Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F41—WEAPONS
  • F41H—ARMOUR; ARMOURED TURRETS; ARMOURED OR ARMED VEHICLES; MEANS OF ATTACK OR DEFENCE, e.g. CAMOUFLAGE, IN GENERAL
  • F41H5/00—Armour; Armour plates
  • F41H5/02—Plate construction
  • F41H5/04—Plate construction composed of more than one layer
  • F41H5/0442—Layered armour containing metal

Definitions

• This invention relates generally to armor systems for structural protection against ballistic impact or explosive blast, and more particularly to the use of a metallic foam as the shock energy-absorbing element in a multi-layer armor system.
• a typical configuration for the armor system in medium weight military vehicles for example, consists of a high strength strike face (either a metal or a ceramic plate), bonded to a ceramic tile, which is subsequently bonded to a metallic backing plate.
• the ceramic tile breaks-up or deforms an incoming projectile, and the metallic backing "catches" the extant penetrator and ceramic fragments.
• the high strength strike plate aids the ceramic tile by providing front face confinement, and may, in some cases, protect the ceramic tile from field damage.
• Metallic foams with a high fraction of porosity are a new class of materials which have attributes that lend themselves to various engineering applications, including sound and heat isolation, lightweight construction, and energy absorption. The latter two applications, in particular, make use of the unique characteristics of a metallic cellular material, specifically the combination of its comparatively high specific strength and its characteristic non-linear deformation behavior.
• certain metal foams are effective in containing rearward deformation of a target under high-speed impact, and therefore are useful in controlling backface deformation and spalling.
• metal foams are capable of mitigating impact-induced stress waves thereby delaying damage to ceramic layers in armor systems employing same.
• an object of the invention to provide an armor system incorporating metal foam as a shock energy-absorbing element to improve protection of equipment and personnel behind the target.
• the metallic foam as a shock-absorbing element in a multi- layer armor system.
• the metallic foam has a closed-cell pore structure and a high fraction of porosity, preferably ranging from about 50-98 percent by volume.
• Metallic foams useful in the practice of the present invention may be, but are not limited to, metal foams of aluminum, steel, lead, zinc, titanium, nickel and alloys or metal matrix composites thereof.
• Metal foams can be fabricated by various processes that are known for the manufacture of metal foams, including casting, powder metallurgy, metallic deposition, and sputter deposition. Exemplary processes for making metal foams are set forth in U.S. Patent Nos. 5,151,246; 4,973,358; and 5,181,549, the text of which is incorporated herein by reference.
• the foamable material is heated to temperatures near the melting point of the matrix metal(s). During heating, the foaming agent decomposes, and the released gas forces the densified material to expand into a highly porous structure.
• the density of the metal foams can be controlled by adjusting the content of the foaming agent and several other foaming parameters, such as temperature and heating rate.
• the density of aluminum foams typically ranges from about 0.5 to 1 g/cm 3 .
• Strength, and other properties of foamed metals can be tailored by adjusting the specific weight (or porosity), alloy composition, heat treatment history, and pore morphology as is known to those of skill in the art.
• the metallic foam will have high mechanical strength.
• Metal foams are easily processed into any desired shape or configuration by conventional techniques, such as sawing drilling, milling, and the like. Moreover, metal foams can be joined by known techniques, such as adhesive bonding, soldering, and welding.
• the shock-absorbing element is closed-cell aluminum foam, and in a specific illustrative embodiment, the shock- absorbing element is closed-cell aluminum foam with a porosity of 80 percent by volume.
• a multi-layered armor system suitable for structural protection against ballistic impact or explosive blast, such as armor systems used in connection with military armored vehicles, includes one or more layers of a metal foam as a shock energy-absorbing element.
• multi-layer armor system means at least two plates of metal, metal foam, ceramic, plastic, and the like, known or developed, for defense or protection systems.
• the multi-layer armor system includes at least a strike plate, or buffer plate, bonded or otherwise held in communication with, a shock-absorbing element that is a layer of metallic foam.
• the metallic foam preferably has a closed-cell pore structure and a high fraction of porosity.
• the metallic foam may be aluminum, steel, lead, zinc, titanium, nickel and alloys or metal matrix composites thereof, with porosity ranging from about 50-98 percent by volume.
• the metallic foam is a closed-cell aluminum foam having a porosity of 80 percent by volume.
• the term "strike plate” refers to a high strength metal or ceramic plate that has a front face surface that would receive the initial impact of a projectile or blast.
• the back surface of the strike plate is adjacent to a first surface of the shock-absorbing element that, in the present invention, is a sheet or layer of metallic foam.
• the term "strike plate,” as used herein, refers to any buffer plate of a high strength material that receives impact or impact-induced stress waves prior to a shock-absorbing element.
• the strike plate may be a flat sheet of a high strength metal, ceramic or polymer-based composite, such as a fiber-reinforced polymer composite.
• the multi-layer armor system of the present invention further includes a deformable backing plate bonded to, or otherwise held in communication with, a face surface of the metallic foam sheet or layer opposite, or distal, to the surface contiguous to the strike plate.
• the backing plate illustratively is a sheet of a deformable metal, such as titanium, aluminum, or steel.
