US20120208032A1 - Helmet designs utilizing an outer slip layer - Google Patents

Abstract

Disclosed herein is a helmet structure for reducing kinetic energy transmission. The helmet receives contact of an object that transfers kinetic energy to a first layer having material that displaces in response to applied shearing force. The helmet uses a second layer having material that displaces in response to applied shearing force and uses a third layer having material that does not displace in response to applied shearing force to transfer kinetic energy laterally with respect to the skull. Helmet layers can have material with different mechanical responses, including elastic or rubbery elastic. The outer slip layer may also contain reinforcement particles such as metal, glass and ceramic. In one embodiment, each layer in the structure has a different shear modulus and each layer has a higher shear modulus than the immediately preceding layer. The shear modulus of each layer is modified by adding rigid reinforcement to the layer.

Description

PRIORITY
• This application claims priority to U.S. Provisional Patent Application No. 61/442,469, filed 14 Feb. 2011, the contents of which are herein incorporated by reference in their entirety.
BACKGROUND
• 1. Technical Field
• The present disclosure relates to safety helmet design and more specifically to reducing kinetic energy transmission after various types of impacts utilizing an outer slip layer.
• 2. Introduction
• In the United States, hundreds of thousands of people each year are involved in athletic, cycling or motorcycle accidents resulting in head injury. Much of the subsequent damage is caused by the transmission of kinetic energy to the brain, as well as shear forces. Although existing bicycle helmets reduce deaths and brain injuries, current designs focus more on aesthetics and aerodynamic performance than safety, in part due to market demands. In addition, the helmet industry is essentially self-regulating and therefore not likely to make significant improvements to helmets unless the improvements prove to be cost-effective and/or markedly more effective. Advances in polymeric materials provide novel approaches to helmet design and construction. Significant improvements in viscoelastic (active) dampening, low loss elastomers, and gradient rigidity materials have already given rise to enhanced athletic equipment and protective gear.
• Crashes and impacts to the head in sports often result in head trauma due to the rigid construction of helmets. The severe consequences of concussive brain injuries have become increasingly recognized in many sports, particularly recently in professional football and ice hockey. It has also long been recognized that boxers often suffer significant cognitive decline, even in non-professional contests where protective head gear is required. Professional and college sports teams would likely switch to a new type of helmet, if such a design were clearly shown to reduce post-traumatic brain injury.
• In addition to athletics, improved helmet designs have applications in the military. Brain injury is the leading cause of disability for military personnel deployed in Iraq and Afghanistan. Although military helmet designs have improved in recent years, they are intended primarily to prevent missile/shrapnel penetration, and do little to reduce the energy transmitted to the brain, which is a major contributor to subsequent disability. The mechanisms of traumatic brain injury due to blast forces remain unclear, but brain injuries related to explosives are by far the most common cause of death and disability in Iraq and Afghanistan. Experimental evidence indicates that the use of advanced body armor may contribute to the increase in brain injuries, both by protecting against death from injury to major non-brain organs such as the lung, and possibly by transmitting kinetic energy through larger blood vessels to the brain.
• Existing helmet designs do not adequately address the critical problem: kinetic energy from the impact is transmitted to the brain through primary, secondary and tertiary mechanisms—resulting in concussion, brain damage and even death.
SUMMARY
• Additional features and advantages of the disclosure will be set forth in the description which follows, and in part will be obvious from the description, or can be learned by practice of the herein disclosed principles. The features and advantages of the disclosure can be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims. These and other features of the disclosure will become more fully apparent from the following description and appended claims, or can be learned by the practice of the principles set forth herein.
• Disclosed is a structure for improved safety helmet designs that reduce both the kinetic energy induced by impact and rotational forces. The safety helmet will better protect the brain by limiting both direct missile trauma and secondary kinetic effects and addresses severe or multiple rotations. The safety helmet receives contact of an object that transfers kinetic energy to a first layer having material that displaces in response to applied shearing force. The helmet uses a second layer adjacent to the first layer having material that displaces in response to applied shearing force and uses a third layer adjacent to the second layer having material that does not displace in response to applied shearing force to transfer kinetic energy laterally with respect to the skull. A helmet may have any number of layers having material that displaces in response to applied shearing force.
• Helmet layers can have material with different mechanical responses, including elastic or rubbery elastic. A helmet layer may also contain reinforcement particles. The particles can have differing sizes, shapes and can be different materials such as metal, glass and ceramic.
• In one embodiment, each layer in the helmet structure has a different shear modulus and each layer has a subsequently higher shear modulus than the immediately preceding layer. The shear modulus of each layer is modified by adding rigid reinforcement to the layer. In another embodiment, deformation of the material in helmet layers is irreversible.
BRIEF DESCRIPTION OF THE DRAWINGS
• In order to describe the manner in which the above-recited and other advantages and features of the disclosure can be obtained, a more particular description of the principles briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which:
• FIG. 1 illustrates a side view of a safety helmet utilizing an outer slip layer.
• FIG. 2 illustrates an exemplary method embodiment of a safety helmet utilizing an outer slip layer;
• FIG. 3 illustrates a side view of a safety helmet utilizing an outer slip layer and an internal layer having a compressible foam structure; and
• FIG. 4 illustrates an example helmet having an outer slip layer with reinforcement and an inner second layer having a compressible foam structure.
DETAILED DESCRIPTION
• Various embodiments of the disclosure are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the disclosure.
