Correlation of damage resistance under low velocity impact and Mode II delamination resistance in CFRP laminates

Investigated in this study was the correlation of the damage resistance und er low velocity impact and Mode II interlaminar fracture toughness in five material systems, namely, T800/3631 (CF/Epoxy), UT500/PEEK (CF/PEEK), AS4/P EEK (CF/PEEK), IM7/PIX-A (CF/Polyimide) and T800/3900-2 (CF/Toughened Epoxy ). These materials can be roughly divided into two types. One is a compatib le type, which shows high impact resistance under low velocities with high Mode II delamination resistance. The other type is a non-compatible type, w hich has poor impact resistance at low velocities, even though it has super ior Mode II delamination resistance. As for the system of T800/3631, T800/3 900-2 and IM7/PIX-A composites, the Impact Energy (IE)/Damage Area (DA) rat io correlates well with GIIC(0 : PMAX), Mode II energy release rate charact erized at PMAX, and GIIR(0), Mode II energy release rate in propagation, fo r the 0/0 interface. The system of these materials is the compatible type. On the other hand, as for the system of T800/3631, UT500/PEEK and AS4/PEEK composites, the IE/DA ratio correlates well with GIIC(PNL), Mode II energy release rate characterized at PNL, for 0/0 and 22.5/-22.5 interfaces. The s ystem of these materials is the non-compatible type. It is suggested that t he main reason for the difference in behavior of these two types is that th e compatible type has the superior Mode II delamination resistance in the s ub-critical crack growth region and propagation. It correlates with the sup erior impact resistance under low velocities.