X-ray microtomography analysis of the damage mechanisms in 3D circular braided carbon fiber/epoxy resin composite tubes under axial impact compression

The dynamic behavior of three-dimensional (3D) circular braided composite tubes with different braided parameters was experimentally investigated subjected to axial impact compression using a Split Hopkinson Pressure Bar (SHPB). The damage characterization of the post-impacted tubes was examined using scanning electron microscope (SEM) and X-ray micro-computed tomography (micro-CT). The influence of braided parameters and strain rate, including braided angle, the number of braided layer and axial yarn, on the dynamic mechanical properties, progressive crush characteristics and failure mechanism of 3D braided composite tubes was analyzed in detail. It was found that the smaller braided angle and the larger numbers of braided layers contributed to better axial dynamic properties. The compressive strength, stiffness and specific energy absorption (SEA) of 3D five direction (3D5D) tubes with axial yarn were larger than those of 3D four direction (3D4D) tubes without axial yarn. Meanwhile, the dynamic mechanical response and damage patterns of braided tubes exhibited significant strain rate effects. The impact compression failure mechanisms of braided tubes were mainly fiber tows crushing, fiber breakage, fiber buckling, shear fracture, resin cracking, interfacial cracks, fiber-matrix debonding, etc.