Rate responsive, stretchable devices further improvements

Rate-dependent, elastically-deformable devices according to various embodiments can be stretched and recovered at low elongation rates. Yet they become stiff and resistive to stretching at high elongation rates. In one embodiment, a rate-dependent, elastically-deformable device includes an elastically-deformable confinement member; one or more filaments placed inside the elastically-deformable confinement member; and a fluid that substantially fills the remaining volume inside the elastically-deformable confinement member. The resistance force to extension of the device is designed to increase as the extension rate of the device increases. At low elongation rates the filaments can readily slide past each other. At high elongation rates, the fluid transforms to a less flowable material that greatly increases the force and energy required for elongation; or transforms to a non-flowable material that resists elongation. The devices thus can be stretched and recovered at low elongation rates, but become extremely stiff and resistive to stretching at high elongation rates.

BACKGROUND OF THE INVENTION

Field

Embodiments of the present invention generally relate to elastic or resilient mechanical devices, and in particular to rate-dependent, elastically-deformable devices.

Description of Related Art

Springs and elastic bands are used in a range of mechanical and assistive devices to provide resilient elastic force. For example, knee braces typically made out of stretchable fabrics or external linkages permit some motion to the knee, but do not effectively restrict rapid motions that can lead to injury. Many joint injuries are associated with rapid twisting and translations of limbs and joints, such as slipping, stepping in a hole, landing from a jump, or planting a foot while changing direction. In fact, musculoskeletal injuries (i.e. twisted knees, ankles, and back injuries) account for 82% of lost time among military personnel. Many of these injuries are associated with dynamic activities such as airdrops or jumping out of vehicles. These injuries may be further exacerbated by the approximately 100 lbs of weight in additional equipment that a soldier or warfighter may be wearing or carrying.

SUMMARY OF THE INVENTION

Rate-dependent, elastically-deformable devices according to various embodiments can be stretched and recovered at low elongation rates. Yet they become stiff and resistive to stretching at high rates.

In one embodiment, the rate-dependent, elastically-deformable device includes an elastically-deformable confinement member; one or more filaments placed inside the elastically-deformable confinement member; and a fluid that substantially fills the remaining volume inside the elastically-deformable confinement member. The resistance force to extension of the device is designed and configured to increase as the extension or elongation rate of the device increases. At low rates the filaments can readily slide past each other. At high rates, the fluid transforms to a less flowable material that greatly increases the force and energy required for increased elongation; or transforms to a non-flowable material that resists further elongation.

The elastically-deformable confinement member may be formed of rubber, silicone, elastomer, fluoroelastomer, urethane, natural latex, synthetic latex, polymer, or thermoplastic elastomer, for example. In some embodiments, the elastically-deformable confinement member is a stretchable tube, which may be approximately 0.01-100 mm in diameter in an initial undeformed state. Moreover, the elastically-deformable confinement member may include spiral wound material or folded material in order to facilitate elastic deformation. The elastically-deformable confinement member might further include material or one or more layers or additives to prevent puncturing by the enclosed filaments. The fluid is contained inside the elastically-deformable confinement member by means of crimps, plugs, barbs, melted ends, heat-crimped ends, glue and/or adhesives to name a few examples. Ends of the elastically-deformable confinement member may be able to engage and/or may further include an end effector for attaching to an object external to the device. The end effector may include, for instance, a crimp, clamp, spring clip, threaded fastener, snap-on fastener, glue and/or adhesive.

The one or more filaments may be formed, for instance, of steel, polymer, glass, or carbon. They can be approximately 0.001-10 mm in diameter, and can be monofilament or multifilament, twisted, untwisted or braided. In some embodiments, the one or more filaments are flat, flexible elements. Also, the filaments may include a helical shape; a wavy shape; a square shape; a triangular shape; a sawtooth shape; or a sinusoidal shape; and/or at least one crimp, barb, bump, or ridge, to further encourage interaction during shear. Ends of the one or more filaments can be modified to inhibit puncturing through the confinement member, where the filament end modifications may include rigid, smooth balls; compression sleeves; soft coatings; filament loops; low-friction coatings; and guide bushings or washers. At least one end of the one or more filaments may be attached to the confinement member in some embodiments.

The fluid may be a non-Newtonian fluid, in some embodiments, such as a shear thickening fluid (STF). In some instances, the fluid may comprise a suspension including solid particles in a liquid, with the particles being composed of polymers, ceramics, metals, silica, alumina, titania, clay, calcium carbonate and the liquid being water, an oil, a polymeric liquid, a glycol, a fluorofluid, or glycerin. In other embodiments, the fluid may be an electrorheological fluid, and the device is further configured to provide an electric field to the fluid, or the fluid may be a magnetorheological fluid, and the device is further configured to provide a magnetic field to the fluid.

According to other embodiments, an apparatus may be formed of one or more of rate-dependent, elastically-deformable devices. The apparatus may be configured as an orthotic device, safety equipment, sporting/athletic equipment, robotic assembly, strapping material, or mechanical assembly.

And, according to further embodiments, a rate-dependent, elastically-deformable device includes an elastically-deformable confinement member; one or more filaments placed inside the elastically-deformable confinement member and having one or more plugs integrally formed therewith that are inserted into the ends of the elastically deformable confinement member to contain the fluid; and a fluid that substantially fills the remaining volume inside the elastically-deformable confinement member. Like other embodiments, the resistance force to extension of the device increases as the extension rate of the device increases.

The one or more filaments are configured to (1) provide shear to internal fluid, (2) seal the ends of the elastically-deformable confinement member to prevent fluid leakage, and (3) mechanically couple to the elastically-deformable confinement member.

The elastically-deformable confinement member can form a friction and/or interference fit with the integrally formed plugs of the one or more filaments. The one or more filaments having integrally formed plugs can be formed by cutting them for a single sheet of material. For example, the sheet of material is composed of polymer, metal, rubber, fabric, fiber-reinforced polymer, or fiber-reinforced rubber. More, the one or more filaments may further comprise an integrally formed attachment section, such as a loop, hook, buckle, grommet, or through-hole. The one or more integrally formed plugs are barbed, in some implementations.

According to yet other embodiments, a rate-dependent, elastically-deformable device includes: an elastically-deformable confinement member; one or more filaments placed inside the elastically-deformable confinement member, wherein the one or more of the filaments include a series of discrete positions or steps, which sequentially engage another structure within the elastically-deformable confinement member as the one or more filaments move; and a fluid that substantially fills the remaining volume inside the elastically-deformable confinement member. Again, the resistance force to extension of the device increases as the extension rate of the device increases.

The positions or steps are configured to engage another filament and/or a fixed detent or tooth member fixed to the interior of the elastically-deformable confinement member. The positions or steps are located at regularly-spaced intervals, increasing or decreasing intervals, or irregular-spaced intervals on the one or more filaments. The one or more filaments may include ratcheting structure, ball and socket means, or bristle or line comb elements to provide the series of discrete positions of steps. The one or more filaments have a helical, wavy, sinusoidal, triangular wave, square wave, or sawtooth shape, for instance.