• The present disclosure addresses the need in the art for improved safety helmet designs. A safety helmet design is disclosed that reduces both the kinetic energy induced by impact and rotational forces. A brief introductory description of safety helmets is provided followed by a discussion of mathematical modeling used to optimize helmet layer design. A more detailed description of improved safety helmet designs utilizing an outer slip layer will then follow. While a helmet is used in the example embodiment, the layering principles can also be applied to a wall, body armor, a vehicle, or any protective layer that could use the principles disclosed herein. Accordingly, various embodiments of the disclosure include a wall having a series of layers and disclosed herein, body armor having the series of layers as well as a vehicle having an outer covering including the series of layers disclosed herein. The disclosure proceeds to discuss primarily a helmet embodiment.
• Traditional design for both military and recreational helmets includes a rigid outer material to prevent penetration of the skull and brain, as well as some type of lining material to absorb some of the shock and to enhance comfort. However, few modern designs adequately address the critical problems leading to brain damage: kinetic energy transmitted to the brain and rotation (particularly axial acceleration/deceleration).
• By using novel materials and composites that are organized upon mathematically defined principles to maximize the relative dissipation of transmitted kinetic energy, as well as to limit rotational components, development of a new design for helmets and body armor should markedly reduce posttraumatic brain injuries from various types of insults and impacts. The initial target outcome is a set of disruptive technological advances in helmet design that improve the survivability of impact trauma to the head for use in military and civilian applications.
• Stacks of various materials can be used in experiments to determine the abilities of the various materials to dissipate and spread out external forces. Mathematical modeling can be used to extrapolate from experimental data to the behaviors of actual helmets constructed of the various material stacks by constructing local models and constructing local-to-global models.
• A local model refers to a mathematical model of a single cylindrical stack. Such a model allows calculation, based upon an exogenous force exerted on the top surface of the stack, the amount of force transmitted to a particular point either internal to the stack or on the surfaces of the stack.
• Consider a particular stack on which is imposed a rectangular coordinate system (x,y,z). Further, suppose that the vector function F(x,y,z) represents the magnitude of the force experienced at point (x,y,z) of the stack from a known exogenous impact on the stack. Yet further, suppose that experimental data results in measurement of the value of F(x,y,z) at N particular stack points, say
• 
  (x_i,y_i,z_i)(i=1, . . . ,N)
• Based on the geometric description of the stack, the properties of the materials composing the stack, and an analysis of the physics of force transmission through the stack, the general mathematical form of the function F(x,y,z), up to a set of parameters. For example, in a simple case, the function might have the form:
• 
  F(x,y,z)=ax+by+cz
• a linear function, involving three parameters a, b, c, which must be determined. Generally, the experimental data results in an over-determination of a, b, c, so that no set of values for a, b, c exactly matches the experimental data. The best that can be done is to determine the values of a, b, cis some “optimal fashion”—that is, so that some error function is minimized. The most common such error function is the sum of squares function:
• $E\left(a,b,c\right)=\sum _{i=1}^N{\left(F\left(x_i,y_i,z_i\right)-{\mathrm{ax}}_i-{\mathrm{by}}_i-{\mathrm{cz}}_i\right)}^2$
• In case F(x,y,z) is linear, as in the above example, the determination of a,b,c is just the well-known problem of linear regression analysis. However, in actual practice, the function F may involve more or fewer parameters and is generally highly non-linear, especially for materials with complicated behaviors. In such instances, the error function E is a much more complex function and the problem of minimizing the sums of the squares of the errors is a non-linear optimization problem, which we have had considerable experience addressing.
• In order to proceed from the local models to actual helmets configurations, an accepted technique from finite-element analysis can be used, namely subdividing a helmet configuration into a large number of elemental configurations, the analysis of each of which can be handled by a local model, and then analyzing the interaction among adjacent elemental configurations.
• For the case of the helmet configurations, the surface of the helmet can be divided into a triangular lattice. Corresponding to each triangle, a triangular prism can be obtained by a radial cut into the helmet along each side of the triangle. Each triangular prism can be regarded as embedded within a circular stack and thus subject to the analysis of a local model, which would allow an assessment of the transmission of forces between adjacent prisms in response to an exogenous force anywhere on the helmet surface.
• Of particular interest would be the proportion of the initial energy which is transmitted to the bottom of the prisms, the maximum forces transmitted, and their respective locations. This information can be used to compare the effectiveness of various material stacks and helmet configurations.
• Having disclosed some mathematical modeling used to optimize helmet layer design, the disclosure now turns toFIG. 1.FIG. 1 andFIG. 2 illustrate an improved safety helmet design that reduces both the kinetic energy induced by impact and rotational forces. The safety helmet will better protect the brain by limiting both direct missile trauma and secondary kinetic effects and addresses severe or multiple rotations. Thesafety helmet102 receives contact of an object that transfers kinetic energy to afirst layer104 having material that displaces in response to appliedshearing force202. Shearing force is an internal force in any material usually caused by an external force, such as a hand grabbing a football helmet face mask. The helmet uses asecond layer106 adjacent to thefirst layer104 having material that displaces in response to appliedshearing force204 and athird layer108 adjacent to thesecond layer106 having material that does not displace in response to appliedshearing force206 to transfer kinetic energy laterally with respect to the skull. Thefirst layer104 serves as an outside layer and is the only layer that comes in direct contact with the object. A safety helmet can have any number of layers having material that displaces in response to applied shearing force such as three, five or ten, with the innermost layer touching the head and having material that does not displace in response to applied shearing force.
