Sharif Digital Repository

In this paper, the extended finite element method is presented for large elasto-plastic deformation in 3D solid mechanics problems. The X-FEM computational algorithm is presented in the framework of Lagrangian description in order to model the arbitrary interfaces in large deformations. In X-FEM, the material interface is represented independently of element boundaries and the process is accomplished by partitioning the domain with several tetrahedral sub-elements whose Gauss points are used for integration of the domain of elements. The interface between two bodies is modeled by using the X-FEM technique and applying a modified level set enrichment function. In order to simulate the... 

An exact elasto-plastic analytical solution for large-strained internal pressurized thick-walled spherical vessels made of elastic-linear and nonlinear hardening material is derived in this paper. This solution is based on the notion of finite strains, the deformation theory of Hencky and the yield criteria of von Mises and Tresca. Nolinear elastic solution of an axisymetric boundary value problem is used as a basis to generate its inelastic solution, whereas the Hyper-elastic constitutive equation is invoked to represent the material response in the elastic region. This method treats the material parameters as field variables. Their distributions are obtained in an iterative manner using... 

In this paper the element free Galerkin method (EFGM) has been extended to be used in the elastoplastic stress analysis. The developed method has been examined in planar stress analysis around the tip of a crack and in its opening mode of loading. To do this, at the first step by using the incremental relations of plastic deformation a system of elastoplastic EFGM equations has been derived. Since the obtained relations are nonlinear, a nonlinear solution technique has been chosen. To examine the validity of this technique, stress fields in two different plates with and without a crack have been calculated and the results have been compared with other similar analytical works in the... 

An Eulerian rate-independent constitutive model for isotropic materials undergoing finite elastoplastic deformation is formulated. Entirely fulfilling the multiplicative decomposition of the deformation gradient, a constitutive equation and the coupled elastoplastic spin of the objective corotational rate therein are explicitly derived. For the purely elastic deformation, the model degenerates into a hypoelastic-type equation with the Green-Naghdi rate. For the small elastic- and rigid-plastic deformations, the model converges to the widely-used additive model where the Jaumann rate is used. Finally, as an illustration, using a combined exponential isotropic-nonlinear kinematic hardening... 

We propose a model based on extreme value statistics (EVS) and combine it with different models for single-asperity contact, including adhesive and elasto-plastic contacts, to derive a relation between the applied load and the friction force on a rough interface. We determine that, when the summit distribution is Gumbel and the contact model is Hertzian, we obtain the closest conformity with Amonton’s law. The range over which Gumbel distribution mimics Amonton’s law is wider than that of the Greenwood–Williamson (GW) model. However, exact conformity with Amonton’s law is not observed for any of the well-known EVS distributions. Plastic deformations in the contact area reduce the relative... 

In this paper, the extended finite element method is presented for large elasto-plastic deformation of continuum problems. The X-FEM computational algorithm is presented in the framework of Lagrangian description in order to model the arbitrary interfaces in large deformations. In X-FEM, the material interface is represented independently of element boundaries and the process is accomplished by partitioning the domain with several tetrahedral sub-elements whose Gauss points are used for integration of the domain of elements. The interface between two bodies is modeled by using the X-FEM technique and applying a modified level set enrichment function. In order to simulate the nonlinear... 

In this paper, the extended finite element method is presented for large elasto-plastic deformation in 3D solid mechanics problems. The X-FEM computational algorithm is presented in the framework of Lagrangian description in order to model the arbitrary discontinuities in large deformations. The discontinuity between two bodies is modeled by using the X-FEM technique and applying a modified level set enrichment function. In order to simulate the nonlinear behavior of materials, the Lagrangian plasticity formulation is coupled with the X-FEM technique. Finally, numerical example is analyzed to demonstrate the efficiency of the X-FEM technique in large plasticity deformations. © CIMNE 2007  

In this paper, a three-invariant cap model is developed for the isotropic-kinematic hardening and associated plasticity of granular materials. The model is based on the concepts of elasticity and plasticity theories together with an associated flow rule and a work hardening law for plastic deformations of granulars. The hardening rule is defined by its decomposition into the isotropic and kinematic material functions. The constitutive elasto-plastic matrix and its components are derived by using the definition of yield surface, material functions and non-linear elastic behavior, as function of hardening parameters. The model assessment and procedure for determination of material parameters... 

In this paper, a 3D Superconvergent Patch Recovery (SPR) method is developed for data transferring in elasto-plasticity. The transfer operators are presented for mapping of the state and internal variables between different meshes. In order to transfer the history-dependent variables from old mesh to new one, the internal variables are firstly mapped from the Gauss points to nodal points of old mesh, the variables are then transferred from nodal points of old mesh to nodal points of new mesh, and the values are finally transferred from the nodal points to Gauss points of new mesh. As the solution procedure cannot be re-computed from the initial state, it is continued from the previously... 

