This invention relates to ammunition and, more particularly, to shaped charge ammunition which is fired at a target with a spin.
Shaped charge ammunition, broadly, may include projectiles which are merely dropped, e.g., bombs, as well as projectiles which are fired from a rifled barrel, e.g., shells. In general, no spin is imparted to the former group of projectiles whereas the second group of projectiles spin as they approach their target. This invention applies to the latter "spinning" projectiles.
In brief, shaped charge ammunition comprises an aerodynamic nose section and a cylindrical rear section. The latter contains a hollow conical liner which is symmetrically positioned about the cylinder axis at the forward end of the cylindrical section with its open end opening forward. It also contains an explosive charge which is carried behind and in contact with the liner. When a detonator in contact with the rear face of the explosive charge is detonated, a detonation wave moves rapidly through the explosive charge to cause the formation of a shaped charge jet which is formed from the inner portion of the metal liner. The jet is a high velocity stream of metal which is projected forward along the axis of the cone. In the absence of spin compensation, the spin imparted to shaped charge ammunition prevents the jet from forming into an axially-aligned stream with maximum penetrating ability. Instead, portions of the jet exit from the shaped charge ammunition as a cluster of discrete metal streams of greatly reduced penetrating power. This results in a plurality of relatively shallow holes in the target rather than a single deep hole. When the target is armor, e.g., tank armor, inability of the jet to form into a single stream generally means that the armor will not be penetrated and that the shaped charge ammunition has failed to perform its intended mission.
This inventor has recently proven experimentally that properly oriented residual tangential shear stresses in shaped charge liners ("cones") explain why certain shear formed or rotary extruded liners will compensate for the spin given to shaped charge ammunition, thereby permitting the formation of a single, highly penetrating metal jet stream from the shaped charge cones. For almost twenty years, it has been known that shear-formed or rotary-extruded cones exhibited spin compensation characteristics. However, it was not known what physical mechanism(s) was responsible for this. Prior to the aforementioned experimental work by this inventor, there were conflicting publications regarding the effect of residual shear stresses in compensating for shaped charge liner spin (G. F. Carrier and W. Prager, Influence of Residual Stresses on Liner Performance, Technical Report No. 1, DA-3426/1, Brown University (1954); C. M. Glass et al., Effects of Anisotropies in Rotary Extruded Liners, BRL Report No. 1084 (1959)).
The effect of this lack of understanding of spin compensation mechanisms was that it was difficult to perform meaningful quality control on the manufacture of the liner and on the control of the degree of spin compensation. The reason for this is that it was not clear what measurements should be made on the manufactured liner to evaluate its expected spin compensation performance, since the physical mechanism responsible for the spin compensation performance had not been identified.
Identification of the residual tangential shear stress mechanism has now provided a logical measurement basis, as well as the new basis for the manufacture of spin compensating cones described herein.