Title:
ARMOR
United States Patent 3705558
Abstract:
1. A lightweight armor plate comprising a mass of sintered hard substantially spherical ceramic balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, and means for rigidly supporting said balls in said pyramidal relationship.
US Patent References:
Armor for gasoline tanks of aeroplanes and for other purposes
Burgess - July 1923 - 1463498
Honeycomb-type structural materials and method of making same
Pfistershammer - March 1956 - 2738297
Armor for gasoline tanks of aeroplanes and for other purposes
Burgess - July 1923 - 1463498
Honeycomb-type structural materials and method of making same
Pfistershammer - March 1956 - 2738297
Inventors:
Mcdougal, John A. (Madison Heights, MI)
Schwartzwalder, Karl (Holly, MI)
Schwartzwalder, Karl (Holly, MI)
Application Number:
04/275402
Publication Date:
12/12/1972
Filing Date:
04/24/1963
View Patent Images:
Export Citation:
Assignee:
General Motors Corporation (Detroit, MI)
Primary Class:
Other Classes:
428/911, 52/783.100, 428/614, 89/36.020, 428/116
International Classes:
F41H5/04; F41H5/00; F41H5/04
Field of Search:
89/36 114/12,13 161/207 109/78,80,82-85
Primary Examiner:
Bentley, Stephen C.
Claims:
We claim
1. A lightweight armor plate comprising a mass of sintered hard substantially spherical ceramic balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, and means for rigidly supporting said balls in said pyramidal relationship.
2. A lightweight armor plate comprising a layer of sintered hard substantially spherical ceramic balls arranged in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls which is adapted to fragmentize a projectile on impact therewith, said balls being rigidly supported in said pyramidal relationship, said layer being attached to a tough ductile energy absorbing backup layer adapted to prevent penetration by the projectile fragments.
3. An integral lightweight armor plate comprising a rigid layer of sintered hard alumina adapted to fragmentize a projectile on impact therewith interposed between and bonded to a pair of aluminum layers, one of said aluminum layers being adapted to backup said alumina layer and prevent penetration by the projectile fragments.
4. A lightweight armor plate comprising a mass of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, said balls being cast in a matrix of aluminum and backed up by a layer of aluminum of substantial thickness.
5. A lightweight armor plate comprising a mass of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each of said balls is in contact substantially with at least three other balls, means for rigidly supporting said balls in said pyramidal relationship, and a backup layer of a ductile energy absorbing material secured thereto, said alumina balls being operative on impact with a projectile to fragmentize the projectile and said backup layer being effective to absorb the energy of the projectile fragments and prevent their penetration thereof.
6. A lightweight armor plate comprising a frontal projectile fragmentizing mass including at least two layers of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, means enveloping said balls and rigidly supporting them in said pyramidal relationship, and a projectile fragment retaining backup layer of a ductile energy absorbing material secured thereto.
7. A lightweight armor plate comprising a frontal projectile fragmentizing mass including at least two layers of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, a metal coating over said balls supporting them in said pyramidal relationship, and a projectile retaining backup layer of a ductile energy absorbing material adhesively secured to said metal coated mass.
8. A lightweight armor plate comprising a frontal projectile fragmentizing mass including at least two layers of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, a matrix of tough synthetic resin material supporting said balls in said pyramidal relationship, and a projectile retaining backup layer of a ductile energy absorbing material secured thereto.
1. A lightweight armor plate comprising a mass of sintered hard substantially spherical ceramic balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, and means for rigidly supporting said balls in said pyramidal relationship.
2. A lightweight armor plate comprising a layer of sintered hard substantially spherical ceramic balls arranged in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls which is adapted to fragmentize a projectile on impact therewith, said balls being rigidly supported in said pyramidal relationship, said layer being attached to a tough ductile energy absorbing backup layer adapted to prevent penetration by the projectile fragments.
3. An integral lightweight armor plate comprising a rigid layer of sintered hard alumina adapted to fragmentize a projectile on impact therewith interposed between and bonded to a pair of aluminum layers, one of said aluminum layers being adapted to backup said alumina layer and prevent penetration by the projectile fragments.
4. A lightweight armor plate comprising a mass of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, said balls being cast in a matrix of aluminum and backed up by a layer of aluminum of substantial thickness.
