Patent ID: 12201176

In accordance with common practice, the various features illustrated in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may not depict all of the components of a given system, method or device. Finally, like reference numerals may be used to denote like features throughout the specification and figures.

DETAILED DESCRIPTION

Numerous details are described herein in order to provide a thorough understanding of the example embodiments illustrated in the accompanying drawings. However, some embodiments may be practiced without many of the specific details, and the scope of the claims is only limited by those features and aspects specifically recited in the claims. Furthermore, well-known processes, components, and materials have not been described in exhaustive detail so as not to unnecessarily obscure pertinent aspects of the embodiments described herein.

Impact absorbing materials and structures are used in a variety of environments and for various purposes including adventure, sporting, police and military purposes. For example, impact absorbing materials and structures are needed for a variety of applications such as dental, medical devices, automobiles, transportation, sporting goods, shoes, military equipment, packaging, playground equipment or any other application for providing attenuation of multiple impacts. For example, helmets may require the use of impact absorbing materials or structures since helmets provide protection against projectiles and blunt force impacts. Helmets typically include a helmet shell having a peripheral edge and a retention system (e.g., chinstrap) that may be attached to helmet shell. Helmets also typically include a liner system coupled to an inside surface of the helmet shell to provide a compressible material such as foam for comfort and impact energy absorption. The liner system may be composed of a single contiguous structure or multiple distinct structures either of which may or may not completely cover the inner surface of the helmet shell. The need for a comfortable liner with high impact attenuation is particularly important for defense forces, emergency responders, and industrial personnel operating in high performance environments, as well as individuals wearing helmets for extended periods of time under harsh conditions.

Referring toFIGS.1A-3Cwherein like reference numerals indicate like elements throughout, there is shown helmet100, generally designated100, in accordance with an exemplary embodiment of the present invention. In certain preferred embodiments of the present invention, helmet100includes shell102, liner108, and padding106. In one embodiment, liner108may be used as a drop-in replacement for the impact liner of an existing helmet. In another embodiment, liner108may be used as a fully integrated system with the helmet.

FIG.1Ais an oblique view of an exemplary helmet100in accordance with some embodiments. The helmet100includes a shell102, an impact absorbing liner108, and padding106. The impact absorbing liner108may be comprised of auxetic foam substrate or articles104. In some embodiments, the auxetic foam articles104are comprised of closed-cell foam for increased impact attenuation. In some embodiments, the auxetic foam article104may include additional padding such as open-celled foam to provide increased comfort. For example, the auxetic foam article104comprised of closed-cell foam may form the base of a helmet liner, while an open-celled foam pad may be provided on top of the auxetic foam article104for contacting the user's head.

The auxetic foam articles104may be used in a variety of applications such as dental, medical devices, automobiles, transportation, sporting goods, shoes, military equipment, packaging, playground equipment, or any other application that requires attenuation of multiple impacts. In some embodiments, auxetic foam articles104are discrete articles. However, auxetic foam articles104may extend over the entire surface of the liner system.

It is noted that the helmet100, and its various components, may not be drawn to scale and is just a single example of the use of the auxetic foam articles104. In some embodiments, the auxetic foam articles104are used in a variety of applications such as dental, medical devices, automobiles, transportation, sporting goods, shoes, military equipment, packaging, playground equipment, or any other application that requires attenuation and energy absorption of multiple impact events. Moreover, while some example features are illustrated, various other features have not been illustrated for the sake of brevity and so as not to obscure pertinent aspects of the example implementations disclosed herein. Sections of the shell102have been removed inFIG.1Afor ease of illustrating the impact absorbing liner108and, in particular, the auxetic foam articles104therein.

In practice, the helmet100is used to protect the head of a person wearing the helmet100. Specifically, the helmet100can be used to absorb and dissipate otherwise harmful energies from numerous impacts (e.g., impacts from falling, impacts from other helmets, impacts from munitions, etc.). As will be discussed in detail below, the helmet100includes multiple means (e.g., the shell102, the impact absorbing liner108comprised of the auxetic foam articles104) for absorbing and dissipating otherwise harmful energies and forces. Importantly, the helmet100may be used in a variety of different applications, and a design (i.e., an overall shape) of the helmet100shown inFIG.1Ais merely one possible design for the helmet100. In one example, illustrated inFIG.1A, the helmet100is designed for military applications. In certain embodiments, the helmet100is a standard infantry ballistic helmet, advanced combat helmet (ACH), enhanced combat helmet (ECH), or lightweight advanced combat helmet (LWACH). In other embodiments, helmet100may be a modular integrated communications helmet (MICH), a tactical ballistic helmet (TBH), a lightweight marine helmet, police general duty helmet, or a personnel armor system for ground troops (PASGT) helmet. In some embodiments, the helmet100is designed for sports applications (e.g., football, hockey, baseball, cycling, vehicle racing, etc.) or for other applications (e.g., firefighting, construction, police, etc.).

