New Testing in Support of LS-DYNA MAT 224 Material Model

LS-DYNA MAT224 is a tabulated plasticity and failure model. The plasticity part of the model can include strain rate, strain hardening and temperature effects, and the failure part is based on a failure surface of the equivalent plastic strain to failure as a function of triaxiality and the Lode parameter. The present paper presents two new experiments that have been developed recently in order to support the model. The first experiment adds new points to the failure surface in a region that is important in simulations of projectile impact and penetration. The second experiment is used for determining the Taylor-Quinney coefficient (β), which controls the magnitude of the temperature increase due to plastic deformation. Simulations of impact and penetration events show that failure occurs under a stress state of biaxial tension and out-of-plane compression. This state of stress on the failure surface is not in the region that is populated with data points obtained from typical experiments (tensile tests of flat and round, parallel and notched specimens, tensile tests of wide parallel and notched specimens, pure shear tests, combined tension-compression/shear tests, and compression tests.) In order to obtain an independent measurement of the equivalent strain to failure under a state of stress of biaxial in-plane tension and out-of-plane compression a new experiment was developed. In this experiment a small diameter punch penetrates a thin specimen plate that is backed by another plate. The deformation of the back surface of the plate is measured with DIC. The value of the equivalent strain to failure is determined from measuring the force and matching the LS-DYNA simulation with the measured deformation and force.