Initial Moving Mechanism of Densely-Packed Particles Driven by a Planar Shock Wave

The initial moving mechanism of densely packed particles driven by shock waves is unclear but vital for the next accurate calculation of the problem. Here, the initial motion details are investigated experimentally and numerically. We found that before particles show notable motion, shock waves complete reflection and transmission, and stress waves propagate downstream on particle skeleton. Due to the particle stress wave, particles successively accelerate and obtain an axial velocity of 6–8 m/s. Then, the blocked gas pushes the upstream particles integrally to move downstream, while the gas flow in the pores drags the downstream particles to separate dramatically and accelerate to the velocity of 60–70 m/s. This gas push-drag dual mechanism transforms densely packed particles into a dense gas-particle cloud, which behaves as the expansion phenomena of the dense particles.

Specifics of generating explosively formed projectiles of variable shape from metal liners

We propose using charges generating explosively formed projectiles of variable shape to remotely demolish structurally unsound concrete or brick walls of buildings and other structures. The paper considers the charges required, their design and operation. The operation of such a charge involves the explosive material accelerating a metal liner, covering a distance of up to several hundred charge diameters. The metal liner deforms while moving and assumes a compact shape. We used variable thickness copper liners, the external and internal surfaces of which are formed by a combination of spherical surfaces. A planar shock wave generator featuring a variable detonation wave slope is considered as the initiation system for the charge. We present the results of numerically simulating our explosive charge operation in order to determine how charge parameters affect performance. We estimated charge performance via two projectile parameters: its shape and velocity. The study also evaluated the effect of the planar shock wave generator slope on the projectile shape. We obtained projectile velocity and aspect ratio as functions of the slope of the converging detonation wave. We determined that decreasing the slope of the converging detonation wave front leads to an increase in the aspect ratio and velocity of the explosively formed projectile.