Load bearing and failure characteristics of perforated square CFRP tubes under axial crushing

Open holes or cutouts have been commonly used in composite structures for various engineering purposes. This paper aims to investigate the load bearing behavior and failure characteristics of the square weave carbon fiber reinforced plastic (CFRP) tubes with open holes subjected to axial compression. Effects of hole size, hole shape and hole distribution on failure modes and mechanical behaviors were evaluated experimentally and numerically. Different with the progressive crushing mode seen in the intact CFRP tubes, mid-height collapse and unstable local buckling were observed in the axial crushing tests. The peak load and specific energy absorption (SEA) of the perforated tubes decreased by around 3-22% and 26-57%, respectively, compared to those of the intact CFRP counterparts. It was found that the effect of hole size on failure strength in tubes was less sensitive than that in perforated composite laminates, but was relatively stronger than the perforation shape and distribution. The damage mechanisms were explored in-depth using strain gauge tests and finite element analysis, which showed a significant increase in shear stress around the holes prior to final failure.