US3613581A

US3613581A - Explosive device for perforating high-strength metal plates

Info

Publication number: US3613581A
Application number: US413678A
Authority: US
Inventors: William B Mclean; Lawrence N Cosner; John Pearson
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1964-11-20
Filing date: 1964-11-20
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

1. An explosive device for removing a circular pluglike fragment from a metal plate structure, comprising; A. CYLINDRICAL METAL OUTER CASING TUBE HAVING FRONT AND REAR ENDS AND CONTAINING A CHARGE OF EXPLOSIVE MATERIAL, B. SAID CHARGE HAVING A FIRST, CYLINDRICAL, AXIAL PORTION IN CIRCUMFERENTIAL CONTACT WITH THE INNER SURFACE OF THE WALL OF SAID TUBE AND EXTENDING FORWARDLY TO A CIRCULAR FORWARD LIMIT OF EXPLOSIVE CHARGE AND TUBE CONTACT, AND HAVING A SECOND, FRONT END, AXIAL PORTION ADJOINING AND EXTENDING FORWARDLY FROM SAID CIRCULAR FORWARD LIMIT AND TERMINATING AT ITS FORWARDMOST PORTION AT AN AXIAL POSITION SUBSTANTIALLY COADJACENT THE FRONT END OF THE TUBE, SAID FRONT END AXIAL PORTION FORMING AN AXIALLY ALIGNED FORWARDLY CONVERGING BODY OF REVOLUTION HAVING ITS OUTER SURFACE IN RADIALLY SPACED RELATIONSHIP TO THE WALL OF THE TUBE DEFINING AN ANNULAR CAVITY THEREABOUT BETWEEN THE BARE OUTER SURFACE OF THE EXPLOSIVE MATERIAL AND THE INNER SURFACE OF THE WALL OF SAID TUBE, SAID ANNULAR CAVITY BEING OF FORWARDLY INCREASING CROSS SECTION FORMING AN EXPLOSIVE PRESSURE FOCUSING CAVITY FOR CONCENTRATING THE INITIAL EXPLOSIVE EFFECT IN AXIALLY FORWARDLY AND LATERALLY OUTWARD DIRECTIONS TO PRODUCE A SEMITOROIDAL CRATER HAVING A MEDIAN CRATER DIAMETER APPROXIMATELY COEXTENSIVE WITH THE DIAMETER OF THE TUBE IN THE SURFACE OF A METAL TARGET PLATE DISPOSED ADJACENTLY AND NORMALLY TO THE FRONT END OF THE TUBE AT THE TIME THE CHARGE IS EXPLODED, C. SAID CHARGE BEING MADE OF AN EXPLOSIVE MATERIAL OF SUCH A CHARACTER THAT IT PRODUCES A TIME DISTRIBUTION OF DYNAMIC EXPLOSIVE LOADING EFFECTS BY WHICH THE HIGH LEVEL OF EXPLOSIVE LOADING IS SUSTAINED MOMENTARILY AFTER FORMATION OF THE SEMITOROIDAL CRATER TO PRODUCE A PUNCHLIKE EXPLOSIVE LOADING UPON THE SURFACE OF THE TARGET PLATE ENCIRCLED BY THE CRATER TENDING TO CAUSE AN APPROXIMATELY FRUSTOCONICAL FRACTURE SURFACE EXTENDING FROM THE BOTTOM OF THE CRATER TO THE OPPOSITE SIDE OF THE PLATE AND DIVERGENT IN THE DIRECTION TOWARD SAID OPPOSITE SIDE, WHEREUPON THE PORTION OF THE PLATE ENCOMPASSED BY THE CRATER AND FRACTURE SURFACE IS REMOVED FROM THE BODY OF THE PLATE.

Description

United States Patent [72] Inventors John Pearson;

William B. McLean; Lawrence N. Cosner, all of China Lake, Calif. [21] Appl. No. 413,678 [22] Filed Nov. 20, 1964 [45] Patented Oct. 19, 1971 [73] Assignee The United States of America as represented by the Secretary of the Navy 7 [54] EXPLOSIVE DEVICE FOR PERFORATING HIGH- STRENGTH METAL PLATES 5 Claims, 4 Drawing Figs.

