Effect of water-filled cylindrical 4340 steel chamber length and sidewall thickness on shaped charge jet penetration

This paper assesses how effective a water-filled cylindrical chamber, constructed using 4340 steel with a 20 mm internal diameter but varying in length and sidewall thickness, is at protecting against M85-shaped charge ammunition. It examines how these chamber dimensions influence the depth of penetration into a 4340 steel witness plate placed behind the chamber. Numerical finite element method (FEM) analyses, employing 2D axisymmetric and multi-material Arbitrary Lagrangian Eulerian (ALE) techniques, are performed using LS-DYNA software. These analyses explore how the stability and particulation of the copper jet affect its ability to penetrate steel targets. The study visually demonstrates and explains the mechanisms behind the instability causing the breakup of the jet into particles as it travels through water-filled chambers with different chamber parameters. Additionally, tests are performed using these chamber parameters derived from the analysis to validate the findings. The experimental results align closely with the numerical analysis for scenarios involving both the absence of a chamber and a chamber without water. However, for water-filled chambers with adequate sidewall thickness, both individual and average test results are lower than predicted. This discrepancy is likely due to slight non-concentricity between the munition and the chamber caused by geometric inaccuracies. These inaccuracies lead to the jet fragmenting and scattering sideways as it exits the chamber, a factor not accounted for in the numerical simulations.