CA2250659C - Composite armor material - Google Patents

Abstract

The invention disclosed relates to a composite armor material comprising an outer ballistic impact resistant layer of a steel material having a Rockwell "C"
scale hardness of 47-54, and an inner blast resistant steel layer having a fracture toughness of 3.6-6.5 J/mm, and a Rockwell "C" scale hardness of 28-36.

Description

I

COMPOSITE ARMOR MATERIAL
FIELD OF THE INVENTION
This invention relates to a new composite material for use in vehicle armoring.
BACKGROUND OF THE INVENTION
Presently in North America armored vehicles are engineered and manufactured primarily to provide protection against ballistic attack. The armor typically comprises a single plate, and is held in place using mechanical fasteners and/or by welding. Ballistic protection is achieved either by overlapping of several armor plates, or by covering joints with additional plates. From a mechanical strength standpoint, these armor materials are basically parasitic and do not add any significant strength to the vehicle.
More recent advances in armor materials include the use of dual hard steel.
The dual property hardness steel armor has several distinct advantages over earlier prior art armor; such advantages include having requirements conducive to unlimited production quantities using existing facilities and having fabricability and intrinsic properties of steel. The earlier concept for dual property steel armor was developed from the knowledge that a high hardness was needed to shatter steel armor piercing projectiles and a high toughness was required to achieve multiple strike integrity.
Although the dual property steel armor principle provides an alloy capable of breaking up the projectile, numerous tested alloys have resulted in panel shattering. When panel shattering occurs the effectiveness of the armor is lost, particularly as an armor suitable for a multiple strike capability.

