Size-dependent mechanical behaviors of 3D woven composite under high strain-rate compression loads

Dynamic characterization of textile composites is confronted with great challenges due to its large unit-cell size and the inherent limitations in specimen size for the Hopkinson bar-based test system. The small specimen size will inevitably introduce variations in effective mechanical response and failure mechanism, and bring about additional problems in determining the realistic dynamic properties of the material. This work experimentally investigated the dynamic compression behavior of three-dimensional angle interlock woven composite (3DWC) using the split Hopkinson pressure bar (SHPB). Specimens with different sizes were designed to explore the size dependency, strain-rate dependency and orientation dependency for the compressive behavior of the 3DWC. A high-speed camera and an optical microscope were introduced to elaborate on the damage progressing process and fracture morphology under different loading conditions. With an increase in strain rate, the measured strength of warp-direction specimens increased by approximately 7.6%, 4.8%, and 2.6% for three different sizes of specimens, accompanied by more severe intra-tow damage. Different-sized dynamic specimens exhibited comparable failure processes but modest variations in measured properties. When the number of unit cells in a specimen increased from two to three and four, the strength was observed to rise by around 14.9% and 21.9% respectively. In comparison to the warp-direction specimen, the weft-direction specimens exhibited substantially higher strength and failure strain, as well as distinct dominant failure modes of yarns. This work provides valuable insights into the determination of dynamic properties for 3D woven composites, and the designing and interpretation of dynamic test methods.