Classification of the collapse of a composite fairing during the oblique high-speed water entry

Abstract

The crushing behaviors of the buffer devices for the projectile in the high-speed oblique water entry process were investigated numerically. The high-speed water entry tests of the aluminum alloy projectile with a sabot were conducted to study the cavity formation, also used to validate the numerical method. Detailed material parameters of three kinds of foams including expanded polystyrene foam (EPS), closed-cell aluminum foam, and rigid polyurethane foam (PU), and the composite material for the fairings were obtained from a series of statics and dynamics mechanics experiments. Twelve collapse modes of the thin-walled fairings were identified during the oblique water impact. The effects of the length of the fairing, foam type, and water entry angle on these failure modes, and the peak impact acceleration of the projectiles were revealed. The results showed that the load reduction efficiency (LRE) is dependent on both entry angle θ and dimensionless length LFA/DPJ. The critical load reduction water entry angle (CLRA) is linearly related to LFA/DPJ. Among the three kinds of foam materials, the closed-cell aluminum foam has the best load reduction performance (up to 72.82%) and the widest range of load reduction water entry angles. Meanwhile, the EPS foam makes the projectile withstand the largest impact overload (up to 11.43%).