A MECHANISM RESPONSIBLE FOR REDUCING COMPRESSION STRENGTH OF THROUGH-THE-THICKNESS REINFORCED COMPOSITE-MATERIAL

A study was conducted to identify one of the mechanisms that contributes to the reduced compression strength of composite materials with through-the-thickness (TTT) reinforcements. In this study a series of thick [0/90] laminates with stitched and integrally woven TTT reinforcements were fabricated and statically tested. In both the stitching and weaving process a surface loop of TTT reinforcement yarn is created between successive TTT penetrations. It was shown that the surface loop of the TTT reinforcement "kinked" the in-plane fibers in such a manner that they were made ineffective in carrying compressive load. The improvement in strength by removal of the surface loop and "kinked" in-plane fibers was between 7 and 35 percent.