Material parameters identification: An inverse modeling methodology applicable for thermoplastic materials

The methodology proposed in this work uses the local measured strain rate history as the applied load to the finite element (FE) material point. Next, with this strain rate history, two objective functions related to the true stressstrain and volumetric strain response could be minimized to identify some of the material parameters of the constitutive model. The whole identification process, of the nine material parameters required, is described in detail. In addition, a short description of the hyperelastic-viscoplastic constitutive model used is given with an experimental program including mainly uniaxial tensile tests at different strain rates. The thermoplastic material investigated here is a mineral and rubber modified polypropylene (PP) compound. The main experimental data uses 3D digital image correlation (DIC) to determine full-field displacements and deduce true stressstrain, volume dilatation, and local strain rates curves during deformation. POLYM. ENG. SCI., 2012. (C) 2011 Society of Plastics Engineers