {Mechanics}, {Artificial} {Intelligence}, {Teaching} and {Training}}, publisher = {Nhà xuất bản Khoa học Tự nhiên và Công nghệ, Hà Nội}, author = {Staat, Manfred and Trần, Ngọc Trình}, year = {2022}, pages = {500--509}, }
@article{tran_direct_2021, title = {Direct plastic structural design under random strength and random load by chance constrained programming}, volume = {85}, copyright = {All rights reserved}, issn = {0997-7538}, url = {https://linkinghub.elsevier.com/retrieve/pii/S0997753820304940}, doi = {10.1016/j.euromechsol.2020.104106}, abstract = {A new formulation to calculate shakedown limit load of structures under stochastic conditions of strength and loading is developed. Direct structural reliability design is based on the required failure probabilities by chance constrained programming, which is an effective approach of stochastic programming if it can be formulated as an equivalent deterministic optimization problem.}, number = {1}, journal = {European Journal of Mechanics - A/ Solids}, author = {Trần, Ngọc Trình and Staat, Manfred}, month = jan, year = {2021}, note = {ZSCC: NoCitationData[s0]}, keywords = {chance constrained programming, limit analysis, lower bound, reliability, shakedown analysis, stochastic programming, upper bound}, pages = {104106}, }
@article{hackl_comma_2021, title = {A "comma sign"-directed subscapularis repair in anterosuperior rotator cuff tears yields biomechanical advantages in a cadaveric model.}, volume = {49}, copyright = {All rights reserved}, issn = {1552-3365}, url = {http://journals.sagepub.com/doi/10.1177/03635465211031506 http://www.ncbi.nlm.nih.gov/pubmed/34398639}, doi = {10.1177/03635465211031506}, abstract = {BACKGROUND Additional stabilization of the "comma sign" in anterosuperior rotator cuff repair has been proposed to provide biomechanical benefits regarding stability of the repair. PURPOSE This in vitro investigation aimed to investigate the influence of a comma sign-directed reconstruction technique for anterosuperior rotator cuff tears on the primary stability of the subscapularis tendon repair. STUDY DESIGN Controlled laboratory study. METHODS A total of 18 fresh-frozen cadaveric shoulders were used in this study. Anterosuperior rotator cuff tears (complete full-thickness tear of the supraspinatus and subscapularis tendons) were created, and supraspinatus repair was performed with a standard suture bridge technique. The subscapularis was repaired with either a (1) single-row or (2) comma sign technique. A high-resolution 3D camera system was used to analyze 3-mm and 5-mm gap formation at the subscapularis tendon-bone interface upon incremental cyclic loading. Moreover, the ultimate failure load of the repair was recorded. A Mann-Whitney test was used to assess significant differences between the 2 groups. RESULTS The comma sign repair withstood significantly more loading cycles than the single-row repair until 3-mm and 5-mm gap formation occurred (P≤ .047). The ultimate failure load did not reveal any significant differences when the 2 techniques were compared (P = .596). CONCLUSION The results of this study show that additional stabilization of the comma sign enhanced the primary stability of subscapularis tendon repair in anterosuperior rotator cuff tears. Although this stabilization did not seem to influence the ultimate failure load, it effectively decreased the micromotion at the tendon-bone interface during cyclic loading. CLINICAL RELEVANCE The proposed technique for stabilization of the comma sign has shown superior biomechanical properties in comparison with a single-row repair and might thus improve tendon healing. Further clinical research will be necessary to determine its influence on the functional outcome.}, number = {12}, journal = {The American journal of sports medicine}, author = {Hackl, Michael and Buess, Eduard and Kammerlohr, Sandra and Nacov, Julia and Staat, Manfred and Leschinger, Tim and Müller, Lars Peter and Wegmann, Kilian}, month = oct, year = {2021}, pmid = {34398639}, note = {ZSCC: NoCitationData[s0] }, keywords = {arthroscopy, biomechanics, comma sign, rotator cuff repair, shoulder, subscapularis}, pages = {3212--3217}, }
@article{hackl_intratendinous_2021, title = {Intratendinous strain variations of the supraspinatus tendon depending on repair technique: {A} biomechanical analysis regarding the cause of medial cuff failure}, copyright = {All rights reserved}, issn = {0363-5465}, url = {http://journals.sagepub.com/doi/10.1177/03635465211006138}, doi = {10.1177/03635465211006138}, abstract = {Background: Double-row (DR) and transosseous-equivalent (TOE) techniques for rotator cuff repair offer more stability and promote better tendon healing compared with single-row (SR) repairs and are preferred by many surgeons. However, they can lead to more disastrous retear patterns with failure at the medial anchor row or the musculotendinous junction. The biomechanics of medial cuff failure have not been thoroughly investigated thus far. Purpose: To investigate the intratendinous strain distribution within the supraspinatus tendon depending on repair technique. Study Design: Controlled laboratory study. Methods: Twelve fresh-frozen cadaveric shoulders were used. The intratendinous strain within the supraspinatus tendon was analyzed in 2 regions—(1) at the footprint at the greater tuberosity and (2) medial to the footprint up to the musculotendinous junction—using a high-resolution 3-dimensional camera system. Testing was performed at submaximal loads of 40 N, 60 N, and 80 N for intact tendons, after SR repair, after DR repair, and after TOE repair. Results: The tendon strain of the SR group differed significantly in both regions from that of the intact tendons and the TOE group at 40 N (P ≤ .043) and from the intact tendons, the DR group, and the TOE group at 60 N and 80 N (P ≤ .048). SR repairs showed more tendon elongation at the footprint and less elongation medial to the footprint. DR and TOE repairs did not provide significant differences in tendon strain when compared with the intact tendons. However, the increase in tendon strain medial to the footprint from 40 N to 80 N was significantly more pronounced in the DR and TOE group (P ≤ .029). Conclusion: While DR and TOE repair techniques more closely reproduced the strains of the supraspinatus tendon than did SR repair in a cadaveric model, they showed a significantly increased tendon strain at the musculotendinous junction with higher loads in comparison with the intact tendon. Clinical Relevance: DR and TOE rotator cuff reconstructions lead to a more anatomic tendon repair. However, their use has to be carefully evaluated whenever tendon quality is diminished, as they lead to a more drastic increase in tendon strain medial to the footprint, putting these repairs at risk of medial cuff failure.}, journal = {The American Journal of Sports Medicine}, author = {Hackl, Michael and Nacov, Julia and Kammerlohr, Sandra and Staat, Manfred and Buess, Eduard and Leschinger, Tim and Müller, Lars P. and Wegmann, Kilian}, month = apr, year = {2021}, pmid = {33872064}, note = {ZSCC: NoCitationData[s0]}, keywords = {biomechanics, double row, intratendinous strain variations, medial cuff failure, medial row failure, rotator cuff repair, rotator cuff tear, single row, supraspinatus, suture bridge}, pages = {1--7}, }
@incollection{huneau_comparative_2019, edition = {1}, title = {A comparative study on hyperelastic constitutive models on rubber: {State} of the art after 2006}, isbn = {978-0-429-32471-0}, shorttitle = {A comparative study on hyperelastic constitutive models on rubber}, url = {https://www.taylorfrancis.com/books/9781000627770/chapters/10.1201/9780429324710-42}, abstract = {The micromechanically based network models are known to be superior over the purely phe- nomenological models in the analysis of unfilled rubber. However, various factors play a crucial role in the selection of the appropriate constitutive model for the analysis of technical rubbers. These are; (i) the number of available experiments under various loading conditions, (ii) maximum stretch level expected in the critical loading scenarios of the rubber component, and (iii) percentage of fillers and additives that might distort the mechanical response from that of an ideal rubber. Moreover, the number of material parameters to be identified should be as low as possible and the parameters should be physically interpretable. 12 years have passed since the celebrated work of Marckmann and Verron [Rubb. Chem. Tech. 79.5, 835-858, 2006] where they have compared 20 hyperelastic constitutive models for rubber. Since then, the rubber community witnessed mergence of many more hyperelastic models. Although the recent reviews have been very useful for the assessment of the strengths and weaknesses of various constitutive models, especially on the modeling of uncrosslinked ideal rubber, it is still a challenging endeavor for engineers to decide the best constitutive model for the specific rubber compound at hand. This paper presents a novel parameter identification toolbox based on various multi-objective optimization strategies for the selection of the best constitutive models from a given set of uniaxial tension, pure shear and equibiaxial tension experiments. The toolbox aims at providing an objective model selection procedure along with the material parameters for the rubber compound at hand. To this end, we utilize the multi-objective optimization using a successive genetic algorithm and gradient based search through the Fmincon utility in Matlab. The novelty of our approach is (i) simultaneous fitting - the use of variable weight factors for uniaxial, equibiaxial, and pure shear data which accommodates for the (in)capability of the spe- cific constitutive model to the specific deformation modes (ii) the sorting of the models based on an objective normalized quality of fit metric and (iii) simultaneous fittings are conducted for the models that are inherently incapable of catching large deformations, starting from zero stretch, and with 5\% stretch increments until the model breaks where its quality of fit value goes above a predetermined set value. This allows identification of their validity region, i.e., the region they can work within an acceptable quality of fit margin. Accordingly, over 40 hyperelastic models are sorted with respect to the experimental data of Treloar and Kawabata.}, language = {en}, urldate = {2024-03-23}, booktitle = {Constitutive {Models} for {Rubber} {XI}}, publisher = {CRC Press}, author = {Dal, Hüsnü and Badienia, Yashar and Açikgöz, Kemal and Denlï, Funda Aksu}, editor = {Huneau, Bertrand and Le Cam, Jean-Benoit and Marco, Yann and Verron, Erwan}, month = jun, year = {2019}, doi = {10.1201/9780429324710-42}, pages = {239--244}, }
@book{staat_proceedings_2019, address = {Jülich, Germany}, title = {Proceedings of 3rd {YRA} {MedTech} {Symposium}, {Young} {Researchers} {Academy} - {MedTech} in {NRW}}, copyright = {All rights reserved}, isbn = {978-3-940402-22-6}, url = {http://yra-medtech.de/daten_medtech/dokumente2019/YRA_2019_PROC_low.pdf}, language = {English}, publisher = {University Duisburg-Essen}, editor = {Staat, Manfred and Erni, Daniel}, year = {2019}, doi = {10.17185/duepublico/48750}, note = {ZSCC: NoCitationData[s0] }, }
@article{tran_direct_2019, title = {Direct plastic structural design under lognormally distributed strength by chance constrained programming}, copyright = {All rights reserved}, issn = {1389-4420}, url = {http://link.springer.com/10.1007/s11081-019-09437-2 https://rdcu.be/bxiaz}, doi = {10.1007/s11081-019-09437-2}, abstract = {We propose the so-called chance constrained programming model of stochastic programming to analyze limit and shakedown loads of structures under random strength with a lognormal distribution. A dual chance constrained programming algorithm is developed to calculate simultaneously both the upper and lower bounds of the plastic collapse limit and the shakedown limit. The edge-based smoothed finite element method (ES-FEM) is used with three-node linear triangular elements.}, journal = {Optimization and Engineering}, author = {Trần, Ngọc Trình and Staat, Manfred}, month = apr, year = {2019}, note = {ZSCC: 0000000}, keywords = {chance constrained programming, limit analysis, primal dual programming, shakedown analysis, stochastic programming, structural reliability}, }
@article{meyer_kyphoplasty_2019, title = {Kyphoplasty of osteoporotic fractured vertebrae: {A} finite element analysis about two types of cement.}, volume = {2019}, copyright = {All rights reserved}, issn = {2314-6141}, url = {https://www.hindawi.com/journals/bmri/2019/9232813/ http://www.ncbi.nlm.nih.gov/pubmed/31143778 http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=PMC6501275}, doi = {10.1155/2019/9232813}, abstract = {If conservative treatment of osteoporotic vertebral compression fractures fails, vertebro- or kyphoplasty is indicated. Usually, polymethylmethacrylate cement (PMMA) is applied coming along with many disadvantageous features. Aluminum-free glass-polyalkenoate cement (GPC) appears to be a benefit alternative material. This study aimed at comparing the mean stress values in human vertebrae after kyphoplasty with PMMA and GPC (IlluminOss™) at hand of a finite element analysis. Three models were created performing kyphoplasty using PMMA or IlluminOss™, respectively, at two native, human lumbar vertebrae (L4) while one remains intact. Finite element analysis was performed using CT-scans of every vertebra. Moreover the PMMA-treated vertebra was used as a model as analyses were executed using material data of PMMA and of GPC. The unimpaired, spongious bone showed potentials of 0.25 MPa maximally. After augmentation stress levels showed fivefold increase, rising from externally to internally, revealing stress peaks at the ventral border of the spinal canal. At central areas of cement 1 MPa is measured in both types of cement. Around these central areas the von Mises stress decreased about 25-50\% (0.5-0.75 MPa). If workload of 500 N was applied, the stress appeared to be more centralized at the IlluminOss™-model, similar to the unimpaired. Considering the endplates the GPC model also closely resembles the unimpaired. Comparing the PMMA-treated vertebral body and the GPC-simulation, there is an obvious difference. While the PMMA-treated model showed a central stress peak of 5 MPa, the GPC-simulation of the same vertebral body presents lower stress of 1.2-2.5 MPa. Finite element analysis showed that IlluminOss™ (GPC), used in kyphoplasty of vertebral bodies, creates lower level stress and strain compared to standardly used PMMA, leading to lower stress concentrations on the cranial and caudal vertebral surface especially. GPC appears to own advantageous biological and clinical relevant features.}, journal = {BioMed Research Iternational}, author = {Meyer, Carolin and van Gaalen, Kerstin and Leschinger, Tim and Scheyerer, Max J. and Neiss, Wolfram F. and Staat, Manfred and Müller, Lars Peter and Wegmann, Kilian}, month = apr, year = {2019}, pmid = {31143778}, note = {ZSCC: 0000000 }, pages = {9232813}, }
@article{leschinger_irreparable_2019, title = {Irreparable rotator cuff tears: a biomechanical comparison of superior capsuloligamentous complex reconstruction techniques and an interpositional graft technique}, volume = {7}, copyright = {All rights reserved}, issn = {2325-9671}, url = {http://journals.sagepub.com/doi/10.1177/2325967119864590 http://www.ncbi.nlm.nih.gov/pubmed/31489328 http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=PMC6709439}, doi = {10.1177/2325967119864590}, abstract = {Background Irreparable rotator cuff tears lead to superior translation of the humeral head. Numerous surgical management options are available to treat the condition. Purpose To compare superior capsule stability among different types of patch grafting in irreparable rotator cuff tears. Methods Six cadaveric shoulders were tested in a custom-designed shoulder testing system. Superior translation of the humerus and subacromial contact pressure were quantified in an intact condition (condition 1), after cutting the supraspinatus tendon (condition 2), and after additionally cutting the superior capsuloligamentous complex (condition 3). The results were compared among 3 types of patch grafting, in which capsule reconstruction was achieved by glenoidal 3-point (condition 4) or 2-point (condition 5) fixation or by affixing a graft below the acromion (condition 6). Results No significant difference in subacromial pressure was measured by reconstruction with 2 or 3 anchors compared with conditions 1 and 2 (P {\textbackslash}textgreater .05). However, with 3-point fixation, lower levels of pressure were measured than with 2-point fixation. Moreover, superior translation values were lower with 3-point fixation; the same applied for values of the preserved capsule as compared with the torn capsule. In condition 6, a significant increase in pressure in the neutral position was documented (P {\textbackslash}textless .05). Conclusion The superior capsuloligamentous complex plays an important role in stabilizing the glenohumeral joint. The results suggest that with additional medial anchoring at the coracoid base, the depressing and centering effect of the superior complex can probably be regained in a more physiological way compared with a reconstructed capsule with 2 glenoid attachments or with an interpositional graft below the acromion.}, number = {8}, journal = {Orthopaedic Journal of Sports Medicine}, author = {Leschinger, Tim and Besch, Katharina and Aydin, Cansu and Staat, Manfred and Scaal, Martin and Müller, Lars Peter and Wegmann, Kilian}, month = aug, year = {2019}, pmid = {31489328}, note = {ZSCC: NoCitationData[s0] }, keywords = {biomechanics, capsule reconstruction, interposition, irreparable rotator cuff tears, superior glenohumeral stability}, pages = {2325967119864590}, }
