Low velocity impact on shape memory alloy stitched composite plates

Delamination of advanced composite materials due to various scenarios such as low velocity and ballistic impacts and high strain rate is one of the major problems for aerospace and automotive structural applications. The low velocity impact does not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures decrease dramatically. Shape memory alloy (SMA) materials possess many unique mechanical, thermal and thermal-mechanical properties compared with other conventional materials. Many studies have reported that the superelastic and hysteresis properties of the SMA materials can absorb energies coming from external excitations or sudden impacts. Stitching is well recognized as a promising technique to enhance the through-the-thickness reinforcement, in order to improve the delamination properties of composite structures. By stitching SMA wires into the composite structures one is theoretically able to reduce the risk of delamination of the structures during impact. In this paper, the damage resistance properties of SMA stitched glass/epoxy composites after low velocity impact are experimentally and theoretically studied. The results show that the tensile strength of composite plates increased and the number of translaminar cracks decreased after being stitched by SMA wires. Theoretical study also proves that the delamination energy of composite plates after stitching by superelastic SMA wires is smaller than that of an unstitched composite plate because of the energy absorbed by the SMA wires.