According to further embodiments, a rate-dependent, elastically-deformable device includes: an elastically-deformable confinement member; a pair of opposing filaments placed inside the elastically-deformable confinement member, with one end of each of the pair attached to opposite ends of the elastically-deformable confinement member and the other end of the each of the pair unattached to the elastically-deformable confinement member; and a fluid that substantially fills the remaining volume inside the elastically-deformable confinement member. In this embodiments and others, the resistance force to extension of the device changes as the extension rate of the device changes. When the elastically-deformable confinement member is in an undeformed state, the filaments at least partially can overlap one another, in some instances. In the devices, the filaments can be configured as cables or ribbons. The cable filaments have a small cross-sectional shape (e.g., cylindrical) and are capable of intertwining with each other, and the ribbon filaments have a generally flat cross-sectional shape and are incapable of intertwining with each other. The elastically-deformable confinement member has anisotropic properties. The elastically-deformable confinement member has a higher resistance to radial extension compared to its resistance to longitudinal extension. The fluid might be a Non-Newtonian fluid, non-shear thickening fluid. These fluids may include, for example, a shear thinning, thixotropic, rheopectic, a Bingham, viscoplastic, or viscoelastic fluid.

According to additional embodiments, a rate-dependent, elastically-deformable device includes: an elastically-deformable confinement member; one or more filaments placed inside the elastically-deformable confinement member; and a shear-thickening fluid that substantially fills the remaining volume inside the elastically-deformable confinement member, the shear-thickening fluid comprising a suspension of non-spherical solid particles in a liquid. The resistance force to extension of the device increases as the extension rate of the device increases. The non-spherical solid particles might have an aspect ratio of about 2:1 or more. And they might comprise precipitated calcium carbonate (PCC) particles, for instance.

Further embodiments can provide apparatuses that include one or more rate-dependent, elastically-deformable devices, which mechanically couple a body-worn device to the body of the individual wearing the apparatus. The body-worn device might be a slip-on glove and the one or more devices are positioned in the glove to encircle the wrist region when worn by the individual and configured to be expended over the hand and wrist when the individual puts on or takes off the glove. Or the body-worn device might be a slip-on shoe or boot and the one or more devices are positioned in the shoe or boot to encircle the ankle region when worn by the individual and configured to be expended over the foot and ankle when the individual puts on or takes off the shoe or boot.

These and other embodiments are further discussed below.

DETAILED DESCRIPTION

Rate-dependent, elastically-deformable devices according to various embodiments can be stretched and recovered at low elongation rates. Yet they become stiff and resistive to stretching at high elongation rates.

FIGS. 1(a)-1(c)illustrates one rate-dependent, elastically-deformable device10and its operation in accordance with one embodiment of the present invention. These figures show a cross-sectional cut-away view along the length of the device10. In general, the rate-dependent, elastically-deformable device10includes an elastically-deformable confinement member1which houses one or more filaments2, as well as a fluid3which substantially fills the remainder interior volume of the confinement member1. The fluid3is sealed within the confinement member1by a crimp seal4. The device10is configured to elongate or otherwise stretch by the application of an external tensile force applied at its ends.

The resistance force to extension of the device1is designed and configured to increase as the rate of extension or rate of elongation of the device10increases. The extension rate or elongation rate of the device can be expressed, for example, as a relative elongation of the device as a function of time or the speed/velocity of the device at one of its ends which displaces with respect to the other. These rates may be measured in units such as meters/sec, inches/sec, mm/sec, etc., although the extension or elongation rate might also be expressed as a dimensionless strain value (e.g., elongation of the device normalized by the initial device length) as a function of time. This may be expressed in units of s−1. Other conventions might also be used for extension or elongation rates. It should also be appreciated that the terms low-rate elongation and high-rate elongation as used herein may be relative to a particular embodiment or application. Put another way, what may be a low rate of elongation for one application may not be a low rate of elongation for another application. Similarly, what may be a high rate of elongation for one application may not be a high rate of elongation for a different application. Thus, a key feature of the innovative technology is the ability to judiciously tailor or otherwise configure the elongation rate response of individual devices to any particular application.

FIG. 1(a)shows the device10in an initial undeformed state with no external tensile force applied. The elastically-deformable confinement member1may be formed of rubber, silicone, elastomer, fluoroelastomer (such as sold under the tradename Viton®), urethane, natural latex, synthetic latex, thermoplastic elastomer, polymer, or the like, which generally are elastic and resilient and capable of confining a fluid therein. Latex may be stretchier than some of the other materials, but is also more porous to certain materials. The fluid3may be confined to interior of the elastically-deformable confinement member1by crimps, plugs, barbs, melted (heat-crimped) ends, glues or adhesives (such as thermoplastic or thermoset resins) provided at the ends of the elastically-deformable confinement member1.

In one embodiment, the elastically-deformable confinement member1may be formed of a stretchable elastic tube. The use of an elastic tube enables flexibility of the device10in multiple directions. For some applications, the tube may have an inner diameter of about 0.01-100 mm, or more preferably 0.1-10 mm in an initial undeformed state. The tube may generally have a circular cross-sectional shape for many applications, but it should be appreciated that other cross-sectional shapes are also possible, such as rectangular, square, hexagonal, etc.

The elastically-deformable confinement member1might also be formed into a planar shape, for example, formed by sealing the edges of two sheets of elastomeric materials to form an elastomeric membrane. This elastomeric body could be shaped like a square sheet, round membrane, or arbitrarily-shaped body. An array of filaments2could be enclosed in this elastomeric body, and with the filaments aligned in parallel, orthogonally, or in any arbitrary combination of in-plane orientations. The precise shape of the body and the orientation of the filaments2will be dictated by the application. It should be appreciated that other stretchable configurations are also possible. For instance, the outer confinement member1could be formed (or partially formed along its length) of spiral wound or folded material which can elongate linearly when stretched, like a bellows, for example.

To prevent puncturing by the enclosed filaments2, the elastically-deformable confinement member1may formed of a reasonable thickness whether formed of one layer or formed of multiple layers. Wire mesh or fibers might further be incorporated into the walls of the elastically-deformable confinement member1for this purpose. In addition, to enhance sliding of the filaments2relative to the elastically-deformable confinement member1, interior surfaces of the elastically-deformable confinement member1may be further provided with a low-friction coating or layer of material, such as Teflon®.

The filaments2may include be formed of wire, cable, ribbon, band, thread, cord or the like, of steel, polymer, glass, carbon or other appropriate material for this purpose. The filaments2may be flexible to provide flexibility of the device10as well, but need not be flexible for all embodiments. The filaments2may be monofilament or multifilament, twisted, untwisted or braided. In one embodiment, the filaments are flat, flexible elements, such as ribbons. And a pair of ribbons may be provided with ones of the pair being connected to opposite ends of the elastically-deformable confinement member1in some instances. The ribbons may be formed of strip-shaped materials formed of nylon or metal, for example. There are certain advantages to using flat ribbons including (i) there is more shear area between a pair of ribbons, as compared to a pair of round cables, so that higher force resistance to elongation is possible, and (ii) ribbons can be stiffer than cables so the ribbon-based device recovers from its stretched state (i.e. relaxes) faster than a cable-based device.

In the preferred embodiment, one end of each and every filament2may be coupled to the elastically-deformable confinement member1, preferably at or near its ends. To this end, the filaments2may be mechanically and/or adhesively coupled to the confinement member1. For mechanical attachment, a crimp, clamp, spring clip, threaded fastener, snap-on fastener, stitch, and/or the like may be used.FIGS. 1(a)-1(c)illustrate the device10having filaments2coupled to the ends of the elastically-deformable confinement member1by a crimp seal4. For adhesive coupling, various thermosetting or thermoplastic (heat-setting) glues and adhesive may be used, including hot-melt, urethane, silicone, epoxy, acrylate, or the like, as some examples. If the filaments2are themselves readily stretchable or elastic, both of their ends could be coupled to opposite ends of the elastically-deformable confinement member1so as to stretch along with the elastically-deformable confinement member1.