s s A further development of armor materials is described in US patent no.
3,694,174, which issued on 26 September 1972. Tfiat patent discloses a composite material having an outer high hardness impact layer capable of breaking up a projectile, and a lower hardness tough backing layer capable of stopping the broken up projectile. The layers are hot-rolled together to form the composite. The difference in hardness being described as being in the range of 5-8 Rockwell C. The outer layer is further described as having a Rockwell C hardness of 58-59, and the inner layer having a Rockwell C
hardness of 52-53. The thickness of the layers is described as being in the range of 2-3.5 inches.
It is apparent that both layers of this material are still relatively hard.
Moreover, it is unlikely that the small relative difference in hardness between the two layers would be sufficient to achieve much of a difference in mechanical properties. Further, the hot-rolling process is bound to have an adverse impact upon such properties. Also, a composite of the described dimensions would add considerable weight to a vehicle. It will be appreciated that added weight will affect vehicle performance, particularly the power and handling requirements. -It is also known, for example, from US patent no. 4,948,673 issued 14 August 1990, to employ sintered ceramic tiles e.g. based on alumina or silica, to break up armor-piercing projectiles. The broken pieces of the projectile are then stopped by an armor plate backing.
SUMMARY OF THE INVENTION
' According to the invention, a novel composite armor material is provided, comprising an outer ballistic impact resistant layer of a steel material having a Rockwell "C" scale hardness of 47-54, and an inner blast resistant steel layer having a fracture toughness of 3.6-6.5 J/mm, and a Rockwell "C" hardness of 28-36.
Optionally, a synthetic resin adhesive is provided between the .two layers.
Depending upon the requirement, various adhesives may be employed. For example, a soft adhesive such as a polysulfide-based adhesive may be used in some embodiments and a harder adhesive such as a polyurethane-based adhesive may be used in other embodiments.
In another embodiment, a layer of a high tensile strength fabric material is provided adjacent to the inner layer. This layer is not bonded to the inner layer, since bonding would detract from its ballistic capability. Accordingly, it may be touching or slightly spaced from the inner layer and is held place by mechanical fasteners. Also, in use, some backing space must be provided to permit the material to flex so as to act as a catcher's mitt to trap any shrapnel which may have penetrated the inner layer.
In yet another embodiment, an additional outermost layer is provided, which is of a high hard steel as described above. In this case, no bonder is present, -and the steel layers are welded together.
In a further embodiment, a ceramic layer may be included as an additional outermost layer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The novel composite armor can be used to protect vehicle doors and roofs. It is comprised of a reasonably hard steel outer layer that is essential so that the lead core bullets and shrapnel meet sufficient resistance to be fundamentally changed or redirected. The subsequent layers can then trap the modified projectile. Yet this outer layer is not so hard that is shatters or a fails catastrophically as some ultra high hard steel armors would. A 3mm thick layer of Bulloy 500 or Compass B555, generally meeting U.S. military specification MIL-A-4.6100D, Armor plate, steel, wrought, high-hardness, has been found to be suitable.
The second layer of steel has been selected specifically for its toughness and ability to elongate a great deal before failure. Generally, these tough steels fall in line with U.S. military specification MIL-1-12560H, Armor plate, steel, wrought, homogenous, Class 2. Its primary role is absorbing great amounts of energy. This layer is also capable of being welded and not losing its mechanical properties as a result. A 3mm thick layer of Jessup 529 or Sanderson Kayser Class II, has been found to be suitable.
The optional bonding layer of 1-2 mm in thickness, may be a soft adhesive like polysulfide, or a harder adhesive like polyurethane. Specific examples of such adhesives are described in T able 1 which foiiows.
The big difference shown above is in tensile strength.
The adhesive plays a much greater role than merely holding the plates together. The adhesive distributes the impact energy over a greater area. It reduces the ability of the outer layer of steel to elongate in a direction normal to the applied force. It also adds the shear strength of the inner layer to that of the outer layer. Therefore, instead of allowing the outer layer of steel to fail independently in shear, the adhesive holds the plates together so that some of the shear strength of the inner plate is added to the outer. Thus, the~ability of the outer plate to fail in shear or tension is reduced. This reduces the opportunity for local sites of high stress that are generated at the site of a ' failure: In addition, the adhesive acts as a medium through which the explosive shock waves must travel. As the waves pass through the outer plate, through the adhesive and then through the inner plate, they meet different levels of impedance. The changes in impedance disturbs the waves and reduces their effect. The net effect of the energy distribution, the combined shear strengths and the shock wave disruption is a reduction in stress experienced by the armour system. This was most apparent when tests 5-1 and 5-3 were conducted. These tests were identical in armour materials, fabrication techniques and test procedures with the exception of the use of an adhesive. Test 5-1 did not have an adhesive between the layers of steel and the resulting depression in the door was 71 mm deep.
Test 5-3 had a polysulfide adhesive between the layers of steel and the resulting 'depression was 57 mm deep. Therefore, it can be seen that the armour systems that employ adhesives between the layers of steel are capable of providing better protection.
The optional inner layer, of ballistic material is a composite comprising high tensile fibers laminated together with a ductile polymer binder e.g.
Spectrashield~, having an aerial density of about 4.9 Kg/m2. This material acts as a catcher's mitt to trap any fragments or pieces of the first two layers of armor that may have become dislodged. Its role is not one of absorbing large amounts of explosive energy but merely dealing with any material that gets through the first two layers. It is this layer that adds significantly to the penetration resistance of the high speed / high hardness shrapnel.
The mechanical structure is also unique.
The layers of armor are continuous. They are inserted into a vehicle door by cutting the rear face of the door open and inserting them. All other armbr systems use at least two pieces of armor which are fastened together. All of the stress of the shock and overpressure is concentrated at the joint and it fails. ' The method of welding the second layer of steel to the hinge pillar plate, the lock pillar plate, the door bottom plate and the beltline bar is unique in that it i ~ i involves a specific configuration of the welded joints.. If one of the welds is over stressed, the crack runs along the weld and out of the structure.
Traditionally, armor manufacturers use straight welds which fail causing the armor plates to crack into the plate resulting in catastrophic failure. This system is the subject of our co-pending laid open Canadian application no.
2,250,634.
EXPERIMENTAL RESULTS
Test reports numbered 3E1, 3E3, 31=5, 4-1, 4-2, 4-6, 4-17, 4-18, 4-21, 5-1, 5-2, 5-3 and 5-4 are appended at the end of the application.
In Table 1 which follows entitled "Threats and Systems", we include the test results for various embodiments of our invention.
Table 1 Product Polysulfide(Thiokol~Polyurethane EssexC~

