Papers by Keyword: Elasto-Plasticity

Abstract: This paper summarizes the implementation of an elasto-plastic constitutive model for a micro-polar continuum in the constitutive models framework of the software INSANE (INteractive Structural ANalysis Environment). Such an implementation is based on the tensorial format of a unified constitutive models formulation, that allows to implement different constitutive models independently on the peculiar numerical method adopted for the solution of the problem. The basic characteristics of the micro-polar continuum model and of the unified formulation of constitutive models are briefly recalled. A generalization of the micro-polar model is then introduced in order to include this model in the existent tensor-based formulation. Finally, an enhanced version of the general closest-point algorithm, ables to manage the generalized micro-polar formulation, is derived. A strain localization problem modeling illustrates the implementation.

Abstract: For the numerical simulation of sheet metal forming processes, the commercial finite element software packages are among the most commonly used. However, these software packages have some limitations; in particular, they essentially contain phenomenological constitutive models and thus do not allow accounting for the physical mechanisms of plasticity that take place at finer scales as well as the associated microstructure evolution. In this context, we propose to couple the Abaqus finite element code with micromechanical simulations based on crystal plasticity and a self-consistent scale-transition scheme. This coupling strategy will be applied to the simulation of rolling processes, at different reduction rates, in order to estimate the evolution of the mechanical properties. By following some appropriately selected strain paths (i.e., strain lines) along the rolling process, one can also predict the texture evolution of the material as well as other parameters related to its microstructure. Our numerical results are compared with experimental data in the case of ferritic steels produced by ArcelorMittal.

Abstract: In order to effectively ascertain the failure mechanism of piled wharf affected by slope deformation in earthquake, numerical analysis is conducted by Finite Element Method in this paper. In the computational model, elastic plastic characteristic of subsoil, discontinuous behavior of pile soil interface, and nonlinearity of structure material are considered to conduct seismic computation in time domain. Numerical results show the possible locations of wharf structure which generate cracks and plastic hinges. Some conclusions are drawn and can be reference for engineering design and practical project.

Abstract: It is generally considered within analysis the residual stresses that unloading occurs on elastic law. For large initial loads, some plasticity theories believe that during unloading secondary plastic deformation can occur. The distinctive work provides a new theorem of unloading, which takes into account irreversible changes in the mechanical characteristics of the material under load. There is an example of the analysis of residual stresses corresponding to the given theorem.

Abstract: The goal of the present paper is to propose a simple methodology to estimate the failure pressure of thin-walled metallic pipelines with arbitrary localized corrosion damage. This methodology is conceived as a preliminary tool for a quick analysis of the structural integrity of real corroded pipelines. Due to the different possible geometries of the corroded region, the exact analysis of this kind of problem can be very complex (in general using an elasto-plastic finite element simulation). The idea is to obtain an approximate exact analytical solution of the problem for any arbitrary geometry of the corroded region considering elasto-plastic constitutive equations and a factor that accounts for the stress concentration due to the metal loss caused by corrosion. With a simple expression, a reasonable lower limit for the failure pressure can be obtained.

Abstract: In order to ensure the enough fracture toughness for the thickness steel structure, based on DNV-OS-C401, using three point bending specimen with a center crack, the test of the typical bridge steel materials were carried out at 20°C. The CTOD value of base metal, heat affect zone and welded seam were obtained. The results show that the plastic displacement of the fracture toughness of the material plays a decisive role.

Abstract: A general formulation of constitutive relations in non-smooth elastoplasticity is presented. The treatment applies to general non-smooth plasticity problems and to problems characterized by non-smooth yield criteria or dealing with non-differentiable functions. The mathematical tools and instruments of convex analysis and subdifferential calculus are suitably applied since they provide the proper mathematical instruments for dealing with non-smooth problems and non-differentiable functions. General formulations of constitutive relations and evolutive laws in non-smooth elastoplasticity are illustrated within the presented theoretical framework. Connections between the proposed mathematical treatment and the classical relations in elastoplasticity are illustrated and discussed in detail. The presented generalized treatment is equipped with considerable advantages since it shows to be ideally suited for the development of variational formulations of structural problems in non-smooth elastoplasticity.

Abstract: By studying the geometrical features and the mechanical characters of the profiles during the roller leveling process and combining the basic elastic-plastic theories, a mechanical model is established which is suitable for analyzing elastic-plastic bending of the profile during roller leveling process. Using this model, the straightening effects have been analyzed under different roller leveling process schemes for the profiles which have typical initial curvatures. The analysis of roller leveling process confirms that the curvature ranges of the profiles can't converged infinitely under any process scheme because of the hereditary effects of residual stress, and the large deformation straightening process scheme has better profile convergence than the small one. Further analysis shows that the residual stress of specific section after straightening process with large deformation straightening process is lower than that with small one, and a diminishing bending process scheme is beneficial to the control of residual stress.

Abstract: Elastic-plastic properties of composite materials are an important part of the study on micromechanics. Based on the plastic strain of matrix, the elastic-plastic constitutive model of composite materials is presented in this paper, while considering the influence of the transient flexibility matrix on the flexibility matrix. In comparison with the experimental results, theoretical analysis of the presented model is validated.

Abstract: The Finite Element Method (FEM) is today the most widely used in numerical simulation of forming processes, due essentially to the continuous improvement of the FEM over the years and the simplicity of its implementation. However, this method has some limitations such as the distortion of elements under large inelastic deformation and the influence of the mesh on the results in several applications. The simulation of metal forming process with large plastic strain is a classical example where the successive remeshing is often the proposed solution in this case. But the remeshing raises the problems of precision and computing time. In this context and in order to avoid the remeshing process, a Meshless method is experimented in the solving of an elastoplastic problem coupled to the isotropic ductile damage. An Element Free Galerkin (EFG) method based on Moving Least Square (MLS) concept is considered in this proposal. A two-dimensional Mechanical problem was studied and solved by a Dynamic-Explicit resolution scheme where the material behaviour is based on an isotropic hardening fully coupled to ductile damage model. In a first step a parametric study is conducted in order to find the most influent parameters on the accuracy of the results. The effect of the number of nodes, of support nodes, of quadrature points, the effect of the time-step and the support domain size are analysed and optimal values are found. In a second step, the meshless results are compared with those of the finite element method and some concluding remarks relative to the accuracy and the computing time are given.