5. A lightweight armor plate comprising a mass of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each of said balls is in contact substantially with at least three other balls, means for rigidly supporting said balls in said pyramidal relationship, and a backup layer of a ductile energy absorbing material secured thereto, said alumina balls being operative on impact with a projectile to fragmentize the projectile and said backup layer being effective to absorb the energy of the projectile fragments and prevent their penetration thereof.
6. A lightweight armor plate comprising a frontal projectile fragmentizing mass including at least two layers of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, means enveloping said balls and rigidly supporting them in said pyramidal relationship, and a projectile fragment retaining backup layer of a ductile energy absorbing material secured thereto.
7. A lightweight armor plate comprising a frontal projectile fragmentizing mass including at least two layers of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, a metal coating over said balls supporting them in said pyramidal relationship, and a projectile retaining backup layer of a ductile energy absorbing material adhesively secured to said metal coated mass.
8. A lightweight armor plate comprising a frontal projectile fragmentizing mass including at least two layers of sintered hard substantially spherical alumina balls disposed in contacting pyramidal relationship whereby each ball is in contact substantially with at least three other balls, a matrix of tough synthetic resin material supporting said balls in said pyramidal relationship, and a projectile retaining backup layer of a ductile energy absorbing material secured thereto.
Description:
This invention relates to armor plate and more particularly to lightweight armor plate for use in armored vehicles or the like. The armor plate of this invention has particular applicability in armored military and domestic vehicle construction where it is the conventional practice to use hardened steel armor plate. While the conventional steel armor plate has been quite satisfactory from the standpoint of protection against typical projectiles such as .30 and .50 caliber shells, the weight of the steel plate adds greatly to the weight of the vehicle to thereby reduce markedly its mobility and usefulness.
It is the basic object of this invention to provide an improved lightweight armor plate which will effectively protect the vehicle against penetration by .30 caliber and similar projectiles which greatly reduces the weight of the vehicle and improves its mobility. It is a more specific object of this invention to provide an improved lightweight armor plate consisting essentially of a laminated or unitary structure which includes a mass of closely packed hard ceramic spheres arranged and suitably supported in abutting pyramid relationship which is backed up by a lightweight, energy absorbing, ductile layer. Another object of the invention is to provide a laminated lightweight armor plate consisting of a hard ceramic layer backed up by a relatively soft, yielding, lightweight, energy absorbing, ductile layer.
Other objects and advantages will be apparent from the following detailed description of the invention and the various embodiments thereof, reference being had to the accompanying drawings, in which:
FIG. 1 is an armor construction comprising a layer of hard alumina balls encased in a metal mesh screen having an aluminum mass cast thereabout including a relatively thick aluminum backing layer;
FIG. 2 is another embodiment of the invention in which the alumina balls are arranged in pyramidal abutting relation backed up and bonded to a backing plate of aluminum;
FIG. 3 is a laminated armor plate consisting of a hard alumina plate sandwiched between and bonded to plates of aluminum; and
FIG. 4 is a group of ceramic spheres arranged in pyramidal close packed relation.
Referring to FIG. 1 of the drawings, the basic concept of construction involved in the applicants' invention is embodied in a plate consisting of the close packed layers of ceramic spheres 10 backed up by a relatively soft, ductile layer 12. As most clearly apparent from the sketch of FIG. 4, the ceramic spheres are arranged in a pyramidal fashion whereby a sphere 14 in an outer or upper plane is supported by three spheres 16 in the next inner or lower plane. Each sphere 16 is in turn supported by three spheres 18 in the next lower plane.
The ceramic spheres are especially strong in compression and are located on the projectile entry side of the plate. When struck by a projectile, the closely packed structure causes a rapid distribution of forces in the lateral plane since each sphere in the outer plane is supported by three spheres in the next backing up plane. Calculation shows that for a force applied normal to the plate on a sphere in the first plane, each of the three spheres in the second plane will receive a normal force component which is approximately 30 percent of the original whereas each of the seven spheres in the third plane receives less than 9 percent of the original force. Thus, rapid and effective force reduction is obtained. In addition a portion of the force is dissipated in the directions parallel to the plate.
The hard ceramic spheres in position on the entry side of the plate also serve to greatly reduce the effectiveness of the projectile by breaking it up or deforming it. In this way, its ballistic efficiency and penetrating power are greatly reduced. For high energy missiles, the shattering of both the projectile and the uppermost ceramic layer affords tremendous advantage of the absorption of energy.