@article{keutmann_untersuchung_2018, title = {Untersuchung der thermischen {Auswirkung} von therapeutischem {Ultraschall}}, volume = {7}, copyright = {All rights reserved}, doi = {10.3238/oup.2018.0518–0522}, abstract = {In der Orthopädie zählt der therapeutische Ultraschall als Mittel zur Prävention und Therapiebegleitung. Er hat mechanische, thermische und physiko-chemische Auswirkungen auf den menschlichen Körper. Um mehr Erkenntnisse über die thermischen Auswirkungen zu erlangen, wurden Versuche an einem Hydrogel- Phantom und an Probanden durchgeführt. Dabei entstand eine signifikante Erwärmung des Gewebes, welche beim Probandenversuch an der Oberfläche und beim Hydrogelversuch in der Tiefe gemessen wurde.}, number = {10}, journal = {OUP ∙ Zeitschrift für die orthopädische und unfallchirurgische Praxis}, author = {Keutmann, Sabine and Staat, Manfred and van Laack, Walter}, year = {2018}, note = {ZSCC: NoCitationData[s0]}, keywords = {Diathermie, Infrarotthermografie, Mechanotherapie, Ultraschall, therapeutischer Ultraschall}, pages = {518--522}, }
@article{bhattarai_surgical_2018, title = {Surgical treatment of vaginal vault prolapse using different prosthetic mesh implants: a finite element analysis}, volume = {85}, copyright = {All rights reserved}, issn = {2196-7113}, url = {http://www.degruyter.com/view/j/teme.ahead-of-print/teme-2017-0115/teme-2017-0115.xml http://www.degruyter.com/view/j/teme.2018.85.issue-5/teme-2017-0115/teme-2017-0115.xml}, doi = {10.1515/teme-2017-0115}, abstract = {Particularly multiparous elderly women may suffer from vaginal vault prolapse after hysterectomy due to weak support from lax apical ligaments. A decreased amount of estrogen and progesterone in older age is assumed to remodel the collagen thereby reducing tissue stiffness. Sacrocolpopexy is either performed as open or laparoscopic surgery using prosthetic mesh implants to substitute lax ligaments. Y-shaped mesh models (DynaMesh, Gynemesh, and Ultrapro) are implanted in a 3D female pelvic floor finite element model in the extraperitoneal space from the vaginal cuff to the first sacral (S1) bone below promontory. Numerical simulations are conducted during Valsalva maneuver with weakened tissues modeled by reduced tissue stiffness. Tissues are modeled as incompressible, isotropic hyperelastic materials whereas the meshes are modeled either as orthotropic linear elastic or as isotropic hyperlastic materials. The positions of the vaginal cuff and the bladder base are calculated from the pubococcygeal line for female pelvic floor at rest, for prolapse and after repair using the three meshes. Due to mesh mechanics and mesh pore deformation along the loaded direction, the DynaMesh with regular rectangular mesh pores is found to provide better mechanical support to the organs than the Gynemesh and the Ultrapro with irregular hexagonal mesh pores.}, number = {5}, journal = {tm - Technisches Messen}, author = {Bhattarai, Aroj and Jabbari, Medisa and Anding, Ralf and Staat, Manfred}, month = apr, year = {2018}, note = {ZSCC: 0000004}, keywords = {Apical prolapse, biomechanical modeling, finite element simulation, prosthetic mesh implants, sacrocolpopexy, vaginal cuff}, pages = {331--342}, }
@incollection{tran_shakedown_2018, address = {Cham}, title = {Shakedown analysis under stochastic uncertainty by chance constrained programming}, copyright = {All rights reserved}, isbn = {978-3-319-59808-6}, url = {http://link.springer.com/10.1007/978-3-319-59810-9_6}, abstract = {In this paper we propose a stochastic programming method to analyse limit and shakedown of structures under uncertainty condition of strength. Based on the duality theory, the shakedown load multiplier formulated by the kinematic theorem is proved actually to be the dual form of the shakedown load multiplier formulated by static theorem. In this investigation a dual chance constrained programming algorithm is developed to calculate simultaneously both the upper and lower bounds of the plastic collapse limit and the shakedown limit. The edge-based smoothed finite element method (ES-FEM) with three-node linear triangular elements is used for structural analysis.}, booktitle = {Advances in {Direct} {Methods} for {Materials} and {Structures}}, publisher = {Springer International Publishing}, author = {Tran, N. T. and Tran, Thanh Ngoc and Matthies, Hermann G. and Stavroulakis, Georgios Eleftherios and Staat, Manfred}, editor = {Barrera, Olga and Cocks, Alan and Ponter, Alan}, year = {2018}, doi = {10.1007/978-3-319-59810-9_6}, note = {ZSCC: NoCitationData[s0] }, pages = {85--103}, }
@article{birgel_calculation_2018, title = {Calculation of muscle forces and joint reaction loads in the shoulder area via an {OpenSim} based computer model}, volume = {85}, copyright = {All rights reserved}, issn = {2196-7113}, url = {http://www.degruyter.com/view/j/teme.ahead-of-print/teme-2017-0114/teme-2017-0114.xml http://www.degruyter.com/view/j/teme.2018.85.issue-5/teme-2017-0114/teme-2017-0114.xml}, doi = {10.1515/teme-2017-0114}, abstract = {Using the OpenSim software and verified anatomical data, a computer model for the calculation of biomechanical parameters is developed and used to determine the effect of a reattachment of the Supraspinatus muscle with a medial displacement of the muscle attachment point, which may be necessary for a rupture of the supraspinatus tendon. The results include the influence of the operation on basic biomechanical parameters such as the lever arm, as well as the calculated the muscle activations for the supraspinatus and deltoid. In addition, the influence on joint stability is examined by an analysis of the joint reaction force. The study provides a detailed description of the used model, as well as medical findings to a reattachment of the supraspinatus.}, number = {5}, journal = {tm - Technisches Messen}, author = {Birgel, Stefan and Leschinger, Tim and Wegmann, Kilian and Staat, Manfred}, month = apr, year = {2018}, note = {ZSCC: 0000002}, pages = {321--330}, }
@incollection{duong_growth_2018, address = {Singapore}, title = {Growth modelling promoting mechanical stimulation of smooth muscle cells of porcine tubular organs in a fibrin-{PVDF} scaffold}, copyright = {All rights reserved}, isbn = {978-981-10-7903-0}, url = {http://link.springer.com/10.1007/978-981-10-7904-7_9}, abstract = {Reconstructive surgery and tissue replacements like ureters or bladders reconstruction have been recently studied, taking into account growth and remodelling of cells since living cells are capable of growing, adapting, remodelling or degrading and restoring in order to deform and respond to stimuli. Hence, shapes of ureters or bladders and their microstructure change during growth and these changes strongly depend on external stimuli such as training. We present the mechanical stimulation of smooth muscle cells in a tubular fibrin-PVDFA scaffold and the modelling of the growth of tissue by stimuli. To this end, mechanotransduction was performed with a kyphoplasty balloon catheter that was guided through the lumen of the tubular structure. The bursting pressure was examined to compare the stability of the incubated tissue constructs. The results showed the significant changes on tissues with training by increasing the burst pressure as a characteristic mechanical property and the smooth muscle cells were more oriented with uniformly higher density. Besides, the computational growth models also exhibited the accurate tendencies of growth of the cells under different external stimuli. Such models may lead to design standards for the better layered tissue structure in reconstructing of tubular organs characterized as composite materials such as intestines, ureters and arteries.}, booktitle = {Biological, {Physical} and {Technical} {Basics} of {Cell} {Engineering}}, publisher = {Springer Singapore}, author = {Dương, Minh Tuấn and Seifarth, Volker and Artmann, Ayşegül and Artmann, Gerhard M. and Staat, Manfred}, editor = {Artmann, Gerhard M. and Artmann, Aysegül and Zhubanova, Azhar A. and Digel, Ilya}, year = {2018}, doi = {10.1007/978-981-10-7904-7_9}, note = {ZSCC: NoCitationData[s1] }, pages = {209--232}, }
@article{hackl_radial_2017, title = {Radial shortening osteotomy reduces radiocapitellar contact pressures while preserving valgus stability of the elbow.}, volume = {25}, copyright = {All rights reserved}, issn = {1433-7347}, url = {http://link.springer.com/10.1007/s00167-017-4468-z http://www.ncbi.nlm.nih.gov/pubmed/28238092}, doi = {10.1007/s00167-017-4468-z}, abstract = {PURPOSE Shortening osteotomy of the proximal radius might represent a potential salvage procedure in symptomatic radiocapitellar osteoarthritis, which could decrease radiocapitellar load while preserving the native radial head. In an in-vitro biomechanical investigation, we sought to determine whether shortening osteotomy of the proximal radius (1) decreases the radiocapitellar joint pressure upon axial loading and (2) retains valgus stability of the elbow. In addition, the anatomic configuration of the lesser sigmoid notch was evaluated to assess possible contraindications. METHODS Axial loading (0-400 N) and valgus torque (7.5 N m) over the full range of motion were applied to 14 fresh-frozen specimens before and after shortening osteotomy of the proximal radius by 2.5 mm. Radiocapitellar and ulnohumeral load distribution during axial compression was evaluated using a digital pressure mapping sensor. Valgus displacement was analyzed with a 3D camera system. The inclination angle (α) of the lesser sigmoid notch was assessed via 50 CT scans. RESULTS Up to axial loading of 250 N, shortening osteotomy caused a significant decrease in radiocapitellar contact pressures (p {\textbackslash}textless 0.041). Valgus stability of specimens did not differ before and after shortening osteotomy (n.s.). The mean inclination angle (α) of the lesser sigmoid notch was 11.3° ± 6.3°. 46\% had an inclination angle of ≤ 10° (type I). 46\% had an inclination angle of 11°-20° (type II). In 8\%, the inclination angle was {\textbackslash}textgreater20° (type III). CONCLUSION Shortening osteotomy of the proximal radius can decrease radiocapitellar contact pressures during axial loading of up to 250 N. Primary valgus stability is not relevantly influenced by this procedure. In few patients, shortening osteotomy may cause radioulnar impingement of the radial head at the distal edge of the lesser sigmoid notch due to an inclination angle of {\textbackslash}textgreater20°. Shortening osteotomy might be a promising treatment option to decrease pain levels in case of isolated radiocapitellar osteoarthritis.}, number = {7}, journal = {Knee Surgery, Sports Traumatology, Arthroscopy : official journal of the ESSKA}, author = {Hackl, Michael and Wegmann, Kilian and Kahmann, Stephanie L. and Heinze, Nicolai and Staat, Manfred and Neiss, Wolfram F. and Scaal, Martin and Müller, Lars P.}, month = jul, year = {2017}, pmid = {28238092}, note = {ZSCC: 0000013 }, keywords = {Biomechanics, Post-traumatic osteoarthritis, Proximal radius, Radial head fracture, Salvage procedure, Shortening osteotomy}, pages = {2280--2288}, }
@article{hackl_suture_2017, title = {Suture button reconstruction of the central band of the interosseous membrane in {Essex}-{Lopresti} lesions: a comparative biomechanical investigation.}, volume = {42}, copyright = {All rights reserved}, issn = {2043-6289}, url = {http://journals.sagepub.com/doi/10.1177/1753193416665943 http://www.ncbi.nlm.nih.gov/pubmed/27573130}, doi = {10.1177/1753193416665943}, abstract = {Surgical reconstruction of the interosseous membrane may restore longitudinal forearm stability in Essex-Lopresti lesions. This study aimed to compare the longitudinal stability of the intact forearm with a single-bundle and a double-bundle reconstruction of the central band of the interosseous membrane using digital image correlation with a three-dimensional camera system. Single and cyclic axial loading of eight fresh-frozen forearm specimens was carried out in the intact state, after creation of an Essex-Lopresti lesion, after a single-bundle and after a double-bundle reconstruction of the central band using a TightRope® (Arthrex GmbH, Munich, Germany) construct. Instability significantly increased after creation of an Essex-Lopresti lesion. The stability of intact specimens was similar to both reconstruction techniques. The results of this study suggest that TightRope® reconstruction of the central band restores longitudinal forearm stability. However, the single-bundle technique may be less reliable than double-bundle reconstruction. LEVEL OF EVIDENCE Basic Science Study.}, number = {4}, journal = {The Journal of Hand Surgery, European volume}, author = {Hackl, Michael and Andermahr, J. and Staat, Manfred and Bremer, I. and Borggrefe, J. and Prescher, Andreas and Müller, L. P. and Wegmann, Kilian}, year = {2017}, pmid = {27573130}, note = {ZSCC: NoCitationData[s0] }, keywords = {Essex-Lopresti injury, TightRope, biomechanics, interosseous membrane, longitudinal forearm instability, reconstruction}, pages = {370--376}, }
@article{hackl_reply_2017, title = {Reply to the letter to the editor: shortening osteotomy of the proximal radius.}, volume = {25}, copyright = {All rights reserved}, issn = {1433-7347}, url = {http://link.springer.com/10.1007/s00167-017-4666-8 http://www.ncbi.nlm.nih.gov/pubmed/28840264}, doi = {10.1007/s00167-017-4666-8}, number = {10}, journal = {Knee Surgery, Sports Traumatology, Arthroscopy : official journal of the ESSKA}, author = {Hackl, Michael and Wegmann, Kilian and Kahmann, Stephanie L. and Heinze, Nicolai and Staat, Manfred and Neiss, Wolfram F. and Scaal, Martin and Müller, Lars P.}, year = {2017}, pmid = {28840264}, note = {ZSCC: 0000000 }, pages = {3328--3329}, }
@inproceedings{staat_smoothed_2016, address = {Hanoi, Vietnam}, title = {Smoothed finite element methods for nonlinear solid mechanics problems: {2D} and {3D} case studies}, copyright = {All rights reserved}, doi = {10.21269/7859}, abstract = {The Smoothed Finite Element Method (SFEM) is presented as an edge-based and a facebased techniques for 2D and 3D boundary value problems, respectively. SFEMs avoid shortcomings of the standard Finite Element Method (FEM) with lower order elements such as overly stiff behavior, poor stress solution, and locking effects. Based on the idea of averaging spatially the standard strain field of the FEM over so-called smoothing domains SFEM calculates the stiffness matrix for the same number of degrees of freedom (DOFs) as those of the FEM. However, the SFEMs significantly improve accuracy and convergence even for distorted meshes and/or nearly incompressible materials. Numerical results of the SFEMs for a cardiac tissue membrane (thin plate inflation) and an artery (tension of 3D tube) show clearly their advantageous properties in improving accuracy particularly for the distorted meshes and avoiding shear locking effects.}, booktitle = {Proceedings of the {National} {Science} and {Technology} {Conference} on {Mechanical} - {Transportation} {Engineering} ({NSCMET} 2016)}, publisher = {Hanoi University of Science and Technology}, author = {Staat, Manfred and Dương, Minh Tuấn}, year = {2016}, note = {ZSCC: NoCitationData[s0]}, pages = {440--445}, }
@incollection{bhattarai_significance_2016, address = {London}, title = {Significance of fibre geometry on passive-active response of pelvic muscles to evaluate pelvic dysfunction}, copyright = {All rights reserved}, isbn = {978-1-138-02910-1}, url = {http://www.crcnetbase.com/doi/pdfplus/10.1201/9781315644622-47}, abstract = {A perfect tone of the pelvic muscle fibres elevates the pelvic organs and maintains the urinary and fecal continence. Prosthetic mesh implants are widely used to reconstruct the pelvic floor dysfunctions due to damaged muscle fibres. This paper focuses on the muscle fibre orientation to simulate the passive stretching of the pelvic muscles under increased intra-abdominal pressure (IAP) during Valsalva maneuver. The Humphrey model is adopted for the passive deformation of the pelvic muscle. With a pressure of 0.2 kPa applied on the internal faces of the muscle, the levator ani (LA) muscle displaces 27.917 mm inferiorly. High stress is observed at the fixation of the muscle to the pubic bones. Without any supports from the anal plate and the perineal body, the posterior movement of the LA muscle is 11.640 mm which is almost 2.5 times larger than that observed from the MRI examination of a nulliparous female.}, booktitle = {{BioMedWomen}: {Proceedings} of the {International} {Conference} on {Clinical} and {BioEngineering} for {Women}'s {Health} ({Porto}, {Portugal}, 20-23 {June}, 2015)}, publisher = {CRC Press/Balkema}, author = {Bhattarai, Aroj and Frotscher, Ralf and Staat, Manfred}, editor = {Jorge, Renato Natal and Mascarenhas, Teresa and Duarte, José Alberto and Ramos, Isabel and Costa, Maria Emília and Figueiral, Maria Helena and Pinho, Olívia and Brandão, Sofia and Roza, Thuane Da and Tavares, João Manuel R.S.}, year = {2016}, note = {ZSCC: NoCitationData[s0]}, keywords = {Muscle fibres, passive relaxation, pelvic dysfunction}, pages = {185--188}, }
