2D adaptive FEM simulation of failures in high-speed impacts

The simulation of high-speed impacts needs the use of advanced constitutive equations required for the accurate prediction of the different thermomechanical fields and their mutual interactions (temperature, large strains, hardening, damage, friction …). Since these fields localize inside intense shear bands (ISB), ductile micro-cracks initiate inside these ISB leading to the initiation of macroscopic crack and its fast propagation until the final fracture occurs. Accordingly, these advanced constitutive equations should take into account not only the strong thermomechanical coupling but also the ductile damage and its strong effect (coupling) on the other thermomechanical fields. In this work a complete set of advanced and fully coupled thermo-elasto-viscoplastic-damage constitutive equations accounting for mixed nonlinear isotropic and kinematic hardening fully coupled with the ductile isotropic damage and the thermal softening for time dependent finite plasticity is presented. Related numerical aspects in the framework of a fully adaptive 2D finite element strategy are developed and briefly discussed. This adaptive procedure is applied to the simulation of simple high velocity impact of thick sheets with dynamic ductile fracture occurrence. Attention is paid to the localization of the main thermomechanical fields inside the ISB as well as to the macroscopic cracks initiation and growth under high velocity impact

New smoothing procedures in contact mechanics

AbstractThis paper presents recent methods to improve numerical simulation of contact problems by smoothing. The main idea is to combine contact surfaces regularization with an automatic adjustment of both penalty parameter and load step. The underlying goal is to provide handle situations frequently met in an industrial context

3D mesh adaptation. Optimization of tetrahedral meshes by advancing front technique

International audienc

Improving numerical simulation of metal forming processes using adaptive remeshing technique

International audienc

A hybrid Meshless-FEM field transfer technique minimizing numerical diffusion and preserving extreme values: Application to ductile crack simulation

International audienc

VOLUME MESH ADAPTATION WITH A MESHFREE SURFACE MODEL

We present a method to adapt a tetrahedron mesh together with a surface mesh with respect to a size criterion. Both surface and tetrahedron mesh adaptation are carried out simultaneously and no CAD is required to adapt the surface mesh. The adaptation procedure consists in splitting or removing interior and surface edges in order to enforce a given size criterion. The enrichment process is based on a bisection technique. Mesh conformity during the refinement process is guaranteed since all possible remeshing configurations of tetrahedra are examined. Surface nodes are projected on a geometrical model once the tetrahedron mesh has been adapted. The building of a surface model method is based on a meshfree technique denoted as Hermite Diffuse Interpolation. Surface and volume mesh optimization procedures are carried out during the adaptation and at the end of the process to enhance the mesh

A new smooth contact element: 3D diffuse contact element

Many difficulties due to geometrical and material non-linearities arise when dealing with numerical simulation of contact problems. Within a finite element context, the contact interface is usually represented by a piecewise differentiable surface. Numerical problems due to the non-smoothness of the contact surface may occur especially when large slips are considered. Major changes of normal and tangential vectors may impede both convergence and precision. In order to smooth the contact interface and to release constraints due to the mesh, we propose a technique in which diffuse approximation is combined with a determination of neighboring nodes by a convex hull strategy. The formulation is developed for three-dimensional applications with frictionless contact and a 3D diffuse contact element has been developed. The efficiency of the approach has been validated with industrial frictionless contact problems