Effect of interleaved non-woven carbon tissue on interlaminar fracture toughness of laminated composites: Part II - Mode I

Interlaminar fracture behavior of non-woven carbon tissue (NWCT) interleaved composites was investigated under a Mode I loading condition using a double-cantilever-beam (DCB) specimen. The NWCT interleaved specimens were made by interleaving NWCT-prepregs between CFRP layers. CFRP specimen ([0₂₄]), NWCT interleaved specimen ([0₁₂/T_n/0₁₂]) and NWCT composite specimen ([T₈₀]) were prepared under the same cure condition of the CFRP specimen. The symbol "/T_n/" means that the NWCT layer is located at the 0/0 mid-plane of the interleaved specimen, and n is the number of NWCT layers. The NWCT has short carbon fibers, discretely distributed with in-plane random orientation fibers. An interlaminar crack is introduced to a center of the interleaved specimens. The DCB testing results were analyzed using the normal distribution. When the short carbon fiber volume fraction in the NWCT layer is about 10%, the Mode I interlaminar fracture toughness of the NWCT interleaved specimen is about 28% higher than that of the CFRP specimen due to the fiber breakage of out-of-plane oriented short carbon fibers in the NWCT layer. The fracture process on the side-section and fracture surfaces of the interleaved specimen was observed with an optical microscope and a scanning electron microscope, and the failure mechanism was discussed.