2326 Class A) 400SF

Shore A Hardness60 maximum 55 - 60 Tensile Strength> 1.38 Mpa > 6.89 Mpa Elongation ~ > 300 % ~ > 400 ~fhe test materials are as follows:
High hard steel = 3 mm layer of Sanderson Kayser Bulloy 500 (8500) or Sleeman Compass 8555 (8555) Bonder = 1 to 2 mm layer of Essex U-400SF (urethane) or Morton Aerospace Polymer Systems Thiokol~ MCT"" - 236 Class A (polysulfide) Tough steel = 3 mm layer of Sanderson Kayser Military Vehicles and Engineering Establishment (MVEE) Class 2 (Class 2) pr Jessop 529 (J529) Spectra = 6 mm layer (4.9 kg/mz)of Spectrashield~

a Please note that the tests that have been conducted and were successful are noted with their test number, i.e. 3F5 or Yes and they are in bold font. The tests that would pass by extrapolation are in regular font and are identified by "EX".
Regarding the door armor system, the following convention will be used for the armor configuration:

System Location Materials RU ~ Roof High hard steel / urethane / tough steel DU Door High hard steel / urethane / tough steel /

Spectrashield DP Door High hard steel / polysulfide / tough steel /

Spectrashield DO Door High hard steel / no bonder / tough steel /

Spectrashield The roof system RU was tested and provided protection against the M67 fragmentation grenade and the pipe bomb when they were detonated in contact (refer to tests 4-6, 4-18).
The three door armor systems DU, DP and DO were all tested with the pipe bomb in contact (refer to tests 3F1, 5-3, 5-1 ). It was found that the Spectrashield was not required to protect against this threat. Therefore, it can be concluded that the roof system would also be effective against the pipe bomb and the M67 grenade (when detonated in contact or close proxirriity) with polysulfide bonder or without any bonder.
' Therefore, the armor configurations will be increased to include:
System Location Materials RP Roof High hard steel / polysulfide / tough steel RO Roof High hard steel / no bonder / tough steel 1 i It was also found that the standard used for high ha~hess shrapnel, a 9.5 mm diameter steel ball bearing, 63 Rockwell "C" hardness, did not penetrate the two layers of steel in door system DU when faced with the highest threat encountered. This threat was test 3F5. In it the ball bearings were accelerated toward the armor system by a 50 kg. 75% Forcite~ dynamite, charge at a distance of 3.0 metres. Thus, the Spectrashield~ was not required and the roof armor system would have sufficed.
The roof armor system has been ballistically tested with the same bullets and speed as the door systems but at an angle of forty-five degrees. This is a lower threat.
Accordingly, the roof armor system is good for:
- ballistic protection at forty-five degrees, - M67 grenade and pipe bomb protection when detonated in contact and - for protection against the 9.5 mm ball bearing accelerated by a 50 kg charge at 3.0 metres.
The addition of the Spectrashield would take the system to a higher standard:
- the roof system protection plus;
- ballistic protection at zero degrees of obliquity, - fragment protection from pipe bombs at a stand off, - a 2.3 kg non-directional charge at 0.5 metres and - a 50 kg non-directional charge at 3.0 metres. ' In some cases, the areas of an armored vehicle that are small in size tfo not lend themselves to the application of an inner layer of fibrous armor due to the fact that fibrous armor cannot provide protection right to the edge of the fibrous panel. In these areas, such as the roof rails (above the doors and windows but below the roof), useful protection can be achieved from the use of steel armors alone. Accordingly another embodiment of the invention involves an armor system constructed by adding another (outer most) 3mm layer of high hard steel to the outside of the roof armour system. This three layer steel armour system provided the protection of: .
- the roof system plus;
- ballistic protection at zero degrees of obliquity and - a 50 kg non-directional charge at 3.5 metres (refer to test 4-1 ).
An even higher standard of protection is provided based on the results of test 4-21. In this test, a ceramic armor panel was placed on the threat side of door system DU. A pipe bomb was detonated in contact with the ceramic armor to ascertain whether or not that ceramic would create a fragmentation threat. The system passed.
As per test 4-21, the ceramic applique system consisted of an outer layer of A n ~ _'IJ _t--1 7 7 .r.r tL:-1- .r:JJI_ 1-.._.- .t f~:17-~.- A1:1 .J. _ _ t:l--n .u rri~n inna sieei, i . i rnrn uucrc rniaaie layer ai ~mcur~ mmae ceramic wes 101.6 mm square and an inner layer of 1.0 mm mild steel. The ceramic tiles were arranged in a staggered array and bonded to the outer and inner layers with polyurethane. The overall applique system was 610 mm high and 508 -mm wide. It was held against the basic two layer steel armor system described above, with sheet metal screws inserted into the outer door skin.
Therefore, it appears that there are four levels of protection possible built on the same backbone:
Level 1 - Roof armor Level 2 - Door armor Level 3 - Roof Rail Armor Level 4 - Door armor enhanced for higher levels of ballistic protection.