In another embodiment, one or more filaments2in the device could be unconstrained to the confinement member1. These filaments would be freely floating in the device, but would provide some mechanical or viscous coupling to other filaments2during device extension.

End effectors (not shown) may be coupled to or otherwise provide mounting points on the ends of member1which may used to connect the device10to other systems such as mechanical linkages. Depending on the application, the end effector mounting may be permanent or readily removable. Such end effectors may include, for instance, threaded attachment (e.g., via screws or eyehooks), clips, clasps, buckles, snaps, buttons, straps, knots, stitches/stitching, staples, hooked fasteners, clamps, cotter pins, nails, glue/adhesives, or the like.

For some applications, the filaments2may have an outer diameter of about 0.01-10 mm in diameter, or more preferably 0.1-1 mm. Smaller and larger filaments might also be used for other applications. In order to inhibit their puncturing through the outer confinement member1, the filaments2, and particularly their ends, may be modified. For example, filament modifications may include rigid, smooth balls; soft coatings; filament loops; low-friction coatings; guide bushings or washers; chamfering; or compression sleeves. Grinding, sanding, or soldering may also be used to blunt or dull the tips the filaments2to inhibit puncturing through the confinement member1.

Generally speaking, the filaments2should have some degree of stiffness for effective operation of the device10. For example, the filaments2may be “push-pull” cables. By push-pull, it is meant that the filament2can readily be pushed and pulled through the fluid3. Most filaments are sufficient to be pulled through a fluid because the drag between the filament and fluid tends to keep the filament in a state of tension generally unfurling the filament. However, when pushed through the fluid, the viscosity of the fluid tends to keep the filament in a state of compression. Thus, a very thin flexible thread might not be an effective filament because it may buckle, ball-up, or tangle-up due to compressive forces between the filament and the fluid when the device retracts. To increase shearing of the fluid3, the filaments2may further include one or more crimps, barb, ridges, waved surfaces (e.g., square, triangular, sawtooth or sinusoidal shaped surfaces), etc. Also, the filaments2might be arranged in a helical (or “corkscrew”) arrangement to encourage entanglement.

One important aspect of the invention is that the resistance force to extension of the device changes, and in particular, increases as the extension rate of the device increases through the use the fluid3. The fluid3may be selected so as to change its rheological properties as the rate of extension of the device changes. For example, the device10may be designed so as to have a predetermined threshold rate of extension in which such a change occurs. Thus, at low rates below the threshold, the filaments2can readily slide through the fluid3and/or past each other. Yet at high rates above the threshold, the fluid3transforms to a more rigid material or higher viscosity fluid which greatly reduces or prevents movement of the filaments2through the fluid3and producing a stiff linear element. Put another way, the device10may be thought of as being easily stretchable at low elongation rates, but “stiffens” or “locks up” (i.e., rigidly resists or substantially prevents any further deformation) when pulled quickly at high elongation rates.

The fluid3substantially fills the remaining volume inside the elastically-deformable confinement member1once the filaments2are installed therein. The fluid3may be a Newtonian or non-Newtonian fluid. Newtonian fluids have a viscosity that may change with temperature, but do not change with the strain rate. By contrast, non-Newtonian fluids have a viscosity that changes with the strain rate which may enable devices to be more tailored for certain operational performance.

In some embodiments, fluid3may be a shear thickening fluids (STFs). STFs, one type of non-Newtonian fluid, are materials that flow like a liquid at low deformation rates, but become highly resistant to flow at high deformation rates. Exemplary thickening fluids which may be used in accordance with the embodiments of the present invention are disclosed in Norman J. Wagner and John F. Brady “Shear thickening in colloidal dispersions,” Phys. Today 62, 27 (2009), herein incorporated by reference. Stretching the device10at low rates does not transition the STF, and the filaments2are free to move through the fluid3and slide past each other. If, instead, the device10is pulled quickly, high shear rates develop between the filaments and the STF material hardens, binding the filaments together and providing high resistance to elongation or a stiff, generally unstretchable device state. Relaxation of the force induces the STF to return to a flowable state, and the device once again becomes stretchable. By using a Newtonian fluid, rather than a true shear thickening fluid, one can get a useful rate-dependent response, although the rate-dependence of the response is not nearly as severe or drastic as devices containing an STF. The ideal rate-dependent response of a device depends on the application. For some applications, severe stiffening may be desirable to “lock” the device and prevent further motion. In other applications, a “locked” response may create an undesirably severe effect; instead, a device that is still extensible, but at considerably higher elongation forces, might be more desirable. The properties of fluid3can be tailored to provide the desired device response.

In some embodiments, the fluid3may be a suspension of solid particles in a liquid (which may also be referred to as a carrier fluid or carrier liquid). For example, the suspension may be formed of colloidal particles generally nano-sized (i.e. 1-1000 nm). Colloidal refers to the fact that the particles are intact solid particles, they may not dissolve in the liquid, and they are generally stabilized in the liquid so that they do not agglomerate, settle, or float to the surface of the liquid system over short periods of time (i.e. they are stable for days, weeks, or longer). However, devices10may be constructed with a fluid3that is a suspension of larger size solid particles (i.e. 10-1000 μm, or even larger), which do not dissolve in the liquid and are generally stable in the liquid too. In these devices, the fluid is technically not a colloid. The term “suspension” as used herein is intended to encompass both colloids and suspensions of larger size solid particles in a liquid.

Depending on the type of particles and liquid, and the desired non-Newtonian response, the solid particles may constitute 10-70% by volume of the fluid3; more preferably, the solid particles constitute 30-60% by volume of the fluid3. For examples, a preferred volume fraction for spherical particles is around 50% by volume; a preferred volume fraction for high aspect ratio precipitated calcium carbonate particle may be as low as 35% The liquid could be water, oil, a polymeric liquid, a glycol, a fluorofluid, or glycerin, for example. The colloidal particles may be composed of ceramics, polymers (such as poly(methyl methacrylate) (PMMA) or polystyrene), or metals. Or, they may comprise of silica, alumina, titania, clay, precipitated calcium carbonate, or ground calcium carbonate. It is believed that precipitated calcium carbonate is more likely to be stable than ground calcium carbonate in some instances. One or more additional additives might also be included in the fluid3which function as stabilizers, emulsifiers, surfactants, pigments, etc. The fluid3may also include gels, gums, and putties.

In other embodiments, the fluid3may be an electrorheological fluid, or a magnetorheological fluid. Electrorheological fluids include a suspension of extremely fine non-conducting particles (e.g., up to 50 micrometers diameter) in an electrically insulating fluid. The viscosity of these fluids can change reversibly (e.g., an order of up to 100,000) in response to an electric field. Magnetorheological fluids include a suspension of fine ferromagnetic particles in a liquid. When subjected to a magnetic field, the fluid greatly increases its viscosity, to the point of becoming a viscoeleastic solid. In the case of using an electrorheological fluid, a voltage may be applied to the fluid3by using a voltage-generating device with opposite electrodes attached to filaments at opposite ends of the device; thus creating an electric field across the fluid3that would trigger a thickening response in the fluid. Similarly, in the case of using a magnetorheological fluid, a magnetic-field-generating device provided in the vicinity of the fluid3(for example, using an electromagnet) generates a magnetic field to the fluid3such that the fluid3can increase in viscosity or transition to a non-flowable state. Suitable microcontrollers, which may include known feedback or feedforward control algorithms, may be further provided to control the voltage-generating device and magnetic-field-generating device thus providing a desired fluid response.

