Behaviour of Composite Materials to Withstand Impact and Compressive Design Allowables

In this paper the relationship between CAI and compressive design allowables of composite structures were discussed and it was pointed out that traditional CAI values could not reflect the behavior of composite materials to withstand impact adequately and no relationship between CAI values and compressive design allowables existed. Based on the integrity requirements of composite structures, it was pointed out that the evaluation system of composite materials to withstand impact should include both damage resistance and damage tolerance. Large numbers of test data verified that the knee point phenomenon of composite laminates to withstand impact existed. Based on failure mechanisms, it was proposed that the behavior evaluation system of composite systems to withstand impact was based on the properties at the knee point, that is, the maximum capability to keep integrity of the front plies (the maximum contact force) characterizing damage resistance and the threshold of dent depth(or impact energy)~compressive strength(or failure strain) curves characterizing damage tolerance.