Referring toFIGS.1A-1C, the shell102may be configured to receive and protect a head of a person wearing the helmet100(called the “user” herein). The shell102may include an inner surface112and an outer surface110. Specifically, the shell102may be configured to protect the head of the user from impacts, such as impacts created by munitions, impacts experienced during sport, etc. The shell102may be made from a variety of impact resistance materials, including numerous rigid polymers (e.g., polycarbonate, ultra-high-molecular-weight polyethylene (UHMWPE), polyether ether ketone (PEEK), and the like) and composite materials (e.g., fiberglass-reinforced polymers, carbon-fiber reinforced polymers, etc.). While the shell102is able to protect the user's head generally from various impacts and ballistic threats, the shell102may not perform particularly well against blunt impacts. A “blunt impact” is an impact from a blunt object that delivers a force to a localized area that may transfer to the user's head (sometimes referred to herein as a “localized impact”). Examples include falling debris, low velocity vehicle crashes, and trips and falls. Because the shell102alone may not sufficiently protect against blunt impacts, the helmet100may also include the impact absorbing liner108.

In some embodiments, the impact absorbing liner108includes a plurality of auxetic foam articles104-A,104-B, . . .104-L that are configured to dissipate forces associated with localized impacts delivered to the outer surface of the shell102. In some embodiments, the auxetic foam articles104-A,104-B, . . .104-L are used to attenuate impact and absorb energy for applications in shoes, automobiles, transportation, dental, medical devices, sporting goods, industrial and manufacturing equipment, packaging, playground equipment, or any other application that requires attenuation of one or more impact events.

The term “auxetic” as used herein generally refers to a material or structure that has a negative Poisson's ratio. As such, when stretched, auxetic materials become thicker (as opposed to thinner) in a direction perpendicular to the applied force. Likewise, when compressed (e.g., by a blunt impact), auxetic materials become thinner in a direction traverse to the applied force. This contraction of the material acts to draw material in from outside of the impact zone to add supplemental energy absorption. One of the ways this can be achieved is through the use of hinge-like structures (sometimes called a “re-entrant” structure) that form within auxetic materials. Conventional materials, including conventional foams (e.g., expanded polypropylene (EPP)), typically have positive Poisson's ratio, meaning that the materials tend to expand in a direction perpendicular to the direction of compression. Conversely, when a conventional material is stretched, it tends to contract in a direction transverse to the direction of stretching. A rubber band is a good example of an article with a positive Poisson's ratio, in that when stretched, the rubber band becomes thinner.

The auxetic foam articles104-A,104-B, . . .104-L may be comprised of closed-celled foam. For example, the closed-cell auxetic foam articles104-A,104-B, . . .104-L may provide better impact attenuation compared to auxetic open-cell foams. Existing polymeric closed-celled foams have traditionally provided better impact attenuation properties compared to polymeric open-celled foams, which are typically used for comfort. In some embodiments, each of the auxetic foam articles104-A,104-B, . . .104-L is a polypropylene auxetic foam article. In other words, each of the auxetic foam articles104-A,104-B, . . .104-L is formed from an expanded polypropylene. In some other embodiments, each of the auxetic foam articles104-A,104-B, . . .104-L is formed from some other closed-cell foam (polyethylene, polystyrene, etc.) or an open-cell foam. For example, the auxetic foam articles104-A,104-B, . . .104-L may be formed from polyurethane, polypropylene, polyvinyl chloride (PVC), vinyl nitrile, or polyesters. In those embodiments where the auxetic foam articles are formed from an expanded polypropylene, a density of the expanded polypropylene is 1.0 lb/ft3to 10.0 lb/ft3, including all integer lb/ft3values and ranges there between. For example, the auxetic foam articles104-A,104-B, . . .104-L may have a density between 1.0 lb/ft3and 10.0 lb/ft3, 2.0 lb/ft3and 9.0 lb/ft3, 3.0 lb/ft3and 8.0 lb/ft3, 4.0 lb/ft3and 7.0 lb/ft3, and 5.0 lb/ft3and 6.0 lb/ft3. In preferred embodiments, the auxetic foam articles104-A,104-B, . . .104-L has a density between 2.0 lb/ft3and 4.0 lb/ft3.

As mentioned above, the auxetic foam articles104-A,104-B, . . .104-L are configured to dissipate forces associated with localized impacts delivered to the outer surface110of the shell102. For example, the auxetic foam articles104-A,104-B, . . .104-L may be configured to maintain the acceleration transmitted to the user's head below a threshold acceleration (e.g., at least below 150 G, 175 G, 200 G, 250 G, 275 G, 300 G, 350 G, or 400 G for air crew helmets, HIC of 1000 or 2400 for motorcycle helmets, or below 2.5 kilonewtons (kN), 3.5 kN, 4.45 kN, 5.0 kN, 10 kN, or 12.5 kN according to European standards) when the shell102is impacted by a localized force. The shell102may be designed to physically stop a bullet, while an auxetic foam article positioned at the impact location is configured to dissipate the forces associated with the stopped bullet (e.g., to prevent those forces and accelerations from injuring the user's head). In another example, the shell102may be designed to generally protect a user's head from a blunt impact, such as a crown of another helmet (e.g., in a football game), while an auxetic foam article positioned at the impact location is configured to dissipate the forces associated with the blunt impact.