The ceramic spheres are preferably formed of alumina in the form of tabular alumina or corundum. A superior ceramic is formed by mixing a batch consisting of 87 percent tabular alumina of which 95 percent is minus 325 mesh, 3 percent tricalcium phosphate as a flux and 10 percent Kentucky ball clay No. 4. The mixed material is balled by means of a rotating drum and fired at about 2,950° F.
In a first specific embodiment of the invention as shown in FIG. 1 a first layer 14 of hard spherical tabular alumina balls having a thickness of about one-half to five-eighths inch is arranged in a plane in pyramidal abutting relation over a second layer 16 of the balls arranged in a second plane. These layers are encased in a stainless steel wire screen 19 of about 10 to 20 mesh. This assembly is cast in a mass of aluminum consisting of 90 percent aluminum and 10 percent magnesium to form a plate having a nominal thickness of about 13/8 inches in which an aluminum alloy backing layer 12 is formed integrally with the aluminum alloy matrix 22. The matrix 22 encases and supports the ball layers 14 and 16 and the screen 19 in the plate. The areal density is about 23.6 pounds per square foot.
In a second embodiment the plate is structurally the same as the first embodiment except that the backup layer 12 and the matrix 22 are a magnesium alloy consisting of 96 percent magnesium, 3.5 percent zirconium and 0.5 percent minor impurities. The areal density is about 20.6 pounds per square foot.
In a third embodiment as shown in FIG. 2 two layers 24 and 26 respectively are arranged in pyramidal relationship as described in connection with FIG. 1. Each alumina sphere is encased in a nickel shell except at the points at which the spheres abut one another. The nickel shell 28 is applied by arranging the spherical balls in the pyramidal arrangement and then subjecting the configuration to a nickel carbonyl nickel coating process in which the structure is exposed to thermally decompose nickel carbonyl under vacuum conditions as is well known in the art. This process results in a 100 percent nickel shell of good ductility and toughness having extreme work hardening capabilities. The resulting structure which may be described as a nickel-alumina honeycomb structure is bonded to a one-fourth inch 5086 aluminum alloy plate 30 by means of a polysulfide plastic adhesive 32. The areal density is about 22.3 pounds per square foot.
A fourth example which embodies the invention in its broad aspects is shown in FIG. 3 which consists of a one-eighth inch 5086-H34 aluminum alloy plate 34 bonded to a three-fourths inch hard alumina tile 36 by means of a polysulfide adhesive layer 38. This laminate is backed by a one-fourth inch thick 5086-H112 aluminum alloy plate 40 bonded thereto by the polysulfide adhesive layer 42. The areal density is about 17.4 pounds per square foot.
The protection ballistics limit for each of the above embodiments was determined with .30 caliber armor piercing M2 projectiles at zero obliquity. As described below, these tests showed a marked improvement over presently used hardened steel armor plate. In general, these tests showed a protection ballistics limit in the neighborhood of about 35 percent greater than that of the conventionally used steel armor plate of the same weight which indicates that the areal density of armor plate to protect against the normal impact of this projectile at the muzzle velocity of the service load may be reduced by approximately the same percentage.
The term "protection ballistics limit" as used herein is defined as the critical or limit velocity at which the specified projectile will be borderlined in penetrating the armor plate. A complete penetration of the projectile through the plate is considered to occur whenever a fragment or fragments from either the impacting projectile or the armor are caused to be thrown back from the armor plate with sufficient remaining energy to pierce a sheet of 0.020 inch thick 2024-T3 aluminum alloy placed parallel to and six inches beyond the target. A flying fragment with this amount of energy is normally expected to produce lethal damage or its equivalent from a variety of mass-velocity combinations. Any impact which rebounds from the armor plate, remains embedded in the plate or passes through the plate, but with insufficient energy to pierce the 0.020 inch thick aluminum alloy plate, is termed a partial penetration.
The procedure for testing the plates involved hand loading a plurality of .30 caliber shells with varied amounts of powder and determining their muzzle velocity in trial tests. These were then fired perpendicularly at the plates and their penetration was observed whereby their protection ballistics limit was determined.