In this paper, a three-invariant cap plasticity with a kinematic hardening rule is presented for powder materials. A general form is developed for the cap plasticity which can be compared with some common double-surface plasticity models proposed for powders in literature. The constitutive elasto-plastic matrix and its components are derived based on the definition of yield surface, hardening parameter and non-linear elastic behavior, as function of relative density of powder. The procedure for determination of powder parameters is described. Finally, the applicability of the proposed model is demonstrated in numerical simulation of triaxial and confining pressure tests. © 2006 Elsevier B.V.... 

Dam failure can result in a catastrophic break followed by a ood wave, often with considerable loss of life or property. One of the main causes of dam failure is loss of shear strength and the existence of discontinuity within the foundation. Dynamic analysis of concrete dams usually considered concrete behavior to be nonlinear and the foundation rock is assumed to be linear. In this study, seismic analysis of a concrete gravity dam was conducted to investigate the effect of the foundation on the nonlinear response. A finite element model of a dam-reservoir-foundation was considered to properly model the foundation as well as dam body nonlinear behaviors. An elasto-plastic formulation was... 

The constitutive modeling of powder is clearly a keystone of successful quantitative solution possibilities. Without a reasonable constitutive model, which can reproduce complicated powder behavior under loading conditions, the computations are worthless. In this paper, a three-invariant cap plasticity model with isotropic-kinematic hardening rule is presented for powder materials. A generalized single-cap plasticity is developed which can be compared with some common double-surface plasticity models proposed for powders in literature. The hardening rule is defined based on the isotropic and kinematic material functions. The constitutive elasto-plastic matrix and its components are derived... 

In the present study, in the first part for a spherical vessel with known dimensions and working pressure, two methods of hoop and equivalent stress optimization across the wall thickness are employed to determine the best autofrettage pressure. In the next part for a predefined working pressure the minimum wall thickness of the vessel is calculated using two other design criteria i.e. (A) optimizing the hoop stress, and (B) assuming a suitable percent for the penetration of yielding within the wall thickness. Finally, the optimum thickness and the necessary strengthening pressure are extracted and different plots are introduced for different types of structural materials under different... 

A study of thick-walled spherical vessels under steady-state radial temperature gradients using elasto-plastic analysis is reported. By considering a maximum plastic radius and using the thermal autofrettage method for the strengthening mechanism, the optimum wall thickness of the vessel for a given temperature gradient across the vessel is obtained. Finally, in the case of thermal loading on a vessel, the effect of convective heat transfer on the optimum thickness is considered, and a general formula for the optimum thickness and design graphs for several different cases are presented. © 2004 Elsevier Ltd. All rights reserved  

In this paper, an h-adaptive mesh refinement is presented based on the gradient of deformation in the modeling of localization due to material instability. As the classical continuum models suffer from pathological mesh dependence in the strain-softening models, the governing equations are regularized by adding rotational degrees-of-freedom to the conventional degrees-of-freedom. Adaptive strategy using element elongation is applied to compute the distribution of required element size using the estimated error distribution. Once the new element size and its alignment have been indicated, an automated procedure is used to construct the mesh according to a predetermined size and elongation... 

In this paper, static response of a sandwich cylindrical shell under elasto-plastic deformation is investigated. The faces are made of some isotropic materials and the core is made of an orthotropic material both with linear work hardening behavior. The faces are modeled as thin cylindrical shells obeying the Kirchhoff-Love assumptions. The core material is modeled as a special orthotropic solid in which its in-plane stresses are assumed to be negligible. The Prandtl-Reuss plastic flow theory and von Mises yield criterion are used in the analysis. The governing equations are derived using the principle of virtual displacements. Using Ritz method, the equations are solved for deformation... 

In the present paper, the nonlinear seismic behavior of a concrete gravity damreservoir- massed foundation system is studied focusing on the foundation material nonlinearity. For this purpose, a finite element program utilizing the elasto-plastic formulation for the foundation medium is provided considering the tensile and shear failure modes. Hoek-Brown and Mohr Coulomb criteria are used as the yield and plastic potential function of the shear failure mode, respectively; and in the tensile failure mode, various levels of the tensile strength are applied to the foundation. Bearing capacity is studied considering the localized plastic elements and forming the sliding path by plastic elements... 

Using harmonic differential quadrature method, an approach to analyze sandwich cylindrical shell panels with any sort of boundary conditions under a generally distributed static loading, undergoing elasto-plastic deformation is proposed. The faces of the sandwich shell panel are made of some isotropic materials with linear work hardening behavior while the core is assumed to be an isotropic material experiencing only elastic behavior. The faces are modeled as thin cylindrical shells obeying the Kirchhoff–Love assumptions. For the core material, it is assumed to be thick and the in-plane stresses are negligible. Upon application of an inner and outer general lateral loading, the governing...