• Helmet layers can have material with different mechanical responses, including elastic or rubbery elastic. In addition to having an elastic material, the outer slip layer that comes in contact with an object may contain reinforcement. The reinforcement is at least one particle and has particles with a size greater than one micron. The particles can have differing sizes, shapes and can be different materials. Rigid reinforcement particles can be metal, ceramic and/or glass. Additionally, each layer in the helmet can have a different rigid reinforcement. For example, a first layer can have metal reinforcement particles, a second layer can have ceramic particles and a third layer can have glass reinforcement. Alternately, layers can have the same rigid reinforcement of one or more layers or a combination of different reinforcement materials. For example, a first layer can have ceramic reinforcement particles, a second layer can have glass, and a third layer can have ceramic and glass reinforcement. Reinforcement particles can be different sizes in different layers, and a layer can have particles of varying sizes. In one embodiment, layer reinforcements have a progressively smaller size than the preceding layers. Any combination of reinforcement materials and particles sizes is possible and should not be limiting.
• The first layer and second layer can be made from rubberized or plasticized polymers. A polymer is a large molecule composed of repeating structural units, the units typically connected by covalent chemical bonds. Polymers are both natural and synthetic materials with varying properties. Natural polymeric materials include shellac, and cellulose and synthetic polymers include neoprene, PVC, silicone and more. A layer can be made from materials such as styrene-butadiene, styrene-butadiene-styrene, or a styrene-isobutylene-styrene block co-polymer with a low modulus. A block copolymer is made up of blocks of different polymerized monomers.
• In one embodiment, the first layer in the structure has a different shear modulus than the second layer and the second layer has a higher shear modulus than the first layer. In helmets with more than three layers, each layer in the structure has a different shear modulus and subsequent layers have a higher shear modulus than the immediately preceding layer. For example, in a helmet having five layers, the first layer has a different shear modulus than the second layer, the second layer has a different shear modulus than the third layer, and so on up to the fourth layer. The fifth layer is adjacent to the fourth layer and has material that does not displace in response to applied shearing force. Shear modulus is the ratio of shear stress to the shear strain. It measures the stiffness of a material and describes the material's response to shearing strains. The shear modulus of each layer is modified by adding rigid reinforcement to the layer. Chemical changes of a material can modify the shear modulus of each layer by cross-linking a polymer chain or adding solvents or different amounts of solvent to make the chain more mobile. Each layer in the structure can have different chemical changes. When a helmet comes into contact with an object, material in the layers becomes temporarily or permanently deformed depending on the force of impact and the material the layers are made from. In one embodiment, deformation of the material in helmet layers is reversible. In another embodiment, deformation of the material in helmet layers is irreversible. A helmet with layers having reversible deformation is appropriate for situations where multiple impacts are expected, such as a football or military helmet.
• FIG. 3 illustrates a top view of a football player having ahelmet302 with an outer slip layer having reversible deformation. Thefootball helmet302 receives contact of ahand304 that transfers kinetic energy to a first layer having material that displaces in response to applied shearing force caused by the hand rotating the facemask on thefootball helmet304. The helmet uses a second layer adjacent to the first layer having material that displaces in response to applied shearing force to transfer kinetic energy laterally with respect to the head. The helmet uses a third layer adjacent to the second layer having material that does not displace in response to applied shearing force to transfer kinetic energy laterally with respect to the head. Utilizing layers having material that displaces redirects kinetic energy away from the head, reducing brain injury. Utilizing layer material having reversible deformation allows a helmet to receive multiple impacts without replacing the helmet.
• FIG. 4 illustrates a helmet having an outer slip layer with reinforcement and an inner second layer having a compressible foam structure. In one embodiment, a helmet can offer increased protection by utilizing an outer slip layer in conjunction with at least one inner layer. For example, a helmet can have anouter slip layer402 having three sub layers and an inner layer having acompressible foam structure304. Thefirst sub layer406 is an outer layer and comes into contact with an object. The first sub layer is made of rubbery elastic and contains glass reinforcement. Thesecond sub layer408 is part of the outer slip layer, but does not come into contact with an object. It can be made of elastic and can be reinforced with ceramic particles. Thethird sub layer410 is also part of the outer slip layer, and does not come into contact with an object. A helmet can have aninner layer404 adjacent to the outer layer having sub layers with material that displaces in response to applied shearing force, the inner layer havingcompressible foam structures412,414,416 that compress and expand intoexpansion zones418,420 upon impact with an object. The foam structure can contain expansion structures having a graded modulus such that the modulus is greatest at the bases of expansion structures and least at the tips of expansion structures. Alternately, the modulus can be the greatest at the tips of the expansion structures and least at the bases of the expansion structures. In one embodiment, a helmet can have an outer slip layer with reinforcement and an inner layer having bubbles or containers containing liquid such that upon impact with an object if the threshold shear yield point of a layer is met, the layer will at least partially liquefy (the bubbles pop or containers open) and liquid flows into holding chambers internal or external to the helmet. A helmet can have an outer slip layer used in conjunction with one or more layers having varying properties and offering different amounts of protection depending on how the helmet is used for example, a bicycle helmet can offer protection against a single impact while football and military helmets can offer protection against multiple impacts.
• The various embodiments described above are provided by way of illustration only and should not be construed to limit the scope of the disclosure. Thus, for a claim that recites a structure that deflects and spreads kinetic energy, the structure could apply in any application disclosed herein (vehicle, helmet, body armor, building protection, etc.) as well as other structures not listed. Those skilled in the art will readily recognize various modifications and changes that may be made to the principles described herein without following the example embodiments and applications illustrated and described herein, and without departing from the spirit and scope of the disclosure.

