TY - CHAP A1 - Tran, Ngoc Trinh A1 - Matthies, Hermann G. A1 - Stavroulakis, Georgios Eleftherios A1 - Staat, Manfred T1 - Direct plastic structural design by chance constrained programming T2 - 6th European Conference on Computational Mechanics (ECCM 6), 7th European Conference on Computational Fluid Dynamics (ECFD 7), 11-15 June 2018, Glasgow, UK N2 - We propose a stochastic programming method to analyse limit and shakedown of structures under random strength with lognormal distribution. 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 or the shakedown limit. The edge-based smoothed finite element method (ES-FEM) using three-node linear triangular elements is used. Y1 - 2018 ER - TY - CHAP A1 - Tran, N. T. A1 - Tran, Thanh Ngoc A1 - Matthies, M. G. A1 - Stavroulakis, G. E. A1 - Staat, Manfred T1 - Shakedown Analysis Under Stochastic Uncertainty by Chance Constrained Programming T2 - Advances in Direct Methods for Materials and Structures N2 - 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. Y1 - 2017 SN - 978-3-319-59810-9 U6 - http://dx.doi.org/10.1007/978-3-319-59810-9_6 SP - 85 EP - 103 PB - Springer CY - Cham ER - TY - JOUR A1 - Topçu, Murat A1 - Madabhushi, Gopal S.P. A1 - Staat, Manfred T1 - A generalized shear-lag theory for elastic stress transfer between matrix and fibres having a variable radius JF - International Journal of Solids and Structures N2 - A generalized shear-lag theory for fibres with variable radius is developed to analyse elastic fibre/matrix stress transfer. The theory accounts for the reinforcement of biological composites, such as soft tissue and bone tissue, as well as for the reinforcement of technical composite materials, such as fibre-reinforced polymers (FRP). The original shear-lag theory proposed by Cox in 1952 is generalized for fibres with variable radius and with symmetric and asymmetric ends. Analytical solutions are derived for the distribution of axial and interfacial shear stress in cylindrical and elliptical fibres, as well as conical and paraboloidal fibres with asymmetric ends. Additionally, the distribution of axial and interfacial shear stress for conical and paraboloidal fibres with symmetric ends are numerically predicted. The results are compared with solutions from axisymmetric finite element models. A parameter study is performed, to investigate the suitability of alternative fibre geometries for use in FRP. KW - Natural fibres KW - Polymer-matrix composites KW - Biocomposites KW - Stress concentrations KW - Finite element analysis Y1 - 2022 U6 - http://dx.doi.org/10.1016/j.ijsolstr.2022.111464 SN - 0020-7683 VL - 239–240 IS - Art. No. 111464 PB - Elsevier CY - New York, NY ER - TY - GEN A1 - Topcu, Murat A1 - Madabhushi, Gopal Santana Phani A1 - Staat, Manfred T1 - Datasets from FEM Simulations done with COMSOL Multiphysics and Code_Aster N2 - Datasets from FEM Simulations done with COMSOL Multiphysics and Code_Aster for an elastic stress transfer between matrix and fibres having a variable radius. KW - Natural fibres KW - Polymer-matrix composites KW - Biocomposites KW - Stress concentrations KW - Finite element analysis (FEA) Y1 - 2022 U6 - http://dx.doi.org/10.6084/m9.figshare.19333295.v2 ER - TY - JOUR A1 - Staat, Manfred A1 - Vu, Khoi Duc T1 - Limit loads of circumferentially flawed pipes and cylindrical vessels under internal pressure JF - International Journal of Pressure Vessels and Piping. 83 (2006), H. 3 Y1 - 2006 SN - 0308-0161 SP - 188 EP - 196 ER - TY - JOUR A1 - Staat, Manfred A1 - Vu, Duc-Khoi T1 - An Algorithm for Shakedown Analysis for Materials with Temperature Dependent Yield Stress JF - Proceedings in Applied Mathematics and Mechanics (PAMM). 