The hybridization effect and damage sequence investigation of biaxial/unidirectional braided composite tubes by micro-CT method

Thanks to the 2D braiding manufacturing method, the hybrid braided composite composed of the biaxial and unidirectional layers is available in a mass-production manner. For enhancing the crashworthiness of braided composite tubes, the damage characteristics and energy absorption capacity of braided composite with biaxial/unidirectional hybridization structures under axial compression were studied in this work. The axial compression tests were conducted on pure biaxial and unidirectional braided tubes (BBB and UUU), and hybrid tubes with different surface and inner layers (BUB and UBU). Micro-CT was utilized to analyze the crack characteristic and propagation inside the tubes. It was found that the easily progressed intra-laminar cracks in unidirectional layers promoted splitting damage feature, leading to enhanced energy absorption capacities in hybrid tubes than pure biaxial braided tube, in which local buckling damage feature was observed attributed to interlaced yarns induced constrained intra-laminar crack propagation and tendency to delamination. In particular, the UBU tube dissipated 20.4% more crushing energy and exhibited 13.0% higher energy absorption per unit area than the BBB tube.