[52] US. Cl 102/24 [51] Int. Cl F42b H00 [50] Field of Search 102/22, 23, 24 HQ 56, 98

[56] References Cited UNITED STATES PATENTS Re. 23,211 3/1950 Mahaupt 102/22 X 2,988,994 6/1961 Fleischer 102/24 I-IC 3,117,518 1/1964 Porter et a1, 102/24 l-IC FOREIGN PATENTS 1,231,003 4/1960 France 102/24 l-IC Primary ExaminerVerlin R, Pendergrass Att0rneys-G. J. Rubens, V. C. Muller and P. H. Firsht b. said charge having a first, cylindrical, axial portion in circumferential contact with the inner surface of the wall of said tube and extending forwardly to a circular forward limit of explosive charge and tube contact, and having a second, front end, axial portion adjoining and extending forwardly from said circular forward limit and terminating at its forwardmost portion at an axial position substantially coadjacent the front end of the tube, said front end axial portion forming an axially aligned forwardly converging body of revolution having its outer surface in radially spaced relationship to the wall of the tube defining an annular cavity thereabout between the bare outer surface of the explosive material and the inner surface of the wall of said tube, said annular cavity being of forwardly increasing cross section forming an explosive pressure focusing cavity for concentrating the initial explosive effect in axially forwardly and laterally outward directions to produce a semitoroidal crater having a median crater diameter approximately coextensive with the diameter of the tube in the surface of a metal target plate disposed adjacently and normally to the front end of the tube at the time the charge is exploded,

c. said charge being made of an explosive material of such a character that it produces a time distribution of dynamic explosive loading effects by which the high level of explosive loading is sustained momentarily after formation of the semitoroidal crater to produce a punchlike explosive loading upon the surface of the target plate encircled by the crater tending to cause an approximately frustoconical fracture surface extending from the bottom of the crater to the opposite side of the plate and divergent in the direction toward said opposite side,'whereupon the portion of the plate encompassed by the crater and fracture surface is removed from the body of the plate.

PATENTEuum 191971 3,613,581

FIG. 3.

B W "56 R;

F|G 4 dfitaw PEARSO LIAM B. MC LEAN LAWRENCE N. COSNER BY V. C. MULLER ATTORN EY.

EXPLOSIVE DEVICE FOR PERFORATING HIGH- STRENGTH METAL PLATES The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a novel-shaped charge device, and more particularly to such a device for producing a circular perforation in relatively thick, high-strength, metal plate structures.

The possibility of obtaining an efficient explosive device for perforating high-strength steel plate structures is of great importance in the field of military ordnance. It is also ofpotential importance in the rapidly expanding field of explosive working of metals, which tends to parallel military ordnance developments. The prior art methods for producing holes in steel plates include conventional shape charge devices, i.e. devices having a lined conical cavity at the output end of a charge, and large blast charges. The disadvantage of the conventional charge is that it produces a hole having a diameter which is small relative to the diameter of the device. The disadvantage of the blast charge is the large amount of explosive energy required, and hence the large size of the device.

The problem is further aggravated in connection with the type of warhead for use against high-strength plate structures and which contains a follow-through projectile which is to be pushed through" the perforation to the other side of the plate. The follow-through projectile is itself explosive and is fused to detonate after it passes to the other side of the plate structure. In these instances it is required that the explosive effects of the device be such that the follow-through projectile may be conveniently disposed in the warhead assembly in a location where the forces of the initial explosion will push it through the perforation formed in the armor. Prior to the present invention, the design of follow-through projectile warheads have at best been difficult. An example, which illustrates the complexity of prior art approaches to the construction of follow-through projectile warheads, is US. Pat. No.

One broad aspect of the development leading to the present invention did not, in fact, originate with the inventors. The broad aspect referred to is that of using an explosive device with an inverted-shaped charge to produce a hole in a target, some tests having been conducted along this line in a foreign country during World War II. However, it is believed that the concept was abandoned before promise of feasibility for any practical use was demonstrated, and that the specific design details and target damage data from these early trails were never published. Moreover, an important feature of the present invention is a discovery which allows the present invention to provide a practical and economical weapon.

