This application claims the priority of United States of America application Serial No. 07/784,171, filed October 25, 1991.

FIELD OF THE INVENTION

This invention relates generally to anti-explosive pads which may be used to protect structures against the disastrous effects of accidental or otherwise unwanted explosions. More particularly, the invention involves stra- tiform anti-explosion pads including multiple layers of lightweight expanded metal net. The invention also involves the method of applying such pads for taking advantage of their anti-explosive characteristics.

BACKGROUND As is well known, the production and use of explo- sives is an extensive and far-reaching industry. Research through the centuries has developed many useful applications for the known explosives, including the industrial blasting utilized in the mining and road building industries, as well as the harnessing of tiny explosions for use in internal combustion engines. The military use of gun powder and

other explosives in rifles, artillery, bombs and the like is also well known. Concurrently with the bene its derived from the useful application of explosives, the world has been forced to endure the disastrous results which too often occur when explosives are accidentally detonated, such as in the case of explosions in coal mines, fuel tank fields, homes, auto- mobiles, ships, airliners, and the like. Similarly, the world is faced with incidents in which bombs are used for terrorist or other illegal purposes. There has been a considerable effort to develop products and methods for protecting structures against the destruction which occurs when explosives are detonated in their vicinity, either accidentally or for sinister pur- poses. Although some progress has been made, the loss of human lives and the destruction of property from explosions continues at an unacceptable rate, and there is continued intense effort to find practical, effective and economical ways of improving anti-explosive products and techniques.

It is an object of the present invention to provide a padding material which possess significantly enhanced explosion suppressing properties. It is another object of the invention to produce an anti-explosion pad containing extremely lightweight co po- nents which serve in a surprisingly effective manner to dissipate the shock waves resulting from the detonation of an explosive material.

It is a further object to provide methods for use of the new anti-explosion pad in the protection of struc- tures which are otherwise subject to severe damage from the explosive force of a detonated bomb. Other objects and advantages will become apparent as the specification proceeds.

SUMMARY OF THE INVENTION This invention is based on the discovery that walls and other structural elements can be effectively protected against bomb explosions by interposing between them and the bomb a lightweight pad containing multiple sheets of expanded metal net separated by a layer of porous material. It has been found that the presence of the expanded metal net effectively deflects and dissipates the shock waves resulting from the detonation of the explosive material, so that the wall or other structural element maintains its physical integrity in spite of the explosion. The product of the present invention therefore is a stratiform anti-explosion pad comprising a first sheet of expanded metal net, a second sheet of expanded metal net, and an inner core layer of air-permeable material separating the said first and second sheets. In a preferred embodi- ment, the pad is retained between front and back covers, and the sheets of expanded metal net are made from slit foil such as a magnesium alloy metal, while the inner core is a porous material such as fiberglass, cotton batting, or an assembly of miniature balls formed from expanded metal net.

The invention also comprises a method for protect- ing structures against the impact of explosions comprising interposing between said structure and said explosive a stratiform anti-explosion pad of the nature described above.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional elevation of the anti- explosion pad of the present invention, showing the various component layers. FIG. 2 is a cross-sectional elevation of an optional variation of the explosion pad of the present invention, showing the inclusion of various additional optional layers. FIG. 3 is a top view of a slitted metal foil sheet, which can be expanded by stretching to provide the expanded metal net usable in the present invention. FIGS. 4 through 7 are top views of the expanded metal net, showing the changes in configuration as the slitted sheet is pulled to open up the expanded metal net.

