Ductile damage prediction in metal forming processes. Advanced modelling and numerical simulation
Résumé
Ductile (or plastic) damage often occurs during sheet or bulk metal forming processes due to the large plastic flow localisation. Accordingly, it is crucial for numerical tools, used in the simulation of that processes, to use fully coupled constitutive equations accounting for both hardening and damage. This can be used in both cases, namely to overcome the damage initiation during bulk and sheet metal forming processes as forging, stamping, deep drawing, ... or to enhance the damage initiation and growth as in sheet metal cutting or metal machining by chip formation. The present talk is dedicated to the presentation of the theoretical and numerical aspects of advanced, multiphysical and strongly coupled constitutive equations and their practical use for the “optimization” of various kinds of sheet and bulk metal forming and machining processes. In a first part, the fully coupled constitutive equations are formulated, in the framework of the thermodynamics of irreversible processes with state variables, under large inelastic strains assumption and accounting for combined isotropic and kinematic hardening as well as the ductile damage considering the anisotropy of the inelastic flow and the ductile damage. Due to the induced softening (thermal and damage) the formulation in the framework of the generalized micromorphic continua is used. Attention will be paid to the interactions between different anisotropic phenomena as the hardening, the plastic flow and the damage with or without the damage induced volume variation. Both the macroscopic phenomenological approach as well as the micro-macro or polycristalline inelasticity approach are used to derive the multiphysical and fully coupled constitutive equations. The second part is dedicated to the associated numerical aspects in the framework of fully adaptive numerical methodology based on the finite element method with time and mesh adaptation. Attention is paid to the adaptive time and space discretization using fully adaptive schemes based on appropriate geometrical and physical error indicators. The efficient local integration procedure of the fully coupled constitutive integration at each quadrature point of each finite element is deeply discussed. Finally, the third part is devoted to the simulation of various 2D and 3D examples where some sheet and bulk metal forming processes are discussed in order to show the capability of the proposed fully adaptive methodology to predict the damage initiation and growth using these advanced models. For each of these parts the state of the art of the advanced modeling is given and the main challenging aspects are highlighted