As distinguished from these and other prior art devices and unsuccessful attempts, the objectives of the present invention include provision of:

l. A novel and highly efficient explosive device for perforating relatively thick high-strength metal plates.

2. An explosive device in accordance with the previous objective which produces a hole having the same order of size as the device.

3. An explosive device in accordance with the first listed objective which is readily adaptable for use with a followthrough projectile.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is a cross-sectional view of one form of invention, shown in position to perforate a target plate;

FIG. 2 is a diagrammatic illustration showing the modes of target damage experienced by the target plate in FIG. 1;

FIG. 3 is a modified form of invention; and

FIG. 4A, B, C and D are other modified forms of invention.

Referring now to the drawing and in particular toFlG. l, the first form of invention to be described is an'explosive device 10 comprising a charge 12 of explosive material and a thin cylindrical outer casing 'tube 14, of any suitable metal, such as stainless steel.

In choice of material for charge '12, it has been discovered that an explosive known as composition C-3" provides certain properties desired for perforating steel plates. Composition C-3 is a conventional explosive composition developed at the time of World War II, and is described at pages 20 l-20'4of the publication Military Explosives, Apr. 1955, Department of the Navy Technical Manual TM 9-l9l0, Department of the Air Force Technical Order TO llAl-34 The nature of the desired properties provided by this explosive will be discussed at a later point in this specification.

Charge 12 and tube 14 are concentrically aligned about an axis A. A suitable detonator 16 is affix'ed to charge "at its rear end. The front end of charge 12 is frustoconically shaped with the bare explosive material forming a frustoconical surface 18 and a circular end face 20. Behind its frustoconical front end, charge 12 is cylindrical withits lateral surface in circumferential contact with the inner wall of tube 14. Theintersection of conical surface 18 and the inner wall of tube 14 forms a circular edge 22 which defines the forward limit of contact between charge 12 and tube 14. Circular face 20, which forms the forwardmost portion of charge [2, lies in the same plane as the front end of tube 14. A cavity 24, having the shape of a volume of revolution, is formed between the casing tube and the frustoconical front end of the charge, the cavity being bounded on its radially outer lateral side by the axially straight inner wall of the casing tube, and bounded on its radially inner lateral side by the forwardly convergent frustoconical surface 18. Frustoconical surface 18 has an included angle B, of approximately 60. However, this angle may be varied considerably, and particularly can be increased in value. A range of values found to produce satisfactory results is between a lower limit of 60 and an upper limit of One factor limiting the geometry of cavity 24, is that distance C, between-circular edge 22, and the front end of the tube wall may not exceed a limit at which lateral relief-will be experienced at the rear end of the cavity before a forward concentration of the explosive forces is effected by the constraining forces of the tube. Such undesired lateral relief effects are typically experienced if distance C exceeds approximately 12 inches. It is to be noted that because there is a limit to the axial length of the cavity, the frustoconical shape is a preferred shape for use in applications in which the diameter of the charge would be large, as for example, in torpedo warhead applications where warheads as large as 20 inches in diameter may be used. With the frustoconical shape, is a simple matter to keep the axial length of the'cavity less than the desired limit by choice of the included angle and diameter of circular face 20.

It will be assumed that the device is disposed over a target plate 26, FIG. 1, of relatively thick mild rolled steel, with the front end of tube 14 resting on the upper face of the plate and with the opposite region of the lower face of the plate free from any contact. It is to be understood that when device 10 is employed as a component of a warhead assembly, this relative disposition is achieved by suitable fusing conventional in the art. FIG. 2 diagrammatically illustrates plate 26 after it has been fragmented by explosion of device 10, but with the removed fragment replaced in its original position in the body of the plate, so that the metal flow and fracture surfaces caused by the explosion may be seen. The relative position of device 10 prior to explosion is shown by phantom lines.