DETAILED DESCRIPTION OF THE INVENTION Referring to the drawings, the basic stratiform anti-explosion pad of the present invention is shown in FIG. l, wherein the pad 10 contains sheets 3 and 4 made of expanded metal net and separated from each other by an inner core 5 made of an air-permeable material. Although not essential to the invention, it is desirable for certain purposes to enclose the above pad between front and back

covers 6 and 7 to maintain the integrity of the pad and prevent slipping or shifting of the elements. For this purpose, the front and back covers 6 and 7 may be bound together by stitching, stapling or other known fastening means at seams 8 and 9. The expanded metal employed in sheets 3 and 4 is formed by slitting a continuous sheet of metal foil in a specialized manner and then stretching the slitted sheet to convert it to an expanded prismatic metal net having a thickness substantially greater than the thickness of the foil. Referring to the drawings, FIG. 3 shows a sheet of metal foil provided with discontinuous slits appropriate for the present invention. The length and width of the sheet may be chosen from any number of practical dimensions, depending on the size of the anti-explosion pad to be pro- duced. As noted in FIG. 3, sheet 10 is provided with dis- continuous slits 11 in spaced apart lines which are parallel to each other but transverse to the longitudinal dimension of the sheet 10. The slits 11 in each line are separated by unslit segments or gaps 12, and it will be noted that the slits 11 in each line are offset from the slits 11 in adja- cent lines. Similarly, the gaps 12 in each line are offset from the gaps 12 in adjacent lines. The lines of slits run parallel to the longitudinal edges 13 and 13A of the conti- nuous sheet of metal foil. Apparatus for producing the slitted metal foil is described in detail in copending application Serial No. 07/605,540, filed October 29, 1990.

2 When the slitted metal foil as shown in FIG. 3 is

3 stretched by subjecting it to longitudinal tension, it is

4 converted into an expanded metal prismatic net, usable as

5 elements 3 and 4 of FIG. 1 of the present invention. In the

6 stretching procedure, the horizontal surfaces of foil are

7 raised to a vertical position, taking on a honeycomb-like

8 structure. This conversion is shown in FIGS. 4 through 7 of

9 the drawings. The slitted metal foil 10 is shown in FIG. 4

10 prior to stretching. When longitudinal tension is applied

11 in the direction of arrow 15, the slits 11 begin to open and

12 are converted to eyes 16, and the product assumes the i- appearance shown in FIG. 5. The application of more tension

14 causes a greater opening of the slits, and the product

15 expands into the honeycomb-like, prismatic form shown in

16 FIG. 6. When even further tension is applied, the configu-

17 ration reaches its desired end point, as in FIG. 7. The

18 conversion illustrated in FIGS. 4 through 7 is accompanied

19 by an increase in thickness of the product, the final thick-

20 ness of the honeycomb product being approximately twice the W value of the space 14 between each line of slits.

22 For the anti-explosion pad usage of the present 3 invention, it is desired that the metal foil be very thin 4 and that the slits in each line and the spaces between the 5 lines be very small. Thus, the thickness of the foil used 6 to produce the metal net should be in the range between 7 0.028 and 1.0 mm, and the preferred thickness is between 8 0.028 and 0.2 mm. The length of each slit 11 is in the 9 range between 1 and 2.5 cm, and the unslit sections or

gaps 12 between each slit are in the range between 2 to 6 mm long. The distance 14 separating lines of slits may be varied, depending on the thickness desired for the resulting expanded metal net. The distance 14 is ordinarily in the range between 1 and 4 mm, so that the thickness of the resulting expanded metal net is normally in the range between about 2 and 8 mm. The preferred value for distance 14 is either l mm or 2 mm. The kind of metal used in the metal foil may be selected from a wide number of metals or alloys which may be produced in the form of a thin foil. For the purposes of the present invention, it is preferred to use alloys of magnesium with certain other compatible substances. Thus, for example, it is desirable to use an alloy of magnesium with substances such as aluminum, copper, zirconium, zinc, strontium, Rn(electron) , silicon, titanium, iron, manganese, chromium, and combinations thereof. Alloys such as the above have the valuable characteristic of not only being lightweight, strong, elastic, heat-conductive, etc., but also the important characteristic of being nonflammable. A particularly useful combination is the alloy of magnesium with aluminum and copper. Another preferred combination is the alloy of magnesium with zirconium and strontium. To a somewhat lesser degree, alloys in which aluminum is substi- tuted for the magnesium, are useful in the practice of the invention. Further advantages are obtained if the expanded metal net is coated with materials such as an alkaline

2 bichromate or an oleate, which are effective in preventing

3 any fire which may be initiated by detonation of the explo-

4 sive. When heated, these materials emit a dense vapor which

5 envelop the area and assist in preventing the ignition of

6 construction materials in the area.