Referring toFIG.1A, auxetic foam article104may be disk shaped and may be configured to maintain a peak acceleration below 150 G (preferably 130 G) when the shell102is subjected to a localized impact of approximately 25 Joules (J). In some embodiments, the auxetic foam article104may be a disk shape having a thickness of approximately 0.50 inches (plus or minus 0.05 inches, i.e., a reasonable manufacturing tolerance). However, the thickness of auxetic foam article104may vary based on the application. The auxetic foam article104may be any shape, such as circular, oval, square, rectangular, diamond, triangular, or any other shape desired. In some embodiments, some of the auxetic foam articles104-A,104-B, . . .104-L are a first shape and some of the auxetic foam articles104-A,104-B, . . .104-L are a second shape different from the first shape. In other embodiments (e.g., when the auxetic foam articles104-A,104-B, . . .104-L form a continuous liner that covers the inner surface of the shell102), the auxetic foam articles104-A,104-B, . . .104-L have a shape that substantially complements a shape of the human head.

The auxetic foam article104may have a thickness between 0.1 inches and 3.0 inches, 0.5 inches and 2.5 inches, or 1 inch and 2 inches. In some embodiments, the auxetic foam article104has a diameter between 0.5 inches and 3 inches, 1 inch and 2.5 inches, or 1.5 inches and 2.5 inches. In a preferred embodiment, the auxetic foam article104has a thickness between 0.5 inches and 1 inch and a diameter of approximately 2.5 inches. The auxetic foam article104may be configured to absorb, for example, approximately 60 joules (J) of energy when subjected to multiple impacts at 10 feet per second, and absorb approximately 115 J of energy when subjected to multiple impacts at 14 feet per second. The auxetic foam article104may be configured to absorb between 25 J and 200 J, 75 J and 175 J, or 125 J and 150 J of energy.

In some embodiments, helmet100includes a plurality of the auxetic foam articles104-A,104-B, . . .104-L. For example, as shown inFIG.1A, helmet100may include three auxetic foam articles104-A,104-B,104-L. However, helmet100may include more than three auxetic foam articles104. Referring toFIG.1B, helmet100may include auxetic foam article104-M positioned opposite to the auxetic foam article104-L on the other side of the shell102. In some embodiments, the auxetic foam articles104-A,104-B, . . .104-L cover an inner surface of the shell102. In some other embodiments, the auxetic foam articles104-A,104-B, . . .104-L are distributed at multiple different locations on the inner surface of the shell102, whereby the multiple different locations are selected based on known locations of the human head that are vulnerable to localized impacts. For example, the auxetic foam articles104-A,104-B, . . .104-L (and104-M) may be positioned at the locations shown inFIGS.1A and1B, and additional auxetic foam articles104may be positioned elsewhere, such as on the back of the helmet100. In other embodiments, the auxetic foam articles104-A,104-B, . . .104-L substantially cover the inner surface112of the shell102. In some embodiments, the impact absorbing liner108is comprised of the auxetic foam articles104-A,104-B, . . .104-L and substantially covers the inner surface112of helmet100. For example, the auxetic foam articles104-A,104-B, . . .104-L may form a continuous liner that covers the inner surface112of the shell102. In some embodiments, the auxetic foam articles104-A,104-B, . . .104-L are positioned in a contiguous fashion to substantially cover the inner surface112of the shell102. In some embodiments, the auxetic foam articles104-A,104-B, . . .104-L cover only a portion of the inner surface112of the shell102.

In some embodiments, the impact absorbing liner108includes one or more structures in addition to the auxetic foam articles104-A,104-B, . . .104-L. For example, the impact absorbing liner108may include one or more traditional foam articles that are paired with the auxetic foam articles104-A,104-B, . . .104-L. In another example, the impact absorbing liner108may include a general foam layer whereby the auxetic foam articles104-A,104-B, . . .104-L are integrated with the general foam layer. In some embodiments, the foam layer substantially covers the inner surface112of the helmet. In some other embodiments, the impact absorbing liner108only includes the auxetic foam articles104-A,104-B, . . .104-L.

Referring toFIG.1C, the padding106may be coupled to the impact absorbing liner108and configured to directly contact the head of the user when helmet100is worn by the user. In some embodiments, the padding106includes individual pieces of padding that are coupled to a respective foam article of the plurality of auxetic foam articles104-A,104-B, . . .104-L. Padding106may be comprised of a non-auxetic material. In some embodiments, the padding106is a continuous structure this is coupled to the plurality of auxetic foam articles104-A,104-B, . . .104-L. For example, the padding106may be a webbed structured that covers each of the plurality of auxetic foam articles104-A,104-B, . . .104-L. The padding106may be made from various textiles and fabrics that can comfortably interact with the human head. For example, padding106may be comprised of foam, cotton, polyester, nylon, or any combination thereof. In some embodiments, the padding106is comprised of a polyether foam and/or an open-celled foam. In some embodiments, auxetic foam articles104may be a pad. The pad may include covering111and the padding106. The padding106may be a comfort layer and may have a thickness less than the thickness of auxetic foam articles104. The padding106may be disposed between the covering111and the auxetic foam article104. Covering111may be configured to cover auxetic foam articles104and/or padding106.

