Quasi-static bending and transverse crushing behaviors for hat-shaped composite tubes made of CFRP, GFRP and their hybrid structures

This study aims to characterize the crushing responses of hat-shaped composite tube under quasi-static three-point bending (TPB) and transverse compression (TC) conditions. The specimens were fabricated with different stacking configurations considering the effect of ply number, ply angle (containing [+/- 45 degrees] layers) and interply hybrid structure (sandwich-like) with carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic (GFRP) through thermo-forming process. Mechanical parameters were also tested with non-hybrid laminates consisted of net carbon and net glass fibers. The crushing performance was evaluated by comparing load-displacement curves and the images taken in course of the testing processes. Cross-sections of the specimens were also inspected visually to identify the failure mechanisms after the tests. The comparative study on the energy absorption and cost efficiency was conducted for all the samples. It was found that failure modes varied with ply angle under the TPB tests but kept the same under the TC tests. Increasing wall thickness seemed to be an effective way to improve energy absorption under both TPB and TC loading. Addition of [+/- 45 degrees] layers exhibited considerable advantages on the TPB performance except the TC scenario. The hybrid structures comprised of both carbon and glass fiber layers exhibited limited improvement on crashworthiness but excellent cost efficiency. In addition, the initiation and propagation of cracks during tests were clearly visible when stacking glass fiber layers outside, which facilitate proper structural health monitoring.