FE-Implementation of a constitutive model for stress-softening based on hydrodynamic reinforcement

With the advancements in computer technology the computation of rubberlike materials with the Finite Element Method becomes more and more a standard in research and development. It enables engineers to predict critical situations and possible failures of machine parts like air springs and conveyor belts without costly experiments. But with the variety of effects in rubber it is often difficult to find a proper material model which on the one hand is able to simulate all the necessary phenomena but on the other hand qualifies a short computation time. In this paper the FE-implementation of a constitutive model for rubber into the programs MSC.Marc and ABAQUS is presented. It describes the stress-strain-behavior and takes into consideration hydrodynamic reinforcement and the Mullins-effect. The model is based on the breakdown and reaggregation of filler clusters and the cluster-size-distribution of broken and yet-unbroken filler-clusters in the filler-network of reinforced rubber. The implementation is done via a modified version of the free energy function and with optimized numerical derivations for the computation of the coordinates of stresses and the material stiffness. For both FE-programs the implementation of the actual material model is done via the user subroutine HYPELA2 which is a MSC.Marc supported user subroutine. In order to use the subroutine with the user interface UMAT in ABAQUS the so called wrapper-technology is applied which enables the transfer of the source code between MSC.Marc and ABAQUS. At the end the possibilities of computational engineering with the presented model are shown with the help of example simulations of specific problems.