Strain-Rates Dependent Constitutive Law for Crashworthiness and Parameter Sensitivity Analysis of Woven Composites

The prediction of dynamic crushing behavior of aerospace-grade composites is a hard challenge for researchers. At coupons scale, such behavior implies the understanding of the initiation and propagation of the elementary damage mechanisms. Many results of the research confirm that the modulus and strength of composites increases with strain-rate. This paper presents the improvement of the constitutive model UL-Crush by adding dynamic stiffness modulus and strengths. The improved tool uses new approach by updating the stiffness and the strength values depending on strain-rates. In addition, parameter sensitivity investigations were conducted to assess the specific energy absorption capabilities of different material configurations. A new on-axis compression fixture was designed and manufactured to carry out tests of plain weave fabric composites, under quasi-static (QS) and low-velocity compression using MTS Insight 100 loading frame and drop tower CEAST Instron9340 facility. Two types of cross-section geometries were used: flat-plate and Hat-Shape coupons. Four types of triggering mechanism were adopted, including saw teeth, chamfer45°, steeple and corrugated, to ensure a continuous and stable crushing mode of failure. Detailed parameter sensitivity investigations were performed, including dimension scale, stacking sequences, trigger types and strain-rates. It was shown that the crush response is strain-rate dependent, and dynamic load decreases absorbed energy, which is indicative of microstructure disintegrating. Globally, big dimension scale, corrugated trigger, [0/45/45/0]s layup and decreasing strain-rate are the parameters to enhance the energy absorption capability of composite coupons. It has been observed that the improved numerical tool UL-Crush was able to significantly capture most crush mechanisms, reasonably correlate with experiments, and give an accurate dynamic response for crashworthy structures.