AN INVERSE METHOD FOR DETERMINING VISCOPLASTIC PROPERTIES OF ALUMINUM-ALLOYS

Parameter identification plays a major role in modelling finite strain viscoplasticity. The tests used to assess the values of the constitutive parameters must reproduce faithfully the deformation state. For such tests, the deformation state is usually non-homogeneous and the only information available is the load-displacement data actually measured during the test, whereas the constitutive model expresses the flow stress as a function of the viscoplastic strain, the viscoplastic strain rate, the temperature and some internal variable. This constitutes a typical inverse problem. A numerical procedure which integrates optimization and finite element analysis is developed for solving a three dimensional parameter estimation problem in elasto-viscoplasticity. The optimization is performed using a modified Levenberg-Marquardt method to take into account the constraints on the parameters. The direct problem is solved using a finite element method based on an implicit prediction-correction algorithm in finite transformation. The method is applied to the plane strain compression test to determine viscoplastic material parameters of aluminium alloys.