7 The inner core layer 5 may be any suitable air-

8 permeable material such as fiberglass, cotton batting, or

9 other similar non-woven substances. A particularly suitable 0 core material for the layer 5 is an assembly of balls formed 1 from expanded metal net. Such balls are most effective when 2 formed in the shape of small ellipsoids. The ellipsoids are - produced by cutting expanded metal net sheets (such as shown 4 in FIGS. 3 through 7) into small segments and then mechani- cally forming them into the ellipsoid shape. The ellipsoids generally have a short diameter in the range of 20 to 30 mm, and a long diameter in the range of 30 to 45 mm. Apparatus for producing the ellipsoids is described in detail in copending application Serial No. 07/605,540, filed Octo- ber 29, 1990. The inner core layer 5 is preferably in the range between 1 to 6 inches thick. A thickness less than this provides diminishing protection, and thicknesses above this range, although effective, add bulkiness which is not prac- tical under most conditions. For certain uses, it is desirable that the layers 3, 4 and 5 be bound together in a cohesive pad by the use of front and back covers 6 and 7, which may be secured at seams 8 and 9. Any suitable material may used for the back

cover 7. However, it is essential that the front cover 6 be made of an air-permeable material such as a metal or fiber screen, which will allow the shock and heat waves of the bomb explosion to reach layers of expanded metal net 3 and 4 and allow said layers to diffuse and dissipate the said waves before they reach the structure to be protected. If the front cover 6 is a solid, impermeable material, the shock waves of the detonated explosive will exert their full unattenuated force against the impermeable surface and will destroy not only the protective pad but also the structure intended to be protected. It is essential therefore that the front cover be air-permeable, as indicated, and also that it be placed in position facing the direction from which the explosive forces will originate. The invention is not limited to the use of only two layers of expanded metal net, separated by a single core layer. For some applications, involving heavier charges of explosives, it is advantageous to employ three or four layers of metal net, separated by matching cores of porous material. It is also useful in some environments to employ two or more sheets of metal net in contact with each other in a single layer. FIG. 2 illustrates an embodiment of the invention, in which a double layer of expanded metal net is employed adjacent the front surface of the pad and additional layers of metal net, separated by layers of ellipsoid filling mate- rial, are laid up behind the front double layer. The extra layers of metal net and spacing material provide enhanced

z protection against explosions. Kererrlng to πs. z, tne

3 enhanced stratiform anti-explosion pad 17 contains layers

4 18, 19, 20 and 21 made of expanded metal net and separated from each other by inner cores 22, 23 and 24 made of an assembly of ellipsoids of the type described above. The front layer 18 is composed of a double layer of expanded metal net. The pad 17 is enclosed between front and back covers 25 and 26, which are bound together by stitching, stapling or other known fastening means such as seam 27. As indicated previously in connection with the embodiment of FIG. 1, it is essential that the front cover 25 be air- permeable and that it be placed facing the direction from which the explosive shock waves will come. Although the cores 22, 23 and 24 are illustrated in the form of ellip- soids, which are preferred, it will be understood that the core material may be any suitable air permeable material such as fiberglass, cotton batting, or other similar non- woven substances. A single pad may, for certain purposes, be made with different core materials in the various core layers, as for example in a pad with core 22 being ellip- soids and the remaining core layers being fiberglass. Statiform pads of the nature described above pro- vide remarkable protection against the destructive forces of an explosion. Although the proportion of expanded metal net to the overall weight of the structure being protected is very minute (i.e., between .05-1%), the special honeycomb configuration and the heat conductivity of the expanded metal net effectively dissipate the shock waves and thermal

2

3 effects of a close range bomb explosion. Thus, for example,

4 a concrete block wall covered with the anti-explosion pad of

5 the present invention, suffers no damage from a one-pound 6 TNT bomb detonated 5 inches in front of the wall; whereas,

7 without the pad, the wall is obliterated.

