Impact Damage Visualization of Heterogeneous Two-layer Materials Subjected to Low-speed Impact

A systematic experimental investigation of the generation and subsequent evolution of impact damage in heterogeneous two-layer materials is presented. Model layered specimens involving a compliant polymer layer bonded with a metal layer were designed and subjected to impact loading to simulate failure mechanisms in real time. High-speed photography and dynamic photoelasticity were utilized to visualize the nature and sequence of dynamic failure modes. A series of complex failure modes was documented. Interlayer crack growth (interfacial delamination) is the dominant dynamic failure mode. These cracks appear to be shear dominated and might proceed with intersonic speeds. Intralayer cracking always occurs in a local Mode I crack inside the weak layer. Both impact speed and interfacial bonding strength have significant influence on the impact failure. High-impact loading leads to high interlayer crack speeds. Specimens featuring ductile and weak bonds subjected to high-impact speeds are shown to feature intersonic cracks with clearly visible shear shock wave (Mach lines) emitted from the crack tips.