When the device10is subjected to an external tensile force, the elastically-deformable confinement member1elongates, and the one or more filaments2are pulled or dragged through the fluid3as it stretches. The relevant movement of the filaments2through the fluid3creates shearing flow(s) in the fluid3. Some shearing flow may also be created by relevant movement of the fluid3and the interior surface(s) of the elastically-deformable confinement member1and/or within the fluid3itself. The shearing flow of the fluid3creates a force within the device10which tends to resist the external tensile force that is elongating the elastically-deformable confinement member1.

In general, the resistive force due to the shearing flow of the fluid3is largely dependent on the speed or rate of elongation/stretching of the elastically-deformable confinement member1, the surface area of the filaments2, and/or the spacing of the filaments2between one another and the interior surface(s) of the elastically-deformable confinement member1. Other factors may also influence the resistive force, such the cross-sectional shape of the elastically-deformable confinement member1, the shape of the filaments2, and/or the viscosity of the fluid3, for instance.

As illustrated inFIG. 1(b), stretching the device10with an external tensile force FLRin an attempt to impose low-rate elongation does not create sufficient resistance force in the device10, such that the filaments2are free to readily be pulled through the fluid3and/or slide past each other. Here, the elastically-deformable confinement member1has been stretched and the filaments2have been pulled and straightened somewhat and slid past each other. The fluid3remains in a flowable state similar to that of the device10in its initial undeformed state. Upon gradual release of the external tensile force FLR, the elastically-deformable confinement member1tends to return to its initial undeformed shape and length as shown inFIG. 1(a).

On the other hand, stretching the device10with external tensile force FHRin an attempt to impose high-rate elongation, as illustrated inFIG. 1(c), changes the operable characteristics of the elastically-deformable device10. For instance, if the device10is pulled quickly and elongates at a high rate, high shearing rates develop between the elastically-deformable confinement member1, the filaments2and the fluid3. The high shearing rates cause the fluid3to generate a high resistance force in the device10, preventing the filaments2from readily sliding through the fluid3and/or past each other. The elastically-deformable confinement member1has stretched a small amount, and the filaments2have straightened slightly. Due to the high shearing of the fluid3, the fluid3has now transformed into a more rigid-state material3′. The filaments2are no longer free to readily slide past one another. This results in the device10transitioning to a device that is highly resistant to elongation, or becomes so resistant to elongation so as to become unstretchable. The device10will remain in the stiffened state as long as force is being applied to the ends of the device. If the force is relaxed, the fluid3′ will return to a flowable state like fluid3, and the device10will gradually reduce in length back to the initial, undeformed state of the material shown inFIG. 1(a).

In some instances, the velocity of the pulling is adjusted to adjust the action of the device10. That is, imposing low extension-rate velocity VLRor high extension-rate velocity VHR. This has the same effect at pulling with low rate force FLRor high rate force FHR.

FIGS. 2(a)-2(b)show experimental force measurements during elongation of a prototype device stretched at different rates. The elongation rates were 50 mm/min, 500 mm/min, 1,000 mm/mm, 3,000 mm/min and 5,000 mm/min. The device gage length in these experiments was 152 mm, so these deformation rates correspond to strain rates of 0.0055, 0.055, 0.11, 0.33, and 0.55 s−1, respectively.FIG. 2(a)shows a plot of force versus displacement, andFIG. 2(b)shows a plot of force versus time, for these elongation rates.

The force versus displacement plotFIG. 2(a)demonstrates the rate-sensitive response of the device. The liquid here was a STF which was formulated by blending 450-nm-diameter silica and ethylene glycol (EG) at a mass ratio of 1.92 g silica:1 g EG. The STF was dispersed using a rolling jar mixer over a period of 24 hours. The STF was then placed inside a 6.35-mm-ID, 7.9375-mm-OD Viton® tube with nylon end caps and 0.794-mm-diameter stainless steel wire rope with compression sleeves on the end. The tubing was filled with shear thickening fluid by partially clamping one end of the tubing with surgical tubing forceps while slowly pouring the fluid in until the fluid reached the surgical forceps. In some cases, it was helpful to apply low amounts of heat using a heat gun or to inject the fluid using a 3-mL syringe. The surgical forceps were removed and then the tubing was plugged at one end using the nylon plugs with attached wires described above. At this point, the tube was gently massaged to push air bubbles to the top of the tube and more fluid was added in order to fill the void space previously occupied by the air bubbles. Afterwards, the second nylon plug was inserted into the tubing.

The force versus time plotFIG. 2(b)shows that the devices respond very rapidly, with the high rate plateau force reached in less than 100 ms after force application. This rapid response means that there would be very little lag time between application of high elongation rate, and transformation of the device to a more resistive state.

As apparent, at the low elongation rates, the device provides very little resistance to stretching. One the other hand, as elongation rate increases, the resistance to deformation (force values during extension) increases. Comparing the highest rate response to the lowest rate response at 100 ms, the resistive force at high rate is approximately 100× higher than the resistive force at low rate. These particular embodiments of the device show a resistive force that peaks and then plateaus, which could be a beneficial feature of a device. For example, the long plateau force indicates high energy absorption during elongation. Also note that if the device is elongated at high rates, but the available elongation force is less than the plateau force, the device would essentially feel unstretchable and provide a rigid response. Other devices can be engineered with considerably higher resistive forces, and resistive forces that do not plateau but reach a limiting displacement beyond which further elongation would require exceedingly high forces.

The device tested was designed to provide much higher resistance to elongation as the elongation rate increases. But it was not designed to rigidly lock-up at high rates of elongation (rather, some elongation continued at higher rates of elongation just at much higher force). The device nonetheless still appeared to lock-up if the rapidly applied force is less than the plateau force, such as during impulse loading. While rigid locking-up of the device may be useful for some applications, for other applications a rigid locking effect would be too severe a response, and a higher elongation force is a preferred response.

According to various embodiments of the present invention, one or more rate-dependent, elastically-deformable devices may be incorporated into various devices and apparatuses to provide rate-dependent operational performance. For example, in some embodiments, one or more rate-dependent, elastically-deformable devices may be incorporated into an apparatus such as an orthotic device to create rate dependent braces. Exemplary orthotic devices which may be benefited in the manner may include, for example, head and helmet braces, knee braces, ankle braces, back braces, neck braces, wrist braces, slings, and other orthotic devices. The rate-dependent, elastically-deformable devices may also be provided in other wearable equipment, such as shoes, boots, headgear, belts, harnesses, or the like. This technology presents a new approach and, thus orthotic devices that can provide higher resistance to motion during higher speed events which a soldier or athlete may encounter. These new and improved devices will be more effective at resisting unplanned loads and preventing injuries. Many joint injuries associated with rapid twisting and translations of limbs and joints, such as slipping, stepping in a hole, landing from a jump, or planting a foot while changing direction may be prevented. In other embodiments, one or more rate-dependent, elastically-deformable devices may be incorporated into safety equipment, sporting/athletic equipment and goods, robotics, restraints (e.g., seat-belts) and mechanical assemblies. According, various applications, such as, linkages, vehicle suspension systems, robotics, “strapping” (e.g., bungee-type cords, self-tightening straps, etc.) clothing and woven textiles may be benefited. One device might be used as a replacement for a simple Velcro® or an elastic strap.

