• Weerasinghe, Dakshitha
• Mohotti, Damith
• Wang, Jiansheng
• Wang, Hongxu
• Hazell, Paul J.
• Escobedo, J. P.
• Cavenagh, Robert

Abstract

This study investigated how mild steel cover plates of various thicknesses affected the collapse of re-entrant auxetic structures under penetration at 500 m/s by ø16 mm spherical projectiles. A combination of experimental and numerical methods was used to capture this effect with auxetic structures made from 3D printed titanium alloy (Ti6Al4V) and ABS plastic (acrylonitrile butadiene styrene), and wire cut 304 stainless steel (SS304). Experimentally, structures were tested with a 2.90 mm cover plate and without the cover plate. Numerically, the effect of the cover plate thickness on the auxetic response of the structure was tested with 0.95 mm, 1.50 mm, 2.2 mm, and 2.90 mm cover plates. The auxetic densification was found to be greatest under the thickest cover. Material characterisation tests were conducted to develop strength and failure models for the mild steel cover and back plates in this study, which produced simulated correlation to the ballistic experiments. The simulations closely matched the overall auxetic densification from the experiments for all structure materials under 2.90 mm cover plates. Although the simulated auxetic effect generally increased with cover plate thickness, like the experiments, the structure material significantly affected the range of this dependence. For the ductile SS304 structures, thin cover plates inhibited energy absorption by constraining auxetic deformation in the top layer, and then began to improve once the cover thickness reached 1.50 mm. The Ti6Al4V structures showed a similar abrupt change in auxetic densification at this cover plate thickness but without the prior drop in performance. Overall densification of the ABS structures was significantly improved by adding cover plates, however collapse was delayed behind the penetrating projectile. These findings therefore indicate that the thickness of cover plates in auxetic sandwiches can be specifically engineered to maximise auxetic effect while considering the ranges of this dependence with different auxetic materials

Topics

• polymer
• stainless steel
• experiment
• simulation
• strength
• titanium
• titanium alloy
• wire
• densification