Referring toFIG.1B, an interior view of helmet100is illustrated in accordance with some embodiments. A section of the shell102has been removed inFIG.1Bfor ease of illustrating one of the auxetic foam articles104. In some embodiments, helmet100includes a structure to cover the auxetic foam articles104-A,104-B, . . .104-L. For example, the auxetic foam articles104-A,104-B, . . .104-L may be covered by covering120. In some embodiments, each auxetic foam article104-A,104-B, . . .104-L includes its own covering111. The covering120or111may be comprised of foam, cotton, polyester, nylon, or any combination thereof. In some embodiments, the covering120or111is comprised of a mesh fabric or other type of fabric to allow for breathability of the padding106and/or the auxetic foam article104. In some embodiments, the covering120is coupled to or part of the inner surface112of the shell102. In such embodiments, the auxetic foam articles104-A,104-B, . . .104-L are positioned between the outer surface110of the shell102and the inner surface112of the shell102. In some embodiments, the covering120is part of the impact absorbing liner108. For example, the auxetic foam articles104-A,104-B, . . .104-L are embedded within impact absorbing liner108. In some embodiments, the auxetic foam articles104-A,104-B, . . .104-L are not covered by the covering120. In some embodiments, the covering120or111is simply the padding106. In such embodiments, the auxetic foam articles104-A,104-B, . . .104-L are coupled to the inner surface112of the shell102and are substantially exposed inside the helmet100. In such embodiments, the padding106may be coupled to the auxetic foam articles104-A,104-B, . . .104-L and configured to directly contact the head of the user. For example, the padding106may form a comfort boundary between the auxetic foam articles104-A,104-B, . . .104-L and the user's head.

Referring toFIG.1C, a cross-sectional view of an exemplary helmet100is illustrated in accordance with some embodiments. The embodiments discussed below with reference toFIG.1Cmay be modified and combined with the embodiments discuss above with reference toFIG.1B. For example, a shape of the respective auxetic foam article104-A discussed with reference toFIG.1Ccan be applied to one or more of the configurations of the shell102, auxetic foam articles104-A,104-B, . . .104-L, and the covering120or111discussed above with reference toFIG.1B.

In some embodiments, the auxetic foam articles104-A,104-B, . . .104-L are coupled to the inner surface112of the shell102.FIG.1Cincludes a magnified view150that shows a close-up of the shell102. For example, the magnified view150shows the outer surface110of the shell102and the inner surface112of the shell102, and the coupling between the inner surface112of the shell102and a respective auxetic foam article104-A. As shown in the magnified view150, a top surface114of the respective auxetic foam article104-A has a convex curvature and a bottom surface116of the respective auxetic foam article104-A has a concave curvature. In some embodiments, the convex curvature of the respective auxetic foam article104-A is designed to generally complement a curvature of the inner surface112of the shell102, while the concave curvature of the respective auxetic foam article104-A is designed to generally complement a curvature of the human head. The magnified view150also shows coupling between the respective auxetic foam article104-A and the padding106. In some embodiments, the respective auxetic foam article104-A is coupled to the inner surface112of the shell102and the padding106using a fastener. For example, the auxetic foam article104-A may be coupled to padding106via a chemical fastener, such as an adhesive or epoxy. Alternatively or in addition, the auxetic foam article104-A may be coupled to the inner surface112of the shell102and the padding106using a mechanical fastener, such as bolts, screws, hook-and-loop mechanism, etc. The characteristics of the respective auxetic foam article104-A discussed with reference toFIG.1Cmay be applied to each of the other auxetic foam articles104discussed herein.

Referring toFIGS.2A and3A, an exemplary foam article200that has not undergone auxetic conversion is illustrated in accordance with some embodiments. In some embodiments, foam article200is a propylene foam article. The foam article200is a closed-cell foam having a positive Poisson's ratios, such that the foam article200becomes thinner in a direction perpendicular to the applied force. The foam article200may be used in a variety of applications such as dental, medical devices, automobiles, transportation, sporting goods, shoes, military equipment, packaging, playground equipment or any other application for providing attenuation of multiple impact events.