FIGS. 3-5show examples of various orthotic devices according to embodiments of the present invention. InFIGS. 3(a)-3(b), the orthotic devices are knee braces which are configured to be worn on a person's leg50on the knee55to provide increase support and/or stability for the knee55. The precise number of elongational devices10that are incorporated into the knee braces, and the orientation of these devices relative to knee physiology or desired kinesiology for a given activity or injury risk, could be tailored to a particular application. The knee braces are designed to permit normal walking and other activities, but stiffen and resist deformation during high rate events, like landing from a jump. Moreover, the knee braces provide rate-dependent operational performance not found in conventional braces.

FIG. 3(a)shows an elastic knee brace100according to one embodiment. The knee brace100includes multiple rate-dependent, elastically-deformable devices10that are fastened to, bonded to, woven into, and/or otherwise attached to the body102of the knee brace100. The body102may be formed of a conventional elastic fabric textile, such as sold under the tradename Spandex®. Or the body102may be formed of a rigid or semi-rigid material which comports to the curvature of the leg50or knee55as generally known. When worn, the body102snugly engages the leg50and knee55and holds the knee brace100in place. Adjustment straps (not shown) having buckles or hook and loop type (e.g., Velcro®) fastening may be further included to better couple the brace100to the leg50and knee55. To facilitate incorporation into the fabric of the body102, the devices10may have a small outer diameter, such as 0.1-10 mm.

FIG. 3(b)shows a hinged knee brace200according to another embodiment. The knee brace200body includes an upper portion202worn above the knee55and a lower portion204worn below the knee55. The upper and lower portions202,204are coupled with a pivot206to provide hinged movement of the brace200at the knee55.

The upper and lower portions202,204may be formed of a conventional elastic fabric textile. Or they may be formed of a rigid or semi-rigid material which comports to the curvature of the leg50and knee55as generally known. When worn, the upper and lower portions202,204of the brace200snugly engage the knee55and holds the knee brace200in place on the person's leg50. Adjustment straps (not shown) having buckles or hook and loop type (e.g., Velcro®) fastening may be further included to better couple the brace200to the leg50and knee55.

The knee brace200further include one or more rate-dependent, elastically-deformable devices10which couple to the upper and lower portions202,204of the brace200. As shown, one rate-dependent, elastically-deformable device10externally couples those elements behind in the rear of the knee55. Because of the greater forces the device10may be subject to in this orientation, it may have a large diameter, such as 1-20 mm. The device(s)10stretches freely during normal motion of the hinged knee brace200, but becomes rigid during high rate motions that may cause injury.

The lengths, positions, number, orientations and/or operational characteristics of the devices10in the knee braces100and200are strategically designed to provide optimal support. The devices10incorporated into the braces100or200may have different characteristics. As shown inFIGS. 3(a) and 3(b), the rate-dependent, elastically-deformable device(s)10may be positioned in a generally parallel orientation parallel to the length of the leg50in both of these knee brace embodiments. However, the devices10may be additionally or alternatively oriented generally orthogonally to the length of the leg50, and/or at some angle thereto. Also, the devices10might further be oriented in a “criss-cross shape” or “X-shape” to provide greater lateral support to the knee55. Other configurations are also possible. Under normal walking conditions, the elements of the devices10deform passively and do not resist motion. Under high loading rate, potentially injurious conditions, such as a knee hyperextension or knee twist during slippage, the devices become rigid and greatly limit or preferably prevent further motion of the knee55.

FIGS. 4(a)-4(b)show an ankle brace300and its operation, according to an embodiment. The ankle brace300includes multiple rate-dependent, elastically-deformable devices10that are fastened to, bonded to, woven into, and/or otherwise attached to the body302of the brace300.

The body302may be formed of a conventional elastic fabric textile. Or the body302may be formed of rigid or semi-rigid material which comports to the curvature of the leg50, foot52or ankle54as generally known. When worn, the body302snugly engages the leg50, foot52and ankle54and holds the ankle brace300in place. Adjustment straps (not shown) having buckles or hook and loop type (e.g., Velcro®) fastening may be further included to better couple the brace300to the leg50, foot52and ankle54. These devices10enable low rate extension but prevent higher rates of extension and rotation of the ankle brace300.

FIG. 4(a)shows a situation of a person walking normally over an inclined surface I. In this situation, the person's foot52(on the left) needs to rotate slightly with respect to the person's leg50for traction and balance. In this situation, the ankle brace300is configured to permit a low rate of inversion of the ankle54and foot52which is typically expected for walking. During the normal gait cycle, the foot both pronates and supinates. Pronation is a combination of three ankle movements, abduction, eversion, and dorsiflexion, while supination is combination of adduction, inversion, and planar flexion. When the foot hits the ground, the ankle pronates to absorb the shock, and when it pushes off, the ankle supinates.

FIG. 4(b)shows a situation of a quick, abrupt drop onto an inclined surface I. It is noted that alike elements to those inFIG. 4(a)are shown here, and will be referenced. Typically, in this situation, the person is not expecting this drop. This may occur for example when one inadvertently steps off a curb. And, because the person is not expecting the drop, the high rate of ankle inversion associated with the landing onto the incline surface I ordinarily (without the aid of the ankle brace300) may cause injury to the person, such as an ankle sprain, or worse yet, possibly a break. It is noted that 70-80% of typical ankle sprains are caused by ankle inversion, whereas a smaller percentage is caused by ankle eversion. But, by wearing ankle brace300, the ankle brace300advantageously resists the high rate of ankle inversion to reduce injury in this situation.

FIGS. 5(a)-5(b)show a head and neck restraint device400according to an embodiment. The person500shown here may be a soldier or warfighter wearing military equipment, such clothing15, a helmet20, a facemask25(e.g., having goggles and face guard), and protective vest30(shown inFIG. 5(a)only).

The head and neck restraint device400couples between to person's head and shoulders. As shown inFIG. 5(a), the device400couples between the helmet20and shoulder portions of the protective vest30via mounting points35. Or, as shown inFIG. 5(b), head and neck restraint device400′ couples between the helmet20and shoulder portions of the clothing15via mounting points35. The mounting points35may include clips, clasps, buckles, snaps, buttons, straps, knots, stitches, hooked fasteners, clamps, or other end effectors, for example. The device400further includes one or more rate-dependent, elastically-deformable device(s)10. A pair of devices10is shown in the figures here positioned axially, one on each side of the person's head. This design is not to be considered limiting; other embodiments can be envisioned that use more devices, different orientations, and different fixturing. For instance, multiple devices10might be positioned axially around the entire neck in an orthotic device similar to a neck brace. Also, one or more devices10may be provided in a radial orientation, additionally or alternatively, to resist head turning or lifting motion at high rates also.

During normal operation, the devices10are free to stretch and do not resist head motion. Under high rate events, such as a blast event or a secondary impact when a soldier is thrown into a wall or vehicle interior, the devices10become stiff and resist extension. Under the latter conditions, loads to the helmet20are transmitted directly to the shoulders, rather than to the head and neck. By reducing head and neck loads, the risk of injury is significantly reduced. A similar head- and neck-protective device is further envisioned for contact sports applications, such as for football, hockey or lacrosse helmets in order to reduce the likelihood of concussions during impact.

