Energy-absorbing textile devices for heavy cargo restraints

This paper describes an analytical and experimental investigation of the energy absorption performance of textile stitch ripping devices (SRDs). SRDs are under consideration for use as lightweight, load-limiting cargo restraints for future heavy lift rotorcraft. The models developed are capable of accounting for energy absorption due to webbing stretch, thread rupture and stitch slippage. The models predict the force-displacement behavior of the device, the total amount of energy absorption, and the amount of absorption due to frictional losses from stitch slip. Experimental testing conducted on small-scale SRDs to validate modeling results exhibits close agreement for the applied load and displacement required to induce thread rupture. Over multiple stitch breaks, the models slightly over estimate the amount of absorbed energy. It was predicted that a lower amount of stitch slip decreases the peak force as well as the fluctuation of force in the "plateau" region of the force-displacement curve. Decreasing the slip therefore increases the amount of energy that can be absorbed for a given peak force and stroke distance. To assess the performance of SRDs under simulated crash conditions, including stroke rate effects, an instrumented dynamic drop rig was constructed. Tests were conducted with a drop sled moving at free-fall velocity, and a higher, elastic-cord-assisted velocity. For velocities from quasi-static to 6 m/s, no significant trends or changes in SRD average activation force and energy absorption were observed in the experiments.