A ballistics limit for the .30 caliber AP-M2 projectile at 0° angle of incidence was determined to be 3,288 feet per second. This compares with a ballistics limit of about 2,450 feet per second for typical homogeneous armor plate of equal weight. The mechanism of penetration of the projectiles in this plate was unusual. The hardened steel bullet core was shattered into many irregular pieces of approximately the size of No. 6 shot. This shattering of the core appeared to give radial velocity to the jacket. The shattering of the core appeared to take place early in the penetration as evidenced by fragments which came to rest less than three-eights inch penetration from the original surface. Those fragments possessing sufficient energy after the break up of the core proceeded to penetrate further, shattering and displacing the ceramic rubble formed and deforming the backing aluminum plate. Those particles having sufficient energy continued into the backing plate where their energy was absorbed.
The mechanism of penetration of the second embodiment was similar to that of the first except that a slightly more extensive crushing of the ceramic occurred. The ballistics limit of this plate was determined to be 3092 feet per second.
The mechanism of penetration of the third embodiment was similar to that of the first and second and the ballistics limit was found to be 3,200 feet per second.
In the fourth embodiment a conical spalling of the alumina occurred with the wide end of the cone being formed at the rear aluminum plate indicating that the impact of the projectile was spread over a large area of the rear plate. The ballistics limit was determined to be in excess of 2,750 feet per second which is markedly superior to conventional steel plate of equal weight. Although the test results given about are in relation to .30 caliber shells, similar improvement is obtained with regard to .50 and similar caliber projectiles over the conventional homogeneous steel plate.
Although in the embodiment set forth above two layers of the ceramic balls have been employed, armor plate including three or more layers of the ceramic balls may be employed for increased effectiveness in breaking up the projectile. However, it may be observed that when the plate is struck by a projectile, it is in compression up to the neutral axis of the plate and in tension beyond the neutral axis. Hence, the inclusion of the ceramic material is of little value beyond this point and is preferably omitted for the sake of cost and weight economy. It is essential, however, that the material beyond the neutral axis have a high tensile strength to resist spalling. It is not particularly important to the effectiveness of the plate whether or not the space between the balls is filled with a matrix material. The primary requirement is that the balls be maintained in a pyramidal relationship within the armor plate. It is to be noted that in the third embodiment the ceramic spheres were held together by means of a nickel shell but the voids in the close packed array were not filled. Since this configuration has no detrimental effect on the ballistics properties of the plate, it may be concluded that the selection of the matrix for that portion of the plate is of secondary importance and that preferably these spaces be not filled for weight reduction purposes. In any event the matrix material should be highly resistant to spalling to avoid the formation of particles which may be thrown rearwardly. Other materials including tough ductile synthetic resins, such as polyamide and polyurethane polymers, which have good energy absorbing characteristics may be used as the matrix material, and other strong and tough adhesive resins such as epoxy adhesives may be employed to bond the backing plate to the alumina sphere structure. Although the preferred ceramic material for use as the projectile fragmentary layer is the alumina described above, other ceramic materials, such as silicon carbide, boron carbide and aluminum boride, also may be advantageously used.
While the embodiments as disclosed herein constitute preferred forms, it is to be understood that other forms may be adopted without departing from the spirit of the invention.
It is the basic object of this invention to provide an improved lightweight armor plate which will effectively protect the vehicle against penetration by .30 caliber and similar projectiles which greatly reduces the weight of the vehicle and improves its mobility. It is a more specific object of this invention to provide an improved lightweight armor plate consisting essentially of a laminated or unitary structure which includes a mass of closely packed hard ceramic spheres arranged and suitably supported in abutting pyramid relationship which is backed up by a lightweight, energy absorbing, ductile layer. Another object of the invention is to provide a laminated lightweight armor plate consisting of a hard ceramic layer backed up by a relatively soft, yielding, lightweight, energy absorbing, ductile layer.
Other objects and advantages will be apparent from the following detailed description of the invention and the various embodiments thereof, reference being had to the accompanying drawings, in which:
FIG. 1 is an armor construction comprising a layer of hard alumina balls encased in a metal mesh screen having an aluminum mass cast thereabout including a relatively thick aluminum backing layer;
FIG. 2 is another embodiment of the invention in which the alumina balls are arranged in pyramidal abutting relation backed up and bonded to a backing plate of aluminum;
FIG. 3 is a laminated armor plate consisting of a hard alumina plate sandwiched between and bonded to plates of aluminum; and
FIG. 4 is a group of ceramic spheres arranged in pyramidal close packed relation.
