ERROR ESTIMATORS FOR VISCOPLASTIC MATERIALS - APPLICATION TO FORMING PROCESSES

The analysis of error estimation is addressed in the framework of visc oplasticity problems, this is to say, of incompressible and non-linear materials. Firstly, Zienkiewicz-Zhu (Z(2)) type error estimators are studied. They are based on the comparison between the finite element s olution and a continuous solution which is computed by smoothing techn ique. From numerical examples, it is shown that the choice of a finite difference smoothing method (Orkisz' method) improves the precision a nd the efficiency of this type of estimator. Then a Delta estimator is introduced. Tt makes it possible to take into account the fact that t he smoothed solution does not verify the balance equations. On the oth er hand, it leads us to introduce estimators for the velocity error ac cording to the L(2) and L(infinity) norms, since in metal forming this error is as important as the energy error. These estimators are appli ed to an industrial problem of extrusion, demonstrating all the potent ial of the adaptive remeshing method for forming processes.