8 The anti-explosion pad may readily be applied to

9 the surface of structures by means of nails, staples, adhe-

10 sives, and the like. When in place, the invention has

11 widespread applicability for the protection of structures

12 against explosions. Applications in homes and commercial 1- buildings include covering the walls of garages, furnace

14 rooms, or other areas where fuel tanks or other explosive

15 materials are located. In automobiles, the firewall between

16 the engine compartment and the passenger area may be covered

17 with the anti-explosive pad. For anti-terrorist purposes,

18 the walls of airliner luggage compartments may readily be

19 covered with the product of the invention, to contain and

20 suppress the shock and concussion of a bomb and prevent ^ damage to the controls and other vital structural elements

22 of the plane. The material may be fabricated into walking

23 shields for use by police and firemen at risk from bomb

24 explosions.

25 The following examples describe specific embodi-

26 ments which illustrate the invention but should not be

27 interpreted as limiting the scope of the invention: 28

29

2 EXAMPLE 1

3 A wall 6 feet long, 6 feet high, and 6 inches thick

4 was constructed of concrete block, resting on a 6 inch

5 poured concrete footing in the ground. The entire front

6 surface of this wall was covered with a pad having the con-

7 struction shown in FIG. 1 of the drawings.

8 The expanded metal net used in the two layers of

9 the pad was made from an alloy comprising 0.25% Si, 0.3% Fe,

10 0.01% Cu, 0.01% Mn, 10% Al, 0.01% Zn, 0.1% Ti, and the

11 remainder Mg. The metal foil was .1 mm thick, and in its

12 expanded form the metal net was 2 mm thick. The inner core 1. was a 2 inch thick layer of fiberglass. The padding mate-

14 rial had front and back covers made of metal screening with

15 a mesh of 4 microns.

16 A one pound bomb of TNT (trinitrotoluene) in a

17 plastic container was placed on the ground 5 inches from the

18 covered surface of the wall and detonated. In spite of the

19 - extreme impact, the wall remained intact and showed no signs

20 of damage. The front surface of the anti-explosive pad W showed only slight scarring.

22 Following this, the pad was removed from the wall, 3 and a second one pound bomb of TNT in a plastic container 4 was placed on the ground 5 inches from the wall and deto- 5 nated. The wall was obliterated. 6 7 EXAMPLE 2 8 A wall was built, having the same dimensions, ate- 9 rials and configuration as in Example 1. The wall was cov-

2 ered with an anti-explosion pad having the structure shown

3 in FIG. 2 of the drawings.

4 The expanded metal net used in the pad was made

5 from an alloy comprising 0.25% Si, 0.3% Fe, 0.01% Cu, 0.01%

6 Mn, 10% Al, 0.01% Zn, 0.1% Ti, and the remainder Mg. The

7 metal foil was .1 mm thick, and in its expanded form the

8 metal net was 2 mm thick. The metal foil was coated with an

9 oleate composition. Each of the inner cores was a 1 inch 0 thick assembly of ellipsoids made from the same material as 1 the layers of expanded metal net. The padding material had 2 front and back covers made of metal screening with a mesh of - 4 microns. 4 A two pound bomb of TNT (trinitrotoluene) in a 5 metal shell was placed on the ground 5 inches from the cov- 6 ered surface of the wall and detonated. In spite of the 7 extreme impact, the wall remained intact and showed no signs of damage or burning. The front surface of the anti- explosive pad showed only slight scarring. Although preferred embodiments of the invention have been described herein in detail, it will be understood by those skilled in the art that variations may be made thereto without departing from the spirit of the invention.

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