Referring to FIG. 1 of the drawings, the basic concept of construction involved in the applicants' invention is embodied in a plate consisting of the close packed layers of ceramic spheres 10 backed up by a relatively soft, ductile layer 12. As most clearly apparent from the sketch of FIG. 4, the ceramic spheres are arranged in a pyramidal fashion whereby a sphere 14 in an outer or upper plane is supported by three spheres 16 in the next inner or lower plane. Each sphere 16 is in turn supported by three spheres 18 in the next lower plane.
The ceramic spheres are especially strong in compression and are located on the projectile entry side of the plate. When struck by a projectile, the closely packed structure causes a rapid distribution of forces in the lateral plane since each sphere in the outer plane is supported by three spheres in the next backing up plane. Calculation shows that for a force applied normal to the plate on a sphere in the first plane, each of the three spheres in the second plane will receive a normal force component which is approximately 30 percent of the original whereas each of the seven spheres in the third plane receives less than 9 percent of the original force. Thus, rapid and effective force reduction is obtained. In addition a portion of the force is dissipated in the directions parallel to the plate.
The hard ceramic spheres in position on the entry side of the plate also serve to greatly reduce the effectiveness of the projectile by breaking it up or deforming it. In this way, its ballistic efficiency and penetrating power are greatly reduced. For high energy missiles, the shattering of both the projectile and the uppermost ceramic layer affords tremendous advantage of the absorption of energy.
The ceramic spheres are preferably formed of alumina in the form of tabular alumina or corundum. A superior ceramic is formed by mixing a batch consisting of 87 percent tabular alumina of which 95 percent is minus 325 mesh, 3 percent tricalcium phosphate as a flux and 10 percent Kentucky ball clay No. 4. The mixed material is balled by means of a rotating drum and fired at about 2,950° F.
In a first specific embodiment of the invention as shown in FIG. 1 a first layer 14 of hard spherical tabular alumina balls having a thickness of about one-half to five-eighths inch is arranged in a plane in pyramidal abutting relation over a second layer 16 of the balls arranged in a second plane. These layers are encased in a stainless steel wire screen 19 of about 10 to 20 mesh. This assembly is cast in a mass of aluminum consisting of 90 percent aluminum and 10 percent magnesium to form a plate having a nominal thickness of about 13/8 inches in which an aluminum alloy backing layer 12 is formed integrally with the aluminum alloy matrix 22. The matrix 22 encases and supports the ball layers 14 and 16 and the screen 19 in the plate. The areal density is about 23.6 pounds per square foot.
In a second embodiment the plate is structurally the same as the first embodiment except that the backup layer 12 and the matrix 22 are a magnesium alloy consisting of 96 percent magnesium, 3.5 percent zirconium and 0.5 percent minor impurities. The areal density is about 20.6 pounds per square foot.
In a third embodiment as shown in FIG. 2 two layers 24 and 26 respectively are arranged in pyramidal relationship as described in connection with FIG. 1. Each alumina sphere is encased in a nickel shell except at the points at which the spheres abut one another. The nickel shell 28 is applied by arranging the spherical balls in the pyramidal arrangement and then subjecting the configuration to a nickel carbonyl nickel coating process in which the structure is exposed to thermally decompose nickel carbonyl under vacuum conditions as is well known in the art. This process results in a 100 percent nickel shell of good ductility and toughness having extreme work hardening capabilities. The resulting structure which may be described as a nickel-alumina honeycomb structure is bonded to a one-fourth inch 5086 aluminum alloy plate 30 by means of a polysulfide plastic adhesive 32. The areal density is about 22.3 pounds per square foot.
A fourth example which embodies the invention in its broad aspects is shown in FIG. 3 which consists of a one-eighth inch 5086-H34 aluminum alloy plate 34 bonded to a three-fourths inch hard alumina tile 36 by means of a polysulfide adhesive layer 38. This laminate is backed by a one-fourth inch thick 5086-H112 aluminum alloy plate 40 bonded thereto by the polysulfide adhesive layer 42. The areal density is about 17.4 pounds per square foot.
The protection ballistics limit for each of the above embodiments was determined with .30 caliber armor piercing M2 projectiles at zero obliquity. As described below, these tests showed a marked improvement over presently used hardened steel armor plate. In general, these tests showed a protection ballistics limit in the neighborhood of about 35 percent greater than that of the conventionally used steel armor plate of the same weight which indicates that the areal density of armor plate to protect against the normal impact of this projectile at the muzzle velocity of the service load may be reduced by approximately the same percentage.
