WO2004039752A1

WO2004039752A1 - A method and apparatus for using low mechanical strength explosive materials and products made thereby

Info

Publication number: WO2004039752A1
Application number: PCT/IL2003/000895
Authority: WO
Inventors: Benjamin Keren; Nahum Erez; Moshe Paz; Samuel Friling; Avraham Luster
Original assignee: Rafael-Armament Development Authority Ltd.
Priority date: 2002-10-30
Filing date: 2003-10-30
Publication date: 2004-05-13
Also published as: IL152564A0; AU2003274673A1

Abstract

A method for providing an explosive layer possessing enhanced mechanical properties, by filling a honeycomb-shaped structure with an injected or pressed explosive material, such that the honeycomb-shaped structure is built from cells having profiles selected from the group consisting of hexagonal or other polygon shapes having three or more sides. The honeycomb-shaped structure may be made of aluminum, steel, titanium, plastic and reinforced plastic. The explosive layer is suitable for use in explosive reactive armor.

Description

A METHOD AND APPARATUS FOR USING LOW MECHANICAL

STRENGTH EXPLOSIVE MATERIALS AND PRODUCTS MADE

THEREBY

Field of the Invention

The present invention relates to the field of high-explosive composite

substance plates. More particularly, the invention relates to a method and

apparatus for using low mechanical strength explosive materials,

especially but not limited to those used for reactive armor.

Background of the Invention

A high explosive is characterized by the extreme rapidity with which its

decomposition occurs: this action is known as detonation. When initiated

by a blow or shock, it decomposes almost instantaneously, with the

rupture and rearrangement of the molecules themselves and the release of

much energy.

Trinitrotoluene, commonly known as TNT, is a well known high-explosive,

which is a constituent of many explosives, such as amatol, pentolite,

tetrytol, torpex, tritonal, picratol, ednatol, and composition B. In its

refined form, TNT is one of the most stable high-explosives and can be

stored over long periods of time. It is relatively insensitive to blows or

friction. Other example of well known explosives is C-4. C-4 is a plastic explosive which contains about 90% RDX (i.e., cyclonite) and 10% of inert

oil.

Explosive Reactive Armor (ERA) is a shield that consists of a high

explosive layer, typically enclosed between two metal slabs. When a hollow

charge jet (e.g., a projectile) strikes an ERA plate, the explosive layer

detonates inducing the metal slabs to move at high velocity at an angle to

the jet, which causes the jet to erode and lose much of its penetrating

power. ERA is typically used for protecting battlefield vehicles, such as

tanks. For example, the T-72BN tank has ERA packages fitted on its hull

and turret.

However, many useful explosive materials are either brittle or paste-like,

due to the fact that they contain a relatively high amount of high explosive

grains (sometimes above 80% in volume) with thermoplastic or

thermosetting binder, or are loaded with a relatively high volume

percentages of microbailoons or fire retardant materials. Therefore, from

the production and durability requirement points of view, the ERA plates

made from such explosive materials are not as effective for operational use

as would be desired. Furthermore, in an ERA plate loaded with a

relatively high quantity of high-explosive grains with thermoplastic

binder, the binder constituent might be squeezed while being tightened between the plates, thereby releasing binder material out of the ERA plate

and increasing its sensitivity.

The production of ERA plates poses problems that are difficult to solve. In

addition to the fact that the high-explosive constituents of ERA plates

require a wide range of attributes, such as a specific energetic profile,

survivability under battlefield conditions, non-burning properties, low cost

etc., the production process and the mechanical requirements of the ERA

plates are laborious. For example, a high-explosive charge for ERA is

required to have a relatively precise thickness with a deviation of no more

than ±0.2 mm. Such a requirement is relatively difficult to achieve.

Furthermore, in order to place the ERA plates on vehicles or on other

locations, some of the plates need to be cut into very complicated shapes,

or to be perforated according to the structure to which they are to be

attached. If the explosive material in the ERA plates is either brittle or,

conversely, paste-like, cutting and perforating the plates presents many

practical problems.

Regarding the survivability, whenever a projectile impacts on an ERA

packet (i.e., an assembly containing two or more ERAs), no matter on what

point of the packet, it usually causes total destruction of that packet. This

causes damage to the tank systems, and has the added disadvantage that such an ERA packet can only be used once. Furthermore, in case of a fire,

the flame may spread over the entire tank.

All the problems , described above have not yet been solved and no

satisfactory solution has been provided to the problems caused by the low

mechanical strength explosive materials, such as brittle or paste-like

materials, that may permit to use them safely and conveniently in ERA

packets.

It is an object of the present invention to provide ERA plates and packets

that overcome the drawbacks of the prior art.

It is another object of the present invention to provide ERA plates and

packets that exhibit injured survivability under battlefield conditions.

It is yet another object of the present invention to minimize the zones of

detonation of the ERA, when hit by a hollow charge jet, to the area that

was hit.