FIGS. 6(a)-(e)show rate-dependent, elastically-deformable device(s)10′ according to other embodiments of the invention. These figures show a cross-sectional cut-away view along the length of the device(s)10′. The device(s)10′ here are shown in their initial undeformed state, but are configured to elongate or otherwise stretch by the application of an external tensile force through their ends, similarly to as shown inFIGS. 1(a)-1(c).

As shown inFIG. 6(a), the rate-dependent, elastically-deformable device10′ includes an elastically-deformable confinement member1′ which houses one or more filaments2′, as well as a fluid3which substantially fills the remainder interior volume of the confinement member1′. Filaments2′ may be formed of are flexible, flat, stiff filaments, such as nylon ribbons. They may have a rectangular cross-section in some embodiments. To confine fluid3′ inside the elastically-deformable confinement member1′, plugs5may be used. The elastically-deformable confinement member1′ may be formed of tubing may have overall length of about 6-in and an outer diameter of about 5/16-in. The filaments2′ may have a length of 4.75-in. The plug5may have a diameter of about 0.3175-in to provide a frictional or interference fit with the confinement material tubing1′. The plugs5seal the ends of outer confinement member1so as to maintain the liquid3therein. Preferably, this is a hermetic seal to prevent evaporation and/or outgassing, as well as prevent the ingress and egress of dirt, debris, moisture, and contaminants which could contaminate the liquid3′ and impede operation of the device10′. The plugs5also may serve as an attachment point for the filaments2′; for example, the plugs may be hollow in the barbed section, so that one end of the filament can be placed in the hollow section, then adhesive can be poured into the plug to permanently attach the filament end to the nylon plug. Furthermore, the outside end of the plug5provides a convenient mounting or attachment point for other hardware (e.g., end effectors) for coupling the device10to other bodies.

FIG. 6(b)shows compression sleeves6placed on the ends of the internal filaments to prevent puncture of the filament2′ ends through the walls of the tubing1′.FIG. 6(c)shows a plurality of compression sleeves6placed not only at the ends but along the length of the filaments2′ to increase the surface area of the filament2′ and/or to increase shearing of the fluid3′.FIG. 6(d)shows elastic recovery components7connected to the end of the opposite filaments2′, which serves to decrease recovery time for the device10′ to return to its initial undeformed state. The elastic recovery components7may be springs or elastic filaments, for example.

FIG. 6(e)shows an inextensible rigid filament8used to limit ultimate extension of the device (i.e. to serve as a “hard stop”). The ends of the hard stop8may be attached to the plug5at location9by adhesive, for example.

FIG. 7shows a modified embodiment of the plug5′ illustrated inFIGS. 6(a)-6(e). The plug5′ may include a central body portion5a, a tapering enlarged diameter front portion5b, and reared flange portion5c. The front portion5b, also known as a barbed portion, is adapted to be inserted into the ends of the elastically-deformable confinement member1′ to confine fluid3therein. The enlarged diameter being slightly larger than that of the elastically-deformable confinement member1′ may facilitate a friction or interference fit, for instance. Glue or adhesive may be further provided to additionally couple the plug5′ to the elastically-deformable confinement member1′. In some instances, the central body portion5amay include “flats” on its exterior sidewalls to resist or limit rotational movement of the plug5′ when it is inserted into the elastically-deformable confinement member1′. An axial bore5dis provided through the body portion5aof the plug. The diameter of the bore5din front of the flanged front portion5cis slightly larger than the diameter of the head11bof the threaded fastener11. However, the diameter of the bore5dthrough the flanged portion5cis slightly larger than the diameter of the threaded portion11a, but slightly less than the diameter of the head11b. As such, the threaded portion11aof the fastener can be inserted into the axial bore from the front side to the rear side, with the head of the fastener engaging an inner wall of the bore5dat the flange where the diameter of the bore changes. The nut12can be threaded onto the threaded portions11aof the threaded fastener from the rear of the plug so as to trap and fix the threaded fastener11to the plug5′.

FIG. 8shows a rate-dependent, elastically-deformable device10″ having an integrated barbed ribbon filament2″ according to further embodiments of the invention. Here, the integrated barbed ribbon filament2″ is used to both seal ends of the elastically-deformable confinement member1and provide internal shearing of the liquid3in the device. The barbed end also serves the important role of mechanically coupling the ribbon filament2″ to the elastically-deformable confinement member1. The mechanical attachment of the filaments2″ to the elastically-deformable confinement member1may be a friction and/or inference fit (e.g., with ends of member1expanding over the ends of integrated barbed ribbon filament2″). The liquid3is contained in the elastically-deformable confinement member1by the integrated barbed ribbon filament2″ itself. To further prevent leakage of the liquid3, the attachment may be aided by adhesively bonding with suitable sealant, glue, or adhesive13, for example.

This structure offers a number of performance and manufacturing advantages relative to the previous embodiments which includes a two-part barbed fitting5with filament2structure (see, e.g.,FIGS. 6 and 7). For instance, because no adhesive bond is needed to join the filament and plug, so there is no risk of adhesive failure at that junction. Also, this eliminates a time-consuming manufacturing step, i.e., gluing the plug to the filament, thus, making manufacturing quicker and easier. The overall device form factor is flatter, which makes it more straightforward to integrate for many strap applications and especially clothing and body-worn applications.

The integral barb and filament structure2″ can be cut from a single sheet of material using a variety of techniques, such as laser cutting and water-jet cutting, which are rapid and low cost. Using sheet-cutting techniques such as laser-cutting or water-jet cutting enables low-cost, detailed control over the ribbon thickness, ribbon length, barb geometry, etc. (rather than having to rely on off-the-shelf injection-molded plugs).

FIG. 9(a)shows one exemplary integrated barbed ribbon filament2″. It includes an attachment section2″a, barbed section2″b, and main ribbon section2″c. The structure2″ may also integrate fastening section2″dshown at the attachment section2″awhich aids in mechanical fastening to other components. The thickness, width, and length of one particular filament structure2″, as well as the details of the barbed section2″bgeometry, are shown. This particular embodiment is configured for a device enclosed within a 15-cm-long piece of Viton tubing with 6.36 mm ID and 7.94 mm OD. These dimensions should be considered exemplary only, and are not limiting; all dimensions can vary depending on the size, length, and desired performance of the device.

The integrated barbed ribbon filament2″ can be cut from a single piece of plastic sheeting, such as Nylon sheeting, with a thickness of 1.5 mm. The attachment section2″ashown is 25 mm long by 15 mm wide, provides a region for end effectors, clamps, or other means of connecting to other bodies. The main ribbon section2″ccould have a width of 5 mm and a length of 10 cm. This section2″ctransitions to the barbed section2″bwith a total width of around 15 mm, with a barb length of 10 mm. To complete the barb section2″b, the ribbon width reduces to around 10 mm for a length of around 8 mm, providing a corner on the trailing edge of the barb to dig into the tubing and lock the tubing in place. Three embodiments of the fastening section2″dare further shown inFIG. 9(b)which comprise one or more through-holes2″d′, buckle structure2″d″, or grommet2″d′″, for example. Of course, various other geometric features, or other end effectors integrated into the attachment section2″afor mechanical fastening to other components may be used for the fastening section2″dthan the ones depicted here.

