Date of Award

Fall 1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering - (Ph.D.)

Department

Mechanical Engineering

First Advisor

John Vincent Droughton

Second Advisor

Per-Anders Persson

Third Advisor

Pasquale J. Florio

Fourth Advisor

Robert P. Kirchner

Fifth Advisor

Rong-Yaw Chen

Abstract

The use of porous tungsten as a liner for shaped charges to improve their penetration was proposed by Ki-Hwan Oh in his invention disclosure "Shock Extrusion of Ingots from Powders or Solids", at the New Mexico Institute of Mining and Technology, Socorro NM on June 7, 1988. The intention was to increase the ductility of the normally brittle metal by heating the liner to a high temperature by shock compaction during its acceleration just before jet formation.

The feasibility of increasing the ductility of tungsten in this way is the subject of the present study. The theory and prior experimental studies of porous metal compression by shock waves are reviewed, with special attention to ways for determining the temperature of the compressed material. In this theoretical study a new equation of state is developed, and experimental shaped charges with porous tungsten liners are designed and tested. One of the shaped charges was also modeled on a computer for this study.

An improved equation of state for porous tungsten is developed and compared with experimental data from the literature and other equations of state. The proposed equation of state shows improved correlation to experimental data for tungsten with high initial porosity. This is achieved while maintaining the close correlation to data obtained by most equations of state at higher initial densities.

After preliminary studies, two shaped charge liner designs having porous tungsten liners with initial densities of 65% and 80% of the solid density were designed, manufactured, and test fired. Steel target plates were used to determine the penetration. As shown by the flash radiography, the jets formed were particulated on a small scale, causing the density of the jets to diminish with distance from the charge. A relatively long distance between the shaped charge and the target plates was required to provide room for the flash radiographs. This caused low jet densities and a particulated jet that had little penetration into the target plates.

The jet formation for the liner with initial density 65% of the solid was modeled by continuum hydrodynamic computations using Lawrence Livermore National Laboratory's CALE computer code. Near zero strength was used for the jet after formation, as well as a fitted equation of state for tungsten with low initial porosity. The modeling confirmed that low strength in the jet formation caused the fine particulation of the jet as it stretches.

By using a combination of techniques developed in this work, improved temperature determinations were made. These indicated that the temperature of the shock-compressed tungsten liner varied from 350°C at the sides of the cone to 2,087°C at the apex. The shaped charge needs to be redesigned in order to achieve the temperatures of approximately 1000°C required to beneficially change the properties of tungsten. The study concludes with recommendations for future work. Proposals for shaped charges with initially porous tungsten liners that may form coherent jets are made. A test method to verify predicted penetration characteristics of finely particulated jets, developed in this study, is discussed.

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