Damage Tolerance of a Composite Sandwich with Interleaved Foam Core

Abstract

A composite sandwich panel consisting of carbon fiber-reinforced plastic (CFRP) skins and a syntactic foam core was selected as an appropriate structural concept for the design of wind tunnel compressor blades. Interleaving of the core with tough interlayers was doen to prevent core cracking and improve damage tolerance of the sandwich. Simply supported sandwich beam specimens were subjected to low-velocity, drop-weight impacts as well as high-velocity, ballistic impacts. The performance of the interleaved core sandwich panels was characterized by localized skin damage and minor cracking of the core. Residual compressive strength (RCS) of the skin, which was derived from flexural test, shows the expected trend of decreasing with increasing size of the damage, impact energy, and velocity. In the case of skin damage, RCS values of around 50% of the virgin interleaved reference were obtained at the upper impact energy range. Based on the similarity between low velocity and ballistic impact effects, it was concluded that impact energy is the main variable controlling damage and residual strength, where as velocity plays a minor role. The superiority (in damage tolerance) of the composite sandwich with interleaved foam core, as compared with its plain version, is well established. This is attributable to the toughening effect of the interlayers which serve the dual role of crack arrestor and energy absorber of the impact loading.