@inproceedings{tran_shakedown_2016, address = {Athens}, title = {Shakedown analysis of plate bending under stochastic uncertainty by chance constrained programming}, copyright = {All rights reserved}, isbn = {978-618-82844-0-1}, url = {https://www.eccomas2016.org/proceedings/pdf/11106.pdf http://www.eccomasproceedia.org/conferences/eccomas-congresses/eccomas-congress-2016/2012}, doi = {10.7712/100016.2012.11106}, abstract = {In this paper we propose a stochastic programming to analyze limit and shakedown of plate bending under uncertainty conditions of strength. The Kirchhoff plate theory is used to formulate chance constrained problems. Based on the duality theory, the shakedown load multiplier formulated by the kinematic theorem is proved actually to be the dual form of the shakedown load multiplier for-mulated by static theorem. In this investigation a dual chance constrained programming algorithm is developed to calculate simultaneously both the upper and lower bounds of the plastic collapse limit and the shakedown limit.}, booktitle = {Proceedings of the {VII} {European} {Congress} on {Computational} {Methods} in {Applied} {Sciences} and {Engineering} ({ECCOMAS} {Congress} 2016)}, publisher = {Institute of Structural Analysis and Antiseismic Research School of Civil Engineering National Technical University of Athens (NTUA) Greece}, author = {Tran, Ngoc Trinh and Tran, Thanh Ngoc and Matthies, H.G. and Stavroulakis, G.E. and Staat, Manfred}, editor = {Papadopoulos, V. and Stefanou, G. and Plevris, V.}, year = {2016}, note = {ZSCC: NoCitationData[s0]}, keywords = {Limit analysis, Shakedown analysis, chance constrained programming, non-linear programming, stochastic programming}, pages = {3007--3019}, }
@article{frotscher_sample-specific_2016, title = {Sample-specific adaption of an improved electro-mechanical model of in vitro cardiac tissue}, volume = {49}, copyright = {All rights reserved}, issn = {00219290}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0021929016301154 http://www.ncbi.nlm.nih.gov/pubmed/26972766}, doi = {10.1016/j.jbiomech.2016.01.039}, abstract = {We present an electromechanically coupled computational model for the investigation of a thin cardiac tissue construct consisting of human-induced pluripotent stem cell-derived atrial, ventricular and sinoatrial cardiomyocytes. The mechanical and electrophysiological parts of the finite element model, as well as their coupling are explained in detail. The model is implemented in the open source finite element code Code\_Aster and is employed for the simulation of a thin circular membrane deflected by a monolayer of autonomously beating, circular, thin cardiac tissue. Two cardio-active drugs, S-Bay K8644 and veratridine, are applied in experiments and simulations and are investigated with respect to their chronotropic effects on the tissue. These results demonstrate the potential of coupled micro- and macroscopic electromechanical models of cardiac tissue to be adapted to experimental results at the cellular level. Further model improvements are discussed taking into account experimentally measurable quantities that can easily be extracted from the obtained experimental results. The goal is to estimate the potential to adapt the presented model to sample specific cell cultures.}, number = {12}, journal = {Journal of Biomechanics}, author = {Frotscher, Ralf and Muanghong, Danita and Dursun, Gözde and Goßmann, Matthias and Temiz-Artmann, Ayşegül and Staat, Manfred}, month = aug, year = {2016}, pmid = {26972766}, note = {ZSCC: 0000011 }, keywords = {Cardiac tissue, Computational biomechanics, Drug simulation, Electromechanical modeling, Frequency adaption, Hodgkin–Huxley models, Homogenization, hiPS cardiomyocytes}, pages = {2428--2435}, }
@article{hackl_shortening_2016, title = {Shortening osteotomy of the proximal radius - a treatment option for isolated osteoarthritis of the lateral column of the elbow joint}, volume = {24}, copyright = {All rights reserved}, issn = {0942-2056}, url = {http://link.springer.com/10.1007/s00167-016-4080-7}, doi = {10.1007/s00167-016-4080-7}, number = {S1}, journal = {Knee Surgery, Sports Traumatology, Arthroscopy}, author = {Hackl, Michael and Kahmann, Stepahine Lucina and Wegmann, Kilian and Ries, Christian and Staat, Manfred and Müller, Lars Peter}, year = {2016}, note = {ZSCC: NoCitationData[s0]}, pages = {S128--S129}, }
@incollection{tran_uncertainty_2015, address = {Cham}, title = {Uncertainty multimode failure and shakedown analysis of shells}, volume = {4}, copyright = {All rights reserved}, isbn = {978-3-319-12927-3}, url = {http://link.springer.com/10.1007/978-3-319-12928-0 http://link.springer.com/10.1007/978-3-319-12928-0_14}, abstract = {This paper presents a numerical procedure for reliability analysis of thin plates and shells with respect to plastic collapse or to inadaptation. The procedure involves a deterministic shakedown analysis for each probabilistic iteration, which is based on the upper bound approach and the use of the exact Ilyushin yield surface. Probabilistic shakedown analysis deals with uncertain-ties originated from the loads, material strength and thickness of the shell. Based on a direct definition of the limit state function, the calculation of the failure probability may be solved efficiently solved by using the First and Second Order Reliability Methods (FORM and SORM). The problem of reliability of structural systems (series systems) will be handled by the application of a special technique, which permits to find all the design points correspond-ing to all the failure modes. Studies show, in this case, that it improves con-siderably the FORM and SORM results.}, booktitle = {Direct {Methods} for {Limit} and {Shakedown} {Analysis} of {Structures}}, publisher = {Springer International Publishing}, author = {Trần, Thanh Ngọc and Staat, Manfred}, editor = {Fuschi, Paolo and Pisano, Aurora Angela and Weichert, Dieter}, year = {2015}, doi = {10.1007/978-3-319-12928-0_14}, note = {ZSCC: NoCitationData[s0] }, keywords = {Limit Analysis, Multimode Failure, Non-linear Optimization, Reliability Analysis, Shakedown Analysis}, pages = {279--298}, }
@incollection{frotscher_simulation_2015, address = {Cham, Heidelberg}, series = {Advanced {Structured} {Materials}}, title = {Simulation of {Cardiac} {Cell}-{Seeded} {Membranes} {Using} the {Edge}-{Based} {Smoothed} {FEM}}, volume = {45}, copyright = {All rights reserved}, isbn = {978-3-319-02534-6}, url = {http://link.springer.com/chapter/10.1007/978-3-319-02535-3_11 http://link.springer.com/10.1007/978-3-319-02535-3_11}, abstract = {We present an electromechanically coupled Finite Element model for cardiac tissue. It bases on the mechanical model for cardiac tissue of Hunter et al. that we couple to the McAllister-Noble-Tsien electrophysiological model of purkinje fibre cells. The corresponding system of ordinary differential equations is implemented on the level of the constitutive equations in a geometrically and physically nonlinear version of the so-called edge-based smoothed FEMfor plates. Mechanical material parameters are determined from our own pressure-deflection experimental setup. The main purpose of the model is to further examine the experimental results not only on mechanical but also on electrophysiological level down to ion channel gates. Moreover, we present first drug treatment simulations and validate the model with respect to the experiments.}, booktitle = {Shell and {Membrane} {Theories} in {Mechanics} and {Biology}: {From} {Macro}- to {Nanoscale} {Structures}}, publisher = {Springer}, author = {Frotscher, Ralf and Goßmann, Matthias and Raatschen, Hans-Jürgen and Temiz-Artmann, Ayşegül and Staat, Manfred}, editor = {Altenbach, Holm and Mikhasev, Gennadi I.}, year = {2015}, doi = {10.1007/978-3-319-02535-3_11}, note = {ZSCC: NoCitationData[s0] }, pages = {187--212}, }
@inproceedings{bhattarai_biomechanical_2015, address = {Aachen, Germany}, title = {Biomechanical study of the female pelvic floor dysfunction using the finite element method}, copyright = {All rights reserved}, abstract = {Pelvic floor dysfunction is considered to be a long run sequel of injuries of the weak pelvic supporting structures during vaginal delivery and their laxity in old age. Besides immediate effects, it becomes a socially embarrassing health issue in the form of incontinence and prolapse. To validate such clinical outcomes and to highlight the importance of supporting ligaments and fascias in the maintenance of continence as suggested Petros' integral theory, computational studies are carried out on a 3D finite element pelvic floor model.}, booktitle = {{YIC} {GACM} 2015, 3rd {ECCOMAS} {Young} {Investigators} {Conference}, 6th {GACM} {Colloquium}, {Aachen}, {Germany}, {July} 20-23, 2015}, author = {Bhattarai, Aroj and Frotscher, Ralf and Staat, Manfred}, year = {2015}, note = {ZSCC: 0000004}, keywords = {Finite Element Method, Integral Theory, Pelvic Floor Dysfunction, Urinary Incontinence}, }
@article{duong_influence_2015, title = {Influence of refrigerated storage on tensile mechanical properties of porcine liver and spleen}, volume = {2}, copyright = {All rights reserved}, issn = {2333-5432}, url = {http://www.tandfonline.com/doi/full/10.1080/23335432.2015.1049295}, doi = {10.1080/23335432.2015.1049295}, abstract = {Preservation conditions may affect internal organs thus influencing the results of protracted biomechanical tests. The influence of the freeze-thaw cycle on the mechanical behaviour of porcine abdominal organs was reported in our previous work. Here we further investigate the effects of refrigerated storage on the mechanical properties of porcine spleen and liver. Twenty-seven swine were chosen for tensile testing. To simulate the conservation conditions before biomechanical experimentation, the total sample was divided into three groups of nine individuals each and tested in a fresh state, after a freeze-thaw cycle, and after refrigerated storage (+4 °C). Fitted stress-stretch curves for each tissue type were obtained by employing a modified Fung model for isotropic behaviour. The results suggest statistically significant effects of refrigerated storage on the spleen but negligible influence on the liver. Similarly to the impact of the freeze-thaw cycle, refrigerated storage caused a decrease in the mechanical properties of the spleen. This again supports the hypothesized cause of the altered behaviour of spleen due to the autolysis of elastin by elastolytic enzymes during and after the cooling period. Spleen and liver are good examples of tissue with and without elastin. These findings have wide biomechanical and decomposition implications for the study of soft tissues.}, number = {1}, journal = {International Biomechanics}, author = {Dương, M. Tuấn and Nguyễn, N. Huynh and Trần, T. Ngọc and Tolba, René Hany and Staat, Manfred}, month = jan, year = {2015}, note = {ZSCC: 0000006}, keywords = {autolysis, freeze-thaw, liver, refrigerated storage, spleen}, pages = {79--88}, }
@incollection{frotscher_homogenization_2015, title = {Homogenization of a cardiac tissue construct}, copyright = {All rights reserved}, isbn = {978-0-9562914-3-1}, url = {http://opus.bibliothek.fh-aachen.de/opus4/files/7263/CMBE2015_Staat_Frotscher.pdf}, abstract = {We extend the modeling of a cardiac tissue composite by proper homogenization of all the different mechanical contributions to the constitutive tensor as well as the contributions to the diffusion tensor and the electrical source current in the parabolic system. The model is applied to support the interpretation of experimental findings in drug testing being able to explain the results at the cellular level. Moreover the model can be used for the prediction of drug effects on cardiac tissue and for computational studies of cardiomyocyte and cardiac tissue electromechanics.}, booktitle = {4th {International} {Conference} on {Computational} and {Mathematical} {Biomedical} {Engineering} - {CMBE2015}, 29 {June} - 1 {July} 2015, {Cachan} ({Paris}), {France}}, publisher = {CMBE Zeta Computational Resources Ltd., Swansea, UK}, author = {Frotscher, Ralf and Staat, Manfred}, editor = {Nithiarasu, Perumal and Budyn, Elisa}, year = {2015}, note = {ZSCC: NoCitationData[s0]}, keywords = {cardiac tissue modeling, electromechanical coupling, homogenization}, }
@article{staat_limit_2014, title = {Limit and shakedown analysis under uncertainty}, volume = {11}, copyright = {All rights reserved}, issn = {0219-8762}, url = {http://www.worldscientific.com/doi/abs/10.1142/S0219876213430081}, doi = {10.1142/S0219876213430081}, abstract = {Structural reliability analysis is based on the concept of a limit state function separating failure from safe states of a structure. Upper and lower bound theorems of limit and shakedown analysis are used for a direct definition of the limit state function for failure by plastic collapse or by inadaptation. Shakedown describes an asymptotic and therefore time invariant structural behavior under time variant loading. The limit state function and its gradient are obtained from a mathematical optimization problem. The method is implemented into a general purpose finite element model (FEM) code. Combined with first-order methods/second-order methods (FORM/SORM) robust and precise analyses can be performed for structures with high reliability. This approach is particularly effective because the sensitivities which are needed by FORM/SORM are derived from the solution of the deterministic problem.}, number = {03}, journal = {International Journal of Computational Methods}, author = {Staat, Manfred}, month = jun, year = {2014}, note = {ZSCC: 0000011}, keywords = {FEM, Shakedown, direct plasticity, mathematical pr}, pages = {1343008}, }
@inproceedings{tran_uncertain_2014, title = {Uncertain multimode failure and limit analysis of shells}, copyright = {All rights reserved}, url = {opus.bibliothek.fh-aachen.de/opus4/files/6508/Barcelona_2014-p819.pdf}, abstract = {This paper presents a numerical procedure for reliability analysis of thin plates and shells with respect to plastic collapse. The procedure involves a deterministic limit analysis for each probabilistic iteration, which is based on the upper bound approach and the use of the exact Ilyushin yield surface. Probabilistic limit analysis deals with uncertainties of the loads, material strength and thickness of the shell. Based on a direct definition of the limit state function, the calculation of the failure probability may be efficiently solved by using the First and Second Order Reliability Methods (FORM and SORM). The problem of reliability of structural systems (series systems) will be handled by the application of a special technique which permits to find all the design points corresponding to all the failure modes. Studies show, in this case, that it improves considerably the FORM and SORM results.}, booktitle = {11th {World} {Congress} on {Computational} {Mechanics} ({WCCM} {XI}), 5th {European} {Conference} on {Computational} {Mechanics} ({ECCM} {V}), 6th {European} {Conference} on {Computational} {Fluid} {Dynamics} ({ECFD} {VI}) {July} 20-25, 2014, {Barcelona}, {Spain}}, publisher = {European Community on Computational Methods in Applied Sciences (ECCOMAS)}, author = {Trần, Thanh Ngọc and Staat, Manfred}, editor = {Oñate, E and J. Oliver, J and Huerta, A}, year = {2014}, note = {ZSCC: NoCitationData[s0]}, keywords = {Limit Analysis, Multimode Failure, Non-linear Optimization, Reliability Analysis, Shakedown Analysis}, pages = {1896--1907}, }
@article{frotscher_stresses_2014, title = {Stresses produced by different textile mesh implants in a tissue equivalent}, volume = {15}, copyright = {All rights reserved}, issn = {2193-066X}, url = {http://www.degruyter.com/view/j/biomat.2014.15.issue-1-2/bnm-2014-0003/bnm-2014-0003.xml}, doi = {10.1515/bnm-2014-0003}, abstract = {In pelvic floor surgery mesh implants are commonly used to recover incontinence and prolapse. There is a huge number of different mesh implants that have largely different mechanical properties, like their dimension, their material, the way of weaving, the number of threads used for the weaving, thickness of the threads, pore size and orientation of the pores. Due to the numerous differences the mesh implants already have been mechanically investigated with respect to all those properties and uniaxial tension tests, tearing tests, bending burst tests and other loading experiments have been conducted to determine maximum forces, strain, stress, pull-out strength, the degree of anisotropy, material parameters and hysteresis. In this paper we compare two different meshes, the Gynecare (GC) of Ethicon, USA and SIS direct (SD) of FEG Textiltechnik, Germany. We choose those meshes because they have a considerably different structure which we identifoed to be very important by means of their pull-out behavior and stress distribution in the surrounding tissue. We present an experimental method for measuring the pull-out strength and visualizing the shear stresses in a muscle tissue equivalent using photoelasticity. The meshes are embedded into a transparent gelatin block. Gelatin serves as a tissue that behaves similar to muscle tissue. The end of the mesh and another textile tissue embedded at the other end of the gelatin block have been clamped into a tension machine. Applying tension to the mesh and looking at the gelatine block through a filter leads to colorful isochromatic lines that represent lines of equal shear stresses.}, number = {1-2}, journal = {BioNanoMaterials}, author = {Frotscher, Ralf and Staat, Manfred}, month = jan, year = {2014}, note = {ZSCC: 0000003}, pages = {25--30}, }
