EVALUATION OF DAMAGE MECHANISM OF ±45° FLAT BRAIDED CFRP COMPOSITES CONTAINING CARBON NANOFIBERS UNDER TENSILE LOADING WITH ASSISTANCE OF SQUID TECHNIQUE

摘要

The aim of this study is to provide an adequate understanding for the damage mechanism of ±45° flat braided CFRP composites containing Vapor Grown Carbon Nano-Fibers (VGCF) under off-axis tensile loading based on in-situ macroscopic surface observations of the in-plane cracking behavior and off-line measurements via Superconducting Quantum Interference Device (SQUID) technique of the state-of-fibers. These three phase composites are successfully produced by modifying the hand lay-up technique by pre-impregnation of flat braided fabrics with mixture of resin and VGCF in vacuum. Stress-strain responses and fracture behavior were conjugated to quantify the effect of VGCF on the mechanical performance of the braided composites. The edges of these composites were cut to analyze the effect of the continuously oriented carbon fibers of all braided bundles on the tensile and in-plane shear properties. This study showed that SQUID technique is an effective tool for inspecting the state-of-failure of carbon fiber bundles, whereas the in-situ surface macroscopic observation technique is a useful technique for observing the surface matrix cracking at different stages of fracture. The damage mechanism of uncut-edges and cut-edges of ±45° flat braided CFRP composites containing VGCF are adequately identified.