Material forming models: to what extent numerical methods can treat physical engineering issues
Résumé
The development of finite element simulation of material forming processes started about 30 years ago in academic laboratories, while the introduction of the corresponding commercial computer codes in industry is less than twenty years old. The main mechanical integral formulations for solid or viscous liquids are briefly recalled: classical Eulerian, Eulerian with a characteristic function, updated Lagrangian and arbitrary Euler Lagrange, with some comments on the finite element discretization using a mixed formulation and mini tetrahedral elements. The crucial remeshing issues are analyzed for non steady-state processes with different levels of sophistication: Updated Lagrangian for solids, or Euler and a characteristic function, possibly combined with error estimation and adaptivity. As real problems are usually very complex in industry, we must consider different levels of coupling such as thermal and mechanical coupling with the tools in forging and gas - liquid - solid coupling as in polymer foaming. In an attempt to model microstructure evolution of the work-piece during the different stages of forming, three approaches are reviewed. In the first example the physical evolution of metal is described by macroscopic parameters and their laws of evolution, while the second one is based on a finite element modeling of the two-phase material at the microscopic level. Finally the third case is the presentation of a new approach of polymer crystallization during injection molding and its introduction in a computer code