In some embodiments, to satisfy impact resistance standards, a thickness of these foam articles is increased, for example, to at least 0.75 inches, which can be undesirable in many applications. Referring toFIG.4A, an impact test of a 0.75 inch thick polypropylene foam article coupled to a crown of a plastic helmet was conducted according to the ACH Purchase Description AR-PD 10-02. The impact test revealed that the 0.75 inch thick polypropylene foam article maintain a peak acceleration below 150 G when the helmet was impacted by a hemispherical impactor. As such, the 0.75 inch thick polypropylene foam article passed the impact test. However, an impact test of a 0.50 inch thick polypropylene foam article coupled to a crown of a plastic helmet revealed that the 0.50 inch thick polypropylene foam article failed to maintain a peak acceleration below 150 G when the helmet was impacted by the hemispherical impactor, and, thus, the 0.50 inch thick polypropylene foam article failed the impact test. Indeed, the 0.50 inch thick polypropylene foam article failed to maintain a peak acceleration below 300 G on at least one occasion during the impact testing.

Referring toFIGS.2B and3B-3C, an exemplary foam article210is illustrated that has undergone auxetic conversion in accordance with some embodiments (referred to henceforth as an “auxetic foam article210”). In some embodiments, the auxetic foam article210is a polypropylene auxetic foam article. The auxetic foam article210may be made from the foam article200, an article similar to the foam article200, or a similar expanded foam, such as expanded polypropylene foam. For example, the auxetic foam article210may have been originally a closed-cell foam that was transformed into an auxetic foam article210during an auxetic conversion process, which is described below with reference toFIGS.7A-7BandFIG.8. The auxetic conversion process may cause cells202in the closed-cell foam (FIGS.2A and3A) to partially collapse, which results in the partially collapsed cells212(FIGS.2B and3B-3C). In some embodiments, collapsed cells212have been reduced in size by approximately 50% to 70% compared to cells202.

Referring toFIGS.5A-6B, a non-auxetic article may be converted to an auxetic article. For example, a non-auxetic article may be converted to an auxetic article by collapsing the cells that make up the non-auxetic article.FIGS.5A and5Bshow microscopy images of a non-auxetic foam comprised of cells. The boundaries of each cell comprising the non-auxetic article ofFIG.5Ahave been annotated inFIG.5B.FIGS.6A and6Bshow a microscopy image of an auxetic foam comprised of cells, which have been collapsed. The boundaries of each cell comprising the auxetic article ofFIG.6Ahave been annotated inFIG.6B.

Referring toFIG.3C, in some embodiments, each cell212has a top surface211, which may include an inner portion215and outer portion217. The outer portion217may surround the inner portion215, and the inner portion215may be collapsed compared to the outer portion217. For example, the inner portion215may be collapsed and thus disposed closer to the bottom surface of foam article210compared to outer portion217. In some embodiments, the top surface211of each cell212is concave. In some embodiments, the top surface114of the auxetic foam article104is an uneven surface comprised of a plurality of concave portions.

In some embodiments, foam article200may be converted to auxetic foam article210while being disposed within a mold or partial mold. For example, during the auxetic conversion process, all or a portion of foam article200may be disposed within a mold or partial mold and may be converted to the auxetic foam article210while remaining within the mold or partial mold. In some embodiments, a coating is applied to the top surface114and/or the bottom surface116of the auxetic foam article210to make the top surface114and/or the bottom surface116smooth. In some embodiments, the top surface114and/or the bottom surface116of the auxetic foam article210may be cut and/or sanded to make the surface smooth.

In some embodiments, each cell212may have a surface angle or re-entrant angle α greater than 180 degrees relative to the top surface211. For example, the cells212may have re-entrant angles from approximately 180° to approximately 360°, approximately 210° to approximately 330°, or approximately 240° to approximately 300°. In some embodiments, the re-entrant angle is any angle that results in the auxetic foam article104having a negative Poisson's ratio.

As mentioned above, an “auxetic” is a material or structure that has a negative Poisson's ratio, such that when stretched, the auxetic material becomes thicker (as opposed to thinner) in a direction perpendicular (and/or transverse) to the applied force. In some embodiments, the auxetic foam article210is configured to become thicker (as opposed to thinner, as is the case with the foam article200), temporarily, in response to a localized impact. Referring toFIG.4B, an impact test of a 0.50 inch thick polypropylene auxetic foam article coupled to a crown of a plastic helmet was conducted to illustrate the benefits associated with the auxetic foam article210. The impact testing was again conducted according to the ACH Purchase Description AR-PD 10-02. The impact test revealed that the 0.50 inch thick polypropylene auxetic foam article maintain a peak acceleration below 150 G when the helmet was impacted by a hemispherical impactor. As such, the 0.50 inch thick polypropylene auxetic foam article passed the impact test, and, surprisingly, demonstrated nearly a 100 percent improvement over the 0.50 inch thick polypropylene foam article (which, as discussed above, did not pass the impact test).