Claims (16)

1. A structure for deflecting and spreading kinetic energy transmission, the structure comprising:

a first layer that makes contact with a source of kinetic energy, the first layer comprising material that displaces in response to an applied shearing force;

a second layer adjacent to the first layer, the second layer comprising material that displaces in response to the applied shearing force; and

a third layer adjacent to the second layer, comprising material that does not displace in response to the applied shearing force.

2. The structure ofclaim 1, wherein the source of kinetic energy is an object.

3. The structure ofclaim 2, wherein the first layer is the only layer that makes contact with the object.

4. The structure ofclaim 1, wherein the first layer is a rigid material.

5. The structure ofclaim 1, wherein the second layer is a polymer.

6. The structure ofclaim 5, wherein the polymer is one of rubberized and plasticized.

7. The structure ofclaim 1, wherein the first layer has a different shear modulus than the second layer.

8. The structure ofclaim 7, wherein the second layer has a higher shear modulus than the first layer.

9. The structure ofclaim 8, wherein the shear modulus of the first layer and the second layer is modified by adding rigid reinforcement.

10. The structure ofclaim 9, wherein the rigid reinforcement is at least one of metal, ceramic and glass.

11. The structure ofclaim 7, wherein chemical changes of a material modify the shear modulus of the first layer and the second layer.

12. The structure ofclaim 1, wherein the first layer has a different rigid reinforcement than the second layer.

13. The structure ofclaim 12, wherein the first layer has different chemical changes than the second layer.

14. The structure ofclaim 1, wherein displacement of at least one of the first layer and the second layer causes deformation of the layer material.

15. The structure ofclaim 14, wherein the deformation of the layer material is reversible.

16. The structure ofclaim 14, wherein the deformation of the layer material is irreversible.

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