US3353187A - Protective helmet - Google Patents

Description

NOV. 21, 1967 A, LA$TN|K ETAL 3,353,187

PROTECTIVE HELMET Filed Nov. 19, 1965 United States Patent Otlice 3,353,187 Patented Nov. 21, 1967 3,353,137 PRGTECTIVE HELP/1E1 Abraham L. Lastniir, Framingharn, Mass, and Meyer 1. Landsberg, St. Louis Park, Mina, assignors to the United States of America as represented by the Secretary of the Army Filed Nov. 19, 1965, Ser. No. 598,875 8 Claims. (Cl. 2-3) This invention relates to a protective helmet and, more particularly, to a protective helmet that provides greater impact energy dissipating characteristics and greater resistance to penetration by ballistic fragments than that heretofore provided by helmets of the same general weight and size.

It has been established that the incidence and severity of head injuries to personnel involved in hazardous, highspeed activities, as for example, military aircraft crew'- men, can be significantly reduced by the use of proper protective helmets. One study indicated that over a 36 month period there were 80% fewer fatal head injuries among personnel involved in military aircraft accidents who wore protective helmets as compared with personnel who did not. A helmet furnishes protection to the head of the wearer by virtue of its ability to dissipate some or all of the energy of an impact delivered to the helmet before that energy can be transmitted to the head. It has been demonstrated that to obtain optimum protection, the energy of the impact applied locally must first be caused to be distributed over as wide an area as possible and then the impact energy which has thus been distributed must be required to do some work before it can be transmitted to the head. It is known in the art that this kind of protection can be obtained by means of a helmet having a rigid outer shell and a liner of energy absorbing material. The outer shell should be sufi'iciently rigid so as to resist localized deformation in response to the force of an impact. Metal shells, for example, while rigid, characteristically deform in a small localized area in response to an impact. Resin-impregnated, glass fabric laminates, on the other hand, form hard, tough, shells highly resistant to localized deformation and capable of distributing the energy of the impact over a wide area of the shell. Glass fabrics were thought to be preferred for this purpose because of the high tensile strength and stretch resistance of glass fibers. However, because of the difiiculty of obtaining a satisfactory laminar bond, it has been necessary to use from 40% to 70% by weight of resin based on the weight of the shell. While such a high resin content is necessary to produce a helmet shell that has the desired degree of rigidity and resistance to deformation, it also results in a material that affords little protection against penetration by ballistic fragments. It is known, on the other hand, that these same glass fabrics when bonded With 25% resin produce structures having significant resistance to ballistic fragment penetration but as the resin concentration increases and the structure becomes more rigid, ballistic fragment penetration resistance decreases.

The inner energy absorbing liners employed in crash protective helmets consist of nonresilient materials that will undergo an irreversible deformation when the energy of an impact exceeds a certain level. Energy is llllillZld in crushing or deforming these liner materials and, as a consequence, this energy never reaches the head. Examples of a good energy absorber for use in a crash protective helmet are the expanded plastics which have a rigid cell structure, such as polystyrene and polyurethane. It is preferred that the expanded plastic material have sufficient strength in compression to resist crushing under low energy impacts, otherwise a number of butfeting (low energy) blows to the head would crush the liner destroying its effectiveness as an energy absorber. The head can normally withstand low energy impacts Without injury when the force of the impact is distributed over a relatively wide area but when the energy of the impact exceeds 50 foot lbs. some means must be employed to absorb and extend the time duration during which the head receives the impact energy.

It is therefore among the objects of the present invention to provide an improved crash protective helmet.

Another object is to provide a helmet that has greater energy dissipating characteristics than helmets of the prior art.

A further object is to provide a crash protective helmet that will also provide a significantly high resistance to penetration by ballistic fragments.

These and other objects of the present invention will become apparent from the following detailed description wherein reference is had to the accompanying drawings in which:

FIGURE 1 is a front elevation of an embodiment of our crash protective helmet.

FIGURE 2 is a sectional view of our helmet taken along the line 22 of FIGURE 1.

FIGURE 3 is a sectional view through the outer shell of the helmet.

The improved crash protective helmet of the present invention consists of a hard outer shell and an inner liner of energy absorbing material, wherein the outer shell is composed of a resin-bonded laminate of nylon cloth" in place of the resin-impregnated laminate of glass cloth used heretofore. The use of nylon cloth to form the outer shell results in a totally unexpected improvement in the crash protective qualities of the helmet since it would be expected that a resin-bonded nylon cloth shell would be less rigid than a resin-bonded glass cloth shell, because of the lower tensile and stretch-resistant properties of nylon. Reduction in rigidity of the shell would be expected to result in a reduction in the ability of the shell to distribute and attenuate the load of the impact.

