On crashing behaviors of aluminium/CFRP tubes subjected to axial and oblique loading: An experimental study

Thin-walled energy-absorbing structures rarely experience in pure axial loading in real crash events, but rather a combination of axial and off-axial loads. In this perspective, it is critical to understand the oblique crushing process of thin-walled structures. To address this issue, circular aluminum and carbon fiber reinforced plastics (CFRP) tubes were experimentally investigated for characterizing their crashworthiness subject to quasi-static axial and oblique compression in this study. The tests were conducted at five different loading angles (theta) of 0 degrees, 5 degrees, 10 degrees, 20 degrees and 30 degrees to the tubal axis. Five sets of specific fixtures were fabricated to apply the desired axial and off-axial loads onto the aluminum and CFRP specimens, respectively. The failure modes, load-displacement curves, crushing force and energy absorption of all the specimens were analyzed; and the effects of loading angle were explored. It is found from the experiments that with the increase in loading angle, aluminum tubes were more prone to collapse in an irregular diamond mode (I-d) instead of axisymmetric concertina mode (A(c)) while the CFRP tubes collapsed in much more complex failure modes which included splaying mode (S-p), tearing mode (T-e), socking mode (S-o), micro-fragmentation mode (M-f) and catastrophic failure (C-f). As for the energy absorption characteristics, the loading angle (theta) ranged from 0 degrees to 10 degrees had little impact on the energy absorption for the both aluminum and CFRP tubes, nevertheless, the energy absorption of the CFRP tubes decreased more significant from theta = 10 degrees to 30 degrees, while that of aluminum tubes declined fairly steadily.