@incollection{tran_shakedown_2014, address = {Dordrecht}, title = {Shakedown analysis of {Reissner}-{Mindlin} plates using the edge-based smoothed finite element method}, volume = {3}, copyright = {All rights reserved}, isbn = {978-94-007-6826-0}, url = {http://link.springer.com/10.1007/978-94-007-6827-7_5}, abstract = {This paper concerns the development of a primal-dual algorithm for limit and shakedown analysis of Reissner-Mindlin plates made of von Mises material. At each optimization iteration, the lower bound of the shakedown load multiplier is calculated simultaneously with the upper bound using the duality theory. An edge-based smoothed finite element method (ES-FEM) combined with the discrete shear gap (DSG) technique is used to improve the accuracy of the solutions and to avoid the transverse shear locking behaviour. The method not only possesses all inherent features of convergence and accuracy from ES-FEM, but also ensures that the total number of variables in the optimization problem is kept to a minimum compared with the standard finite element formulation. Numerical examples are presented to demonstrate the effectiveness of the present method.}, booktitle = {Direct {Methods} for {Limit} {States} in {Structures} and {Materials}}, publisher = {Springer Netherlands}, author = {Trần, Thanh Ngọc and Staat, Manfred}, editor = {Spiliopoulos, Konstantinos and Weichert, Dieter}, year = {2014}, doi = {10.1007/978-94-007-6827-7_5}, note = {ZSCC: NoCitationData[s0] }, pages = {101--117}, }
@article{jung_flight_2014, title = {Flight style optimization in ski jumping on normal, large, and ski flying hills}, volume = {47}, copyright = {All rights reserved}, issn = {1873-2380}, url = {http://www.ncbi.nlm.nih.gov/pubmed/24388531 http://linkinghub.elsevier.com/retrieve/pii/S0021929013005733}, doi = {10.1016/j.jbiomech.2013.11.021}, abstract = {In V-style ski jumping, aerodynamic forces are predominant performance factors and athletes have to solve difficult optimization problems in parts of a second in order to obtain their jump length maximum and to keep the flight stable. Here, a comprehensive set of wind tunnel data was used for optimization studies based on Pontryagin's minimum principle with both the angle of attack α and the body-ski angle β as controls. Various combinations of the constraints αmax and βmin(t) were analyzed in order to compare different optimization strategies. For the computer simulation studies, the Olympic hill profiles in Esto-Sadok, Russia (HS 106m, HS 140m), and in Harrachov, Czech Republic, host of the Ski Flying World Championships 2014 (HS 205m) were used. It is of high importance for ski jumping practice that various aerodynamic strategies, i.e. combinations of α- and β-time courses, can lead to similar jump lengths which enables athletes to win competitions using individual aerodynamic strategies. Optimization results also show that aerodynamic behavior has to be different at different hill sizes (HS). Optimized time courses of α and β using reduced drag and lift areas in order to mimic recent equipment regulations differed only in a negligible way. This indicates that optimization results presented here are not very sensitive to minor changes of the aerodynamic equipment features when similar jump length are obtained by using adequately higher in-run velocities. However, wind tunnel measurements with athletes including take-off and transition to stabilized flight, flight, and landing behavior would enable a more detailed understanding of individual flight style optimization.}, number = {3}, journal = {Journal of biomechanics}, author = {Jung, Alexander and Staat, Manfred and Müller, Wolfram}, month = feb, year = {2014}, pmid = {24388531}, note = {ZSCC: 0000017 }, keywords = {Aerodynamics, Computer simulation, Optimal control, Ski jumping}, pages = {716--22}, }
@article{baaser_reformulation_2013, title = {Reformulation of strain invariants at incompressibility}, volume = {83}, issn = {0939-1533, 1432-0681}, url = {http://link.springer.com/10.1007/s00419-012-0652-2}, doi = {10.1007/s00419-012-0652-2}, abstract = {The description of (quasi-)incompressible materials such as elastomers is well established in modern continuum mechanics for many years now as well as from a theoretical background as in the numerical implementation in commercial software packages in the context of finite elements. Nevertheless, some questions arise in the practical application of that matter describing technical components, e.g., in the discussion What are valid equivalent measures in order to compare different deformations? Here, one could request for expressions that arise in a deformation intensity and an indication of the deformation mode locally at each material point. We propose an extension of the well-known description of incompressible kinematics. We reformulate the strain invariants at incompressibility in terms of (I1, I2) leading to an equivalent pair (λ,m) in order to determine a distance of an arbitrary deformation state, e.g., to its equivalent shearing state. Therefore, we postulate and define an associated deformation state and give the mathematical derivation of quite nice relationships, which we demonstrate on a shear example using the finite elements method to visualize the “new” measure quantity.}, language = {en}, number = {2}, urldate = {2023-11-30}, journal = {Archive of Applied Mechanics}, author = {Baaser, H. and Hopmann, Ch. and Schobel, A.}, month = feb, year = {2013}, pages = {273--280}, }
@article{linden_untersuchungen_2013, title = {Untersuchungen bezüglich der {Einschränkung} von {Taluskippung} und -vorschub durch verschiedene {Sprunggelenkorthesen} nach fibularer {Bandruptur} [{Constraint} of talar tilt and anterior drawer by differerent ankle braces after the rupture of fibular ligament]}, volume = {2}, copyright = {All rights reserved}, url = {http://opus4.bibliothek.fh-aachen.de/opus4/files/5227/van_Laack Beleg.pdf http://opus.bibliothek.fh-aachen.de/opus4/frontdoor/index/index/docId/5227}, doi = {10.3238/oup.2013.0306-0309}, abstract = {Die fibulare Bandruptur z\{ä\}hlt zu einer der am h\{ä\}ufigsten auftretenden Verletzungen des Bewegungsapparats. In den meisten F\{ä\}llen wird heute die konservativ fr\{ü\}hfunktionelle Therapie mit Sprunggelenkorthesen allgemein bevorzugt. Im Rahmen der vorliegenden Studie wurden 14 verschiedene Sprunggelenkorthesen im Hinblick auf ihre Einschr\{ä\}nkung von Taluskippung und Talusvorschub untersucht. Zur Simulation einer fibularen Bandruptur wurde ein Unterschenkelmodell aus Holz mit Fu\{ß\}teil, mit angelegten Orthesen in einen Scheuba-Halteapparat eingespannt und mit 150 N seitlich sowie anterior-posterior belastet. Anhand der erstellten „gehaltenen“ R\{ö\}ntgenaufnahmen konnten Taluskippung und Talusvorschub jeder einzelnen Orthese eindeutig bestimmt werden. Die meisten Orthesen erreichten zufriedenstellende Ergebnisse. Es stellte sich heraus, dass vor allem eine eng anliegende, im Gelenkbereich anatomisch angepasste Form vorteilhaft zu sein scheint. [The ankle sprain is actually one of the most common injuries. Nowadays the conservative pre-functional therapy with ankle braces is generally preferred. In the present study 14 different ankle braces were tested with regard to their ability to constrict the talar tilt and anterior drawer displacement. As part of the tests a wooden model of a foot was used in order to simulate an ankle sprain. This model was clamped in a Scheuba-device with different ankle braces and a force of 150 N was applied to it. The stress radiographs showed different talar tilts and anterior drawers of each brace. Most ankle braces achieved a satisfying result. It has become obvious that a tight fitting and an anatomically designed shape seem to be favourable..]}, number = {6}, journal = {OUP Zeitschrift f\{ü\}r die orthop\{ä\}dische und unfallchirurgische Praxis}, author = {Linden, A and Fischöder, M and Staat, Manfred and van Laack, Walter}, year = {2013}, note = {ZSCC: NoCitationData[s0]}, keywords = {Soccer, damping, efficiency, impact test, protection, soccer shin guards}, pages = {306--309}, }
@article{staat_limit_2013, title = {Limit analysis of flaws in pressurized pipes and cylindrical vessels. {Part} {II}: {Circumferential} defects}, volume = {97}, copyright = {All rights reserved}, issn = {00137944}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0013794412002573}, doi = {10.1016/j.engfracmech.2012.05.017}, abstract = {Upper and lower bound theorems of limit analyses have been presented in part I of the paper. Part II starts with the finite element discretization of these theorems and demonstrates how both can be combined in a primal–dual optimization problem. This recently proposed numerical method is used to guide the development of a new class of closed-form limit loads for circumferential defects, which show that only large defects contribute to plastic collapse with a rapid loss of strength with increasing crack sizes. The formulae are compared with primal–dual FEM limit analyses and with burst tests. Even closer predictions are obtained with iterative limit load solutions for the von Mises yield function and for the Tresca yield function. Pressure loading of the faces of interior cracks in thick pipes reduces the collapse load of circumferential defects more than for axial flaws. Axial defects have been treated in part I of the paper. ► This paper presents plastic limit loads for cracked thick-walled pipes for von Mises yield function and for Tresca yield function. ► Limit loads are given for the whole parameter range: from shallow to penetrating cracks, from short to fully-circumferential defects. ► Limit loads are derived for exterior cracks and for interior surface flaws with and without pressure on crack faces. ► All limit loads are compared with direct primal–dual FEM limit analyses and with burst tests.}, number = {1}, journal = {Engineering Fracture Mechanics}, author = {Staat, Manfred and Vu, Duc Khôi}, month = jan, year = {2013}, note = {ZSCC: 0000018}, keywords = {Circumferential crack, Global collapse, Limit load, Plasticity, Pressure loaded crack-face}, pages = {314--333}, }
@article{anding_introducing_2013, title = {Introducing a method of in vitro testing of different anchoring systems used for female incontinence and prolapse surgery}, volume = {2013}, copyright = {All rights reserved}, issn = {2314-6133}, url = {http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3881509&tool=pmcentrez&rendertype=abstract http://www.hindawi.com/journals/bmri/2013/401417/}, doi = {10.1155/2013/401417}, abstract = {AIMS: To develop a method for in vitro testing to compare different intracorporeal anchoring systems (AS) used, for example, in single-incision slings or vaginal meshes. Intracorporeal fixation needs reliable anchorage systems, which keep the implant in the operative and early postoperative phase in place. Up to now, the impact of the design of current anchor systems and their capability to provide sufficient retention forces is not known. METHODS: Four AS ("PelFix", "Surelift", "TFS", and "MiniArc") were evaluated in an animal model and a ballistic gelatine model with pull-out tests. We performed ANOVA with post hoc Bonferroni. Results were presented as mean values whereby a significance level of {\textbackslash}textless0.05 was considered significant. RESULTS: The four systems showed significantly different pull-out forces. Depending on mesh structure, size, and form of the AS, mechanical strain resulted in deformation with local peak stresses. Under the condition of form stability, relative differences of pull-out forces did not change in different tissues. CONCLUSIONS: Reliable testing of different AS in their ability to keep mesh implants in place can be done in animal models and in especially designed ballistic gelatine. These methods of testing will help to modify AS in novel pelvic floor implants.}, journal = {BioMed Research International}, author = {Anding, Ralf and Tabaza, Ruth and Staat, Manfred and Trenz, Eva and Lohmann, Philipp and Klinge, Uwe and Kirschner-Hermanns, Ruth}, month = jan, year = {2013}, pmid = {24455692}, note = {ZSCC: 0000009 }, keywords = {Animal, Animals, Disease Models, Female, Gelatin, Gelatin: chemistry, Gelatin: therapeutic use, Humans, Pelvic Floor, Pelvic Floor: pathology, Pelvic Floor: surgery, Prolapse, Prostheses and Implants, Swine}, pages = {1--7}, }
@article{levers_gonarthrosetherapie_2013, title = {Gonarthrosetherapie auf {Kernspinresonanzbasis} mit {MBST}-{Vierjahresbeobachtungen}}, volume = {2013}, copyright = {All rights reserved}, number = {7/8}, journal = {Orthopädische Nachrichten}, author = {Levers, A and Staat, Manfred and van Laack, Walter}, year = {2013}, note = {ZSCC: 0000001}, pages = {13}, }
@article{kim_comparison_2012, title = {A comparison among {Neo}-{Hookean} model, {Mooney}-{Rivlin} model, and {Ogden} model for chloroprene rubber}, volume = {13}, issn = {2234-7593, 2005-4602}, url = {http://link.springer.com/10.1007/s12541-012-0099-y}, doi = {10.1007/s12541-012-0099-y}, abstract = {Neo-Hookean model and Mooney-Rivlin model are hyperelastic material models where the strain energy density function is made from invariants of the left Cauchy-Green deformation tensor. Even though Ogden model is a hyperelastic material model, its strain energy density function is expressed by principal stretch ratio. These three models have been widely used in industries. Recently, Ogden model, especially Ogden 3rd model, shows better agreement with the test data than others. In spite of the limitations to describe particular stress states, it is known that reasonable results using these models can be obtained for various structural components. In this research, three kinds of models are considered for Chloroprene rubber. Three kinds of tests (Uniaxial tension test, Biaxial tension test, and Planar shear test) are performed for Chloroprene specimen and through four kinds of test combinations (Uni+Bi, Uni+Pl, Bi+Pl, Uni+Bi+Pl), numerical simulations are carried out for Neo-Hookean model, Mooney-Rivlin model, and Ogden model. It is shown that Mooney-Rivlin model and Ogden model can be used for Chloroprene Rubber in the specific ranges for Isotropic Hyperelastic model.}, language = {en}, number = {5}, urldate = {2024-03-20}, journal = {International Journal of Precision Engineering and Manufacturing}, author = {Kim, Beomkeun and Lee, Seong Beom and Lee, Jayone and Cho, Sehyun and Park, Hyungmin and Yeom, Sanghoon and Park, Sung Han}, month = may, year = {2012}, pages = {759--764}, }
@article{nguyen_influence_2012, title = {Influence of a freeze–thaw cycle on the stress–stretch curves of tissues of porcine abdominal organs}, volume = {45}, copyright = {All rights reserved}, issn = {00219290}, url = {http://www.ncbi.nlm.nih.gov/pubmed/22867765 http://linkinghub.elsevier.com/retrieve/pii/S0021929012003983}, doi = {10.1016/j.jbiomech.2012.07.008}, abstract = {The paper investigates both fresh porcine spleen and liver and the possible decomposition of these organs under a freeze-thaw cycle. The effect of tissue preservation condition is an important factor which should be taken into account for protracted biomechanical tests. In this work, tension tests were conducted for a large number of tissue specimens from twenty pigs divided into two groups of 10. Concretely, the first group was tested in fresh state; the other one was tested after a freeze-thaw cycle which simulates the conservation conditions before biomechanical experiments. A modified Fung model for isotropic behavior was adopted for the curve fitting of each kind of tissues. Experimental results show strong effects of the realistic freeze-thaw cycle on the capsule of elastin-rich spleen but negligible effects on the liver which virtually contains no elastin. This different behavior could be explained by the autolysis of elastin by elastolytic enzymes during the warmer period after thawing. Realistic biomechanical properties of elastin-rich organs can only be expected if really fresh tissue is tested. The observations are supported by tests of intestines. © 2012 Elsevier Ltd.}, number = {14}, journal = {Journal of Biomechanics}, author = {Nguyễn, N. Huynh and Dương, M. Tuấn and Trần, T. Ngọc and Phạm, P. Tình and Grottke, Oliver and Tolba, R. and Staat, Manfred}, month = sep, year = {2012}, pmid = {22867765}, note = {ZSCC: 0000010 }, keywords = {Autolysis, Decomposition, Freeze-thaw process, Liver, Spleen}, pages = {2382--2386}, }
@inproceedings{nix_implementation_2012, title = {Implementation of the edge-based smoothed extended finite element method}, copyright = {All rights reserved}, url = {https://www.scopus.com/record/display.uri?eid=2-s2.0-84871626747&origin=inward&txGid=3242fda8b10367fbcb86133a8618d38f}, abstract = {Cutting is an essential manipulation task in surgery. For these and other discontinuities T. Belytschko et al. introduced the Extended Finite Element Method (XFEM), that allows the simulation of cuts, cracks or interfaces in virtual environments. To reduce the high computational costs in FE simulations and to improve the accuracy, G.R. Liu et al. developed the Smoothed Finite Element Method (SFEM). Combining these two methods results in the Smoothed Extended Finite Element Method (SXFEM) which was first introduced by St.P.A. Bordas et al.. They used the cell-based strain smoothing with triangular and quadrangular elements to show the ability for FE simulations. In this paper we describe our implementation of the edge-based SXFEM in the large FE software Code Aster of Electricit´e de France SA. These elements can be implemented easily because they only require the modification of the discretized gradient operator B. The implementation works for linear problems, e.g. problems with material interfaces, discretized with linear triangular elements. We compare the simulation results obtained by this method with those obtained with the standard XFEM using triangular elements. The principle of strain smoothing extended to the partition of unity enrichment simplifies the numerical integration of discontinuous approximations in the XFEM.}, booktitle = {Proceedings {European} {Congress} on {Computational} {Methods} in {Applied} {Sciences} and {Engineering} ({ECCOMAS} 2012) {Vienna}, {Austria}, {September} 10-14, 2012}, publisher = {European Community on Computational Methods in Applied Sciences (ECCOMAS)}, author = {Nix, Yvonne and Frotscher, Ralf and Staat, Manfred}, editor = {Eberhardsteiner, Josef and Böhm, Helmut J. and Rammerstorfer, Franz G.}, month = sep, year = {2012}, note = {ZSCC: NoCitationData[s0]}, keywords = {exte, smoothed extended finite element method SXFEM, smoothed extended finite elementmethod SXFEM}, pages = {8117--8123}, }