The outer shell of the helmet of our invention is a resin-bonded laminate of nylon fabric and, as illustrated in the drawings and described in detail hereinafter by way of example, is constructed of nine plies of nylon ballistic cloth. This cloth is formed by weaving a high tenacity, continuous filament nylon prepared from hexamethylenediamine and adipic acid or its derivatives and having a melting point of 250i6 C. The warp and filling yarns are 1050 denier, multifilament with 3 to 4 turns per inch Z twist and the weave is 2 by 2 basket weave with two ends weaving as one and two picks Weaving as one. The cloth weighing approximately 14 oz. per sq. yard is thoroughly scoured and heat treated and has a minimum of 46 yarns per inch in the warp and 42 yarns per inch in the filling and has a minimum breaking strength in the warp of 900 lbs. and in the filling of 825 pounds, and a minimum ultimate elongation of 25% in the warp and 20% in the filling. Further details relative to this nylon ballistic cloth may be found in Military Specification MIL-C-12369D (GL) entitled, Cloth, Ballistic, Nylon. The nine plies of nylon cloth are surface-coated on each side with a resin composition, such as a thermosetting resin modified with a thermoplastic resin, e.g., a modified system of polyvinyl butyral and phenol-formaldehyde resins. A suitable modified system contains a mixture of 87 parts by weight of an ethanol solution of polyvinyl butyral (25% solids), 10 parts by weight of phenolic varnish (57% solids), 27 parts by weight of trimethylol phenol (60% solids) and 2.6 parts by weight of phthalic anhydride dissolved in 5 parts by weight of methanol. It is essential that the resin composition. be sufficiently viscous so as to remain on the surface of the fabric and not flow into the fabric. The resin composition is knife coated onto each side of the fabric to effect an add-on of from 35 to 50% and preferably about 40% by weight of the resulting structure. The exposed surfaces of the laminate are coated with a phenolformaldehyde resin to create a hard, rigid surface. The coated cloth plies are trimmed so as to form pin-wheel like cutouts when inserted in a mold to form a rough helmet shape. Each ply isinserted in the mold so as to stagger the overlapped areas and so as to avoid gaps. Following the placement of the requisite number of plies of coated fabric in the mold, a rubber bag is inserted within the cavity and inflated with steam heated water under pressure. The temperature of the water is aproximately 330 to 360 F., the pressure within the bag is from 300 to 400 p.s.i. and the molding time is aproximately 45 minutes. The mold in which the plies are inserted consists of a split metal cavity which is cored for heating by steam. It is desirable that heat be applied to .both sides of the shell structure being formed in order to obtain a uniform cure.

The energy absorbing liner is an expanded plastic, molded, for example, from an expandable polystyrene bead material, having a thickness of approximately 1 /2- inch, a minimum density of at least 4 lbs. per cubic foot and a minimum compressive strength of 80 p.s.i., i.e., the ability to withstand this load without breaking or being compressed more than 25% of original thickness. This material is molded in the, general shape of the helmet and is cemented in place to the inner Wall of the shell either in one piece, or cut into sections which are assembled in place.

Resilient material, such as expanded latex may be used in the form of pads to make the helmet more comfortable to wear and as means for adjusting the size and fit of the helmet. Such resilient materials, however, do not contribute to the protection afforded the head since they only absorb a small amount of energy when compressed, which energy is returned with the recovery of the material. As a consequence, the head may be subjected to greater accelerative forces than normally expected because of the sudden change in direction as a result of the rebound.

Various studies have shown that damage to the head and brain are related to the time span during which the force of the impact is transmitted to the head, and to the maximum accelerative forces transmitted to the head. Head and brain damage tolerance limits cited in terms of peak acceleration and duration of impact vary among investigators but there is general agreement to the effect that a helmet, when impacted should not bottom, nor permit an excess of 400 G to be transmitted to the head nor should the duration of transmission of impact forces be less than 4, milliseconds. Bottoming is defined as that phenomenon occurring during impact or crushing of energy absorbing systems when input energy is transmitted to the sensing element with little or no attenuation, as will be reflected by a sudden and rapid rise in the forcetime curve.

The crash protective properties of a helmet can be ascertained, therefore, by subjecting the helmet to the force of an impact and measuring the peak accelerative forces transmitted through the helmet, the time span during which these forces are transmitted, and the resistance of the helmet to bottoming. These impact tests are performed on a free swinging, hollow, magnesium alloy head form weighing 13 pounds. An accelerometer is mounted to the inner surface of the head form below the point to be impacted and connected to instrumentation to record acceleration and the time span. of the impact. The helmet being tested is placed on the head form and is impacted with a 16 pound steel mass with a 1.9 radius impacting surface dropped from a height of 6.25 feet above the helmet. The results of two successive impacts on the forehead region of the nylon shell helmet of this invention and the glass shell helmet, both helmets having essentially the same dimensions and weight, are set forth below in Table I. It is noted that acceleration is expressed in Gs, i.e., a unit of force applied to a body equal to the force exerted on it by gravity.

