Dynamic crushing of a dedicated buffer during the high-speed vertical water entry process

Abstract

A composite buffer has been designed to reduce the impact load of high-speed water entry projectile. Rigid Polyurethane (PU) foams of different densities have been used to make the damper of the buffer. A series of compression tests for PU foam specimens are implemented to obtain the stress-strain curves under different loading speeds. The constitutive model used in the simulation for PU foam has been validated by comparing the results with the experimental data. Six different failure modes have been found in the dynamic crushing process of the nose cap. The effects of PU foam density, the length of the nose cap on these failure modes are presented quantitatively by introducing a time-related non-dimensional number that represents the beginning time of each failure mode. The results show, the complete disintegration of the nose cap strongly depends on PU foam density, its effect is more pronounced in the cases when the ratio of the length of the buffer to the diameter of the projectile is greater than 0.92. The dedicated buffer is very efficient in reducing the impact load imposed in the cavitator of the projectile (the highest load-reducing ratio up to 51%).