Ballistic Threats Ballistic testing has taken place for all four door armor and roof rail systems and was successful in stopping the 5.56 mm M193 ball ammunition at muzzle velocity (991 +/- 8 m/s) at zero degrees of obliquity and the 7.62 mm M80 ball ammunition at muzzle velocity (838 +/-8m/s) at zero degrees of obliquity.
The roof system RU was tested with the same thrEats but at forty-five degrees. ~ It passed easily and thus by extrapolation the other two roof systems should as well.
Armor piercing ammunition presents a higher ballistic threat. The door armor system DU was subjected to a pipe bomb test when a ceramic applique armor system was attached to the door, test 4-21. This test proved that the ceramics did not degrade the explosive resistance of the door in what is the hardest test. Therefore, it will be apparent to those skilled in the art, that the two other door systems would perform similarly.
Shrapnel A 9.5 mm diameter steel ball bearing was selected as the standard for shrapnel testing because it is common for a terrorist to encase a non-directional bomb in high hardness shrapnel to enhance the effect of the blast.
Usually this shrapnel is in the form of hardened nuts and bolts etc. However, it is extremely difficult to duplicate their impact characteristics in the laboratory because of their shapes. Thus, it was decided to use the ball bearing as the standard as it is relatively easy to propel at desired speeds and trajectories.
The highest threat faced with the ball bearing was the 50 kg non-directional charge at 3.0 metres. In test 3F5 is was shown that the ball bearings would penetrate the outer layer of steel but not the inner layer of steel. Thus, the Spectrashield was not required to defeat this threat. The system tested was the door system DU.
The laboratory tests that were conducted with the ball bearing involved taking the ball bearing up to speeds of 1435 m/s. In these tests involving all three door armor systems, the ball bearings completely penetrated both layers of steel but not the Spectrashield. Therefore, it can be proven by extrapolation that all roof systems and all doors systems could defeat the ball bearing shrapnel threat of 50 kg non-directional charge at 3.0 metres.
The second type of shrapnel threat tested comes from a pipe bomb breaking into pieces at a close distance from the armor system. All three door armor systems were tested with the pipe bomb at a stand off and all three were successful in defeating the threat.
Explosive Device in Contact The pipe bomb in contact was tested with the roof system RU and all three door systems. What was proven is that only the two layers of steel are required to defeat this threat. Therefore, all roof systems could be used against pipe bombs in contact.
Only roof system RU was tested against the hand grenade in contact, test 4-6. The inner layer of steel was depressed 25.4 mm and the system was far from failing. It would follow that all roof and door systems would defeat~this threat as the minimum depression from a pipe bomb in contact was found to be 57 mm, test 5-1, door system DP.