The results shown above indicate that the nylon helmet transmits significantly less accelerative forces to the headform and that the accelerative forces transmitted are spread over a wider time frame than in the case of the glass helmet. The second impact delivered to the glass helmet generating forces in excess of 400 G caused bottoming.

The helmet of this invention was evaluated as a barrier which will resist penetration by. ballistic shell fragments and was compared with a glass helmet of essentially the same weight and size. A caliber .22 17 grain fragment simulating projectile having a hardness of Rockwell C30- 2 was fired on each helmet to produce an impact normal to the line of fire. The V i.e., the impact velocity at which there is a 50% probabilityof penetration by the projectile, was determined for each helmet type. Replicate tests resulted in an average V of 1,110 feet per second for the nylon helmet and an average V of 400 feet per second for the glass helmet.

Referring to the drawing, there is shown an embodiment of a helmet 10 according to our invention which is shaped so as to provide a protective covering for the head of a wearer. The principal components of the helmet are a rigid outer shell 11 and an inner liner 12 of energy absorbing material cemented in place against the inner surface of the shell. There is also shown a visor housing 13 constructed of the same material as the shell 11 which serves to enclose a transparent visor 14. A visor lock assembly 15 holds the visor in position within the visor housing and when released from its locked position allows the visor to be moved into position in front of the face. A chin strap 16 mounted on the front of the helmet and a nape strap 17 on the rear of the helmet function 'to hold the helmet to the head of the wearer. An enlarged fragmentary view in section of the resin-bonded plies of nylon fabric is shown in FIGURE 3 with the plies of fabric identified as 20, the modified resin composition layer as 21 and the phenol-formaldehyde layers as 22. V

The invention described in detail in the foregoing specification is susceptible to changes and modifications as may occur to persons skilled in the art without departing from the principle and spirit thereof. The terminology used is for purpose of description and not limitation, the

scope of the invention being defined in the claims.

We claim:

1. A crash and ballistic protective helmet comprising a rigid outer shell formed of a plurality of plies of a Woven nylon fabric, said plies bonded togetherby a resin where said resin comprises at least 35% by weight based on the weight of the. shell, an inner energy absorbing liner of, irreversibly crushable expanded plastic material and means attaching said inner energy absorbing liner to the inner surface of said rigid outer shell.

2. A crash and ballistic protective helmet according to claim 1 wherein said resin is a thermosetting resin modified with a thermoplastic resin.

3. A crash and ballistic helmet according to claim 2 in which said woven nylon fabric is a 2 x 2 basket weave fabric, weighing about 14 02., having a minimum of 42 yarns per inch in the filling and warp.

4. A crash and ballistic helmet according to claim 3 in which said nylon fabric has a minimum breaking strength of 900 pounds in the warp and 825 pounds in the filling and a minimum ultimate elongation of in the warp and 20% in the filling.

5. A crash and ballistic helmet according to claim 3 wherein said resin is a modified system of polyvinyl butyral phenol-formaldehyde resins and where said resin comprises from to by weight based on the weight of the shell.

6. A crash and ballistic helmet according to claim 5 wherein said inner energy absorbing liner has a density of at least 4.0 lbs. per cubic ft. and a minimum com pressive strength of p.s.i.

7. A crash and ballistic helmet according to claim 6 wherein said inner energy absorbing liner is an expanded polystyrene bead material having a thickness of not less than about /2-inch.

8. A crash and ballistic helmet according to claim 7 wherein said outer shell is constructed of nine plies of nylon fabric.

References Cited UNITED STATES PATENTS 2,351,235 6/1944 Shroyer et al. 2-6 2,879,513 3/ 1959 Hornickel et al. 23 2,971,195 2/1961 Voss 2-3 3,018,210 1/1962 Frieder et al. 23 XR 3,237,202 3/1966 Aileo 26 JORDAN FRANKLIN, Primary Examiner. I. R. BOLER, Assistant Examiner.

Claims (1)

1. A CRASH AND BALLISTIC PROTECTIVE HELMET COMPRISING A RIGID OUTER SHELL FORMED OF A PLURALITY OF PLIES OF A WOVEN NYLON FABRIC, SAID PLIES BONDED TOGETHER BY A RESIN WHERE SAID RESIN COMPRISES AT LEAST 35% BY WEIGHT BASED ON THE WEIGHT OF THE SHELL, AN INNER ENERGY ABSORBING LINER OF IRREVERSIBLY CRUSHABLE EXPANDED PLASTIC MATERIAL AND MEANS ATTACHING SAID INNER ENERGY ABSORBING LINER TO THE INNER SURFACE OF SAID RIGID OUTER SHELL.

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