@article{klinge_op18-4_2011, title = {{OP18}-4 {Modified} stapler configuration for optimisation of colonic anastomosis}, volume = {98}, copyright = {All rights reserved}, issn = {1365-2168}, url = {https://academic.oup.com/bjs/article/98/Supplement_5/S1/6150540}, abstract = {.}, language = {English}, number = {S5}, journal = {Proccedings of ESSR 2011, 46th Annual Congress of the European Society of Surgical Research, Aachen, Germany, May 25-28, 2011}, author = {Klinge, Uwe and Trần, T N and Nováček, Vit and Staat, Manfred and Alizai, Patrick and Miesse, A M and Tolba, Rene}, editor = {Tolba, René Hany}, year = {2011}, note = {ZSCC: NoCitationData[s0]}, keywords = {anastomoses, finite element ana, surgical staplers}, pages = {S31}, }
@inproceedings{klinge_modified_2011, title = {Modified stapler configuration for optimisation of colonic anastomosis}, copyright = {All rights reserved}, abstract = {.}, booktitle = {Proccedings of {ESSR} 2011, 46th {Annual} {Congress} of the {European} {Society} of {Surgical} {Research}, {Aachen}, {Germany}, {May} 25-28, 2011}, publisher = {MEDIMOND, Pianoro, Italy}, author = {Klinge, Uwe and Trần, T N and Nováček, Vit and Staat, Manfred and Alizai, Patrick and Miesse, A M and Tolba, Rene}, editor = {Tolba, René Hany}, year = {2011}, note = {ZSCC: NoCitationData[s0]}, keywords = {anastomoses, finite element ana, surgical staplers}, pages = {21--25}, }
@article{tolba_influence_2011, title = {Influence of stapler configuration on mechanics of connecting tissues}, volume = {25}, copyright = {All rights reserved}, issn = {0930-2794}, url = {http://www.sages2011.org/influence-of-stapler-configuration-on-mechanics-of-connecting-tissues/ http://link.springer.com/10.1007/s00464-011-1598-0}, doi = {10.1007/s00464-011-1598-0}, abstract = {Surgical staplers are used to perform several intestinal procedures including reconstructions and anastomoses with highly standardised techniques. However, postoperative bleeding, anastomotic dehiscence, or stenosis cannot be completely prevented. Considering the significant variations of tissue we analysed whether an optimised design of staples and staple lines can be defined, in particular looking for the impact of staple size, closure mechanism and the number of staple lines on the local compression of the surrounding tissue.}, number = {S1}, journal = {Surgical Endoscopy}, author = {Tolba, Rene and Ngọc, Trần T and Klinge, Uwe and Segan, R and Nováček, Vit and Turquier, Frédéric and Staat, Manfred}, year = {2011}, note = {ZSCC: NoCitationData[s0]}, keywords = {anastomoses, finite element ana, surgical staplers}, pages = {261}, }
@article{doorschodt_hypothermic_2011, title = {Hypothermic machine perfusion of kidney grafts: {Which} pressure is preferred?}, volume = {39}, copyright = {All rights reserved}, issn = {0090-6964}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21161683 http://link.springer.com/10.1007/s10439-010-0228-7}, doi = {10.1007/s10439-010-0228-7}, abstract = {To assess the effect of the perfusion pressure (PP) during machine perfusion (MP) on the preservation quality of kidney grafts, we compared mean PPs of 25 and 30 mmHg using a porcine autotransplantation model. After assessment of the microcirculation, animals underwent left nephrectomy. Thereafter, kidneys were washed out followed by 20 h of MP at 25 mmHg (MP25, n = 7) or 30 mmHg (MP30, n = 7) using a novel MP system for hypothermic pulsatile perfusion. After MP preservation, the contralateral kidneys were removed and the preserved kidneys heterotopically autotransplanted. Ten minutes after reperfusion, the microcirculation was reassessed. Seven days posttransplant, animals were euthanized and the kidney grafts removed for histological analysis. MP using a mean PP of 25 mmHg resulted in higher capillary blood flow after reperfusion. In the MP30 group, 6 out of 7 animals survived, whereas in the MP25 group all animals survived. Overall, improvement in recovery of renal function and a better preservation of structural integrity were seen in the MP25 group compared to the MP30 group. Using a novel system for hypothermic MP, a mean PP of 25 mmHg is preferred over a mean PP of 30 mmHg.}, number = {3}, journal = {Annals of Biomedical Engineering}, author = {Doorschodt, B. M. and Schreinemachers, M. C J M and Behbahani, Mehdi and Florquin, S. and Weis, J. and Staat, Manfred and Tolba, René Hany}, year = {2011}, pmid = {21161683}, note = {ZSCC: 0000019 }, keywords = {Perfusion pressure, Pig, Preservation, Transplantation}, pages = {1051--1059}, }
@inproceedings{tran_shakedown_2010, title = {Shakedown analysis of two dimensional structures by an edge-based smoothed finite element method}, copyright = {All rights reserved}, url = {https://www.eccm-2010.org/complet/fullpaper_1042.pdf}, abstract = {.An edge-based smoothed finite element method (ES-FEM) is extended for limit and shakedown analysis of structures. A primal-dual algorithm which is based upon the von Mises yield criterion and a nonlinear optimization procedure is used to calculate both the upper and lower bounds of the plastic collapse limit and the shakedown limit. Using a constant smoothing function which leads to local constant smoothing domains constructed on edges of elements, only one Gaussian point is required for each domain ensuring that the total number of variables in the resulting optimization problem is kept to a minimum compared with standard finite element formulation. Numerical examples are presented to show that stable and accurate solutions are obtained by the present method.}, booktitle = {Proceedings {ECCM} 2010, {IV} {European} {Conference} on {Computational} {Mechanics}, {Paris}, {France}, {May} 16-21, 2010}, publisher = {European Conference on Computational Mechanics}, author = {Trần, Thanh Ngọc and Staat, Manfred}, year = {2010}, note = {ZSCC: NoCitationData[s0]}, }
@incollection{tran_reliability_2009, address = {Dordrecht}, title = {Reliability analysis of inelastic shell structures under variable loads}, volume = {1}, copyright = {All rights reserved}, isbn = {978-1-4020-9633-4}, url = {http://www.springerlink.com/index/10.1007/978-1-4020-9634-1_7 http://link.springer.com/10.1007/978-1-4020-9634-1_7}, abstract = {This paper concerns the development of a primal-dual algorithm for limit and shakedown analysis of Reissner-Mindlin plates made of von Mises material. At each optimization iteration, the lower bound of the shakedown load multiplier is calculated simultaneously with the upper bound using the duality theory. An edge-based smoothed finite element method (ES-FEM) combined with the discrete shear gap (DSG) technique is used to improve the accuracy of the solutions and to avoid the transverse shear locking behaviour. The method not only possesses all inherent features of convergence and accuracy from ES-FEM, but also ensures that the total number of variables in the optimization problem is kept to a minimum compared with the standard finite element formulation. Numerical examples are presented to demonstrate the effectiveness of the present method.}, booktitle = {Limit {States} of {Materials} and {Structures}}, publisher = {Springer Netherlands}, author = {Trần, T.N. and Phạm, P.T. and Vũ, ÐK and Staat, Manfred}, editor = {Dieter, Weichert and Alan, Ponter}, year = {2009}, doi = {10.1007/978-1-4020-9634-1_7}, note = {ZSCC: NoCitationData[s0] }, pages = {135--156}, }
@article{tran_upper_2008, title = {Upper bound limit and shakedown analysis of thin plates and shells}, volume = {86}, copyright = {All rights reserved}, issn = {00457949}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0045794908000461}, doi = {10.1016/j.compstruc.2008.02.005}, abstract = {This paper concerns the development of a kinematic formulation for the finite element limit and shakedown analysis of shells. The technique is based upon an upper bound approach using the re-parameterized exact Ilyushin yield surface and a nonlinear optimization procedure. The solution of the problem is obtained by discretizing the shell into finite elements. Numerical examples are presented to show the validity of the present method.}, number = {17-18}, journal = {Computers \& Structures}, author = {Tran, Thanh Ngọc and Kreißig, Reiner and Vu, Duc Khôi and Staat, Manfred}, month = sep, year = {2008}, note = {ZSCC: NoCitationData[s0]}, keywords = {Exact Ilyushin yield surface, Limit analysis, Nonlinear programming, Shakedown analysis, Shells}, pages = {1683--1695}, }
@article{ciobanu_use_2008, title = {The use of open source software in biomechanical finite element analysis}, volume = {7/8}, copyright = {All rights reserved}, number = {4}, journal = {Buletinul Institutului Politehnic Din Iaşi}, author = {Ciobanu, Octavian and Staat, Manfred and Rahimi, A}, year = {2008}, note = {ZSCC: NoCitationData[s0]}, pages = {213--220}, }
@incollection{staat_soft_2008, address = {Berlin, Heidelberg}, title = {Soft materials in technology and biology – characteristics, properties, and parameter identification}, copyright = {All rights reserved}, isbn = {978-3-540-75408-4}, url = {http://link.springer.com/10.1007/978-3-540-75409-1_12}, abstract = {The growing interest in flexible structures has also brought biomechanics into the focus of engineers. Elastomers and soft tissues consist of similar networks of macromolecules. After a brief introduction to the concepts of continuum mechanics, typical isotropic models of soft materials in technology and biology are presented. Similarities and differences of the thermo-mechanical behavior are discussed. For rubber-like materials a modification of the Kilian network is suggested which greatly simplifies the identification of material parameters. Finally the dynamical loading of biopolymers and volume changes with phase transitions are considered.}, booktitle = {Bioengineering in {Cell} and {Tissue} {Research}}, publisher = {Springer Berlin Heidelberg}, author = {Staat, M. and Baroud, G. and Topcu, M. and Sponagel, S.}, editor = {Artmann, Gerhard M and Chien, Shu}, year = {2008}, doi = {10.1007/978-3-540-75409-1_12}, note = {ZSCC: NoCitationData[s0] }, pages = {253--315}, }
@inproceedings{tran_reliability_2008, title = {Reliability analysis of shells based on direct plasticity methods}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/257/}, booktitle = {{CD}-{ROM} {Proceedings} of 8th {World} {Congress} on {Computational} {Mechanics} ({WCCM8}) 5th {European} {Congress} on {Computational} {Methods} in {Applied} {Sciences} and {Engineering} ({ECCOMAS} 2008) {June} 30 – {July} 4, 2008, {Venice}, {Italy}}, author = {Trần, Thanh Ngọc and Phạm, Phú Tình and Staat, Manfred}, editor = {Schrefler, Bernhard A. and Perego, Umberto}, year = {2008}, note = {ZSCC: NoCitationData[s0]}, keywords = {First-order reliability method FORM, Limit analysis, Second-order reliability method SORM, Sensitivity, Shakedown analysis}, pages = {1--2}, }
@inproceedings{staat_limit_2008, title = {Limit and shakedown reliability analysis by nonlinear programming}, volume = {1}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/258/}, abstract = {Analysis of advanced structures working under extreme heavy loading such as nuclear power plants and piping system should take into account the randomness of loading, geometrical and material parameters. The existing reliability are restricted mostly to the elastic working regime, e.g. allowable local stresses. Development of the limit and shakedown reliability-based analysis and design methods, exploiting potential of the shakedown working regime, is highly needed. In this paper the application of a new algorithm of probabilistic limit and shakedown analysis for shell structures is presented, in which the loading and strength of the material as well as the thickness of the shell are considered as random variables. The reliability analysis problems may be efficiently solved by using a system combining the available FE codes, a deterministic limit and shakedown analysis, and the First and Second Order Reliability Methods (FORM/SORM). Non-linear sensitivity analyses are obtained directly from the solution of the deterministic problem without extra computational costs.}, booktitle = {Assessment of {Reliability} of {Materials} and {Structures}: {Problems} and {Solutions}. {Proceedings} of {RELMAS} 2008, {June} 17-20, 2008, {Saint} {Petersburg} {State} {Polytechnical} {University}, {Russia}}, publisher = {Минск: Изд. центр БГУ}, author = {Staat, Manfred and Trần, Thanh Ngọc and Phạm, Phú Tình}, year = {2008}, note = {ZSCC: NoCitationData[s0]}, keywords = {First an, Limit and shakedown reliability analysis}, pages = {354--358}, }
@article{vu_shakedown_2007, title = {Shakedown analysis of structures made of materials with temperature-dependent yield stress}, volume = {44}, copyright = {All rights reserved}, issn = {00207683}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0020768306005099}, doi = {10.1016/j.ijsolstr.2006.11.038}, abstract = {In this work, the shakedown of structures made of materials with temperature-dependent yield stress is considered. Under some restrictions on the thermal loading condition the yield stress is linearized and shakedown theorems are established. Based on these linearized shakedown theorems, the shakedown limit is formulated as a problem of convex optimization. An algorithm is built to compute shakedown limits. Numerical tests show good agreement with analytic solutions and experimental data. ?? 2006 Elsevier Ltd. All rights reserved.}, number = {13}, journal = {International Journal of Solids and Structures}, author = {Vu, Duc Khôi and Staat, Manfred}, month = jun, year = {2007}, note = {ZSCC: 0000014}, keywords = {Convex nonlinear optimization, Shakedown analysis, Temperature-dependent yield stress}, pages = {4524--4540}, }
@inproceedings{tran_calculation_2007, title = {Calculation of load carrying capacity of shell structures with elasto-plastic material by direct methods}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2007/227/}, abstract = {In this paper, a method is introduced to determine the limit load of general shells using the finite element method. The method is based on an upper bound limit and shakedown analysis with elastic-perfectly plastic material model. A non-linear constrained optimisation problem is solved by using Newton's method in conjunction with a penalty method and the Lagrangean dual method. Numerical investigation of a pipe bend subjected to bending moments proves the effectiveness of the algorithm.}, booktitle = {{CD}-{ROM} {Proceedings} of the {International} {Conference} on {Material} {Theory} and {Nonlinear} {Dynamics}. {MatDyn} 2007. {Hanoi}, {Vietnam}, {Sept}. 24-26, 2007}, author = {Tran, Thanh Ngoc and Staat, Manfred and Kreißig, Reiner}, year = {2007}, note = {ZSCC: 0000000}, keywords = {Ilyushin yield surface, limit analysis, shakedown analysis, shells}, pages = {1--8}, }
@article{staat_limit_2007, title = {Limit analysis of flaws in pressurized pipes and cylindrical vessels. {Part} {I}: {Axial} defects}, volume = {74}, copyright = {All rights reserved}, issn = {00137944}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0013794406002062}, doi = {10.1016/j.engfracmech.2006.04.031}, abstract = {Within the theory of plasticity recently developed primal-dual limit analyses with the finite element method (FEM) give upper and lower bounds of the limit load. The method can be iterated until both bounds have converged to the same value which is then considered the exact plastic collapse load. This new numerical method is used in part I of the paper to derive improved lower bound limit load formulae for axial defects in pressurized cylinders for any defect geometry and loading. Based on the observation that even long slits in thick pipes have a residual strength a simple formula for the stress magnification factor is justified also for thick pipes. Global collapse loads are compared with primal-dual FEM limit analyses and with a large number of burst tests. For axial defects it is possible to find corresponding local collapse loads. Part II of the paper will discuss the FEM discretization of the limit load theorems and will consider circumferential defects.}, number = {3}, journal = {Engineering Fracture Mechanics}, author = {Staat, Manfred and Vu, Duc Khoi}, month = feb, year = {2007}, note = {ZSCC: 0000036}, keywords = {Axial crack, Global and local collapse, Limit load}, pages = {431--450}, }
@inproceedings{tran_finite_2007, title = {Finite element shakedown and limit reliability analysis of thin shells}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2007/233/}, abstract = {A procedure for the evaluation of the failure probability of elastic-plastic thin shell structures is presented. The procedure involves a deterministic limit and shakedown analysis for each probabilistic iteration which is based on the kinematical approach and the use the exact Ilyushin yield surface. Based on a direct definition of the limit state function, the non-linear problems may be efficiently solved by using the First and Second Order Reliabiblity Methods (Form/SORM). This direct approach reduces considerably the necessary knowledge of uncertain technological input data, computing costs and the numerical error.}, booktitle = {Computational {Plasticity}. {Fundamentals} and {Applications}. {COMPLAS} {IX}. {Part} 1. {International} {Center} for {Numerical} {Methods} in {Engineering} ({CIMNE}), {September} 5-7, 2007, {Barcelona}, {Spain}}, publisher = {CIMNE, Barcelona}, author = {Trần, Thanh Ngọc and Staat, Manfred and Kreißig, Reiner}, editor = {Oñate, Eugenio and Owen, D R J and Suárez, B}, year = {2007}, note = {ZSCC: NoCitationData[s0]}, keywords = {First Order Reliabib, exact Ilyushin yield surface}, pages = {186--189}, }
