Interaction between High-velocity Penetrators and Moving Armour Components

Sammanfattning: This work was aimed at understanding mechanisms of importance for the design of weight-efficient armour against long-rod projectiles (LRP) and shaped charge (SC) warheads. The focus was on how to achieve effective mechanical disturbances on the threat before it hits the target.Methods were developed for laboratory tests in full and reduced scale, and for registration and evaluation of the fast and violent events involved. For numerical simulations, the Xue-Wierzbicki fracture model was implemented and used for the LRP in order to allow fractures due to shear load without extensive damage of the entire projectile. In order to reproduce the scattering of the SC jet after interaction with reactive armour, use was made of a very fine computational mesh.Severe disturbances and fractures of the penetrators (LRP and SC jet) originate from the interaction phase in which a plate slides along the penetrator. In the case of an SC jet, this sliding contact results in severe scattering of the SC jet due to instabilities of the same kind as those between two fluids in contact, moving in parallel with different tangential velocities (Kelvin-Helmholtz instabilities). The generation of such instabilities is caused by the very high velocity (in the order of 10000 m/s) and the relatively low material strength of the SC jet in combination with the high contact pressure and the motion of the plate. In the case of an LRP, the high strength of the material of the projectile and its low velocity (in the order of 2000 m/s) relative to that of an SC jet, prevent the generation of KH-instabilities. Instead, fractures of the projectile may occur due to abrupt change of contact pressure at the exit of the plate. The positive pressure gradient and longer interaction time of forwards moving plates compared to backwards moving plates make the former plates more effective. A side-hitting steel rod gives approximately the same effect on an LRP as that of a steel plate with the same thickness, velocity and angle of obliquity.The results obtained can be used for assessment and optimisation of reactive armour modules and active protection systems.