Novel Steel Combat Helmet and Method of Production Thereof

Abstract

The invention relates to helmets designed to protect their wearers from ballistic impacts and shrapnel. Such helmets are well-known, and are the current standard for law enforcement and military use alike. Whereas such helmets used to be made solely of steel, combat helmets are today manufactured primarily from polymer composites such as aramid and ultra-high molecular weight polyethylene, and metal helmets have been largely superseded in common use, if not considered entirely obsolete, since the 1980s. The present invention, described herein, allows for the production of a modern steel helmet which is lightweight and exhibits excellent ballistic performanceperformance which is comparable if not superior to that exhibited by the best polymer composite helmets of our day.

Claims

1. A method for manufacturing a high-strength ballistic-resistant steel helmet shell, comprising the steps of: a) Preparing a steel blank by punching or cutting a steel plate, a steel sheet, or a section bar to appropriate dimensions. b) Pre-treating the blank by austenitization or cold-drawing followed by austenitization. c) Forming the helmet shell by pressing the heated and austenitized pre-form in a die. Once the draw depth is reached the part is hardened in the die by targeted cooling. d) Finishing the forming process by tempering and quenching, to whatever extent necessary for optimal ballistic resistance, and then trimming the formed blank to its final shape. e) Subjecting the exterior of the helmet shell to shot peening, severe shot peening (SSP), surface mechanical attrition treatment (SMAT), or ultrasonic nanocrystalline surface modification (UNSM), to induce the formation of a hard nanocrystalline surface layer, to whatever extent necessary for the degree of ballistic resistance required.

2. A steel helmet shell, produced via hot stamping, press hardening, hydroforming, stamping, stretch forming, or super-plastic forming, wherein the finished shell is greater than 1.6 mm in thickness, and wherein the alloy contains >0.20% Al or Si, and more than 0.5% but less than 3% Mn, in addition to >0.18% carbon and other alloying elements, and wherein the finished helmet shell has a tensile strength over 1400 MPa.

3. The steel helmet shell of claims 1 and 2, wherein the exterior surface of the shell is coated with an hard corrosion-resistant ceramic material via physical vapor deposition, chemical vapor deposition, thermal spray, or cold spray.

4. A steel combat helmet comprised of the steel shell of claim 1 or 2, a harness, a padding system, and optional points for the attachment of accessories, wherein the stand-off distance between the shell and the wearer's skull is less than 16 mm, and wherein the helmet is nevertheless compliant with the NIJ Standard 0106.01, Ballistic Helmets, Type II.

Description

[0031] In one or more embodiments of the invention, further surface hardness is required, thus the steel helmet shell is coated with a hard ceramic material. Suitable coatings include diamondlike carbon (DLC), titanium nitride (TiN), aluminum titanium nitride (AlTiN), aluminum chromium nitride (AlCrN), rhenium diboride (ReB2), silicon nitride (Si3N4), and their combinations and composites. Coating with these materials can be accomplished via thermal spray, cold spray, vapor deposition, or other methods known to those versed in the art.

[0032] FIG. 1 depicts a view of a representative hot stamping production process. It illustrates 1 the sheet steel cutting and forming process. In 2 the sheet steel blank is furnace heated to 900-950 C. so as to achieve a homogenous austenitic microstructure. It is then rapidly transferred to the press, 3, where it is stamped (formed) into a helmet shell geometry. Owing to the high temperature austenitic microstructure that is maintained throughout the stamping process, the blank exhibits low strength (often 200 MPa), high ductility (often >50% true strain), plastic isotropicity, and thus ultimately exhibits very high formability. This enables even very high-strength steels, in thick sections of >2 mm, to be formed into hemispherical, helmet-like geometries.

[0033] Note that the press stage can vary widely. In some cases, a pre-formed blank, which has been cold pressed to 20-90% of its final shape, can subsequently be hot stamped to its final geometry. In other cases, the blank need not be heated in a furnace to an austenitic microstructure; instead, it can be resistance-heated in the stamping die at a very high rate. Other methods for hot stamping exist and may be utilized. The fundamental point is that the blank or pre-form is pressed to shape under heat, or in a heated condition, and subsequently cooled and hardened in the die.

[0034] Following the stamping stage depicted in 3, the unfinished shell can be trimmed to its final shape via laser-cutter, 4. It can also be tempered, if necessary, which is undepicted in the image owing to the fact that it is rarely necessary.

[0035] The trimmed and tempered shell can then be subjected to a plastic deformation treatment, e.g. in the SMAT chamber depicted in 5.

[0036] This process allows for steel helmets with an ultimate tensile strength of well over 2000 MPa, a surface microhardness from 500 Vickers to well over 800, and excellent ballistic performance.

[0037] Furthermore, this process allows for steel helmets which are cheap to manufacture. The materials costs are typically no more than $10 per shell, and can be under $5 per shell. Material costs are therefore lowand manufacturing costs are also generally low at high output levels. Stamping or hydroforming and plastic deformation treatments are extremely high-throughput production methods which can be run in bulk quantities suitable for rapid military production.