4 (2004), H. 1 Y1 - 2004 SN - 1617-7061 SP - 231 EP - 233 ER - TY - JOUR A1 - Staat, Manfred A1 - Vu, Duc-Khoi T1 - Limit analysis of flaws in pressurized pipes and cylindrical vessels. Part I: Axial defects JF - Engineering Fracture Mechanics. 74 (2007), H. 3 Y1 - 2007 SN - 0013-7944 SP - 431 EP - 450 ER - TY - JOUR A1 - Staat, Manfred A1 - Vu, Duc Khoi T1 - Limit analysis of flaws in pressurized pipes and cylindrical vessels Part II: Circumferential defects JF - Engineering Fracture Mechanics ; 97(2013), H. 1 N2 - 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. Y1 - 2012 U6 - http://dx.doi.org/10.1016/j.engfracmech.2012.05.017 SN - 0013-7944 VL - 97 SP - 314 EP - 333 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Staat, Manfred A1 - Trenz, Eva A1 - Lohmann, Philipp A1 - Frotscher, Ralf A1 - Klinge, Uwe A1 - Tabaza, Ruth A1 - Kirschner-Hermanns, Ruth T1 - New measurements to compare soft tissue anchoring systems in pelvic floor surgery JF - Journal of Biomedical Materials Research Part B: Applied Biomaterials N2 - Suburethral slings as well as different meshes are widely used treating stress urinary incontinence and prolaps in women. With the development of MiniSlings and special meshes using less alloplastic material anchorage systems become more important to keep devices in place and to put some tension especially on the MiniSlings. To date, there are many different systems of MiniSlings of different companies on the market which differ in the structure of the used meshes and anchors. A new objective measurement method to compare different properties of MiniSling systems (mesh and anchor) is presented in this article. Ballistic gelatine acts as soft tissue surrogate. Significant differences in parameters like pull-out strength of anchors or shrinkage of meshes under loading conditions have been determined. The form and size of the anchors as well as the structural stability of the meshes are decisive for a proper integration. The tested anchorings sytems showed markedly different mechanical function at their respective load bearing capacity. As the stable fixation of the device in tissue is a prerequisite for a permanet reinforcement, the proposed test system permits further optimisation of anchor and mesh devices to improve the success of the surgical treatment Y1 - 2012 U6 - http://dx.doi.org/10.1002/jbm.b.32654 SN - 1552-4981 VL - 100B IS - 4 SP - 924 EP - 933 PB - Wiley CY - Hoboken, NJ ER - TY - CHAP A1 - Staat, Manfred A1 - Tran, Thanh Ngoc A1 - Pham, Phu Tinh T1 - Limit and shakedown reliability analysis by nonlinear programming N2 - 7th International Conference on Reliability of Materials and Structures (RELMAS 2008). June 17 - 20, 2008 ; Saint Petersburg, Russia. pp 354-358. Reprint with corrections in red Introduction 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. KW - Finite-Elemente-Methode KW - Limit analysis KW - Shakedown analysis Y1 - 2008 ER - TY - JOUR A1 - Staat, Manfred A1 - Tran, Thanh Ngoc A1 - Kreißig, R. T1 - Load bearing capacity of thin shell structures made of elastoplastic material by direct methods JF - Technische Mechanik. 