Following the discovery of the particular efiectiveness-of composition C-3, exhaustive experiments were undertaken to gain a better understanding of the physical processes which are involved. The physical process by which device 10 acts upon plate 26, as presently understood, will now be described by reference to FIG. 2. The metal damage experienced by the plates includes formation of a circular crater 28 whichv is generally semitoroidal in cross section and is disposed with its median diameter approximately under, or slightly radially outward from, the former location of the end of the tube wall. Also, a concentric fracture surface which is approximately of frustoconical shape with a 45 included angle, extends from bottom of crater 28 to the opposite side of plate 26. The portion of the plate encompassed by the crater and fracture surface forms a pluglike fragment 32. Fragment 32 is, of course, blown clear of the body of plate 26 under the impact of the explosion leaving a circular perforation of minimum diameter D. Fragment 32 also contains internal spalling cavities 34 which run along the direction of the grain of the rolled steel plate.

It was found that the fundamental physical mode, which results in the formation of circular crater 28, is metal flow in radially outward direction, and that this is produced by the pressure-focusing effect of cavity 24.

Upon closer examination of the approximately frustoconical fracture surface 30, it will be seen to include a short segment 30a which extends in the direction parallel to the direction of the explosive forces, and another short adjoining segment 30a which extends radially outwardly in the direction of the grain of rolled plate 26. It was found that the primary physical mode resulting in such a fracture pattern is failure, in shear, of the metal remaining in the zone between the bottom of the crater and the opposite side of the plate under a force applied over the area the plate encompassed by the crater.

Several explosive materials were employed and of these composition C-3 proved to be the most effective for producing holes in the target plate. This effectiveness appears to be related to the force-time distribution of the load on the target surface. That is, the cratering and the fracturing are events which occur in sequential order, with the fracturing occurring after a crater of some required depth has been produced. Accordingly, the formation of fracture surface 30 is the result of a loading effect which persists at a high enough force level for a sufficient period of time after formation of the crater. This persisting load effect acts on the area of the plate encompassed by the crater and punches out the pluglike fragment 32. While composition C-3 demonstrates excellent properties for both cratering and fracturing of the target plate, it is to be appreciated that other explosives could possess the same degree of capability.

Referring now to FIG. 3, there is illustrated a device 100, like that of FIG. 1 except that a follow-through projectile 36 is disposed in a central bore which is formed in the charge and opens into front end of the charge. It has been found that device 10a punches out a circular pluglike fragment, in essentially the same manner as the device of FIG. 1, and in addition the explosive efi'ects are such that projectile 36 is delivered to the other side of a target through the perforation formed in the plate.

FIGS. 4A, B, C and D show modified forms of the invention which differ from that of FIG. 1 in the shape of the front ends of their respective charge. In FIG. 4A the charge 120 has a frustoconical front end which is spaced a short axial distance away from the front ends of the tube wall. It has been found that the forwardmost portion of a charge may be axially spaced away from the front end of tube wall by relatively short distances, without appreciably effecting the damage process. There is, however, a critical limit beyond which the device fails to produce the desired damage effects. In devices having a diameter of 3 inches, this limit of spacing was found to be of the order of one-half inch. The flexibility to provide such slight spacing at the front end of the device can be of significance in certain ordnance applications, such as torpedo warheads, where it may be desirable to recess acoustic equipment in the front face of the weapon. Charge 12b, FIG. 4B has a compositely shaped front end consisting of a frustoconical portion and cylindrical portion; charge 12c, FIG. 4C, has a conically shaped front end forming a pointed tip; and charge 12d, FIG. 4D, has a bullet-shaped front end.