i r Non-directional Charges The threat from a bare. non-directional charge comes primarily from the shock and over pressure. There were two very high threats that were tested, the 2.3 kg charge at 0.5 metres and the 50 kg charge at 3.0 metres. In both cases the door system DU was tested. In test 3E3 the door was depressed 57 mm by the 2.3 kg charge. The same door was retested with the 50 kg charge in test 3F5 and was found to be depressed 76 mm. , .
If one considers the fact that the pipe bomb places the greatest amount of stress in a localized area on the door and the pipe bomb depressions for all three door systems are in the same order of magnitude, it would follow that all three door armor systems could handle the 2.3 kg charge at 0.5 metres and the 50 kg charge at 3.0 metres. The only reason door armor systems DP and DO were not tested at these higher threats was merely a resource issue and not a technical issue.
Mechanical Properties The outer layer of steel was selected for the fact that it was not so hard (ultra high hard, minimum 57 Rockwell "C" scale) that it would shatter and cause catastrophic failure but that it was hard enough (high hard 47-51 Rockwell "C"
scale) to fundamentally change or re-direct lead core bullets or shrapnel.
Generically, these high hard steels fall in line with the aforementioned U.S.
military specification 46100. Mechanical tests were conducted on the steels used as the outer layer and the results are shown in Table 3 titled '-'Mechanical Test Results". The hardnesses ranged from 47 to 51 Rockwell ~ "C" sole, the ultimate tensile strengths from 1559 to 1688 Mpa, the percent elongation from 13.7 to 19.9 and the fracture toughness from 3.4 to 3.8 J/mm.
Preferably, the hardness for this outer layer is 49-51 Rockwell "C" scale.

The inner layer of steel was selected from steels that offer toughness so that the shock of the blast and the impact of shrapnel do 'not cause these steels to fail. Generically, these tough steels fall in line with U.S. military specification MIL-A-12560H, Armor plate, steel, wrought, homogeneous, Class 2.
Mechanical tests were conducted on the steels used as the inner layer and the results are also shown in Table 3. The hardnesses ranged from 30 to 36 Rockwell "C" scale, the ultimate tensile strengths from 980 to 1101 Mpa, the percent elongation from 13.6 to 17.2 and the fracture toughness from 3.8 to 6.5 J/mm~. Although the tests were successful with these steels, the preferred steel for this application would be 28-30 Rockwell "C" scale and have a fracture toughness of 5.4-6.5 J/mm. These steels do not lose their mechanical properties as dramatically as the high hard steels when welded and were, therefore, able to be used very effectively as structural members as well as armor plate.
In applications where greater ballistic resistance is required, and the use of ceramic or fibrous armors is impractical or cost prohibitive, a second 3 mm thick outer layer of the high hard steel is included. In this embodiment, the composite comprises three layers of steel, the outer two layers being of the high hard steel and the inner layer being of the high toughness steel materials as described above. The layers are welded together by edge and/or plug welds, with no bonder being present. See Tables 2 and 3 for test data.

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Claims (9)

1. A composite armor material comprising, an outer ballistic impact resistant layer of a steel material having a Rockwell "C" scale hardness of 47-54, and an inner blast resistant steel layer having a fracture toughness of 3.6-6.5 J/mm and a Rockwell "C" scale hardness of 28-36.

2. A material according to Claim 1, further comprising a synthetic resin bonder between the inner and outer layers.

3. A material according to Claim 1, further comprising a layer of a composite of high tensile fibers laminated together with a ductile polymer binder, held in place adjacent to the inner layer by mechanical fasteners, such that in use the material will stretch to trap shrapnel which penetrates the inner layer.

4. A material according to Claim 1, further comprising an outermost layer of a ballistic impact resistant steel material having a Rockwell C hardness of 47-54, wherein the layers are held together by welding.

5. A material according to Claim 1, further comprising an outermost layer of a composite applique material, said applique material comprising two layers of mild steel, sandwiching a middle layer of ceramic tiles bonded in place by an adhesive.

6. A material according to Claim 1, wherein the outer ballistic steel layer has a Rockwell "C" scale hardness of 49-51, and the inner impact resistant steel has a Rockwell "C" scale hardness of 28-30 and a fracture toughness of 5.4-6.5 J/mm.

7. A material according to Claim 2, wherein the bonder is a polysulfide-based material having a tensile strength of >1.38 Mpa.

8. A material according to Claim 2, wherein the bonder is a polyurethane-based material having a tensile strength of >6.89 Mpa.

9. A material according to claim 3, wherein the composite is Spectrashield®, having an aerial density of about 4.9 kg/m2.