Crack Tip Field Mapping and Crack Initiation at Polymer-Metal Interfaces Under Transient Loading Conditions

Dynamic interfacial crack tip fields are mapped and fracture parameters are measured in polymer-metal bi-material systems. Low velocity impact loading experiments are conducted using bimaterial sandwiches made of model materials to study crack initiation toughness under dynamic loading conditions. The optical method of coherent gradient sensing (CGS) is used in conjunction with high speed photography for recording interfacial crack tip fields. The transient fracture parameters are extracted from the interference patterns up to crack initiation. Complementary finite element computations using experimental boundary conditions show good agreement with the optical measurements. Preliminary dynamic crack initiation data suggests significant reduction in the initiation toughness relative to quasi-static conditions. Post-initiation data suggests instantaneous crack speeds of 1.1cR of the less compliant material in this bimaterial system when the impact occurs on the metallic half of the specimens.