US3176613A

US3176613A - Shaped explosive charge

Info

Publication number: US3176613A
Application number: US299824A
Authority: US
Inventors: Charles S Godfrey; Donald F Martin
Original assignee: Physics International Co
Current assignee: Physics International Co
Priority date: 1963-08-05
Filing date: 1963-08-05
Publication date: 1965-04-06
Anticipated expiration: 1982-04-06

Description

April 1965 c. s. GODFREY ETAL 3, 76,613

SHAPED EXPLOSIVE CHARGE Fild Aug. 5, 1963 2 Sheets-Shae L 1 HTTO/Q/VEXS.

" April 6, 1965 c. s. GODFREY ETAL 3,176,613

SHAPED EXPLOSIVE CHARGE Filed Aug. 5, 1963 2 Sheets-Sheet, 2

Fig.4

67m 55 .5 600mm).

INVENTORS.

United States Patent 3,176,613 SHAPED EXPLOSIVE CHARGE Charles S. Godfrey, Berkeley, and Donald F. Martin, Alamo, Calif., assignors, by mesne assignments, to Physics International Company, Berkeley, Calif, a corporation of California Filed Aug. 5, 1963, Ser. No. 299,824 0 Claims. (Cl. 102-24) This invention relates to shaped explosivecharges and more particularly to such charges used for piercing armor plate, digging postholes, digging ditches, breaking rock, quarrying, perforating oil well casings and so forth.

Shaped charges employing the well known Munroe effect and the equally well known lined cavity effect, have long been used in the prior art. Generally speaking, shapedcharges employing the Munroe effect, that is an unlined cavity effect, usually form a smooth hemispherical crater within the target. On the other hand, lined cavity charges. usually produce a relatively deep and narrow hole in the target. For the most part, lined cavities have been conical in shape and in all cases of lined cavities, the relationship of the liner to the explosive has been such as to produce a successive collapse of the liner initiating at the point of detonation (that is remote from the target) and progressing toward and along the axis of the liner. Consequently, in lined cavities the explosion forms a liner into a relatively narrow wedge shaped jet of the liner material. The lined cavities of the prior art then produce a relatively high velocity, low mass elongated jet capable of making narrow holes with deep penetration.

This invention differs from the prior art in that it relates to a shaped explosive charge in which a relatively high concentration of the mass of the jet makes it capable of less penetration than former lined cavities but creating considerably larger holes. This invention further differs over the prior art in the high efliciency of coupling through the explosive means within the charge.

In general terms, the present invention relates to a shaped explosive charge which includes a bowl shaped liner defining a concave and a convex surface together with explosive and detonating means disposed adjacent the convex surface of the liner. The explosive and detonating means are shaped and. positioned such that upon detonation the material of the liner is made to arrive at the focal point of the system almost simultaneously whereby a considerably large concentrated slug whose length is only several times its diameter, is projected.

In an alternative embodiment of the invention the shaped explosive charge is surrounded by a body of water whereby the energy to the liner is increased and safety hazards are reduced. I

In view of the above, it is a general object of this invention to provide an improved shaped explosive charge.

It is a more particular object of this invention to provide a shaped explosive charge producing modest velocity but high mass jets capable of less penetration than that of the prior art but with considerably larger holes.

It is another object of this invention to provide a shaped explosive charge of the aforementioned character wherein the volume of material eroded by the jet is much greater than that produced by equivalent sized charges in accordance with the prior art.

These and otherobjects and features of the invention will become more clearly apparent upon a review of the following description in conjunction with the accompanying drawing, in which: a

FIGURE 1 is a sectional view through the axis of a shaped explosive charge in accordance with a preferred embodiment of this invention;

ness t is less than one FIGURE 2, at A, B and C shows the progressive collapse of a liner in the prior art systems;

FIGURE 3, at A, B and C shows the progressive collapse of the liner of FIGURE 1; and

FIGURE 4 is a view similar to FIGURE 1 but showing an alternative embodiment of the invention.

Referring to FIGURE 1 there is shown a liner 11 which may be formed of metal such as steel or copper, shaped in the form of a hemisphere or near hemisphere, which, of course, includes a concave and a convex surface. High explosive material 13 is disposed about the convex surface of the liner 11 and adjacent thereto. A tamping case 15 is disposed about the exterior of the high explosive l3 and a detonator 17 is situated in contact with the high explosive 13. As can be seen from the drawing, the thickness 1 of the high explosive near the center of the liner surface is somewhat smaller than the thickness t near the edge of the liner surface.

