|M.Sc Student||Sterman-Cohen Elad|
|Subject||Modeling the Influence of Machining Copper Liners on|
the Formation Process of Explosively Formed
Projectiles - EEPs
|Department||Department of Mechanical Engineering||Supervisor||Professor Emeritus Miles Rubin|
|Full Thesis text|
An explosively formed projectile (EFP) charge consists of an explosive, a liner (usually copper) and a metallic casing. There are indications from field tests that the performance of the EFP is influenced by surface effects of machining of the copper liner. The main objective of this work is to propose a model which can be used to assess influences of these surface effects on the performance of specific EFP designs. A typical EFP charge with a copper liner has been manufactured using three different techniques: turning on a lathe; milling with a sharp edged tool; and milling with a spherical tool. Each of these liners has been analyzed by means of a micro-hardness measurement and an explosive field test. These tests indicate that there is a variance in hardness near the surfaces of the liners and that the measures of performance of the EFP are influenced by the different machining techniques. The EFP formation process was analyzed using 2D axisymmetric numerical simulations with Lagrangian elements in the hydrocode Autodyn. This work shows that the Steinberg-Guinan strength model, which is standard in Autodyn, can be used to model the effects of machining. Specifically, the material parameters in this model can be adjusted to shift the starting point on the curve of the yield strength versus the plastic strain, to capture the hardening effects of machining. Using this model the simulations are in good agreement with the results of the field tests. Two EFP designs were analyzed: one associated with the field tests, which is relatively insensitive to the effects of machining; and another design with a liner that is susceptible to necking and is sensitive to differences in machining techniques.