Modeling Crack Propagation in Rubber

Traditional bulk failure models are based on the approach of continuum damage mechanics involving internal variables which are difficult to measure and interpret in simple physical terms. Alternative approach was proposed by Volokh [1-5], in which the function of the strain energy density was limited. The limiter enforces saturation – the failure energy – in the strain energy function, which indicates the maximum amount of energy that can be stored and dissipated by an infinitesimal material volume. The limiter induces stress bounds in the constitutive equations automatically. The work presents a numerical implementation of the energy limiter theory using the LS-DYNA ® user defined material. This approach will be tested in few examples. First, the FE subroutine is checked against a simple uniaxial tension case that can be solved analytically. Next, we will model the Deegan-Petersan-Marder-Swinney (DPMS) experiments [6-7] for the dynamic fracture of rubber. These tests use biaxial pre-stretched rubber sheets which are pricked at a point. The pricking initiates a crack which runs along the sheet. We simulate these tests using the user defined subroutines of the hyper-elastic material models enhanced with energy limiters. The numerical results regarding the crack shape and speed are compared to the test observations.