The tamper case may be formed of any suitable material'compatible with the high explosive used, such as steel, wood, rubber, lead or as shown, it may be of plastic. The high explosive 13 may be any conventional high explosive material but nitromethane (NM) a liquid explosive, is preferred in many instances since it reduces fabrication costs and makes the tolerances of the various parts relatively unimportant.

In the embodiment shown, the tamper case 15 is coaxial with the liner 11 but its effective center F is displaced from the center F of the liner whereby the variation in spacing between the two, as exemplified by the measurements t and t are provided.

As a particular example of the apparatus shown in FIGURE 1, the liner 11 may be formed of steel having a radius R 11.4 centimeters and a thickness of AR of 0.23 centimeter. The tamper case 15 may be formed of polyethylene plastic having a thickness of 0.2 centimeter and an approximate radius of 16.0 centimeters. The center P of the tamper case 15 is displaced from the center P of the liner 11 by 3.0 centimeters. The position of the detonator is coaxial with the liner 11 and tamper case 15 and spaced such that its lower end lies 0.2 centimeter from the convex surface of liner 11. With a charge, asset forth above, the ratio of the total mass of the liner 11 to the total mass of the high explosive 13 is at an optimum one to three, using composition C3 as the high explosive.

Upon detonation, the result is the acceleration of the entire metal liner 11 at a velocity of three to five millimeters per microsecond. Moreover, it is noted that with the above measurements the effective high explosive thickquarter of the liner radius R whereby reasonably high efliciency of coupling to the high explosive charge, on the order of 30%, is provided. 7 In this respect the efficiency of coupling is defined as the ratio of energy both kinetic and potential actually given to the liner 11 to the potential energy initially possessed by the high explosive employed. One of the primary factors in obtaining this relatively high eificiency of 30% is in keeping the effective thickness t of the high'explosive small with respect to the radius of the liner.

With the above measurements and values given, detonation of the shaped explosive charge causes the liner 11 to be collapsed such that all parts thereof converge simul taneously at the focal point P By Varying the thickness of the high explosive 13 and/or the thickness of the metal liner 11, variations of the particular shape of the charge may be made in accordance with principles of calculation well known in the art. Thus, the thickness of the high explosive could remain constant about the metal liner with the thickness of the liner 11 varied such that the liner is thinner near its edges than it is at that area adjacent the detonator 17. Thus upon detonation the area of the liner adjacent the detonator would resist movement to a greater extent than with the area of the liner adjacent its edges. With the constant thickness of the high explosive material 113 and the realization of the propagation time of the detonation throughout the high explosive, the entire liner 11 could be made to converge on the focal point F simultaneously.

While the use of the tamper case 15 is not entirely critical particularly in cases where solid high explosives are employed, a tamper case especially of high inertial mass will increase the efficiency of coupling to the high explosive whenever it is important to minimize the amount of high explosive used. 7

Referring to FIGURES 2 and 3, the drastic differences of the instant invention over the prior art employing lined cavity systems is emphasized. Thus in FIGURE 2, at A, B and C is shown a progressive collapse of the cavity liner in accordance with the well known prior art. As shown at A the cavity 19 is conical in shape and is defined by a conical liner 21. Although in the example shown in FIGURE 2 the high explosive charge 23 disposed behind the liner 21 is in the form of a cylinder, similar action is caused by hemispherical, conical or beehive type high explosives charges. Thus upon initiation of detonation and as shown at B of FIGURE 2, the conical liner 11 collapses progressively along its axis beginning at the point of the liner closest to the detonated charge. Clearly, each axial element of the liner 21 collapses on the axis of the cone at a different time and such acceleration causes a relatively long needle-like jet 25 as shown at B in FIGURE 2, and 25a as shown at a later time at C of FIGURE 2.

Referring to FIGURE 3, however, it is noted that the liner l1 converges on the focal point F simultaneously such that almost all of the liner material is projected along the jet path as a slug 27 having a length only several times its diameter.

Referring to FIGURE 4, an alternative embodiment of the invention is shown, wherein a liner 11, a high explosive 13, tamper case 15 and detonator 17 are included substantially as shown in FIGURE 1. There is further included, however, a container 29 filled with water 31. The container 29 may be formed of any suitable material such as a plastic sheet and is disposed concentric with the tamper case 15 such that the thickness of water throughout is approximately constant. As an optimum the mass of the water 31 should be ten times that of the high explosive whereby the water serves as an effective tamper for the high explosive to produce a relatively high efficiency coupling between the high explosive and the liner 11. Additional advantages of the container 29 and water 31 are that it reduces the blast energy in the form of noise which is transmitted to the surrounding air and furthermore, reduces the fire hazard to surrounding areas as well as the possibility of hazardous shrapnel or flying debris.

