An inverse analysis using a finite element model for identification of rheological parameters

In order to reduce the discrepency between experimental and numerical development, a parameter automatic identification procedure from rheological test is formulated as an inverse problem. The direct model which permits to simulate the large strain behaviour during the rheological test is a Finite Element Code. The inverse problem is formulated as finding a set of rheological parameters starting from a known constitutive equation. The goal is to compute the parameter vector which minimizes an objective function representing, in the least square sense, the difference between experimental and numerical data. The high nonlinearity of the problem to be solved, requires the use of an accurate evaluation of the sensitivity matrix by analytical differentiation of governing equations with respect to the parameters. Thus the optimisation algorithm is strongly coupled with the finite element simulation. This method, namely a Computer Aided Rheology (CAR) methodology is possible in principle for all tests able to be simulated. This paper concerns the thermoviscoplastic deformation during torsion and tension tests.