The term "protection ballistics limit" as used herein is defined as the critical or limit velocity at which the specified projectile will be borderlined in penetrating the armor plate. A complete penetration of the projectile through the plate is considered to occur whenever a fragment or fragments from either the impacting projectile or the armor are caused to be thrown back from the armor plate with sufficient remaining energy to pierce a sheet of 0.020 inch thick 2024-T3 aluminum alloy placed parallel to and six inches beyond the target. A flying fragment with this amount of energy is normally expected to produce lethal damage or its equivalent from a variety of mass-velocity combinations. Any impact which rebounds from the armor plate, remains embedded in the plate or passes through the plate, but with insufficient energy to pierce the 0.020 inch thick aluminum alloy plate, is termed a partial penetration.
The procedure for testing the plates involved hand loading a plurality of .30 caliber shells with varied amounts of powder and determining their muzzle velocity in trial tests. These were then fired perpendicularly at the plates and their penetration was observed whereby their protection ballistics limit was determined.
A ballistics limit for the .30 caliber AP-M2 projectile at 0° angle of incidence was determined to be 3,288 feet per second. This compares with a ballistics limit of about 2,450 feet per second for typical homogeneous armor plate of equal weight. The mechanism of penetration of the projectiles in this plate was unusual. The hardened steel bullet core was shattered into many irregular pieces of approximately the size of No. 6 shot. This shattering of the core appeared to give radial velocity to the jacket. The shattering of the core appeared to take place early in the penetration as evidenced by fragments which came to rest less than three-eights inch penetration from the original surface. Those fragments possessing sufficient energy after the break up of the core proceeded to penetrate further, shattering and displacing the ceramic rubble formed and deforming the backing aluminum plate. Those particles having sufficient energy continued into the backing plate where their energy was absorbed.
The mechanism of penetration of the second embodiment was similar to that of the first except that a slightly more extensive crushing of the ceramic occurred. The ballistics limit of this plate was determined to be 3092 feet per second.
The mechanism of penetration of the third embodiment was similar to that of the first and second and the ballistics limit was found to be 3,200 feet per second.
In the fourth embodiment a conical spalling of the alumina occurred with the wide end of the cone being formed at the rear aluminum plate indicating that the impact of the projectile was spread over a large area of the rear plate. The ballistics limit was determined to be in excess of 2,750 feet per second which is markedly superior to conventional steel plate of equal weight. Although the test results given about are in relation to .30 caliber shells, similar improvement is obtained with regard to .50 and similar caliber projectiles over the conventional homogeneous steel plate.
Although in the embodiment set forth above two layers of the ceramic balls have been employed, armor plate including three or more layers of the ceramic balls may be employed for increased effectiveness in breaking up the projectile. However, it may be observed that when the plate is struck by a projectile, it is in compression up to the neutral axis of the plate and in tension beyond the neutral axis. Hence, the inclusion of the ceramic material is of little value beyond this point and is preferably omitted for the sake of cost and weight economy. It is essential, however, that the material beyond the neutral axis have a high tensile strength to resist spalling. It is not particularly important to the effectiveness of the plate whether or not the space between the balls is filled with a matrix material. The primary requirement is that the balls be maintained in a pyramidal relationship within the armor plate. It is to be noted that in the third embodiment the ceramic spheres were held together by means of a nickel shell but the voids in the close packed array were not filled. Since this configuration has no detrimental effect on the ballistics properties of the plate, it may be concluded that the selection of the matrix for that portion of the plate is of secondary importance and that preferably these spaces be not filled for weight reduction purposes. In any event the matrix material should be highly resistant to spalling to avoid the formation of particles which may be thrown rearwardly. Other materials including tough ductile synthetic resins, such as polyamide and polyurethane polymers, which have good energy absorbing characteristics may be used as the matrix material, and other strong and tough adhesive resins such as epoxy adhesives may be employed to bond the backing plate to the alumina sphere structure. Although the preferred ceramic material for use as the projectile fragmentary layer is the alumina described above, other ceramic materials, such as silicon carbide, boron carbide and aluminum boride, also may be advantageously used.
While the embodiments as disclosed herein constitute preferred forms, it is to be understood that other forms may be adopted without departing from the spirit of the invention.