@article{staat_limit_2006, title = {Limit loads of circumferentially flawed pipes and cylindrical vessels under internal pressure}, volume = {83}, copyright = {All rights reserved}, issn = {03080161}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0308016106000184}, doi = {10.1016/j.ijpvp.2006.01.002}, abstract = {Published limit load formulae for circumferential defects overestimate the burst pressure for penetrating defects in pipes by the factor two in the short crack limit, because they only consider axial stress. Therefore, a class of limit load solution is discussed which takes the triaxial state of stress into account. The solutions for pressure loaded crack faces are improved analytically. Primal–dual limit analysis with the finite element method is used to adjust all solutions to numerical results. Limit loads are obtained for circumferential cracks of all sizes in thick-walled cylinders.}, number = {3}, journal = {International Journal of Pressure Vessels and Piping}, author = {Staat, Manfred and Vu, Duc Khoi}, year = {2006}, note = {ZSCC: 0000015}, keywords = {Circumferentially cracked pipe, Global collapse, Limit analysis, Limit load}, pages = {188--196}, }
@article{staat_direct_2005, title = {Direct finite element route for design-by-analysis of pressure components}, volume = {82}, copyright = {All rights reserved}, issn = {03080161}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0308016104001073}, doi = {10.1016/j.ijpvp.2004.04.006}, abstract = {In the new European standard for unfired pressure vessels, EN 13445-3, there are two approaches for carrying out a Design-by-Analysis that cover both the stress categorization method (Annex C) and the direct route method (Annex B) for a check against global plastic deformation and against progressive plastic deformation. This paper presents the direct route in the language of limit and shakedown analysis. This approach leads to an optimization problem. Its solution with Finite Element Analysis is demonstrated for mechanical and thermal actions. One observation from the examples is that the so-called 3f (3Sm) criterion fails to be a reliable check against progressive plastic deformation. Precise conditions are given, which greatly restrict the applicability of the 3f criterion.}, number = {1}, journal = {International Journal of Pressure Vessels and Piping}, author = {Staat, Manfred and Heitzer, Michael and Lang, H. and Wirtz, Klaus}, month = jan, year = {2005}, note = {ZSCC: 0000016}, keywords = {Alternating plasticity, Design-by-analysis, Progressive plastic deformation, Shakedown analysis, Shakedown criterion}, pages = {61--67}, }
@article{heitzer_shakedown_2003, title = {Shakedown and ratchetting under tension–torsion loadings: analysis and experiments}, volume = {225}, copyright = {All rights reserved}, issn = {00295493}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0029549303001341}, doi = {10.1016/S0029-5493(03)00134-1}, abstract = {Structural design analyses are conducted with the aim of verifying the exclusion of ratchetting. To this end it is important to make a clear distinction between the shakedown range and the ratchetting range. The performed experiment comprised a hollow tension specimen which was subjected to alternating axial forces, superimposed with constant moments. First, a series of uniaxial tests has been carried out in order to calibrate a bounded kinematic hardening rule. The load parameters have been selected on the basis of previous shakedown analyses with the PERMAS code using a kinematic hardening material model. It is shown that this shakedown analysis gives reasonable agreement between the experimental and the numerical results. A linear and a nonlinear kinematic hardening model of two-surface plasticity are compared in material shakedown analysis.}, number = {1}, journal = {Nuclear Engineering and Design}, author = {Heitzer, Michael and Staat, Manfred and Reiners, H. and Schubert, Florian}, year = {2003}, note = {ZSCC: 0000021}, pages = {11--26}, }
@incollection{heitzer_limit_2002, series = {Lecture {Notes} in {Economics} and {Mathematical} {Systems}}, title = {Limit and shakedown analysis with uncertain data}, volume = {513}, copyright = {All rights reserved}, isbn = {978-3-540-42889-3}, abstract = {The structural reliability with respect to plastic collapse or to inadaptation is formulated on the basis of the lower bound limit and shakedown theorems. A direct definition of the limit state function is achieved. The suggested approach which combines the FE method with first order reliability methods (FORM) leads to a better understanding of the influences on the structural behaviour. The theorems are implemented into a general purpose FEM program in a way capable of large-scale analysis. The limit state function and its gradient are obtained from a mathematical optimization problem. This direct approach reduces considerably the necessary knowledge of uncertain technological input data, the computing time, and the numerical error, leading to highly effective and precise reliability analyses.}, booktitle = {Stochastic {Optimization} {Techniques}, {Numerical} {Methods} and {Technical} {Applications}}, publisher = {Springer, Berlin, Heidelberg}, author = {Heitzer, Michael and Staat, Manfred}, editor = {Marti, Kurt}, year = {2002}, note = {ZSCC: NoCitationData[s0]}, pages = {253--267}, }
@inproceedings{staat_restricted_2002, title = {The restricted influence of kinematic hardening on shakedown loads}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2005/79/}, abstract = {Structural design analyses are conducted with the aim of verifying the exclusion of ratcheting. To this end it is important to make a clear distinction between the shakedown range and the ratcheting range. In cyclic plasticity more sophisticated hardening models have been suggested in order to model the strain evolution observed in ratcheting experiments. The hardening models used in shakedown analysis are comparatively simple. It is shown that shakedown analysis can make quite stable predictions of admissible load ranges despite the simplicity of the underlying hardening models. A linear and a nonlinear kinematic hardening model of two-surface plasticity are compared in material shakedown analysis. Both give identical or similar shakedown ranges. Structural shakedown analyses show that the loading may have a more pronounced effect than the hardening model.}, booktitle = {Proceedings of {WCCM} {V}, {Fifth} {World} {Congress} on {Computational} {Mechanics}, {July} 7-12, 2002, {Vienna}, {Austria}}, author = {Staat, Manfred and Heitzer, Michael}, editor = {H.A. Mang F.G. Rammerstorfer, J Eberhardteiner}, year = {2002}, note = {ZSCC: NoCitationData[s0]}, keywords = {linear kinematic hardening, material shakedown, nonlinear kinematic hardening, ratcheting, shakedown}, pages = {10}, }
@inproceedings{staat_achievements_2002, title = {Some achievements of the {European} project {LISA} for {FEM} based limit and shakedown analysis}, volume = {2002}, copyright = {All rights reserved}, isbn = {0-7918-4652-0}, url = {http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1585683}, doi = {10.1115/PVP2002-1300}, abstract = {The load-carrying capacity or the safety against plastic limit states are central questions in the design of pressure equipment. The new European standard prEN 13445-3 reflects the fact that plastic limit states can be calculated simply by perfectly plastic limit and shakedown analyses. These methods can be derived from static and kinematic theorems for lower and upper bound analysis, respectively. Both may be formulated as optimization problems for finite element discretizations of structures. The problems of large-scale analysis have been solved in an European research project. The methods could be made more realistic by extension to other material models such as a two-surface plasticity model of kinematic hardening. Limit and shakedown analyses are briefly demonstrated with illustrative examples, which are chosen to show some limitations of the 3Sm criterion and the effect of kinematic hardening.}, booktitle = {Computational {Mechanics}: {Developments} and {Applications}}, publisher = {ASME}, author = {Staat, Manfred}, editor = {{Badie}}, year = {2002}, note = {ZSCC: NoCitationData[s0]}, keywords = {Design, Finite element analysis, Finite element methods, Finite element model, Hardening, Load bearing capacity, Optimization, Plasticity, Pressure, Theorems (Mathematics)}, pages = {177--185}, }
@article{staat_rezension_2002, title = {Rezension zu: {K}. {Zimmermann}, {Technische} {Mechanik} – multimedial. {Fachbuch} {Verlag} {Leipzig} (2000).}, volume = {22}, copyright = {All rights reserved}, number = {1}, journal = {Technische Mechanik}, author = {Staat, Manfred}, year = {2002}, note = {ZSCC: NoCitationData[s0]}, pages = {76--77}, }
@inproceedings{heitzer_shakedown_2001, title = {Shakedown und {Ratchetting} bei {Zug}- und {Torsionsbelastung}: {Analyse} und {Experimente} [{Shakedown} and ratchetting under tension-torsion loadings: analysis and experiments]}, volume = {2}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/241/}, abstract = {Traglast- und Einspielanalysen sind vereinfachte doch exakte Verfahren der klassischen Plastizitätstheorie, die neben ausreichender Verformbarkeit keine einschränkenden Voraussetzungen beinhalten. Die Vereinfachungen betreffen die Beschaffung der Daten und Modelle für Details der Lastgeschichte und des Stoffverhaltens. Eine FEM-basierte Traglast- und Einspielanalyse für ideal plastisches Material wurde auf ein kinematisch verfestigendes Materialgesetz erweitert und in das Finite Element Programm PERMAS implementiert. In einem einfachen Zug-Torsionsexperiment wurde eine Hohlprobe mit konstanter Torsion und zyklischer Zugbelastung beansprucht, um die neue Implementierung zu verifizieren. Es konnte gezeigt werden, dass die Einspielanalyse gut mit den experimentellen Ergebnissen übereinstimmt. Bei Verfestigung lassen sich wesentlich größere Sicherheiten nachweisen. Dieses Potential bedarf weiterer experimenteller Absicherung. Parallel dazu ist die Eisnpieltheorie auf fortschrittliche Verfestigungsansätze zu erweitern.}, booktitle = {27. {MPA}-{Seminar}: {Sicherheit} und {Verfügbarkeit} in der {Anlagentechnik}, {Stuttgart}, 4.-5. {Oktober} 2001}, publisher = {Staatliche Materialpr\{ü\}fungsanstalt Stuttgart}, author = {Heitzer, Michael and Reiners, H and Schubert, Florian and Staat, Manfred}, editor = {Roos, Eberhard}, year = {2001}, note = {ZSCC: NoCitationData[s0]}, keywords = {ratcheting, shakedown, tension torsion experiment}, pages = {24.1. 24.16}, }
@article{staat_lisa_2001, title = {{LISA} — a {European} project for {FEM}-based limit and shakedown analysis}, volume = {206}, copyright = {All rights reserved}, issn = {00295493}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0029549300004155}, doi = {10.1016/S0029-5493(00)00415-5}, abstract = {The load-carrying capacity or the safety against plastic limit states are the central questions in the design of structures and passive components in the apparatus engineering. A precise answer is most simply given by limit and shakedown analysis. These methods can be based on static and kinematic theorems for lower and upper bound analysis. Both may be formulated as optimization problems for finite element discretizations of structures. The problems of large-scale analysis and the extension towards realistic material modelling will be solved in a European research project. Limit and shakedown analyses are briefly demonstrated with illustrative examples.}, number = {2-3}, journal = {Nuclear Engineering and Design}, author = {Staat, Manfred and Heitzer, Michael}, month = jun, year = {2001}, note = {ZSCC: 0000086}, pages = {151--166}, }
@inproceedings{staat_kollapsanalyse_2001, title = {Kollapsanalyse von längsfehlerbehafteten {Rohren} und {Behältern} [{Collapse} analysis of longitudinally flawed pipes and vessels]}, volume = {1}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/242/}, abstract = {Berstdrücke von 134 Rohren und Behältern mit axialen Oberflächenfehlern mit vier Ingenieurmethoden wurden bei Rißtiefen ab 85\% der Wanddicke besonders große Streuungen beobachtet. Die benutzten Formeln stellten im Kern Traglastnäherungen für dünnwandige Rohre dar. Vorversuche mit verschiedenen Temperaturen, Kerbformen und Rissen hatten gezeigt, dass bei allen Oberfllächenrissen Versagen durch vollplastischen Kollaps angenommen werden konnte. Deshalb wurden die Versuche in der Regel vereinfacht mit eingefrästen Kerben durchgeführt. Bruchmechanische Kennwerte lagen i.a. nicht vor. Daher ist eine Bewertung nach der Traglastmethode angemessen und durchführbar. Die genannten Abweichungen konnten nicht alleine auf die statistischen Unsicherheiten in Geometrie und Werkstoffkennwerten zurückgeführt werden. Vielmehr wurde vermutet, dass die benutzten Traglastnäherungen für tiefe Risse ungeeignet sind. Daher wurde der Datensatz um die tiefen Risse reduziert. Bei den verbliebenen 90 Datensätzen konnte mit der besten Traglastnäherung in 40\% (60\%) der Fälle eine Genauigkeit von ±10\% (±20\%) erreicht werden. Dieser Beitrag geht davon aus, dass die Werkstoffe in allen Fällen ausreichend duktil waren, so dass plastischer Kollaps vorlag, und stellt daher neue Näherungen für Traglasten vor, die alle Rissabmessungen gleich gut beschreiben: lang, kurz, flach (bis rissfrei) und tief (einschließlich Durchriss). Außerdem werden alle Näherungen für dickwandige Rohre formuliert. Dieser Zielrichtung entsprechend wurde die Datenbasis auf 281 Berstversuche erweitert und schließt jetzt ungerissene und geschlitzte Rohre mit ein.}, booktitle = {27. {MPA}-{Seminar}: {Sicherheit} und {Verfügbarkeit} in der {Anlagentechnik}, {Stuttgart}, 4.-5. {Oktober} 2001}, publisher = {Staatliche Materialpr\{ü\}fungsanstalt Stuttgart}, author = {Staat, Manfred and Szelinski, Ernst and Heitzer, Michael}, editor = {Roos, Eberhard}, year = {2001}, note = {ZSCC: NoCitationData[s0]}, keywords = {axial crack, burst test, limit analysis, plastic c}, pages = {4.1--4.20}, }
@incollection{heitzer_reliability_2000, address = {Dordrecht}, series = {Solid {Mechanics} and {Its} {Applications}}, title = {Reliability analysis of elasto-plastic structures under variable loads}, volume = {83}, copyright = {All rights reserved}, isbn = {978-1-4020-0382-0}, url = {http://www.springerlink.com/index/10.1007/978-94-010-9421-4_17}, abstract = {Structural reliability analysis is based on the concept of a limit state function separating failure from safe states of a structure. The paper discusses some difficulties of different reliability methods for FEM-discretized nonlinear structures. It is proposed that theorems of limit and shakedown analysis are used for a direct definition of the limit state function for failure by plastic collapse or by inadaptation. Shakedown describes an asymptotic and therefore time invariant structural behaviour under time variant loading. The limit state function and its gradient is obtained from a mathematical optimization problem. For application to large FEM models a basis reduction method is used. The method is implemented into a general purpose FEM code. Combined with FORM highly effective, robust and precise analyses could be performed for high-reliabilty problems.}, booktitle = {Inelastic {Analysis} of {Structures} under {Variable} {Loads}: {Theory} and {Engineering} {Applications}}, publisher = {Springer Netherlands}, author = {Heitzer, Michael and Staat, Manfred}, editor = {Weichert, Dieter and Maier, Giulio}, year = {2000}, doi = {10.1007/978-94-010-9421-4_17}, note = {ZSCC: NoCitationData[s0] }, pages = {269--288}, }
@inproceedings{heitzer_direct_2000, title = {Direct {FEM} limit and shakedown analysis with uncertain data}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2006/112/}, abstract = {The structural reliability with respect to plastic collapse or to inadaptation is formulated on the basis of the lower bound limit and shakedown theorems. A direct definition of the limit state function is achieved which permits the use of the highly effective first order reliability methods (FORM) is achieved. The theorems are implemented into a general purpose FEM program in a way capable of large-scale analysis. The limit state function and its gradient are obtained from a mathematical optimization problem. This direct approach reduces considerably the necessary knowledge of uncertain technological input data, the computing time, and the numerical error, leading to highly effective and precise reliability analyses.}, booktitle = {{CD}-{ROM} {Proceedings} of the {European} {Congress} on {Computational} {Methods} in {Applied} {Sciences} and {Engineering}, {ECCOMAS} 2000, {Barcelona}, {Spain}, 11-14 {September} 2000}, author = {Heitzer, Michael and Staat, Manfred}, editor = {Oñate, E and Bugeda, G and Suarez, B}, year = {2000}, note = {ZSCC: NoCitationData[s0]}, keywords = {FORM, limit analysis, reliabili, skaedown analysis}, pages = {1--13}, }
@inproceedings{heitzer_direct_2000-1, address = {Frankfurt/Main}, title = {Direct {FEM} approach to design-by-analysis of pressurized components}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/239/}, booktitle = {{ACHEMA} 2000, {Lecture} groups {Safety} {Technology}, {Equipment} and {Plant} {Engineering}, {Multiproduct} {Plants}, {Packaging}/{Tank} {Cleaning}}, publisher = {Achema}, author = {Heitzer, Michael and Staat, Manfred}, year = {2000}, note = {ZSCC: NoCitationData[s0]}, pages = {79--81}, }
