Damage Tolerance of a Composite Sandwich with Interleaved Foam Core

Abstract

A composite sandwich panel consisting of carbon fiber-reinforcedplastic (CFRP) skins and a syntactic foam core was selected as anappropriate structural concept for the design of wind tunnel compressorblades. Interleaving of the core with tough interlayers was done toprevent core cracking and improve damage tolerance of the sandwich.Simply supported sandwich beam specimens were subjected tolow-velocity, drop-weight impacts as well as high-velocity, ballisticimpacts. The performance of the interleaved core sandwich panels wascharacterized by localized skin damage and minor cracking of the core.Residual compressive strength (RCS) of the skin, which was derived fromflexural test, shows the expected trend of decreasing with increasingsize of the damage, impact energy, and velocity. In the case of skindamage, RCS values of around 50% of the virgin interleaved referencewere obtained at the upper impact energy range. Based on the similaritybetween low velocity and ballistic impact effects, it was concludedthat impact energy is the main variable controlling damage and residualstrength, where as velocity plays a minor role. The superiority (indamage tolerance) of the composite sandwich with interleaved foam core,as compared with its plain version, is well established. This isattributable to the toughening effect of the interlayers which servethe dual role of crack arrestor and energy absorber of the impactloading.