Methods for forming munitions casings and casings and munitions formed thereby

1. A method for forming a fragmentation explosive munition, the method comprising:

providing a casing; and

forming microholes in the casing using electrical discharge machining (EDM), thereby forming a modified casing;

wherein each of the microholes provides an initiation site in the modified casing for fracture of the modified casing as the modified casing expands under explosive loading;

wherein the microholes each have a length to diameter ratio of at least 50 to 1; and

wherein an elastic modulus, a yield strength, and an ultimate strength of the casing remain substantially unaffected by the microholes.

2. The method of claim 1 wherein the casing is formed of metal.

3. The method of claim 2 wherein the metal includes a metal selected from the group consisting of steel and titanium.

4. The method of claim 1 wherein the casing has an outer surface and forming microholes in the casing includes forming the microholes in the outer surface.

5. The method of claim 1 including heat treating the casing prior to forming the microholes.

6. The method of claim 1 including filling the modified casing with explosive material after forming the microholes.

7. The method of claim 6 wherein the explosive material is a high energy (HE) explosive.

8. The method of claim 1 wherein the microholes each have a depth in the range of from about 25% to 75% of a thickness of the casing.

9. The method of claim 1 wherein the microholes each have an inner diameter in the range of from about 100 μm to 600 μm.

10. The method of claim 1 wherein the microholes each have:

a depth in the range of from about 25% to 75% of a thickness of the casing; and

an inner diameter in the range of from about 100 μm to 600 μm.

11. The method of claim 1 wherein forming microholes in the casing includes forming the microholes in the casing using a hole drilling electrical discharge machine.

12. The method of claim 1 wherein the casing is substantially tubular.

13. The method of claim 1 wherein the casing has a substantially cylindrical, conical or frustoconical outer surface.

14. The method of claim 1 wherein forming microholes in the casing includes forming the microholes in the casing in an offset pattern.

15. The method of claim 14 wherein the offset pattern includes a plurality of sequential rows of the microholes, and at least one of the sequential rows is rotationally offset about a munition axis with respect to at least one adjacent one of the sequential rows.

16. The method of claim 1 wherein forming microholes in the casing includes forming the microholes such that the spacing between adjacent microholes is in the range of from about 0.1 inch to 5 inches.

17. The method of claim 1 wherein:

the method includes filling the modified casing with a high energy (HE) explosive; and

the microholes each have an inner diameter in the range of from about 100 μm to 600 μm.

18. The method of claim 17 wherein forming microholes in the casing includes forming the microholes such that the spacing between adjacent microholes is in the range of from about 0.1 inch to 5 inches.

19. A method for forming a munition casing, the method comprising:

providing a casing; and

forming microholes in the casing using electrical discharge machining (EDM), thereby forming a modified casing;

wherein each of the microholes provides an initiation site in the modified casing for fracture of the modified casing as the modified casing expands under explosive loading;

wherein the microholes each have a length to diameter ratio of at least 50 to 1; and

wherein an elastic modulus, a yield strength, and an ultimate strength of the casing remain substantially unaffected by the microholes.