It is yet a further object of the present invention to provide ERA plates and

packets with improved durability in case of fire. It is yet another object of the present invention to provide ERA plates and

packets that are simple and relatively inexpensive to manufacture.

It is still a further, object of the present invention to provide ERA plates

and packets that can employ high-explosives of types which heretofore

were difficult to utilize because of their low mechanical strength.

Other objects and advantages of the invention will become apparent as the

description proceeds.

Summary of the Invention

The present invention relates to a method for enhancing the mechanical

properties of an explosive material, comprising filling a honeycomb-shaped

structure with the explosive material.

The term "honeycomb-shaped structure", as used herein, is meant to

indicate any planar structure consisting of a plurality of cells, regardless of

the shape of the individual cell. Preferably the cells are essentially

identical. By "planar structure" is meant herein a structure wherein all

cell have the shape of parallel open cylinders the axes of which are

perpendicular to a plane, hereinafter called "the structure plane". The

direction of said axes or parallel thereto will be called "the axial direction" and the direction perpendicular to said axial direction, viz. parallel to said

structure plane, will be called "the transverse direction".

Preferably, the honeycomb-shaped structure is built from polygonal cells of

hexagonal shape and/or having the shape of other polygons having three or

more sides.

Still preferably, the honeycomb-shaped structure is made of materials

selected from the group consisting of aluminum, steel, titanium, plastic

and reinforced plastic.

According to a preferred embodiment of the invention, the honeycomb-

shaped structure is filled with the explosive material by injection or by

pressing.

A preferred cell dimension is between of 1/16 inch to 1 inch in plan and

length, wherein by "cell dimension in plan" is meant the length of any

transversal segment inscribed in the cell, viz. a transverse dimension, and

by "cell dimension in length" is meant the axial length of the cell, viz. the

axial dimension, and a preferred thickness of the partitions between the

cells is between of 0.02 mm to 1 mm. However, the above dimensions are

only provided by way of illustration, as the invention is not limited to any

particular shape or dimension. The invention further relates to an explosive layer having improved

mechanical properties, comprising a honeycomb-shaped structure filled

with an explosive material.

According to one preferred embodiment of the invention, the explosive

layer is for use in a reactive armor.

The invention further encompasses a reactive armor comprising a layer of

explosive material consisting of a honeycomb-shaped structure filled with

an explosive material, and comprises such a reactive armor enclosed

between two metal plates.

Brief Description of the Drawings

The above and additional characteristics and advantages of the invention

will be better understood through the following illustrative and non-

limitative detailed description of preferred embodiments thereof, with

reference to the appended drawings, wherein:

Fig. 1 schematically illustrates in plan view a honeycomb-shaped

structure having cells with hexagonal profile, according to an

embodiment of the present invention; Fig. 2 schematically illustrates in horizontal cross-section the

honeycomb-shaped structure of Fig. 1.

Detailed Description of Preferred Embodiments

According to a preferred embodiment of the invention, the high explosive is

inserted into a honeycomb-shaped structure as herein defined. The

honeycomb-shaped structure imparts to the ERA packet the required

mechanical properties, as will be further discussed hereinafter.

Fig. 1 schematically illustrates a typical honeycomb -shaped structure 10

for use in ERA. Typically, the honeycomb-shaped structure 10 is built from

a plurality of cells that, preferably but not limitatively, have a hexagonal

profile, such as cell 11. Of course, the honeycomb-shaped structure can

have cells with other polygonal shapes of three or more sides, or cells other

than polygonal, but only whenever those alternative structures impart

mechanical properties similar to those of a honeycomb-shaped structure

having cells with the hexagonal profile. The honeycomb-shaped structure,

when filled with high-explosive, possesses high mechanical strength in the

axial direction (essentially perpendicular to the structure's bottom

surface), therefore it can easily be subjected to pressure between the metal

plates that complete the ERA plate, but maintains high elasticity

compared to other explosive structures. This is particularly true when it is

filled with explosives rich in filler, which are especially useful for ERA. According to a preferred embodiment of the invention, the cells of the

honeycomb-shaped structure are filled with high-explosive, such as the

paste-like high-explosive C4, a high-explosive rich in RDX, or a brittle

high-explosive loaded with microballoons, fire retardant, etc. Preferably,

but non-limitatively, the honeycomb -shaped structure is made of materials

such as aluminum, steel, titanium, plastic, reinforced plastic, etc.

According to another aspect of the present invention, whenever a brittle

high explosive, such as an explosive made of high explosive grains (above

80% in volume) with thermoplastic binder, or a high-explosive having high

percentages of microballoons or fire retardant, is inserted into the

honeycomb-shaped structure, the explosive exhibits mechanical properties

derived from the honeycomb-shaped structure. Therefore, the production of

the high-explosive composite that fills the cells of the honeycomb-shaped

structure can be easily perforated, if required, and the honeycomb-shaped

structure can be easily cut into the required shape.