FIGS. 10(a)-10(e)show exemplary devices which providing additional mechanical locking during high rate loading according to other embodiments.FIG. 10(a)shows a rate-dependent, elastically-deformable device10″′awhich incorporates ratcheting means according to an embodiment. More particularly, the device10′″ahas one or more ratcheting filaments2′ placed inside the elastically-deformable confinement member1. Two are shown. These ratcheting filaments2′″ include a series of discrete positions or steps, which sequentially engage another structure within the elastically-deformable confinement member as the one or more filaments move to provide the “ratcheting” effect. These positions or steps are configured to engage another structure within the elastically-deformable confinement member, such as another ratcheting filament2′″ and/or a detent or tooth member (not shown). As shown, a pair of opposing ratcheting filaments2′″awith discrete positions or steps can engage one other as they move in opposing direction. More particularly, these ratcheting filaments2′″ahave wavy or “zig-zag” features which need to displace outward so as to slide past each other to the next position or step thus creating outward normal force. Alternatively or additionally, the inner surface of the confinement member1could include a fixed or attached tooth or detent which engages a filament's discrete positions or steps.

This behavior is analogous to a strap with multiple discrete adjustment positions, such as a strap with a series of holes that interfaces with a buckle. Unlike a conventional buckle, which requires significant manual manipulation to readjust, the ratcheting effect of the device with a wavy ribbon allows readjustment simply by pulling on the strap. This feature could be useful for strap applications, as the straps tend to settle into a series of discrete positions or “steps,” and require higher force to move from one position to the next.

The positions or steps could be equally-spaced apart at regular intervals, for instance, as illustrated inFIG. 10(a). Also, the spacing there between could be configured to increase or decrease in a non-linear manner, such as an exponential, or irregular pattern. This provides the designer with various tailored options for ratcheting behavior.

FIG. 10(b)is a plot of the force-displacement response of wavy ribbon device10′″aofFIG. 10(a), showing the ratcheting effect for various stretching rates (in millimeters per seconds). As the rates increase, the force necessary to effect displacement greatly increases which is consistent with the increased shearing of liquid3. Additionally, the ratcheting effects can be appreciated in the displacements for all rates.

FIG. 10(c)shows another exemplary ratcheting filament device10′″bhaving a sawtooth configuration according to an embodiment. The sawtooth configuration has a particular utility in that it can be designed to exhibit directionally-dependent resistance; for example, a pair of sawtooth configured filaments2′″bproperly oriented results in a device that exhibits considerably more resistance during extension than during compression and relaxation. This is a special geometry because, unlike the wave, triangular, sinusoid geometries, a sawtooth has directionality, i.e., flat butt-faces engage in one direction (very binding), inclined faces engage in another direction (easier to slide past). For most device embodiments, high resistance in tension is of primary importance, but having low resistance in compression is nonetheless advantageous so that they can quickly relax.

FIG. 10(d)shows another exemplary ratcheting filament device10′″chaving a ball and socket configuration according to an embodiment. A filament21having one or more ball members22is connected to one of the ends plug. The ratcheting filaments2′″cmust spread to allow the balls22to be pulled-through. The liquid3will be highly resistant to these outward normal forces. Here, both ratcheting filaments2′″care shown attached to the same end plug (or the right) and the filament21is shown attached to the other end plug (or the left). In other implementations, the ratcheting filaments2′″cmight be attached to different end plugs.

FIG. 10(e)shows another exemplary ratcheting filament device10′″dhaving bristle or line comb elements23attached to the filaments2′″daccording to an embodiment. The comb elements23need to displace outward so that the filaments2′″dcan slide past each other. They can be oriented so have more resistance to extension, less resistance to retraction for instance. The comb elements23generally should be slightly flexible or very flexible.

FIGS. 11(a)-11(c)show a rate-dependent, elastically-deformable device10″ having one or more ribbon filaments2″″ according to embodiments.FIG. 11(a)shows the device10″″ in an initial, undeformed state, whereasFIG. 11(b)shows the device in a state during low-rate elongation andFIG. 11(c)shows the device in a state during high-rate elongation.

One end of each of the flat ribbon filaments2″″ is attached to opposite ends of the elastically-deformable confinement member1(via plugs5) and the other end of the each of the pair is unattached to the elastically-deformable confinement member1. The ribbons filaments2″″ have a generally flat, two-dimensional cross-sectional shape facing each other. In this arrangement, when the elastically-deformable confinement member1is in an undeformed state (FIG. 11(a)), the ribbon filaments2′ at least partially overlap one another and may continue to overlap as they are drawn away from one another as further illustrated inFIGS. 11(b) and 11(c). It has been found that flat ribbon-based filaments have a number of advantages for some applications, most notably, they simply work more consistently and predictably because the ribbons have a consistent configuration (i.e., they unlikely not to get intertwined with one another).

FIG. 12(a)-12(c)show a rate-dependent, elastically-deformable device10″″′ having one or more cable filaments2″″′ according to embodiments. The cable filaments2″″′ are long and thin elements. They can be cylindrical in cross-section with a diameter of approximately 0.001-10 mm, for example.FIG. 12(a)shows the device10″″′ in an initial, undeformed state, whereasFIG. 12(b)shows the device in a state during low-rate elongation andFIG. 12(c)shows the device in a state during high-rate elongation.

In contrast to the ribbon filaments2″″ (seeFIG. 11), the cable filaments2′″″ have a different response depending on how “intertwined” they are (i.e., the degree of which the filaments twist upon and around each other) creating a more complex entanglement than would be possible for straight and parallel filaments. This could resemble a helical entanglement, for instance. A concern with intertwined filaments is that there are multiple configuration options that can lead to slightly different responses for the same device, and these configurations can vary during multiple operation cycles of a given device leading to minor inconsistencies in device response. However, the intertwining of the cables provides an opportunity for a stronger locking effect compared to flat ribbons. Flat ribbons cannot readily entangle, so the peak resistance of a flat ribbon device can be limited by factors such as slip of the enclosed liquid3relative to the ribbon. For a cable device, the cables can intertwine and, if the liquid (e.g., a STF) prevents the cables from disentangling, can create a very high resistance force even if cable-to-liquid slip is possible. For these reasons, cable-based devices provide unique features relative to flat ribbon designs, and may prove advantageous for some applications or geometries.

One material which may be used for the elastically-deformable confinement member1is a stretchable tubing material. Typical soft, high elongation tubing materials like Viton or silicone have Young's moduli of 1-10 MPa in both the longitudinal and hoop directions. (Viton® is a well-known brand of synthetic rubber and fluoropolymer elastomer trademarked by DuPont Performance Elastomers LLC.). It has been found that the peak forces in the silicone tubing STF devices are approximately 50% lower than STF devices constructed with Viton tubing.

FIG. 13(a)is a plot of response of a STF device with higher modulus Viton® tubing, andFIG. 13(b)is a plot of response of a STF device with lower modulus silicone tubing. Both devices use identical filament ribbons and STF fluid. This data shows that silicone tubing is more compliant than the Viton tubing but, since the elastic tubing forces are far less than the peak STF device extensional resistance, the compliance of the tubing is not directly responsible for the observed differences in device peak force. Instead, the more rigid Viton tubing may provide higher confinement, and therefore normal forces, on the enclosed STF. These increased normal forces are known to induce increases in shear resistance for STFs and dense granular media. It is possible that an ideal tubing material would be anisotropic, with low resistance to longitudinal elongation and high resistance to radial expansion to maximize the transitional effects in the STF. Thus, according to embodiments, the confinement member may be designed or selected to have anisotropic properties. For instance, the confinement member may have high compliance in the longitudinal direction, and low compliance (stiffness) in the radial or hoop direction. Or put a different way, the elastic confinement member has a higher resistance to radial or hoop extension compared to its resistance to longitudinal extension.