@book{staat_limit_2000, address = {Jülich, Germany}, series = {Bericht des {Forschungszentrums} {Jülich}}, title = {Limit analysis of defects}, volume = {Jül-3746}, copyright = {All rights reserved}, url = {http://hdl.handle.net/2128/20601}, abstract = {The present report introduces the use of numerical limit analysis in ductile fracture mechanics. Limit analysis is a structural mechanics method, which finds increasing application in engineering fracture mechanics. Emphasis is put on possible improvements in the integrity assessment of crack containing components which may be achieved by combining the approach with the Finite Element Method (FEM). Several applications and examples for numerical and experimental validations are presented. This report describes the LISA developments in connection with current practice of defect assessment and material testing. The Brite-EuRam III project LISA: FEM-Based Limit and Shakedown Analysis for Design and Integrity Assessment in European Industry is planned to extend and generalize the numerical methods of the so-called direct approach for the assessment of maximum load carrying capacity due to monotonic and cyclic loading (limit and shakedown load). Die Traglastanalyse ist eine strukturmechanische Methode, welche zunehmend in bruchmechanischen Bewertungskonzepten angewandt wird. Dieser Bericht gibt eine Einführung in die numerische Traglastanalyse in der Bruchmechanik duktiler Werkstoffe. Durch die Verbindung dieser Theorie mit Finite-Element Methoden (FEM) können Verbesserungen in der Bewertung rißbehafteter Bauteile erreicht werden. Zahlreiche Anwendungen und Beispiele zur numerischen und experimentellen Validierung werden vorgestellt. Dieser Bericht beschreibt die neuen Konzepte, die im LISA-Projekt im Rahmen der bruchmechanischen Bewertung erzielt wurden. Das Brite-EuRam III Projekt LISA: FEM-Based Limit and Shakedown Analysis for Design and Integrity Assessment in European Industry zielt auf die Erweiterung und Verallgemeinerung sogenannter direkter numerischer Methoden zur Berechnung von maximal tragbaren monotonen und zyklischen Belastungen (Trag- und Einspiellasten).}, publisher = {Research Centre Jülich}, author = {Staat, Manfred and Heitzer, Michael and Ai-Min, Yan and Khoi, Vu Duc and Hung, Nguyen Dang and Voldoire, François and Lahousse, A}, year = {2000}, note = {ZSCC: 0000017}, }
@inproceedings{lang_zyklische_1999, title = {Zyklische {Einspielversuche} zur {Verifikation} von {Shakedown}-{Analysen} mittels {FEM} [{Cyclic} plastic deformation test to verify {FEM}-based shakedown analysis]}, volume = {2}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/245/}, abstract = {Im Rahmen von Ermüdungsanalysen ist nachzuweisen, daß die thermisch bedingten fortschreitenden Deformationen begrenzt bleiben. Hierzu ist die Abgrenzung des Shakedown-Bereiches (Einspielen) vom Ratchetting-Bereich (fortschreitende Deformation) von Interesse. Im Rahmen eines EU-geförderten Forschungsvorhabens wurden Experimente mit einem 4-Stab-Modell durchgeführt. Das Experiment bestand aus einem wassergekühlten inneren Rohr und drei isolierten und beheizbaren äußeren Probestäben. Das System wurde durch alternierende Axialkräfte, denen alternierende Temperaturen an den äußeren Stäben überlagert wurden, belastet. Die Versuchsparameter wurden teilweise nach vorausgegangenen Einspielanalysen gewählt. Während der Versuchsdurchführung wurden Temperaturen und Dehnungen zeitabhängig gemessen. Begleitend und nachfolgend zur Versuchsdurchführung wurden die Belastungen und die daraus resultierenden Beanspruchungen nachvollzogen. Bei dieser inkrementellen elasto-plastischen Analyse mit dem Programm ANSYS wurden unterschiedliche Werkstoffmodelle angesetzt. Die Ergebnisse dieser Simulationsberechnung dienen dazu, die Shakedown-Analysen mittels FE-Methode zu verifizieren.}, booktitle = {25. {MPA}-{Seminar}: {Sicherheit} und {Verfügbarkeit} in der {Anlagentechnik} mit dem {Schwerpunkt} {Sicherheit} und {Zuverlässigkeit} - {Integritätsnachweise}, {Komponentenqualifikation}, {Schadensverhütung}, {Stuttgart}, 6.-7. {Oktober} 1999}, publisher = {Staatliche Materialpr\{ü\}fungsanstalt Universit\{ä\}t Stuttgart}, author = {Lang, H and Wirtz, Klaus and Heitzer, Michael and Staat, Manfred}, editor = {K, Kussmaul}, year = {1999}, note = {ZSCC: 0000000}, keywords = {ratcheting, thermal cyclic loading}, pages = {44.1--44.18}, }
@inproceedings{heitzer_structural_1999, title = {Structural reliability analysis of elasto-plastic structures}, copyright = {All rights reserved}, abstract = {Limit and shakedown therorems are exact theories of classical plasticity for the direct computation of the load carrying capacity of structures under constant and varying loads. The theorems may be used for a direct definiton of the limit state function for failure by plastic collapse or by indaptation. The theorems are implemented into a general purpose FEM program in a way capable of large-scale analysis. Then the limit state function is obtained from a mathematical optimization problem. This direct approach reduces cosnsiderably the necessary knowledge of uncertain technological input data, the computing time, and the numerical error. Moreover, the direct way leads to highly effective and precise reliability analyses.}, booktitle = {Safety and {Reliability}}, publisher = {AA Balkema, Rotterdam, Brookfield}, author = {Heitzer, Michael and Staat, Manfred}, editor = {Schuëller, G I and Kafka, P}, year = {1999}, note = {ZSCC: NoCitationData[s0]}, keywords = {F, limit analysis, reliability, shakedown analysis}, pages = {513--518}, }
@inproceedings{burgazzi_reliability_1998, title = {Reliability assessment of passive safety systems}, copyright = {All rights reserved}, url = {http://hdl.handle.net/10840/3114}, abstract = {Innovative reactor concepts make use of passive safety features to a large extent in combination with active safety or operational systems. Following the IAEA definitions a passive component does not need external input (especially energy) to operate. This is why it is expected that passive systems combine among others the advantages of simplicity, reduction of the need for human interaction, reduction or avoidance of external electrical power or signals. Besides the open feedback on economic competitiveness special aspects like lack of data on some phenomena, missing operating experience over the wide range of conditions and the smaller driving forces as - in most cases - compared to active safety systems must be taken into account. Both for active and passive systems, the effective reliability versus the achievement of safety functions is considered as an essential criteria for judging the real potential of the systems. Generally speaking, the reliability assessment of passive safety functions defined as the probability to fail the requested mission to achieve a generic safety function, depends, more than for active systems, on environment, physical, nuclear or chemical phenomena. This remark is entirely applicable to the passive B systems (i.e. implementing moving working fluids, cf. IAEA). Their mission is defined through a nominal requested time dependent evolution, for a set of selected and representative parameters and an allowable range is allocated around the nominal evolution. It is stated that the mission fails when the plant parameters are outside the allowable range. As a first approach, it is considered that the reliability assessment of passive safety functions can be estimated evaluating the probability for having the mission failure. This assessment is achieved comparing the distribution of the expected parameters values to the allowable range. This implies the identification and quantification of the uncertainties in the prediction of physical phenomena performances or interdependencies. In parallel, an adequate effort must be devoted to the improvement of thermalhydraulic computer codes that model the passive safety system behaviour to integrate those uncertainties. Finally, the transfer of the structural methodology assessment methodology (i.e. for passive A systems) must be checked to verify its applicability for the thermalhydraulic passive systems, too. The paper is focused particularly on passive B safety functions and related systems and illustrates a possible methodology for their reliability assessment. The example explained in the report can be used as a preliminary basis to motivate and to organise the content of a work that could be conducted within the framework of the European Commission sponsored activities on Reliability Methods for Passive Safety Functions.}, booktitle = {Proc. of the 6th {Internat}. {Conf}. on {Nuclear} {Engineering}, {San} {Diego}, {Calif}., {May} 10-15, 1998, {ICONE} 6-6340}, publisher = {ASME, New York, N.Y.}, author = {Burgazzi, L and Fiorini, G L and De Magistris, F and Von Lensa, Werner and Staat, Manfred and Altes, Jürgen}, year = {1998}, note = {ZSCC: NoCitationData[s0]}, pages = {1--14}, }
@inproceedings{staat_lisa_1998, title = {{LISA}, ein europäisches {Projekt} zur direkten {Berechnung} der {Tragfähigkeit} duktiler {Strukturen}}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/240/}, abstract = {Auslegung und Bemessung von Komponenten und Bauwerken erfolgen im Maschinenwesen und Konstruktiven Ingenieurbau überwiegend mit dem Ziel eines Spannungsnachweises unterhalb der Streckgrenze. Im Apparatebau wird die plastische Auslegung nach Regelwerk weitgehend aus der elastischen Spannungsanalyse durch Extrapolation experimenteller und analytischer Ergebnisse im Sinne der Traglast- und Einspieltheorie gewonnen. Deshalb bilden linear elastische Rechnungen heute noch den überwiegenden Teil der Finite Elemente Anwendungen. Begünstigt durch die schnelle Rechnerentwicklung gewinnen aber zunehmend inelastische Analysen des plastischen (zeitunabhängigen) oder viskosen (zeitabhängigen) Verhaltens an Bedeutung. Das Ziel ist die kostengünstige Entwicklung betriebs- und sicherheitsoptimierter Strukturen. Inkrementelle elasto-plastische Analysen des Strukturverhaltens lösen die mit der Spannungsbewertung verbundenen Probleme nur teilweise. Daneben sind sie mit einem nicht immer zu rechtfertigenden hohen Aufwand an Rechnerzeit, Personaleinsatz und Daten-Beschaffungskosten verbunden. Mit der Traglast- und Einspielanalyse bietet sich eine Methode an, die eine Spannungsbewertung umgeht und deren Aufwand eher einer elastischen Rechnungen entspricht. Im Regelwerk ist das Traglastkonzept für Balkenbiegung seit 1947 in Großbritannien und seit 1959 in den U.S.A. akzeptiert. Es ist in den neuen Eurocodes enthalten und findet Anwendung in der Zähbruchmechanik. Trag- und Einspiellast bilden in der einen oder anderen Weise die Grundlage der Auslegungskonzepte aller Regelwerke für Druckbehälter und Rohrleitungen.}, booktitle = {{PERMAS}–{Benutzertagung}, 8.-9.10.1998, {Stuttgart}}, publisher = {INTES GmbH, Stuttgrt}, author = {Staat, Manfred and Heitzer, Michael and Hicken, Enno F}, year = {1998}, note = {ZSCC: NoCitationData[s0]}, keywords = {limit analysi, shakedown analysis}, }
@article{kaliske_finite_1997, title = {On the finite element implementation of rubber‐like materials at finite strains}, volume = {14}, copyright = {https://www.emerald.com/insight/site-policies}, issn = {0264-4401}, url = {https://www.emerald.com/insight/content/doi/10.1108/02644409710166190/full/html}, doi = {10.1108/02644409710166190}, abstract = {Derives a formulation for spatial stress tensors and spatial material tensors of hyperelastic material. Looks at a class of materials with the strain energy function decomposed into a volumetric and a deviatoric part. Separate terms formulate the strain energy with respect to the invariants of the left Cauchy‐Green tensor. Stress and material tensors, which play a crucial role in the solution process of the finite element formulation, are derived solely in the current configuration. Applies the described framework to several different constitutive models based on phenomenologically and physically motivated material descriptions. Proposes a formulation for the finite element implementation of van der Waals material. Compares numerical results with experimental investigations given in the literature. For three‐dimensional finite element computations standard elements and mixed elements, based on a three‐field variational principle where displacements, the hydrostatic pressure and the dilatations are independent variables, are used.}, language = {en}, number = {2}, urldate = {2024-03-26}, journal = {Engineering Computations}, author = {Kaliske, M. and Rothert, H.}, month = mar, year = {1997}, pages = {216--232}, }
@inproceedings{fiorini_reliability_1997, title = {Reliability methods for passive safety function}, copyright = {All rights reserved}, url = {http://hdl.handle.net/10840/3114}, booktitle = {Proceedings of {Post} {SMiRT} 14, {Seminar} 18 {Passive} {Safety} {Features} in {Nuclear} {Installations}, {Pisa}, {August} 25-27, 1997}, publisher = {International \& American Associations for Structural Mechanics in Reactor Technology}, author = {Fiorini, G L and Staat, Manfred and von Lensa, Werner and Burgazzi, L}, year = {1997}, note = {ZSCC: 0000005}, keywords = {reliabilty}, }
@inproceedings{staat_limit_1997, title = {Limit and shakedown analysis using a general purpose finite element code}, volume = {97}, copyright = {All rights reserved}, booktitle = {Proceedings of {NAFEMS} {World} {Congress} '97 on {Design}, {Simulation} \& {Optimisation} : reliability \& applicability of computational methods ; {Stuttgart}, {Germany}, 9 - 11 {April} 1997}, publisher = {Bell\&Bain Ltd Glasgow}, author = {Staat, Manfred and Heitzer, Michael}, month = apr, year = {1997}, note = {ZSCC: 0000019}, pages = {522--533}, }
@inproceedings{staat_limit_1997-1, title = {Limit and shakedown analysis for plastic safety of complex structures}, volume = {B}, copyright = {All rights reserved}, url = {https://repository.lib.ncsu.edu/handle/1840.20/31910}, abstract = {Limit and shakedown theorems are exact theories of classical plasticity for the direct computation of the load carrying capacity under constant and varying loads. They are implemented in a general purpose FEM program in a way capable of large-scale analysis. The method deviates from the current approach in several aspects: No load history is used, stresses and strains are not calculated, and the safety factor is obtained from a mathematical optimization problem. This reduces considerably the necessary technological input data, the computing time, and the numerical error.}, booktitle = {Transactions of the 14th {International} {Conference} on {Structural} {Dynamics} in {Reactor} {Technology} ({SMiRT}-14), {Lyon}, {France}, {August} 17-22, 1997}, publisher = {International \& American Associations for Structural Mechanics in Reactor Technology}, author = {Staat, Manfred and Heitzer, Michael}, editor = {Livolant, M}, year = {1997}, note = {ZSCC: NoCitationData[s0]}, pages = {33--40}, }
@inproceedings{staat_limit_1997-2, address = {Stuttgart}, title = {Limit and shakedown analysis for plastic design}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2008/244/}, abstract = {Limit and shakedown theorems are exact theories of classical plasticity for the direct computation of safety factors or of the load carrying capacity under constant and varying loads. Simple versions of limit and shakedown analysis are the basis of all design codes for pressure vessels and pipings. Using Finite Element Methods more realistic modeling can be used for a more rational design. The methods can be extended to yield optimum plastic design. In this paper we present a first implementation in FE of limit and shakedown analyses for perfectly plastic material. Limit and shakedown analyses are done of a pipe–junction and a interaction diagram is calculated. The results are in good correspondence with the analytic solution we give in the appendix.}, booktitle = {Proceedings of 7th {German}-{Japanese} {Joint} {Seminar} on {Research} in {Structural} {Strength} and {NDE}-{Problems} in {Nuclear} {Engineering}}, publisher = {Staatliche Materialprüfungsanstalt, Stuttgart}, author = {Staat, Manfred and Heitzer, Michael}, editor = {Kussmaul, Karl}, month = sep, year = {1997}, note = {ZSCC: NoCitationData[s0]}, keywords = {limit analysis, shakedown analysis}, pages = {4.3.1--4.3.19}, }
@inproceedings{staat_problems_1996, address = {Vienna}, title = {Problems and chances for probabilistic fracture mechanics in the analysis of steel pressure boundary reliability}, volume = {IAEA-TECDO}, copyright = {All rights reserved}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2006/189/ https://www-pub.iaea.org/MTCD/Publications/PDF/te_920_web.pdf http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/28/021/28021623.pdf}, abstract = {It is shown that the difficulty for probabilistic fracture mechanics (PFM) is the general problem of the high reliability of a small population. There is no way around the problem as yet. Therefore what PFM can contribute to the reliability of steel pressure boundaries is demonstrated with the example of a typical reactor pressure vessel and critically discussed. Although no method is distinguishable that could give exact failure probabilities, PFM has several additional chances. Upper limits for failure probability may be obtained together with trends for design and operating conditions. Further, PFM can identify the most sensitive parameters, improved control of which would increase reliability. Thus PFM should play a vital role in the analysis of steel pressure boundaries despite all shortcomings.}, booktitle = {Technical feasibility and reliability of passive safety systems for nuclear power plants. {Proceedings} of an {Advisory} {Group} {Meeting} held in {Jülich}, 21-24 {November} 1994}, publisher = {International Atomic Energy Agency, Vienna}, author = {Staat, Manfred}, year = {1996}, note = {ZSCC: 0000004}, keywords = {leak-before-brea, probabilistic fracture mechanics}, pages = {43--55}, }
