No abstract

In another paper [1], the authors presented an approach to penetration of a particulate target. This theory is based on the friction that the particles of target material present to the entire penetrator surface, including its shank. The shank of the penetrator affords a very large surface area compared to that of the nose. Even modest friction acting on the shank can provide a fairly large retarding force. Normal pressure acting on the projectile is assumed to be velocity-squared dependant, as indicated by a number of methods, including cavity expansion modeling [2]. Penetration of sand and soil has been considered by numerous investigators, e.g. [3–5]. These investigations did not directly address the frictional component of the net resisting force acting on the penetrator. A series of laboratory scale penetrations tests were performed. Data from these tests was used to evaluate the parameters in the model. Fine foundry sand is a high-density medium (1960 kg/m3) with a small amount of friction. This contrasts the target used by the authors in [1], which had a sizable amount of friction. Results from the theory are in excellent agreement with the experiments with velocities as high as 630 m/sec.

This paper presents a theory for the normal rigid body penetration of particulate media. This theory consists of two separate force regimes divided by a critical velocity at which the transition between the two regimes takes place. Also included in this theory is sliding friction, separated into two different regimes, one for the nose and one for the shank.In order to verify this new penetration theory, a set of laboratory experiments was performed where 7075-T6 Aluminum projectiles were shot into coarse foundry sand. Utilizing the total penetration depth and impact velocity of each projectile in the test, along with known projectile geometry, analyses of the penetration events were completed. The results of these experiments and analyses, which confirm the required use of a friction coefficient on the shank, are reported.

In this paper, the authors use recent results for predicting the onset of lateral instability to discuss the limitations on rigid body penetration. An analysis of lateral instability was proposed in [1] and verified experimentally for laboratory-scale projectiles [2]. After the onset of lateral instability, declining performance was observed even though the projectile does not catastrophically fail. The authors utilized an analysis to estimate the critical velocity at which the penetrator becomes laterally unstable. With this estimate, a maximum penetration depth for each penetrator aspect ratio is predicted. The objective of the analysis is to determine the velocity limits to achieve the maximize penetration depth. The results are supported by a limited set of experimental data.