Assessment of Fracture Behavior of Flat Braided CFRP Composites Under Tensile Loading With Assistance of SQUID Technique

Abstract

The goal of this research is to provide a sufficient understanding for the damage mechanism of ±45° flat braided CFRP composites under tensile loading based on in-situ macroscopic observations of surface cracking and off-line measurements for the state-of-fibers by Superconducting Quantum Interference Device (SQUID) technique to analyze the effect of the continuously oriented of all braided fiber bundles on the tensile and in-plane shear properties. SQUID technique displays an effective capability in inspection the state-of-fiber failure, whereas the in-situ surface macroscopic observation technique is very useful in observing the surface matrix cracking at different stages of damage. The damage mechanism of uncut-edges and cut-edges of ±45° flat braided CFRP composites are identified adequately by the above-mentioned experimental procedure. The cut-edges ±45° flat braided CFRP composites exhibit a pure shear damage mechanism associated with large shear deformation and no significant fiber failure, while the uncut-edges ±45° flat braided CFRP composites exhibit a slight fiber scissoring mechanism followed by a partially fiber failure. The enhancement of the tensile and in-plane strengths of the uncut-edges ±45° flat braided CFRP composites by about 60% higher than those of the cut-edges ±45° flat braided CFRP composites achieves not only by the effect of the continuously oriented carbon fibers at the edges but also by the effect of re-orientation of braiding fiber bundles with smaller angle than the original ±45° braiding angle of the fabricated composites, or so called fiber scissoring mechanism in composites.