@article{kawabata_mechanism_1995, title = {Mechanism of carbon-black reinforcement of rubber vulcanizate}, volume = {68}, issn = {1943-4804, 0035-9475}, url = {https://meridian.allenpress.com/rct/article/68/2/311/92164/Mechanism-of-CarbonBlack-Reinforcement-of-Rubber}, doi = {10.5254/1.3538745}, abstract = {The mechanism of reinforcing rubber with carbon black particles is investigated by comparing the strain energy density functions of pure and reinforced rubbers. Finite deformation biaxial extension experiments are used to measure the strain energy density. The functional form of the reinforced system, which has been proposed by Kawabata, is examined and its validity was confirmed over a temperature range of −20°C to 80°C. The functional form is: W(I1,I2)=CT(I1−3)+β(I1,I2)+γ(I1), where I1 and I2 are the invariants of the deformation tensor. Parameter C is a constant and T is the temperature. The reinforcement effect on W appears as the γ function which is not affected by temperature. The results are analyzed with respect to a network mechanical model consisting of molecule bundles connecting carbon-black aggregates. The function W is calculated and it is shown that the functional form of Wis very similar to that of the reinforced rubber.}, language = {en}, number = {2}, urldate = {2024-03-26}, journal = {Rubber Chemistry and Technology}, author = {Kawabata, Sueo and Yamashita, Yoshihiro and Ooyama, Hajime and Yoshida, Shuichi}, month = may, year = {1995}, pages = {311--329}, }
@article{staat_reliability_1995, title = {Reliability of an {HTR}-module primary circuit pressure boundary {Influences}, sensitivity, and comparison with a {PWR}}, volume = {158}, copyright = {All rights reserved}, issn = {00295493}, url = {http://linkinghub.elsevier.com/retrieve/pii/002954939501040O}, doi = {10.1016/0029-5493(95)01040-O}, abstract = {The reliability of the HTR-module for electricity and steam generation was analysed for normal operation, as well as accident conditions. The probabilistic fracture mechanics assessment was performed with a modification of the zerberus code on the basis of widely used data. The calculated failure probabilities may thus be compared with similar investigations. The HTR-module primary circuit pressure boundary as a unit showed leak-before-break behaviour in a probabilistic sense, although a break was more probable than a leak for some of its parts. However, the findings may depend greatly on the stochastic data. Therefore a stochastic reference problem is defined and the results are compared with the Japanese round robin on a PWR section. Possible changes of failure probabilities and of the leak-before-break behaviour are discussed for different criteria for the events leading to a leak, and for modifications of the stochastic reference problem such as the inclusion of NDE. The results may be used to identify those stochastic variables which have the greatest influence on the computed failure probabilities, and to perhaps justify further work which would provide more detailed information on these probabilities. Furthermore, there is an obvious need for reduction of the non-statistical reasons for great variations of failure probabilities.}, number = {2-3}, journal = {Nuclear Engineering and Design}, author = {Staat, Manfred}, month = sep, year = {1995}, note = {ZSCC: 0000003}, pages = {333--340}, }
@article{yeoh_forms_1993, title = {Some forms of the strain energy function for rubber}, volume = {66}, issn = {1943-4804, 0035-9475}, url = {https://meridian.allenpress.com/rct/article/66/5/754/92039/Some-Forms-of-the-Strain-Energy-Function-for}, doi = {10.5254/1.3538343}, abstract = {According to Rivlin's Phenomenological Theory of Rubber Elasticity, the elastic properties of a rubber may be described in terms of a strain energy function which is an infinite power series in the strain invariants I1, I2 and I3. The simplest forms of Rivlin's strain energy function are the neo-Hookean, which is obtained by truncating the infinite series to just the first term in I1, and the Mooney-Rivlin, which retains the first terms in I1 and I2. Recently, we proposed a strain energy function which is a cubic in I1. Conceptually, the proposed function is a material model with a shear modulus that varies with deformation. In this paper, we compare the large strain behavior of rubber as predicted by these forms of the strain energy function. The elastic behavior of swollen rubber is also discussed.}, language = {en}, number = {5}, urldate = {2024-03-26}, journal = {Rubber Chemistry and Technology}, author = {Yeoh, O. H.}, month = nov, year = {1993}, pages = {754--771}, }
@inproceedings{staat_sensitivity_1993, title = {Sensitivity of and influences on the reliability of an {HTR}-module primary circuit pressure boundary}, volume = {M}, copyright = {All rights reserved}, url = {http://www.iasmirt.org/transactions/12/MG10-2 http://www.lib.ncsu.edu/resolver/1840.20/24499}, abstract = {In this paper different failure modes of the primary circuit pressure boundary of a planned HTR-Module reactor for process heat generation under accident conditions with loss of all heat sinks are assessed probabilistically. It is shown why failure probabilities cannot be expected to represent absolute values but nevertheles, as relative values they permit an effective comparison of components and failure modes. Failure probabilities are calculated under the condition that the postulated accident has actually occurred. They are compared for various cross sections and different failure modes. The failure of the crack-free base material of the forgings as well as the Leak-Before-Break behaviour of the welds is considered. The conditional failure probabilities are to be multiplied with the cumulative frequency, still to be determined, of all event sequences leading to the accident in question to give its contribution to the total failure frequency. This contribution is low.}, booktitle = {Transactions of the 12th {International} {Conference} on {Structural} {Dynamics} in {Reactor} {Technology} ({SMiRT}-12), {Stuttgart}, {Germany}, {August} 15-20, 1993}, publisher = {Elsevier, Amsterdam}, author = {Staat, Manfred}, editor = {Kussmaul, Karl}, year = {1993}, note = {ZSCC: NoCitationData[s0]}, keywords = {leak-before-break, probabilistic fracture mechanics}, pages = {147--152}, }
@inproceedings{staat_reliability_1993, title = {Reliability of the primary circuit pressure boundary of an {HTR}-module under accident conditions}, copyright = {All rights reserved}, booktitle = {Safety and {Reliability} {Assessment}. {An} {Integral} {Approach}, {ESREL} '93,, {München}, 10 - 12 {May} 1993}, publisher = {Balkema, Elsevier, Amsterdam}, author = {Staat, Manfred}, editor = {Kafka, Peter and Wolf, Josefa}, year = {1993}, note = {ZSCC: NoCitationData[s0]}, pages = {331--342}, }
@inproceedings{staat_probabilistische_1992, title = {Probabilistische {Bewertung} des bruchmechanischen {Verhaltens} der {Primärkreisdruckumschließung} eines {HTR}-{Moduls} [{Probabilistic} {Assessment} of the {Fracture} {Mechanical} {Behaviour} of an {HTR}-{Module} {Primary} {Circuit} {Pressure} {Boundary}]}, volume = {1}, copyright = {All rights reserved}, abstract = {Im Rahmen von Ermüdungsanalysen ist nachzuweisen, daß die thermisch bedingten fortschreitenden Deformationen begrenzt bleiben. Hierzu ist die Abgrenzung des Shakedown-Bereiches (Einspielen) vom Ratchetting-Bereich (fortschreitende Deformation) von Interesse. Im Rahmen eines EU-geförderten Forschungsvorhabens wurden Experimente mit einem 4-Stab-Modell durchgeführt. Das Experiment bestand aus einem wassergekühlten inneren Rohr und drei isolierten und beheizbaren äußeren Probestäben. Das System wurde durch alternierende Axialkräfte, denen alternierende Temperaturen an den äußeren Stäben überlagert wurden, belastet. Die Versuchsparameter wurden teilweise nach vorausgegangenen Einspielanalysen gewählt. Während der Versuchsdurchführung wurden Temperaturen und Dehnungen zeitabhängig gemessen. Begleitend und nachfolgend zur Versuchsdurchführung wurden die Belastungen und die daraus resultierenden Beanspruchungen nachvollzogen. Bei dieser inkrementellen elasto-plastischen Analyse mit dem Programm ANSYS wurden unterschiedliche Werkstoffmodelle angesetzt. Die Ergebnisse dieser Simulationsberechnung dienen dazu, die Shakedown-Analysen mittels FE-Methode zu verifizieren.}, booktitle = {18. {MPA}-{Seminar}: {Sicherheit} und {Verfügbarkeit} in der {Anlagentechnik} mit dem {Schwerpunkt} {Sicherheit} und {Zuverlässigkeit} - {Integritätsnachweise}, {Komponentenqualifikation}, {Schadensverhütung}, {Stuttgart}, 8.-9. {Oktober} 1992}, publisher = {Staatliche Materialprüfungsanstalt Universität Stuttgart}, author = {Staat, Manfred}, editor = {Kussmaul, K}, year = {1992}, note = {ZSCC: NoCitationData[s0]}, keywords = {ratcheting, thermal cyclic loading}, pages = {27.1--27.18}, }
@incollection{staat_fundamental_1989, address = {Wiesbaden}, series = {Notes on {Numerical} {Fluid} {Mechanics}}, title = {Fundamental aspects of numerical methods for the propagation of multi-dimensional nonlinear waves in solids}, volume = {24}, copyright = {All rights reserved}, isbn = {978-3-528-08098-3}, url = {http://opus.bibliothek.fh-aachen.de/opus/volltexte/2007/206/ http://www.springerlink.com/index/10.1007/978-3-322-87869-4 http://link.springer.com/10.1007/978-3-322-87869-4_56}, abstract = {The nonlinear scalar constitutive equations of gases lead to a change in sound speed from point to point as would be found in linear inhomogeneous (and time dependent) media. The nonlinear tensor constitutive equations of solids introduce the additional local effect of solution dependent anisotropy. The speed of a wave passing through a point changes with propagation direction and its rays are inclined to the front. It is an open question whether the widely used operator splitting techniques achieve a dimensional splitting with physically reasonable results for these multi-dimensional problems. Maybe this is the main reason why the theoretical and numerical investigations of multi-dimensional wave propagation in nonlinear solids are so far behind gas dynamics. We hope to promote the subject a little by a discussion of some fundamental aspects of the solution of the equations of nonlinear elastodynamics. We use methods of characteristics because they only integrate mathematically exact equations which have a direct physical interpretation.}, booktitle = {Nonlinear {Hyperbolic} {Equations} — {Theory}, {Computation} {Methods}, and {Applications}}, publisher = {Vieweg+Teubner Verlag}, author = {Staat, Manfred and Ballmann, Josef}, editor = {Ballmann, Josef and Jeltsch, Rolf}, year = {1989}, doi = {10.1007/978-3-322-87869-4_56}, note = {ZSCC: NoCitationData[s0] }, keywords = {Hamiltonian, Hayes-Thomas formula, Monge cones, acceleration waves, method of characteristics}, pages = {574--588}, }
@inproceedings{ballmann_wave_1988, title = {Wave propagation and focussing in plates}, volume = {2}, copyright = {All rights reserved}, isbn = {3-88355-126-0}, abstract = {A method of bicharacteristics for the computation of stress waves in linear elastic plates with straight boundaries was first devised by CLIFTON on the basis of a proposal for gas dynamics. Also starting from gas dynamics we applied this method to plates with curved boundaries and plate structures including shear and bending. Of major interest was the computation of stress concentrations as a result of the focussing of waves that were reflected from concave boundaries, as well as from internal boundaries. We compared our numerical results with experiments that were carried out in the Shock Waves Laboratory of Aachen Technical University. Good correlations were observed which we wish to further improve upon by means of a higher order plate theory. Currently we have developed methods of characteristics for non-elastic and nonlinear materials. In regard to non-elastic materials, we have previously considered linear elastic-viscoplastic laws such as the PERZYNA model, as well as the BODNER-PARTOM model. They lead to semi-linear hyperbolic laws, i.e. the highest derivatives appear only linearly. In the case of nonlinear materials with large deformations and physical nonlinearity, we have considered isotropic elastic media. If homogeneously prestressed they show anisotropic wave propagation, resembling the observations made in linear transversely isotropic elastic media. Also in plasticity very similar effects of anisotropic wave propagation are expected, if e.g. PRANDTL-REUSS-like laws are used. Generally the strain induced anisotropy changes from point to point according to the local deformation. Attempts have been made to use this anisotropic effect in the non destructive evaluation of residual stresses with ultrasonics. A numerical method of bicharacteristics for the computation of strong stress waves in nonlinear elastic plates has been proposed by the authors for points in the interior of the domain of calculation. It was demonstrated that the numerical scheme based on this method maintains very well the form of the wave front in cases with strong anisotropy. Nonlinear behaviour of plastic materials could currently only be taken into account using deformation theory. As with many materials, especially for some rubber-like plastics and brittle materials like concrete and metal castings the nonlinear part is often dominant. With this in mind, valid statements can be made with the available program in many cases.}, booktitle = {Impact {Loading} and {Dynamic} {Behaviour} of {Materials}, {IMPACT} '87 - {International} {Conference} on {Impact} {Loading} and {Dynamic} {Behaviour} of {Materials}. {May} 18-22, 1987, {Bremen}, {Germany}}, publisher = {Deutsche Gesellschaft für Metallkunde Informationsgesellschaft, Oberursel}, author = {Ballmann, Josef and Staat, Manfred}, editor = {Chiem, C Y and Kunze, H D and Meyer, L W}, year = {1988}, note = {ZSCC: NoCitationData[s0]}, keywords = {Rayleigh waves, acceleration waves, von Schmidt waves}, pages = {949--956}, }
@incollection{ballmann_high_1985, title = {High stress intensities in focussing zones of waves}, copyright = {All rights reserved}, isbn = {978-0-444-42520-1}, url = {http://linkinghub.elsevier.com/retrieve/pii/B9780444425201500153}, abstract = {The propagation of mechanical waves in plates of isotropic elastic material is investigated. After a short introduction to the understanding of focussing of stress waves in a plate with a curved boundary, the method of characteristics is applied to a plate of hyperelastic material. Using this method the propagation of acceleration waves is discussed. Based on this a numerical difference scheme is developed for solving initial-boundary-value problems and applied to two examples: propagation of a point disturbance in a homogeneously finitely strained non-linear elastic plate and geometrical focussing in a linearly elastic plate.}, booktitle = {Local {Effects} in the {Analysis} of {Structures}.}, publisher = {Elsevier, Amsterdam}, author = {Ballmann, Josef and Raatschen, Hans-Jürgen and Staat, Manfred}, editor = {Ladeveze, P}, year = {1985}, doi = {10.1016/B978-0-444-42520-1.50015-3}, note = {ZSCC: NoCitationData[s0] }, pages = {235--252}, }
@phdthesis{staat_untersuchung_1980, address = {Aachen, Germany}, type = {Diploma {Thesis}}, title = {Untersuchung der {Biegeschwingungsanregung} gerader elastischer {Führungen} durch bewegte, schwere {Körper} mit {Hilfe} der {Methode} der {Finiten} {Elemente}}, copyright = {All rights reserved}, language = {German}, school = {RWTH Aachen University, Faculty of Mechanical Engineering}, author = {Staat, Manfred}, year = {1980}, note = {ZSCC: NoCitationData[s0]}, }
@article{truesdell_static_1963, title = {Static grounds for inequalities in finite strain of elastic materials}, volume = {12}, issn = {0003-9527, 1432-0673}, url = {http://link.springer.com/10.1007/BF00281217}, doi = {10.1007/BF00281217}, language = {en}, number = {1}, urldate = {2024-03-22}, journal = {Archive for Rational Mechanics and Analysis}, author = {Truesdell, C. and Toupin, R.}, month = jan, year = {1963}, pages = {1--33}, }
@article{truesdell_ungeloste_1956, title = {Das ungelöste {Hauptproblem} der endlichen {Elastizitätstheorie}}, volume = {36}, issn = {0044-2267, 1521-4001}, url = {https://onlinelibrary.wiley.com/doi/10.1002/zamm.19560360304}, doi = {10.1002/zamm.19560360304}, abstract = {Die bemerkenswerten Fortschritte der letzten Jahre in der endlichen Elastizitätstheorie verdankt man der Vermeidung spezieller Ansätze. Die Lösungen, ob exakt oder numerisch, sind für beliebige Formänderungsarbeitsfunktionen Σ gültig. In der gewöhnlichen linearen Theorie ist Σ eine quadratische Form, die aber schon hier nicht völlig willkürlich sein darf, sondern positive definit sein muß. Vor drei Jahren hat der Verfasser die entsprechende Frage in der endlichen Theorie ‐ nämlich welchen Einschränkungen Σ unterworfen werden muß ‐ aufgeworfen und gleichzeitig einige Ungleichungen, die er als notwendige, aber nicht als hinreichende Bedingungen vermutete, vorgeschlagen. In diesem Bericht faßt er die späteren Untersuchungen in dieser Frage zusammen. , The remarkable progress of the last few years in the finite theory of elasticity is due to the avoidance of special assumptions. The solutions, whether exact or numerical, are valid for arbitrary strain energy function Σ. In the usual, linear theory, Σ is a quadratic form, but even here it cannot be completely arbitrary, but must be positive definite. For the finite theory, three years ago the author raised the analogous question of what restriction should be placed upon Σ, and at that time he suggested certain inequalities, which he conjectured to be necerssay but not sufficient. This report summarizes later investigations of this question.}, language = {en}, number = {3-4}, urldate = {2024-03-22}, journal = {ZAMM - Journal of Applied Mathematics and Mechanics / Zeitschrift für Angewandte Mathematik und Mechanik}, author = {Truesdell, C.}, month = jan, year = {1956}, pages = {97--103}, }