In some embodiments, the auxetic foam article210, with a thickness of 0.50 inches, is incorporated into, for example, the helmet100and sufficiently protects a user of the helmet100. For example, helmet100having the auxetic foam article210may provide protection that complies with impact safety standards. Previous impact attenuation systems, such as helmet100, relied on foam articles with thicknesses of 0.75 inches or more in order to comply with impact safety standards, as discussed above with reference toFIGS.2A and3A. However, increasing the size, and thus the weight, of a helmet (even by 0.25 inches) increases the rotational inertia of the helmet, which can lead to an increased risk of brain injury, in addition to being uncomfortable to the user and impairing their situational awareness. As such, while a reduction in thickness of 0.25 inches may seem insignificant, the auxetic foam article210detailed herein, when incorporated into the helmet100, may reduce the rotational inertia of the helmet100, thereby creating an overall safer helmet system. However, auxetic foam article210may be used for a variety of applications such as dental, medical devices, automobiles, transportation, sporting goods, shoes, military equipment, packaging, playground equipment or any other application for providing impact attenuation. In some embodiments, the auxetic articles104may be used to reduce the thickness of helmets while providing impact attenuation. For example, helmets, such as baseball helmets, hockey helmets, football helmets, using the auxetic foam article104may have a thickness less than helmets using non-auxetic material.

Referring toFIG.7A, an example foam article300positioned in an oven305before the auxetic conversion process is initiated, for example, before the application of heat and pressure, is illustrated in accordance with some embodiments. Foam article300may be a polypropylene foam article or a polystyrene foam article. The foam article300may be an example of the foam article200(FIGS.2A and3A). As shown, the foam article300is suspended in an oven305via a hanger307. In some embodiments, the foam article300is suspended by a single point. In other embodiments, the foam article300is suspended by two or more points. The foam article300may be suspended such that it does not contact the walls of the oven305. However, foam article300may be placed within oven305in any manner desired. For example, foam article300may be placed on a surface within oven305. The resulting auxetic foam article310(FIG.7C) may be an isotropic material, if desired. InFIG.7A, the oven305is at or near atmospheric pressure and room temperature. In some embodiments, the oven305is maintained at the desired temperature to prevent having to heat or cool the oven305, which can be time consuming.

Referring toFIG.7B, the auxetic foam article300being heated in the oven305is shown, as indicated by the temperature gauge inFIG.7B. As explained in more detail below inFIG.8, the auxetic foam article300may be heated to a predefined temperature, such as a softening temperature of the article. In some embodiments, heating the auxetic foam article300may occur at least partially under vacuum. In some embodiments, the auxetic foam article300may be subject to a pressure between approximately −14 PSI and approximately 100 PSI and a temperature between approximately 35° Celsius and approximately 150° Celsius. The heating may cause cells202in the closed-cell foam of the article300, which is similar to the foam article200, to soften. The softening of the cells202and the applied pressure allows the cells202to at least partially collapse when the article300is subjected to the pressure, which is a necessary step in the auxetic conversion process. In some embodiments, pressure may be applied in a vacuum to cause the cells202to at least partially collapse.

FIG.7Cshows an example auxetic foam article310, which is obtained by subjecting the article300, where the cells have been softened, to an elevated pressure for a period of time, as indicated by the pressure gauge inFIG.7C. Subjecting the article300to the changes in pressure (increasing or decreasing) causes gas in the cells softened by the heating to at least partially escape from the cells, which transforms the article300into the auxetic foam article310with a plurality of partially collapsed cells, such as the partially collapsed cells212shown inFIGS.2B and3B-3C. For example, the foam article300ofFIGS.7A and7Bmay be converted into the auxetic foam article310ofFIG.7Cas a result of an auxetic conversion process. ComparingFIGS.7A and7BwithFIG.7C, the auxetic foam article310may shrink relative to the size of the foam article300as a result of the auxetic conversion process. The shrinkage of the auxetic foam article310may be attributed to the cells of the foam article300partially collapsing during the pressurizing step shown inFIG.7C. In some embodiments, the auxetic conversion process results in a material undergoing the auxetic conversion process, such as the foam article300, having a negative Poisson's ratio. The auxetic conversion process may result in converting the foam article300into the auxetic foam article310having a Poisson's ratio of less than 0 to approximately −1. For example, the auxetic conversion process may result in creating the auxetic foam article310having a Poisson's ratio between 0 and −1, −0.1 and −0.8, and −0.3 and −0.6.

Referring toFIG.8, a flowchart showing a method400of converting a non-auxetic foam article into an auxetic foam article is illustrated. The foam article may be a polypropylene foam article, a polystyrene foam article, or any other type of foam article. For example, a polypropylene foam article may be converted into a polypropylene auxetic foam article. By way of another example, a polystyrene foam article may be converted into a polystyrene auxetic foam article. The non-auxetic foam article may be an example of the foam article200/300, while the auxetic foam article may be an example of the auxetic foam article210/310. As such, the auxetic foam article formed from the method400may be 0.5 inches thick and configured to maintain a peak acceleration below 150 G (preferably 130 G) when subjected to a localized impact (e.g., a localized impact of 25 J to 100 J). In some embodiments, the auxetic foam article formed from the method400may have a thickness between approximately 0.5 inches and 1 inch and may be configured to maintain a peak acceleration below 300 G when subjected to a localized impact.

