Patent Application
20140109298
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 helmets may slightly 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.
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. Any two adjacent layers can be in chemical attachment and/or physically bonded.
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.
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:
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
(xi,yi,zi) (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:
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 to
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 consists of multiple particles with a size less than one micron. The particles can have differing sizes, shapes and can be different materials. The particles and matrix are in intimate contact and may be chemically bound or not. Rigid reinforcement particles can be metal, ceramic and/or glass. Additionally, each layer in the helmet can have a different rigid reinforcement. Each layer can be chemically and/or physically bound to the preceding layer. 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 is chemically attached to the adjacent layer and can have different chemical changes or characteristics. 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.
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.
This application is a continuation-in-part of U.S. Non-Provisional application Ser. No. 13/267,604 filed Oct. 6, 2011, which 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.
| Number | Date | Country | |
|---|---|---|---|
| 61442469 | Feb 2011 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13267604 | Oct 2011 | US |
| Child | 14139012 | US |
