Influence of the Soil and Rocky Target Strength Properties on Projectiles Penetration Depth with Additional Action of the Jet Thrust Impulse

The purpose of this work was to analyze the influence of additional jet thrust impulse enclosed to the projectile in the course of its movement in a target on a possible increment of penetration depth into soil and rocky targets with various strength properties. The analysis was performed by the calculation method. We defined the dynamics of projectile penetration within the model of a non-deformable body of variable weight moving under the target resistance force and jet force (in operating time of the jet engine). We calculated soil and rocky target resistance force using the empirical resistance law which establishes the dependence of mechanical tension on a contact surface of the projectile head part for the target on the projectile velocity. We considered penetration into such targets as dense soil, low-strength rock and high-strength rock at initial interaction velocities in the range from 250 to 1000 m/s. Consequently, for soil and rocky targets with various strength properties we defined the beginning time and duration of the jet impulse action considering the most possible increment of penetration depth. In many cases the greatest increase in penetration depth is reached not at preliminary (prior to interaction with a target) operation of the jet engine, but during its work already in the course of the projectile movement in a target. For projectile velocity of 500 m/s and mass of solid rocket propellant charge making 20 % of the projectile mass, additional action of the jet thrust impulse allows for the increase in penetration depth approximately twice for all considered types of soil and rocky targets. With the increase in initial velocity, the relative increment of penetration depth decreases at the fixed mass of a solid propellant charge. It is caused by the decrease in a relative share of chemical energy of rocket propellant combustion in comparison with initial kinetic energy of the projectile. For projectile velocity of 1000 m/s and a reserve of rocket propellant in 20 % of projectile weight, the penetration depth increment reaches 60 % for dense soil, 45 % for low-strength rock and 40 % for high-strength rock at a rational choice of jet impulse parameters.

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