The method400in step402includes providing a non-auxetic article that is a closed-cell foam. In some embodiments, the article is one of polypropylene or polystyrene. The foam article may have a density between approximately 1.0 lb/ft′ to approximately 10.0 lb/ft3as indicated in step404. In some instances, the article is referred to herein as an expanded polypropylene (EPP). In some other embodiments, the method400may include providing a polyethylene article that is a closed-cell foam, a polystyrene article that is a closed-cell foam, or other similar types of closed-cell foam articles. In some embodiments, the article provided is an isotropic material. In some other embodiments, the article provided is an anisotropic material. In some embodiments, the article provided has a thickness between 0.125 inches and 3 inches. The article provided may have various widths and lengths, such as at least 2 inches wide and at least 2 inches long. In some embodiments, step404includes step404and the non-auxetic article has a density between approximately 1.0 lb/ft3and 10.0 lb/ft3.

The method400also includes step406of placing the article in an oven, such as oven305, to prevent contact between the article and walls of the oven. The oven305may be a vacuum oven and/or a pressure vessel, such as an autoclave. For example, the oven305may be a pressure vessel configured to apply an elevated pressure and a pressure above atmospheric pressure. However, oven305may be configured to apply a negative pressure and a pressure below atmospheric pressure. In some embodiments, the article is suspended within the oven305by one or more points. For example, with reference toFIG.7A, the article300is suspended away from the walls of the oven305by the hanger307. In some other embodiments, the article may be suspended by other means, such as multiple hangers, hooks, strings, slip surfaces, particle beds, etc., or the article may be suspended in a liquid.

The method400includes step408of heating the article, such as article300, for a first period of time. Stated differently, when placed in the oven305in step406, the oven305is at an initial temperature, such as room temperature or a first desired temperature, as shown inFIG.7A. In some embodiments, the oven305is maintained at a constant temperature. However, a temperature inside the oven305may be increased from the initial temperature to a second desired temperature and may be held at that second desired temperature for a period of time. The heating of the article at step408causes cells, such as cell202inFIG.2, in the closed-cell foam of the article to soften. The first period of time may range from 5 minutes to 45 minutes. For example, the first period of time may be between 5 minutes and 45 minutes, 10 minutes and 40 minutes, 15 minutes and 35 minutes, or 20 minutes and 30 minutes. In preferred embodiments, the first period of time is between 10 minutes to 20 minutes. The first period of time is selected so that the material has a uniform internal temperature, which ensures that the cells collapse in a uniform fashion in step414.

In some embodiments, step408of heating the oven305includes step410of heating the article placed within the oven305to a temperature between approximately 100° Celsius to approximately 220° Celsius, including all integer Celsius values and ranges there between. In some embodiments, heating the oven305in step408includes step412of heating the article placed within the oven to a temperature between approximately 120° Celsius to approximately 140° Celsius, including all integer Celsius values and ranges there between. In some embodiments, the polypropylene article has a softening temperature, which can be determined through experimentation before the steps of the method400shown inFIG.8. In such instances, heating the oven305may involve heating the article to the softening temperature, and holding the article at its softening temperature for the predetermined period of time. In some embodiments, the article may be heated to a softening temperature between approximately 35° Celsius and 150° Celsius and may be held at the softening temperature for between approximately 5 minutes to 60 minutes.

The method400includes, after the first period of time has elapsed, step414of pressurizing the oven305containing the article placed therein for a second period of time, such as when air is evacuated from the oven305. For example, the oven305may be under a vacuum and a pressure may be applied. In some embodiments, a pressure above atmospheric pressure is applied. However, a pressure below atmospheric pressure may be applied. During step406of placing the article within oven305and step408of heating, the article is subjected to an initial pressure as shown inFIGS.7A and7B. In some embodiments, the initial pressure is between approximately −14 PSI and approximately 0 PSI. After step408of heating, a pressure inside the oven305is adjusted, such as increased or decreased, from the initial pressure to a desired pressure and at step414is held at that desired pressure for a second period of time, as shown inFIG.7C. In some embodiments, the desired pressure is between approximately −14 PSI and 200 PSI. The second period of time may range from 30 seconds to 30 minutes. However, the second period of time may be greater than 30 minutes. For example, the second period of time may be dependent on the size of the article and may be greater than 30 minutes for larger sizes of the article. In some embodiments, the second period of time is between 30 seconds and a sufficient amount of time for the article to reach a homogenous temperature throughout the entirety of the article. The second period of time may be between 30 seconds and 60 minutes, between 1 minute and 55 minutes, between 5 minutes and 40 minutes, or between 10 minutes and 30 minutes. In preferred embodiments, the second period of time is between 2 minutes and 7 minutes. The pressurizing at step414may cause cells to collapse by the heating at step408. For example, the heating at step408may result in the gas at least partially escaping from the cells, which transforms the article into an auxetic foam article with a plurality of partially collapsed cells, such as the partially collapsed cells212inFIGS.2B and3B-3C.