28 (2008), H. 3-4 Y1 - 2008 SP - 299 EP - 309 ER - TY - CHAP A1 - Staat, Manfred A1 - Tran, Ngoc Trinh T1 - Strain based brittle failure criteria for rocks T2 - Proceedings of (NACOME2022) The 11th National Conference on Mechanics, Vol. 1. Solid Mechanics, Rock Mechanics, Artificial Intelligence, Teaching and Training, Hanoi, December 2-3, 2022 N2 - 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. KW - Extension fracture KW - Extension strain criterion KW - Mohr–Coulomb criterion KW - Evolution of damage Y1 - 2023 SN - 978-604-357-084-7 SP - 500 EP - 509 PB - Nha xuat ban Khoa hoc tu nhien va Cong nghe (Verlag Naturwissenschaft und Technik) CY - Hanoi ER - TY - JOUR A1 - Staat, Manfred A1 - Sponagel, Stefan A1 - Nguyen, Nhu Huynh T1 - Experiment and material model for soft tissue materials JF - Constitutive models for rubber VI : proceedings of the sixth European Conference on Constitutive Models for Rubber, Dresden, Germany, 7 - 10 September 2009 / eds. Gert Heinrich ... Y1 - 2010 SN - 978-0-415-56327-7 SP - 465 EP - 470 PB - CRC Press CY - Boca Raton [u.a.] ER - TY - JOUR A1 - Staat, Manfred A1 - Schwartz, M. A1 - Lang, H. A1 - Wirtz, K. A1 - Heitzer, M. T1 - Design by Analysis of Pressure Components by non-linear Optimization JF - The 10th International Conference on Pressure Vessel Technology, July 7-10, 2003, Vienna, Austria, Proceedings ICPVT-10 / Zeman, J. L. [ed] Y1 - 2003 SN - 3950152814 SP - 59 EP - 65 PB - ÖGS, Österreichische Gesellschaft für Schweißtechnik CY - Wien ER - TY - CHAP A1 - Staat, Manfred A1 - Heitzer, Michael T1 - Limit and shakedown analysis for plastic design N2 - 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. KW - Einspielen KW - Traglast KW - Finite-Elemente-Methode KW - Traglastanalyse KW - Einspielanalyse KW - FEM KW - limit analysis KW - shakedown analysis Y1 - 1997 ER - TY - CHAP A1 - Staat, Manfred A1 - Heitzer, Michael T1 - The restricted influence of kinematic hardening on shakedown loads N2 - 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. KW - Biomedizinische Technik KW - Einspielen KW - Shakedown KW - Ratcheting KW - Bruchmechanik KW - shakedown KW - material shakedown KW - linear kinematic hardening KW - nonlinear kinematic hardening KW - ratchetting Y1 - 2002 ER - TY - CHAP A1 - Staat, Manfred A1 - Heitzer, Michael T1 - Direct static FEM approach to limit and shakedown analysis N2 - Safety and reliability of structures may be assessed indirectly by stress distributions. Limit and shakedown theorems are simplified but exact methods of plasticity that provide safety factors directly in the loading space. These theorems may be used for a direct definition of the limit state function for failure by plastic collapse or by inadaptation. In a FEM formulation the limit state function is obtained from a nonlinear optimization problem. This direct approach reduces considerably 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. The theorems are implemented into a general purpose FEM program in a way capable of large-scale analysis. KW - Einspielen KW - Nichtlineare Optimierung KW - Shakedown KW - Shakedown KW - limit load KW - lower bound theorem KW - nonlinear optimization KW - reliability Y1 - 2000 ER - TY - CHAP A1 - Staat, Manfred A1 - Heitzer, Michael ED - Staat, Manfred ED - Heitzer, Michael T1 - Probabilistic limit and shakedown problems T2 - Numerical methods for limit and shakedown analysis. Deterministic and probabilistic problems Y1 - 2003 SN - 3-00-010001-6 N1 - NIC Series VL - 15 SP - 217 EP - 268 PB - John von Neumann Institute for Computing (NIC) CY - Jülich ER - TY - BOOK A1 - Staat, Manfred A1 - Heitzer, Michael T1 - Numerical methods for limit and shakedown analysis. Deterministic and probabilistic problems. Y1 - 2003 SN - 3-00-010001-6 N1 - NIC Series Vol. 15 / Ed. by Staat, M; Heitzer, M. PB - John von Neumann Institute for Computing (NIC) CY - Jülich ER - TY - BOOK A1 - Staat, Manfred A1 - Heitzer, M. A1 - Yan, Ai-Min A1 - Khoi, Vu Duc A1 - Nguyen, Dang Hung A1 - Valdoire, F. A1 - Lahousse, A. T1 - Limit Analysis of Defects Y1 - 2000 SN - 0944-2952 N1 - Bericht des Forschungszentrums, Jül-3746, Jülich (2000) PB - Forschungszentrum Jülich CY - Jülich ER -