Conclusions
3D woven angle-interlock composites have excellent enhanced inter-laminar performance over 2D woven composite laminates and hence are increasing favored for the aircraft and space applications. In the current study, experimental investigations are carried out to assess the effects of off-axis directions on the flexure mechanical behaviors and failure mechanism of 3D woven angle-interlock carbon/epoxy composites. Based on the detailed analysis, following conclusions are made: 1) Compared to 0 degree and 90 degree samples, 30 degree and 45 degree samples show lower flexure strength, initial modulus and larger flexure deflection. Also, the stress-deflections of 0 degree and 90 degree samples exhibit an obvious quasi-brittle behavior, whereas that of 30 degree and 45 degree samples show an important ductile feature. 2) With 30% of the received echo amplitude as the threshold, the calculated damage area proportions of off-axis samples are larger than that of on-axis samples. This phenomenon is because that off-axis samples are capable to produce a larger bending deflection. 3) Under the flexural loading, 30 degree and 45 degree off-axis samples show small localized cracks with little delamination. However, 0 degree and 90 degree on-axis samples exhibit serious damages, mainly including the inter-ply delamination and fiber bundles fracture. For afore-mentioned results, further study is expected to examine how the manipulation and design of wide range of off-axis angles can optimize the maximum stress, dissipation, and damage initiation/evolution. More importantly, developing a reasonable mechanical theory is promising to be exploited for the evaluation of anisotropy characteristics of 3D woven composites.
