• PDF / 5,362,154 Bytes
• 13 Pages / 612 x 792 pts (letter) Page_size
• 16 Downloads / 209 Views

DOWNLOAD

REPORT

---

I.

INTRODUCTION

BECAUSE tungsten heavy alloy is mainly used as a penetrator material against an armor plate, studies have focused on the improvement of its penetration performance. Another important material, widely used so far for penetrators, is a depleted uranium (DU). While DU is fabricated by a casting process, tungsten heavy alloy is fabricated by powder metallurgy. The DU alloy has better properties, and its penetration performance is superior to a tungsten alloy by about 10 pct, under the same conditions. However, the use of a DU alloy poses serious problems regarding environmental pollution and health care, as well as hydrogen embrittlement, corrosion, and radioactivity. A tungsten alloy, on the other hand, has high stability and is easy to store. Therefore, many studies have recently been made on ways to improve the penetration performance of the tungsten heavy alloy, so that it can serve as a replacement for the DU alloy. The superior penetration performance of a DU alloy can be attributed to the distinctive difference in its deformation mode at the time of penetration.[1] In the case of a tungsten alloy, the penetration performance is hindered by the heavy plastic deformation in the head of a penetrator upon penetration, resulting in a mushrooming effect and an enlargement of the diameter of the overall penetration tunnel. However, with a DU alloy, the diameter of the penetration tunnel gets smaller, and is kept so during penetration, because fracture occurs easily at the edge of the penetrator head. Owing to this ‘‘self-sharpening’’ effect, which keeps the diameter unchanged during penetration, the penetration performance can be highly improved.[1] As reported by DONG-KUK KIM, Research Assistant, and SUNGHAK LEE, Professor, are with the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang, 790-784 Korea. HEUNGSUB SONG, Senior Research Scientist, is with the Agency for Defense Development, Daejeon, 300-600 Korea. Manuscript submitted January 20, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS A

Magness and Farrand,[2] the self-sharpening effect can be explained by the formation of adiabatic shear bands arising from the abrupt temperature rise and plastic instability in the process of dynamic deformation. If many adiabatic shear bands can be easily initiated in the penetrator head along which cracks can be propagated, the edge of the penetrator head will easily fall off, and the diameter of the tunnel can be reduced, thereby effectively improving the penetration performance. Lately, there have been many studies on the fabrication process and microstructural control needed to initiate as many adiabatic shear bands in a tungsten heavy alloy as those which occur in a DU alloy, in order to improve its penetration performance.[3] However, the penetration performance can also be affected by microstructural factors such as the shape and size of tungsten particles; mechanical properties such as hardness, strength, ductility, and fracture toughness; and dynamic properties