One anisotropic tubing material could have a ratio of hoop Young's modulus to longitudinal Young's modulus of, for example, 10× or 100×. For example, if the longitudinal Young's modulus is 10 MPa, then the preferred hoop direction modulus would be 100-1000 MPa. Higher hoop moduli could be achieved by embedded, hoop-oriented fibers; a wrap of fiber reinforcement, with the fibers preferentially oriented in the hoop direction; or a confinement body, such as a spiral wound metal wire or discrete rings of metal or hard plastic.

The embodiments thus far have described rate-dependent, elastically-deformable devices containing a fluid, with special interest in Newtonian and non-Newtonian fluids, and more particularly, non-Newtonian fluids that are shear thickening. Non-Newtonian fluid devices which are not shear thickening fluids may also be considered in other embodiments. Examples of these fluids include shear thinning, thixotropic, rheopectic, a Bingham fluid, viscoplastic, or viscoelastic.

Depending on the particular fluid3incorporated in the rate-dependent, elastically-deformable devices10, their resistance force to extension of the device10changes as the extension rate of the device increases. Indeed, the resistance force to extension can “change”— i.e., to increase, decrease, and/or suddenly yield—as the extension rate of the device10increases. Heretofore, the disclosed embodiments, have generally been configured such that the resistance force to extension of the device “increases” as the extension rate of the device increases. But, other changes to their rate resistance are also contemplated.

For example, whereas an elastically-deformable device hosting a typical shear thickening fluid exhibits an increase in resistance force to extension as the extension rate of the device increases, for a device hosting other non-Newtonian fluids the resistance force to extension would exhibit different and potentially useful behaviors as the extension rate of the device increases. Example behaviors include a resistance force that decreases gradually as extension rate of the device increases, or decreases suddenly at a critical extension rate. Considering one specific example, a Bingham fluid behaves like a solid material up until a certain stress level, then above a critical “yield stress” converts into a flowable liquid. Upon relaxation of the stress, the fluid converts back to a solid-like material. The effect is observed in a material like ketchup, which will hold shape but then will flow if acted upon by stress. A rate-dependent, elastically-deformable device hosting a Bingham fluid would show resistance to force up until a critical internal stress was exceeded, and then would yield and extend with little resistance. This type of device could be used, for example, as a “soft fail” connector in a more complex structure to control the progression of damage and limit damage in critical regions, analogous to the crush zone in an automobile. (An example would be a seat belt in a military vehicle, designed to hold the wearer close to the seat during normal off-terrain action, but would yield during a high rate underbody explosion to provide higher extension and more gradual body loads). Alternatively, the “soft fail” of the tether could be used to drive loads from the primary seat belt into a parallel, secondary seat belt that is normally slack during routine use. Another example would be a garment application, where this device could act as a garment closure (for example, a wrist closure on a glove) that holds the garment on the body during normal motion, but stretches when pulled suddenly for easy doffing and donning of the garment.

The disclosed embodiments thus far have generally been shown stretching and thus in tension. This motion is envisioned as a more typical operation for most device applications. However, devices10should also be adaptable for compression situations in which the devices, do not stretch, but actually decrease or shrink in size with compressive force or velocity. Such compression embodiments of the invention also contemplated, in which the resistance force to compression of the device changes the compression rate of the device increases.

According to yet further embodiments, the shear-thickening fluid may comprise a suspension of non-spherical solid particles in a liquid. The non-spherical solid particles may comprise precipitated calcium carbonate (PCC) particles having an aspect ratio of 2:1 or more. The inventors investigated devices in which the STFs comprise water with 2:1 aspect ratio precipitated calcium carbonate (PCC) particles. The source material is a water-based precipitated calcium carbonate slurry from Specialty Minerals (Bethlehem, Pa.) called “Albaglos S,” having a mean particle size of 600 nm. (This research was reported in the journal article by the inventors P. T. Nenno and E. D. Wetzel. “Design and properties of a rate-dependent ‘dynamic ligament’ containing shear thickening fluid.” Smart Materials and Structures. v23 n125019 p 1-10. 30 Oct. 2014, which was incorporated in and formed a basis of the aforementioned '689 prov. application).

The plots ofFIG. 14compare the device response for the spherical silica (in glycol) system (FIG. 14(a)and the PCC STF system (FIG. 14(b). The PCC system shows higher forces at high speeds, and a more drastic transitional behavior from low speed to high speed response. The driving mechanism for the particle shape effect is that elongated particles tend to tumble during shear flow. This tumbling allows particles to interfere and collide at lower volume fractions than would be necessary for a spherical system, so PCC STFs can be formulated with lower nominal (low strain rate) viscosities than spherical particle STFs. These lower volume fractions and viscosities result in less device resistance at low speeds, and also result in a slight increase in the critical shear rate necessary to achieve shear thickening. More importantly, the tumbling action of these particles are believed to induce outward normal stresses perpendicular to the shear direction. For rate-dependent, elastically-deformable devices, the elastic confinement member necessarily decreases in diameter during extension. The fact that the PCC STF is pushing outward in opposition to the contraction of the confinement member is believed to create a compaction force that clamps onto the ribbons and increases resistance force during extension.

Another important category of application for the STF devices is straps and closures for body-worn devices, which require some amount of low-speed “give” for comfort, as well as conformability to complex geometries. Body-worn systems that require a tight fit for good function but still need compliance for comfort are preferred applications for our devices. Examples include prostheses, braces, body armor, chest plates, protective athletic padding, helmet chin straps and suspension systems, glove closures, and shoe closures.

For glove and shoe closures, in particular, rate-dependent, elastically-deformable device(s) placed at the wrist or ankle locations (respectively) could allow for self-adjusting, “slip-on” gloves and shoes/boots that can be slowly stretched to pass over the foot and hand, but then contract onto the ankle or wrist to achieve a tight comfortable fit. For instance, these applications may make use of a device having a pair of opposing filaments. Although, it will be appreciated that these can use the any of the various embodiments of rate-responsive, stretchable devices.

FIG. 15shows a glove closure1500incorporating a rate-dependent, elastically-deformable device10according to an embodiment. The glove portion may be conventional. The rate-dependent, elastically-deformable device is positioned in the glove at the wearer's wrist location. In its initial position, the device keeps the diameter of glove at the wrist relatively small. It must be stretched slowly to increase the diameter to slip over the wearer's wrist. Once the glove is slipped over the wearer's wrist, the device relaxes and reduces the diameter of the glove to snugly close around the wearer's wrist. If the wearer slowly pulls the glove off, the device will permit the wrist portion to expand in diameter to slip around the wearer's wrist. On the other hand, if the glove is pulled too fast, the device will not enable to the glove to expand in this manner.

FIG. 16shows a shoe closure1600incorporating a rate-dependent, elastically-deformable device10according to an embodiment. The rate-dependent, elastically-deformable device is positioned in the shoe at the wearer's ankle location. Like the glove, the device permits the shoe to be easily slipped over or off the wearer's ankle. But, if pulled too fast, it will not easily be removed.

These closures would resist sudden forces to hold the shoe or glove in place during action such as sports or combat, but would slowly conform to the body to provide comfort, and could be slowly stretched to open the closure for removal. In these applications, our device would permit a shoe to be designed without conventional strap closures such as hook-and-loop (Velcro-type) fasteners or laces.