Rate-dependent tensile failure behavior of 2D triaxially braided composites: Experimental characterization and Meso-FE simulation

As two-dimensional triaxially braided composites (2DTBC) are increasingly employed in aerospace applications and anti-impact structures, it is important to study their dynamic mechanical behavior. In this work, the dynamic tensile behaviors of dogbone specimens with different fabric layers were investigated by utilizing high-speed imaging and an electromagnetic split Hopkinson bar (E-SHB) system. A full-scale meso-scale finite element (FE) model established to simulate the tensile failure behavior under different loading rates shows high consistency with the experimental results in its predictions of the stress-strain response and progressive damage behavior. Through examination of the effect of number of fabric layers on the quasi-static and dynamic mechanical behavior, specimen with multiple layers was concluded to be suitable for representing the dynamic tensile behavior of 2DTBC. Analysis and revelation of rate-dependent performance was conducted based on two-layer specimens utilizing both the test data and simulation results. The transverse failure mode was observed to transform from intra-yarn fracture under quasi-static loads to fiber breakage under dynamic loads for a reduced free-edge effect. The rate strengthening effect is attributed to the enhanced interface and matrix properties, ultimately resulting higher tensile properties at higher loading rates. Thickness effect under dynamic loads are investigated by simulation, and the incomplete fiber breakage damage as well as inadequate properties are again revealed in single-layer specimen. The findings of this study offer valuable insights for understanding the strain-rate behavior and thickness-dependent behavior of 2DTBC, thereby providing valuable knowledge for designing structures with better impact resistance.