[0038] Lastly, and perhaps most importantly, this process allows for extremely stiff helmets that do not deform significantly upon impact. A prototype helmet of the current invention was tested in ballistic and fragmentation experiments. This prototype was 2 mm thick and exhibited an areal density similar to today's aramid and UHMWPE helmetsa size M mid-cut helmet shell would weigh under three pounds. Backface deformation following a high-velocity 9 mm impact was undetectable. The residual impact force a wearer would experience was measured at a minimum of 0 joules to a maximum of under 3 joulesin all cases, very far below even the most cautious injury threshold. The fragmentation performance of this shell exceeded the PASGT standard, with a V50 of over 2000 feet per second against the 17 gr. FSP. With optimization of alloy selection and surface treatment, performance can be improved further, to a V50 of over 2500 feet per second.

[0039] The combination of a stiff steel shell with modern high-performance padding systems enables the design of closely-fitting helmets. As steel doesn't deform significantly upon impact, and as multiple shell sizes can easily be manufactured via conventional and hot stamping processes, the steel helmet of the present invention can be made so that it provides a closer fit, with less of a standoff between the helmet and the wearer's head. This would offer enhanced stability, better weight distribution, and a smaller presented target area; as the standoff decreases, so does the area and weight of the helmet, with no decrease in protection, and the helmet becomes a smaller target. These parameters directly influence both soldier acceptance and the protective capability of the helmet. Even if the steel helmet shell rests less than 10 mm from the wearer's head, which is to say that the helmet's pads are relatively stiff and roughly thick, the helmet would be fully compliant with Standard 0106.01, Ballistic Helmets, Type II, and would exhibit an average backface deformation value of less than 10 mm at all fair-hit impact locations.

[0040] As previously noted, there is a pressing and as-yet unmet need for the helmet of the present invention. Mild traumatic brain injury has become so common in recent years that it is sometimes called the War on Terror's signature woundand it is indeed among the most common traumatic injuries sustained by military personnel. The optimized, modern steel helmet of the current invention would offer enhanced protection from this signature injury.

[0041] In one or more embodiments of the present invention, the steel alloy used in the helmet of the present invention is a hot-stamping alloy such as 22MnB5, 37MnB5, 38MnB5Nb. These are low to moderate-carbon, low-alloy steels, which include >1% Mn, >0.2% Si.

[0042] In one or more embodiments, the steel alloy used in the helmet of the present invention is in the Fe-(15-30)% Mn alloy system with additions of C, Al and/or Si to fully stabilize the f.c.c. phase and control stacking fault energy. In a particularly preferred embodiment of the present invention, stacking fault energy is controlled within the narrow range of 15-30 mJ/m.sup.2.

[0043] In one or more embodiments, the steel alloy used in the helmet of the present invention is an ultra-high-strength martensitic armor steel, with a tensile strength over 2000 MPa, and a nominal composition:

[0044] 0.4 C

[0045] 4 Ni

[0046] 1.5 Mn

[0047] 0.9 Cr

[0048] 0.6 Mo

[0049] 1 Si

[0050] Bal Fe

[0051] In one or more embodiments, the steel alloy used in the helmet of the present invention is a high-toughness low-alloy steel with the nominal composition:

[0052] 0.25 C

[0053] 1.6 Mn

[0054] 0.9 Si

[0055] Bal Fe

[0056] It is noteworthy that all prospective helmet alloys include substantial amounts of the alloying element Mn, as well as Si and/or Al.

[0057] An example of a steel helmet provided for by the present invention is comprised of a 1.65 mm steel shell manufactured via deep drawing, of the composition 0.25 C 1.6 Mn 0.9 Si, lightly coated with sealant and/or paint to military specifications. The interior of this helmet is lined with hook-and-loop fasteners, to which foam pads are attached. A harness or retention system is bonded via a polymer adhesive to the helmet shell's interior, or is attached via bolt holes drilled or laser-cut into the helmet's shell.

[0058] It is noteworthy that steel helmets over 1.1 mm in thickness have never been issued to troops, and, in the vast majority of instances, steel helmets in military service were well under 1 mm thick. The steel helmet of the present invention represents a significant improvement in terms of metallurgy, in terms of processing, and ultimately in terms of performancein part, if not only, because of the enhanced thickness it is capable of attaining. What's more, a steel helmet with pads instead of webbing has never before been seen or issued to troops, yet would represent a tremendous improvement over all old steel helmets and most composite helmets both in terms of comfort and in terms of performance. For it is well known that blast waves often travel underneath the helmet, between the shell and a harness comprised of leather or fabric webbing, and the blast wave typically becomes amplified in those tight spaces. The best way to prevent or mitigate blast wave underwash, and thereby improve the functional performance of the helmet, is to remove the airgap between the helmet shell and the wearer's head. This is best achieved with a key manifestation of the present inventiona low-profile, high-performance steel helmet that fits closely to the wearer's head, combined with a padded liner.

[0059] It should be noted that, when employed in the present disclosure, the terms comprises, comprising, and other derivatives from the root term comprise are intended to be open-ended terms that specify the presence of any stated features, elements, steps, or components, and are not intended to preclude the presence or addition of one or more other features, elements, integers, steps, components, or groups thereof.

[0060] While it is apparent that the illustrative embodiments of the invention herein disclosed fulfill the objectives of the present application, it will be appreciated that numerous modifications and other embodiments may be devised by one of ordinary skill in the art. Accordingly, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which come within the spirit and scope of the present invention.