In some embodiments, step414of pressurizing the oven305includes subjecting the article placed within the oven305to a vacuum pressure between approximately 16 kPa to approximately 100 kPa, including all integer pressure values and ranges there between. In some embodiments, step414of pressurizing the oven305includes subjecting the article placed within the oven305to a vacuum pressure between approximately 50 kPa to approximately 95 kPa, including all integer pressure values and ranges there between. In some embodiments, step414of pressurizing the oven305includes subjecting the article placed within the oven305to a vacuum pressure between approximately 80 kPa to approximately 88 kPa, including all integer pressure values and ranges there between. In some embodiments, step414of pressurizing the oven305includes subjecting the article placed within the oven305to a pressure between 10 kPa and 1000 kPa. For example, the article contained within in oven305may be pressurized to between 10 kPa and 1000 kPa, 50 kPa and 900 kPa, 150 kPa and 800 kPa, 250 kPa and 750 kPa, or 350 kPa and 700 kPa. In some embodiments, the oven305is pressurized to a pressure multiple times atmospheric pressure. In some embodiments, step414of pressurizing the oven305includes subjecting the article placed within the oven305to a vacuum pressure, while heating the oven305includes subjecting the article placed within the oven305to an elevated temperature. In some embodiments, a magnitude of the pressure may be inversely related to a magnitude of the elevated temperature. For example, an increase in the pressure may result in a decrease of the temperature within the oven305. However, an increase in the pressure may result in an increase in temperature within the oven305.

The method400further includes step420which occurs after the second period of time has elapsed. Step420may include ceasing pressurization of the oven305or adjusting the pressure to a pressure above atmospheric. For example, step420may include releasing a vacuum applied to oven305. The method400also includes step422of cooling the auxetic foam article placed within the oven305for a third period of time. The third period of time may range from 5 seconds to 50 minutes. However, the third period of time may be greater than 50 minutes. For example, the third period of time may be dependent on the size of the article and may be greater than 50 minutes for larger sizes of the article. In some embodiments, the third period of time is between 5 seconds and a sufficient amount of time for the article to reach a homogenous temperature throughout the entirety of the article. For example, the third period of time may be between 5 seconds and 50 minutes, 30 seconds and 45 minutes, 1 minute and 40 minutes, 5 minutes and 35 minutes, 10 minutes and 30 minutes, or 15 minutes and 25 minutes. In preferred embodiments, the third period of time is between 25 minutes and 35 minutes. The cooling of step422may cause a structure of the plurality of partially collapsed cells of the auxetic foam article to become fixed. In some embodiments, releasing the vacuum of step420causes room temperature air to rush back into the oven305, which provides a convective cooling effect. In some embodiments, step420is where the auxetic conversion of the article300occurs.

In some embodiments, step422of cooling the auxetic foam article involves exposing the auxetic foam article to a temperature below room temperature. Alternatively, step422of cooling the auxetic foam article may involve exposing the auxetic foam article to room temperature. The auxetic foam article may remain within the oven305during the cooling and may remain within the oven305during the heating at step408and the pressurizing at step414. In some embodiments, the third period of time is reduced by subjecting the auxetic foam article to artificial cooling means, such as by fans, cooled air, liquid nitrogen bath, etc. In some embodiments, step422of cooling the auxetic foam article occurs before step420or simultaneously with step420. For example, the auxetic foam article may be cooled prior to releasing the pressure.

In some embodiments, the foam article undergoes an isotropic auxetic conversion when transformed into the auxetic foam article due to the polypropylene foam article being placed within the oven305. In embodiments where the foam article is an isotropic material, the auxetic conversion maintains the isotropic nature of the foam article in the auxetic foam article. In some embodiments, one or more tools/molds are attached to the foam article placed within the oven305. The one or more tools/molds are used to impart a desired geometry to the auxetic foam article, such as the convex and/or concave geometries discussed above with reference toFIG.1C.

Referring toFIGS.7A-7C, the auxetic foam article created may have an increased resistance to localized impacts, relative to a resistance to localized impacts of the foam article. For example, the auxetic foam article, such as article104ofFIG.1A, produced by the method400may maintain a peak acceleration below 200 G, or preferably 150 G, when subjected to a localized impact (e.g., a localized impact of 25 J to 100 J). In some embodiments, the auxetic foam article104-A is configured to dissipate a force from a localized impact such that a peak acceleration transferred to an object covered by the auxetic foam article104-A, such as user's head wearing a helmet having the auxetic foam article104-A disposed within, remains below 150 G, preferably 130 G. In this example, the localized impact contacts the helmet100at a location of the auxetic foam article104-A. The other auxetic foam articles104discussed inFIGS.1A-1Care designed to perform in the same fashion as the auxetic foam article104-A.

The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof.

Further, to the extent that the methods of the present invention do not rely on the particular order of steps set forth herein, the particular order of the steps should not be construed as limitation on the claims. Any claims directed to the methods of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the steps may be varied and still remain within the spirit and scope of the present invention.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.