Patent Application
20140090139
In some helmet designs inner and outer helmet shells, if included in the design at all, are both part of the same composite that is formed at the same time in a single press cycle. What is needed are two separate processes: one to mold and form the helmet shells and one to form the ballistic core as a separate component. I have previously disclosed various optimal ballistic helmet cores and associated processes.
Such a novel protective helmet shell and separately manufactured core system is disclosed. The disclosed helmet is optimized for wearers desiring light weight protection from fire arms and flying debris or shrapnel from explosions. The disclosed helmet desirably has at least three layers: an inner shell, a core made from ballistic resistant material, and an outer shell or cover. The helmet also desirably includes an edge trim component to cover the edge of the composite(s) and also has retention studs (also called binding posts) in the inner shell for anchoring a conventional helmet suspension system to the inner helmet shell.
The inner and outer shells advantageously have means for adhering to the core, and they include an edge trim component. Holes may then be drilled in the inner helmet shell for suspension mountings without providing the usual ballistic weakness attributed to holes that penetrate the entire helmet assembly. This eliminates the need for ballistic rated bolts for such a suspension system that become necessary to obviate the risk of a weakness in the helmet at the bolt points.
In some embodiments, the inner shell and the edge trim are the same part, and while both the shells can be plastic or composite material, when they are assembled they lock together via adhesive bond or with a mechanical snap or lock that advantageously cannot be field opened without a special helmet shell unlock tool. When the shells are thus locked together there is an empty or hollow space between them that is reserved for the helmet core, or may be optionally left empty, or otherwise filled with foam, honeycomb or special ribbed material. When the shells are locked together without a core, they look generally like a helmet but on their own have little or no ballistic value. In optimal practice however, a ballistic resistant helmet shaped layer of composite material (helmet core) is inserted during assembly between the two shell parts, inner and outer, before they are snapped or otherwise adhered shut.
In addition to bolts in the inner shell to mount a suspension system there are other accessories that are sometimes desired on the outside of a combat helmet, such as night vision goggles, head mounted video cameras, face visors, flashlights or strobe lights. Selected members of these optional attachment points are now molded directly into the outer shell of the helmet system, thus reducing overall weight, lowering cost and increasing value.
The helmet shells, inner and outer, may be injection molded of thermoplastic such as HDPE or polycarbonate or may be vacuum formed, and advantageously include mechanical snap lock parts that lock when the inner and outer shells are pushed together. Alternatively to snap locking parts, an adhesive foam may be injected or sprayed into the shells to bond the ballistic core material to the shells.
This allows for the rapid assembly of the inner and outer shells by simply snapping them together while also lowering cost of production and allowing the helmet core to be optimized in its purpose of ballistic resistance while not being diluted by ancillary concerns such as heat resistance, impact or ear-to-ear compression on the helmet.
Thermoplastics used for the shells are specified to hold up to selected extreme environments, as called for by design. Examples would be: polycarbonate/ABS blend, PEEK, Nylon 66, carbon fiber reinforced nylon or PEEK, or polyethylene and its associated blends.
During the assembly of the helmet system additional properties may be desired, such as greater impact resistance, or greater ear-to-ear compression or rigidity. These properties may readily be augmented by the addition of composite materials to the shells during assembly to increase the desired property. For example, a strip of carbon fiber unidirectional tape may be wet out with a resin such as epoxy and placed in the edge trim area of the shell piece just prior to assembly. As the resin sets, the spring like property and rigidity of the carbon fiber is transferred to the helmet's overall properties.
The core is made of semi-flexible ballistic material that may advantageously be formed in a Boroclave or similar machine producing extreme high pressures and very high heat. One such material is a number of layers of gel spun high-density polyethylene (HDPE) fibers either cross-oriented or unidirectional or aramid fibers in a conventional resin. Surprisingly, it is actually desirable, in producing the optimum light weight helmet, to use a quantity (measured in psf) of such core material generally thought incapable of stopping a given ballistic projectile without unacceptable backface deformation. Similar materials used as helmet material in other applications outside this disclosure have to have 2-3 times the psf (and/or composite thickness) in order to achieve acceptably minimal backface deformation.
The core, whether formed in a Boroclave, HIP, other high heat/high pressure press, or other conventional press, is then sandwiched between the two layers of thermo-vacuum formed or injection molded thermoplastic material that make up the inner and outer shells. The outer, relatively less flexible, shell is designed to protect the helmet from daily usage impacts, and may in some embodiments be quite thin (about 0.020 inch). The inner shell, with its own plastic deformation, absorbs most of the backface energy from the ballistic impact to the core, thus lowering the overall backface signature of the helmet.
In the Figures, this sequence is partially and schematically illustrated. In
Example: a helmet made in a Boroclave from 19 plies of Dyneema HB26 laid in a 0/90 laminate configuration (ie, where each sheet is angularly offset from the other by 90 degrees) will backface up to 70 mm when struck by a 9 mm 124 gr bullet at 1500 fps. When an inner shell of thermoplastic such as ⅛″ HDPE is placed inside the same 19 ply helmet, the backface of the same bullet is reduced to as little as 20 mm (NIJ standards).
A further advantage of using such an inner thermoplastic shell is that the “edge trim” may be molded right in to the inner shell form. Edge trim is conventionally a rubber trim glued to the edge of a helmet to hide the exposed fibers and to protect the helmet edges. Currently all US military helmets and police helmets have such an edge trim separately made from rubber or carbon fiber. With the disclosed helmet system, the edge trim is optionally an extension of, and made from, the same thermoplastic sheet as the inner liner that is designed to absorb backface energy. This advantageously ensures that the edge of the helmet is of the same toughened plastic as the inner liner.
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It is believed that this shell-core-shell system works just as well in reducing weight and increasing ballistic protective performance per unit of weight for other protective structures such as radomes, shields, or body armor.
This application claims priority to the following U.S. Provisional Patent Applications: 61/543810 filed Oct. 5, 2011; 61/553452 filed Oct. 31, 2011; and 61/698595 filed Sep. 8, 2012.
