Strain Rate Effects in Ballistic Analyses of Bonded & Co-Cured Composite Structures

"The aim of our Phase II activity is to incorporate the Cohesive Volumetric Plate and Shell (Finite) Elements into LS-DYNA3D, thus enhancing its capabilities in modeling HRAM loading and damage in composite structures. In Phase I, we reported oninterlaminar failure criteria and modes, based on fracture mechanics. A damage-dependent bilinear cohesive element is used to capture the crack initiation, propagation, and arrest, while accounting for inertial effects. An algorithm was developed tocompute essential toughness parameters (strain energy release rate G, stress intensity factor K) and the variations thereof, with crack length and adhesive effects. Experimental testing of double cantilever beam (DCB) specimens at various stroke rates,using an electronic circuit to measure crack-opening displacement, yielded data which enabled the calculation of material parameters used in the explicit CVFE/LS-DYNA formulation. As the next step, we propose to develop rate-dependent cohesive elements,and use this technique to analyze mixed-mode failure in stitched, z-pinned and other joint types. We shall investigate and incorporate contact-impact algorithms in LS-DYNA with filtering and damping. Experimental work will focus on hydrodynamic pulsetests, using the impact machine developed at the 46th test wing, thus simulating high-rate fracture dynamical scenarios. The material property data obtained in these tests will be incorporated into the