Mechanisms and Quantification of Spalling Failure in Laminated Composites under Shock Loading

The free surface spalling phenomenon in 2D carbon/carbon (C/C) and carbon-polyimide (C/P) laminates was studied by subjecting them to laser-produced nano-second rise-time compressive stress pulses. The compression pulse travels through the laminate normal to the plies and, upon reflection into a tension pulse from the sample's front surface, leads to fiber/matrix debondings either in the bundles within a ply or at the interply interface. The stress pulse amplitude responsible for initiating such a damage was determined by recording the free surface velocity by an optical interferometer, and on the continuum scale, this is referred to as the effective interply strength. Since by employing a special specimen geometry we were able to determine the onset of such delaminations, its characterization in terms of an effective interply strength should be acceptable. Additional information on the attenuation and the dispersion characteristics associated with the propagation of such stress pulses was also obtained for both types of composite micro-structures. Using the interply strength as the local failure criterion, the information on the dispersion characteristics allows for a complete design of a composite component under impact conditions.