The thickness of the honeycomb-shaped structure determines the

thickness of the ERA packet, and therefore the production of the high

explosive composite becomes comparatively easy. Therefore, the invention

eliminates the need of operations for controlling the thickness of the high

explosive, which are complicated and require special tools. Ehminating that need also reduces the cost of the high-explosive composite production.

The honeycomb-shaped structure also will withstand environmental

conditions such as, vibration, accelerations etc.

Varying the honeycomb-shaped structure, e.g., by changing parameters

such as the cell size, the thickness of the partitions between the cells, etc.,

has an effect on the properties of the honeycomb-shaped explosive

structure. In this way, properties such as survivability under battlefield

conditions, durability in case of fire, etc., can be improved. High

survivability of the ERA is obtained due to the fact that detonation of the

explosive is limited by the walls of the honeycomb cells. In cases when

detonation occurs, the non-detonated part of the ERA package can be

further used, and the damage to tank due to further attacks may be

reduced. For example, providing the honeycomb-shaped structure with a

relatively high density of cells and large thickness of the partitions

between the cells, improves the ERA packet survivability when it is hit by

a hollow charge jet, in that this restricts the detonation of the packet to

the area that was hit by said hollow charge jet. The undamaged portion of

that packet will continue to protect the area that it covers. The partitions

between the cells also enhance the durability of the ERA packets in case of

fire, due to the fact that they restrict the spreading of fire. A typical honeycomb structure of Fig. 1 may have cells of transverse and

axial dimensions between of 1/16 inch to 1 inch, with a wall thickness

between of 0.02 mm to 1 mm.

According to a preferred embodiment of the invention, the high-explosive

is inserted into one or more cells of the honeycomb-shaped structure by

injecting or by pressing the high-explosive into them.

Fig. 2 schematically illustrates a transverse cross-section of an ERA taken

on plane I-I of Fig. 1. The ERA comprises the honeycomb-shaped structure

10 of Fig. 1 and two metal plates 21 and 22. The honeycomb-shaped

structure 10 is placed between the two metal plates 21 and 22.

The following are comparative examples of technical properties achieved

by high explosives, such as the C-4 and the R-80s, with and without the

honeycomb reinforcement. Compression strength, tensile strength and

elongation ability are measured as follows:

by compression test

tensile strength and elongation by tensile test

Example No. 1: C-4 explosive

As well known in the art, the C-4 is a pasty explosive having no

compressive strength. But, by filling the C-4 into a honeycomb-shaped structure having a 1/8 inch cell size, typical foil thickness of 0.001 Mil and

compression strength of approximately 4 MPa, the honeycomb-shaped

structure will impart to the C-4 the following typical mechanical

properties:

compression strength which will be much higher than 4 MPa;

tensile strength of approximately 0.1 MPa.

Example No. 2: R-80s explosive

R-80s is a sheet form of brittle vulcanized explosives having the following

typical mechanical properties:

Tensile strength of approximately 0.1 MPa; and

Elongation ability of 1.5%.

Filling and vulcanizing the R-80s explosive in a honeycomb-shaped

structure having a 1/8 inch cell size, nominal foil thickness of 0.001 Mil

and compression strength of approximately 4 MPa, will result in imparting

the R-80s explosive the following typical mechanical properties:

Tensile strength of approximately 0.3 MPa; and

Elongation ability of 5%.

The above examples and descriptions have of course been provided only for

the purpose of illustration, and are not intended to limit the invention in

any way. As will be appreciated by the skilled person, the invention can be used in a great variety of ways, employing more than one technique from

those described above, all without exceeding the scope of the invention.

Claims

1. A method for providing an explosive layer possessing enhanced

mechanical properties, comprising filling a honeycomb-shaped

structure with an explosive material.

2. A method according to claim 1, wherein the honeycomb-shaped

structure is built from cells having profiles selected from the group

consisting of hexagonal or other polygon shapes having three or more

sides.

3. A method according to claim 1, wherein the honeycomb-shaped

structure is made of one or more material selected from the group

consisting of aluminum, steel, titanium, plastic and reinforced plastic.

4. A method according to claim 1, wherein the explosive material is

injected or pressed into the honeycomb-shaped structure.

5. A method according to claim 2, wherein a cell transverse and axial

dimensions are between of 1/16 inch to 1 inch.

6. A method according to claim 2, wherein the thickness of the partitions

between cells is between of 0.02 mm to 1 mm.

7. An explosive layer having improved mechanical properties, comprising

a honeycomb-shaped structure filled with an explosive material.

8. A layer according to claim 7, in which the honeycomb-shaped structure

is built from cells having profiles selected from the group consisting of

hexagonal or other polygon shapes having three or more sides.

9. A layer according to claim 7, in which the honeycomb-shaped structure

is made of one or more material selected from the group consists of

aluminum, steel, titanium, plastic or reinforced plastic.

10. An explosive layer according to any one of claims 8 to 10, for use in a

reactive armor.

11. A reactive armor comprising a layer of explosive material consisting of

a honeycomb-shaped structure filled with an explosive material.