• a shock-absorbing layer of metallic foam is sandwiched between a high strength strike plate and a deformable backing plate.
• the multi-layered armor system may comprise additional elements, in any sequence, and the embodiments presented herein are solely for the purposes of illustrating the principles of the invention.
• Fig. 1 is a schematic representation of an illustrative armor system incorporating metallic foam as a shock energy-absorbing element in accordance with the principles of the present invention
• Fig. 2 is a photomicrograph of a high porosity, closed-cell aluminum foam showing the typical microstructure in cross-section;
• Fig. 3 is a graphical representation of the typical behavior of a metal foam, of the type shown in Fig. 2, under a uniaxial load;
• Fig. 4 is photomicrograph of the aluminum foam of Fig. 2 showing a cross- sectional view of the microstructure following deformation by high energy impact.
• Fig. 1 is an illustrative schematic representation of an improved armor system 10 of the type having a high strength strike plate 11 , at least one shock energy- absorbing element 12, and a backing plate 13.
• a closed- cell metal foam is used as shock energy-absorbing element 12.
• High strength strike plate 11 may be ceramic or metal.
• Backing plate 13 is typically a highly deforming metal, such as titanium, aluminum, or steel. However, backing plate 13 may comprise one or more layers of metal and/or ceramic, as well as polymer-based composites.
• the closed-cell metal foam is effective in containing rearward deformation of the strike plate 11 in a ballistic target structure.
• the metal foam has the ability to control backface deformation, without sacrificing ballistic efficiency behind targets with highly deforming back plates, via a mechanism that will be discussed more completely hereinbelow.
• the shock energy-absorbing element 12 preferably comprises a closed-cell metallic foam which, illustratively, may be aluminum, steel, lead, zinc, titanium, nickel, and alloys or metal matrix composites thereof.
• Preferred metal foams have a high fraction of porosity, typically ranging from about 50-98 by volume percent.
• shock energy-absorbing element 12 is a closed-cell aluminum foam having a porosity of 80 by volume.
• Fig. 2 shows the microstructure (i.e. , the pore structure) of this particular aluminum foam material.
• This type of pore structure provides a substantial increase in the stiffness/weight ratio (SWR) of the material with a low fractional density. Under deformation, this microstructure features localized cell collapse and rapid compaction energy dissipation, which leads to unique deformation behaviors and material properties including high SWR and energy absorption in the material.
• SWR stiffness/weight ratio
• Fig. 3 is a graphical representation of the behavior of the metal foam of Fig. 2 under uniaxial load referred to as a "loading curve.”
• the vertical axis of Fig. 3 represents stress and the horizontal axis represents strain.
• the loading curve of Fig. 3 is divided into three regions: linear elastic region 31, collapse region 32 (where plateau stress remains relatively constant) and densification region 33. In linear elastic region 31, the elastic portion of the stress-strain curve is only partially reversible.
• small-scale localized plastic deformation has already taken place within the sample.
• Metal foams can be fabricated to maximize the energy absorption capability by adjusting foam parameters including alloying elements, density level, cell size, wall thickness, and uniformity. Improvements in modulus and plateau stress via heat treatment of the metal foam, or via addition of particulate or whisker reinforcements to the metal foam, are additional techniques known to increase the energy absorption capability. Metal foams are capable of mitigating the impact-induced stress waves from the strike plate, thereby delaying or eliminating damage to underlying layers, which in some embodiments might be a ceramic tile, and improving protection of the personnel and equipment behind the target. The deformation energy due to shock impact first densifies the front portion (in the loading direction) of the metal foam layer that forms the shock energy-absorbing element.
• Fig. 4 is a cross-sectional view of the microstructure of the aluminum foam of Fig. 2 showing deformation following high energy impact.
• This type of deformation mechanism reduces the transmitted deformation energy behind the target in the loading direction.
• the energy of the impact-induced stress waves is also dissipated efficiently within the cellular network.
• the high degree of porosity in metal foam is beneficial for the absorption of the wave energy, and the cellular network generates the cavity effect for scattering the wave energy within the network.
• the armor systems of the present invention would be useful as protection systems for ballistic impact and for blast.
• the illustrative embodiment presented herein is directed to a three element system, it is to be understood that invention contemplates the use of closed-cell, high strength metal foams having a high fraction of porosity, as a shock energy-absorbing element in any other configuration developed, or to be developed, wherein its ability to contain rearward deformation under high-speed impact, would be useful.

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• Engineering & Computer Science (AREA)
• Ceramic Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Aiming, Guidance, Guns With A Light Source, Armor, Camouflage, And Targets (AREA)
• Laminated Bodies (AREA)
• Vibration Dampers (AREA)
• Building Environments (AREA)
• Toys (AREA)

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• 2000
  • 2000-03-10 WO PCT/US2000/006220 patent/WO2000055567A1/en active IP Right Grant
  • 2000-03-10 EP EP00937503A patent/EP1078215B1/de not_active Expired - Lifetime
  • 2000-03-10 DE DE60007237T patent/DE60007237T2/de not_active Expired - Lifetime
  • 2000-03-10 AT AT00937503T patent/ATE256853T1/de active
  • 2000-03-10 ES ES00937503T patent/ES2213021T3/es not_active Expired - Lifetime

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