Three-dimensional textile structural composites under high strain rate compression: Z-transform and discrete frequency-domain analysis

Z-transform theory was applied to several three-dimensional (3D) textile structural composites, including an angle-interlock woven composite, a multilayer multi-axial warp knitted composite and a 4-step braided composite, to characterize their system dynamic behaviour in the frequency domain. More specifically, the analysis focused on the relationship between the compressive load and the system response under static (strain rate 0.001?s^?1) and impulsive (strain rate up to 2700?s^?1) strain along both the in-plane and out-of-plane directions, respectively. The high strain rate compressions were tested using a split Hopkinson pressure bar apparatus, and the input and output (the stress–strain curve) of the test specimen was obtained by recording the signals using a computer for further analysis. Z-transform was then used to analyze the dynamic response and stability of the composites of different preform structures and at various loading conditions. This is the first such attempt to study the compression behaviour of 3D textile structural composites at various strain rates in the frequency domain in order to reveal their mechanical behaviour and features of the materials from a new perspective.