Obviously many modifications and variations of the present invention are possible in the light of the above teachin s. It is therefore to be understood that within the scope of t 0 appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

I. An explosive device for removing a circular pluglike fragment from a metal plate structure, comprising;

a. cylindrical metal outer casing tube having front and rear ends and containing a charge of explosive material,

b. said charge having a first, cylindrical, axial portion in circumferential contact with the inner surface of the wall of said tube and extending forwardly to a circular forward limit of explosive charge and tube contact, and having a second, front end, axial portion adjoining and extending forwardly from said circular forward limit and terminating at its forwardmost portion at an axial position substantially coadjacent the front end of the tube, said front end axial portion forming an axially aligned forwardly converging body of revolution having its outer surface in radially spaced relationship to the wall of the tube defining an annular cavity thereabout between the bare outer surface of the explosive material and the inner surface of the wall of said tube, said annular cavity being of forwardly increasing cross section forming an explosive pressure focusing cavity for concentrating the initial explosive effect in axially forwardly and laterally outward directions to produce a semitoroidal crater having a median crater diameter approximately coextensive with the diameter of the tube in the surface of a metal target plate disposed adjacently and normally to the front end of the tube at the time the charge is exploded.

c. said charge being made of an explosive material of such a character that it produces a time distribution of dynamic explosive loading effects by which the high level of explosive loading is sustained momentarily after formation of the semitoroidal crater to produce a punchlike explosive loading upon the surface of the target plate encircled by the crater tending to cause an approximately frustoconical fracture surface extending from the bottom of the crater to the opposite side of the plate and divergent in the direction toward said opposite side, whereupon the portion of the plate encompassed by the crater and fracture surface is removed from the body of the plate.

2. A device in accordance with claim 1, wherein said charge is made of a composition C-type explosive material.

3. A device in accordance with (12) claim 1,

e. said body of revolution, at its forwardmost end, having a substantial cross-sectional area.

4. A device in accordance with claim 3 and further for delivering a follow-through projectile through the perforation left in the plate structure, said device further comprising;

f. said body of revolution having formed therein an axial bore for containing a follow-through projectile for delivery through the perforation in the metal plate under force of explosion, said bore at its front end forming a central opening in said substantial cross-sectional area, and

g. a follow-through projectile disposed in said bore.

5. A device in accordance with claim I, and

h. said body of revolution forming a sharp tip at its forwardmost end.

Claims

1. An explosive device for removing a circular pluglike fragment from a metal plate structure, comprising; a. cylindrical metal outer casing tube having front and rear ends and containing a charge of explosive material, b. said charge having a first, cylindrical, axial portion in circumferential contact with the inner surface of the wall of said tube and extending forwardly to a circular forward limit of explosive charge and tube contact, and having a second, front end, axial portion adjoining and extending forwardly from said circular forward limit and terminating at its forwardmost portion at an axial position substantially coadjacent the front end of the tube, said front end axial portion forming an axially aligned forwardly converging body of revolution having its outer surface in radially spaced relationship to the wall of the tube defining an annular cavity thereabout between the bare outer surface of the explosive material and the inner surface of the wall of said tube, said annular cavity being of forwardly increasing cross section forming an explosive pressure focusing cavity for concentrating the initial explosive effect in axially forwardly and laterally outward directions to produce a semitoroidal crater having a median crater diameter approximately coextensive with the diameter of the tube in the surface of a metal target plate disposed adjacently and normally to the front end of the tube at the time the charge is exploded. c. said charge being made of an explosive material of such a character that it produces a time distribution of dynamic explosive loading effects by which the high level of explosive loading is sustained momentarily after formation of the semitoroidal crater to produce a punchlike explosive loading upon the surface of the target plate encircled by the crater tending to cause an approximately frustoconical fracture surface extending from the bottom of the crater to the opposite side of the plate and divergent in the direction toward said opposite side, whereupon the portion of the plate encompassed by the crater and fracture surface is removed from the body of the plate.

3. A device in accordance with (12) claim 1, e. said body of revolution, at its forwardmost end, having a substantial cross-sectional area.

4. A device in accordance with claim 3 and further for delivering a follow-through projectile through the perforation left in the plate structure, said device further comprising; f. said body of revolution having formed therein an axial bore for containing a follow-through projectile for delivery through the perforation in the metal plate under force of explosion, said bore at its front end forming a central opening in said substantial cross-sectional area, and g. a follow-through projectile disposed in said bore.

5. A device in accordance with claim 1, and h. said body of revolution forming a sharp tip at its forwardmost end.