Thus it is seen that an improved shaped explosive charge has been provided which is suitable for various uses, examples of which may include piercing of heavy duty armor plate, digging postholes, ditching operations in rock, breaking rock, or perforating oil well casings. It is seen that the invention provides a shaped explosive charge wherein a lined re-entrance cavity is formed and wherein high explosive and detonating means are provided to produce collapse of the liner itself to converge simultaneously on the focal point of the liner. Thus, the liner forms a moderate velocity high mass jet capable of making relatively large holes but of somewhat less penetration than that as formed by the prior art lined cavity systems.

We claim:

1. A shaped explosive charge comprising a bowlshaped liner formed by a figure of revolution about an axis thereof and being defined by concentric outer convex and inner concave surfaces extending away from said axis and a terminating edge joining said surfaces, explosive means disposed in contact with said convex surface and terminating in an edge adjacent said liner edge, said explosive means regularly increasing in radial thickness as the explosive extends away from said axis and being thickest at the edge thereof, and detonator means disposed adjacent said explosive means to ignite said explosive progressivelyfrom the axis to the edge.

2. A shaped explosive charge as defined in claim 1 wherein said bowl shaped liner defines substantially a hemisphere.

3. A shaped explosive charge as defined in claim 2 wherein the effective thickness of the explosive means along said axis is less than one fourth the radius of the liner.

4. A shaped explosive charge as defined in claim 1 wherein the ratio of the mass of the liner to the mass of the explosive means is one to three.

5. A shaped explosive charge as defined in claim 1 together with a tamper case disposed adjacent that surface of the explosive means remote from the liner.

6. A shaped explosive charge as defined in claim 1 together with tamper means disposed adjacent that surface of the explosive means remotefrom the liner, said tamper means including a container and Water disposed within said container.

7. A shaped explosive charge as defined in claim 6 wherein said container and water have a constant thickness about said surface of the explosive means.

8. A shaped explosive charge as defined in claim 7 wherein the mass of the water is ten times greater than the mass of the explosive means.

9. A shaped explosive charge comprising a substantially hemispherically shaped liner defining a concave and a convex surface, explosive and detonating means disposed about the convex surface of said liner for collapsing all portions of said liner to arrive essentially simultaneously at the focal point defined by said concave surface, the surface of the explosive means remote from said liner defining substantially a hemisphere larger than said liner and having its effective focal point displaced from the focal point of the liner in a direction away from the liner whereby the thickness of the explosive means is greater at the edge of the liner than at the center of the liner surfaces, and a tamper case disposed adjacent said remote surface of the explosive means, the mass of the explosive means being three times greater than the mass of the liner and the thickness of the explosive means at the center of the liner surfaces being less than one fourth the radius of the liner.

10. A shaped explosive charge as defined in claim 9 together with a hemispherical container disposed about and concentric with said tamper case, and water disposed Within said container, the mass of the water in said container being ten times as great as the mass of the explosive means.

References Cited by the Examiner UNITED STATES PATENTS 232,640 9/80 Hallock 102-23 2,616,370 11/52 Foster 10221 2,667,836 2/54 Church et al. 102-20 2,797,892 7/57 Ryan 102-24 X 2,833,215 5/58 Spencer 102-20 OTHER REFERENCES Clark et al.: Behavior of Metal Liners in Shaped Explosive Charges, in American Instituteof Mining and Metallurgical Engineers, Technical Publication No. 2158, pages l12, March 1947.

SAMUEL FEINBERG, Primary Examiner.

Claims

1. A SHAPED EXPLOSIVE CHARGE COMPRISING A BOWLSHAPED LINER FORMED BY A FIGURE OR RESOLUTION ABOUT AN AXIS THEREOF AND BEING DEFINED BY CONCENTRIC OUTER CONVEX AND INNER CONCAVE SURFACES EXTENDING AWAY FROM SAID AXIS AND A TERMINATING EDGE JOINING SAID SURFACES, EXPLOSIVE MEANS DISPOSED IN CONTACT WITH SAID CONVEX, SURFACE AND TERMINATING IN AN EDGE ADJACENT SAID LINER EDGE, SAID EXPLOSIVE MEANS REGULARLY INCREASING IN RADIAL THICKNESS AS THE EXPLOSIVE EXTENDS AWAY FROM AXIS AND BEING THICKEST AT THE EDGE THEREOF, AND DETONATOR MEANS DISPOSED ADJACENT SAID EXPLOSIVE MEANS TO IGNITE SAID EXPLOSIVE PROGRESSIVELY FROM THE AXIS TO THE EDGE.