The Experts below are selected from a list of 876 Experts worldwide ranked by ideXlab platform
An Chao - One of the best experts on this subject based on the ideXlab platform.
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Application of gradient Plastic theory based on FEPG platform
yantu gongcheng xuebaochinese journal of geotechnical engineering, 2012Co-Authors: Du Xiu-li, Hou Shi-wei, Lu De-chun, Liang Guo-ping, An ChaoAbstract:Based on the FEPG platform, the finite element program using gradient Plastic theory is developed to solve mesh dependence after strain softening. A u-?? algorithm with damp factor is proposed, which can solve the equation of displacement and yield surface simultaneously. The algorithm can not only get displacement and Plastic Multiplier together, but also avoid the stress haul back calculation in stress return algorithm widely used in finite element solution procedures. The softening modulus and the internal character length are introduced into D-P yield function, and the constitutive model can consider strain softening and gradient effect. The damp Newton algorithm is used to calculate softening problems. The results of a case study show that the u-?? algorithm with damp factor can be used to solve softening problems, the gradient Plastic theory described by finite element weak form has no requirement of continuity, and appropriate outcome can be obtained by the first-order element, thus the mesh dependence of simulation is basically solved.EI061094-11013
Minna Karstunen - One of the best experts on this subject based on the ideXlab platform.
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Modeling creep and rate effects in structured anisotropic soft clays
Acta Geotechnica, 2010Co-Authors: Gustav Grimstad, Samson Abate Degago, Steinar Nordal, Minna KarstunenAbstract:In simulations of undrained triaxial tests, most soil models fail to capture the effect of post peak strain rate variation. This is due to the fact that no “swelling” is allowed for the viscoPlastic volume strain. Imposing such restriction implies that dilative behavior cannot be modeled. Therefore, a model incorporating creep has been formulated using the so-called time resistance concept that uses a single creep parameter determined from an incremental oedometer test. The key feature of the proposed model is the introduction of the time resistance concept on the Plastic Multiplier rather than on the volumetric viscoPlastic strain. This allows the viscoPlastic volume strain to be either positive or negative depending on whether the state of the soil is on the “wet” or “dry” side of critical state line. The proposed model is based on an existing elastoPlastic model for structured soft clay (S-CLAY1S). The paper gives a description of the constitutive model and the numerical scheme used in the implementation of the model. Capabilities of the model are illustrated with simulations of oedometer and triaxial tests. Results from such analyses show that the model is able to capture essential features of soft clay behavior.
M L Peterson - One of the best experts on this subject based on the ideXlab platform.
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variational principles for softening gradient dependent Plasticity
International Journal of Solids and Structures, 2001Co-Authors: Z M Wang, M L PetersonAbstract:Abstract A gradient dependent Plasticity model is analysed in which the yield function not only depends on the stress tensor and an invariant Plastic strain measure, but also on the spatial derivatives of the latter quantity. A minimum variational principle is obtained by analysing the structure discretized into sufficiently small Plastic elements and thus the uniqueness of FE solutions can be ensured for softening Plasticity. The positive definiteness of the variational functional is determined only by the sign of the diffuse coefficient associated with the highest order derivative of the Plastic Multiplier in the yield function. In order to adopt mix/hybrid elements, several general variational principles are obtained by relaxing the associated constraints on the displacement–strain–stress and/or Plastic Multiplier-gradient-radiation fields.
Gerd Wachsmuth - One of the best experts on this subject based on the ideXlab platform.
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Existence and regularity of the Plastic Multiplier in static and quasistatic Plasticity
2015Co-Authors: Christian Meyer, Gerd WachsmuthAbstract:Existence of the Plastic Multiplier withL1 spatial regularity for quasistatic and static Plasticity is proved for arbitrary continuous and convex yield functions and linear hardening laws. L2 regularity is shown in the particular cases of kinematic hardening, or combined kinematic and isotropic hardening. c © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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c stationarity for optimal control of static Plasticity with linear kinematic hardening
Siam Journal on Control and Optimization, 2012Co-Authors: Roland Herzog, Christian Meyer, Gerd WachsmuthAbstract:An optimal control problem is considered for the variational inequality representing the stress-based (dual) formulation of static elastoPlasticity. The linear kinematic hardening model and the von Mises yield condition are used. Existence and uniqueness of the Plastic Multiplier is rigorously proved, which allows for the reformulation of the forward system using a complementarity condition. In order to derive necessary optimality conditions, a family of regularized optimal control problems is analyzed, wherein the static Plasticity problems are replaced by their viscoPlastic approximations. By passing to the limit in the optimality conditions for the regularized problems, necessary optimality conditions of C-stationarity type are obtained.
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C-stationarity for optimal control of static Plasticity with linear kinematic hardening. in revision
2012Co-Authors: Roland Herzog, Christian Meyer, Gerd WachsmuthAbstract:Abstract. An optimal control problem is considered for the variational in-equality representing the stress-based (dual) formulation of static elastoplas-ticity. The linear kinematic hardening model and the von Mises yield condi-tion are used. Existence and uniqueness of the Plastic Multiplier is rigorously proved, which allows for the re-formulation of the forward system using a com-plementarity condition. In order to derive necessary optimality conditions, a family of regularized optimal control problems is analyzed, wherein the static Plasticity problems are replaced by their viscoPlastic approximations. By passing to the limit in the optimality conditions for the regularized problems, necessary optimality conditions of C-stationarity type are obtained.
Qiushi Chen - One of the best experts on this subject based on the ideXlab platform.
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return mapping for nonsmooth and multiscale elastoPlasticity
Computer Methods in Applied Mechanics and Engineering, 2009Co-Authors: Jose E Andrade, Qiushi ChenAbstract:Abstract We present a semi-implicit return mapping algorithm for integrating generic nonsmooth elastoPlastic models. The semi-implicit nature of the algorithm stems from “freezing” the Plastic internal variables at their previous state, followed by implicitly integrating the stresses and Plastic Multiplier. The Plastic internal variables are incrementally updated once convergence is achieved (a posteriori). Locally, the algorithm behaves as a classic return mapping for perfect Plasticity and, hence, inherits the stability of implicit integrators. However, it differs from purely implicit integrators by keeping the Plastic internal variables locally constant. This feature affords the method the ability to integrate nonsmooth ( C 0 ) evolution laws that may not be integrable using implicit methods. As a result, we propose and use the algorithm as the backbone of a semi-concurrent multiscale framework, in which nonsmooth constitutive relationships can be directly extracted from the underlying micromechanical processes and faithfully incorporated into elastoPlastic continuum models. Though accuracy of the proposed algorithm is step size-dependent, its simplicity and its remarkable ability to handle nonsmooth relations make the method promising and computationally appealing.