BACKGROUND OF THE INVENTION
1. Technical Field
This disclosure generally relates to conformable fabrics, coverings, and methods of donning, applying, or employing the same; and more particularly, to those that utilize shape memory alloy or electroactive polymer actuation to effect functionality.
2. Background Art
Fabrics, coverings, and other protective layers have long been developed to form superjacent layers with, or otherwise overlay an object or space. For example, fabrics and coverings are often employed in clothing and apparel as a means to protect a human wearer, in tent or canopy construction to present a habitable confine; in food storage and consumer goods protection to present various types of wraps; and finally, in automotive and boating settings to protect at least a portion of the vehicle or boat, or its cargo, from harmful exterior elements.
With particular respect to food storage and consumer goods, an air-tight or wrinkle-free fit between the covering and the object or container storing the object is often desirous and/or beneficial. To that end, shrinkable coverings, such as shrink wrap plastic, are known in the art. Upon the application of heat, these coverings re-orient the chains of the constituent polymer (e.g., PVC), so as to cause the film to shrink into place and hold its shape. Other types of conventional food wraps employ static charges to form temporary bonds with non-metallic containers. Concernedly, however, these types of wraps typically present limited application, and a limited number of uses due to the irreversibility of the polymeric changes.
It is also known in the art to employ shape memory polymer (SMP) fibers in the construction of a fabric, such that the fabric, as a result, is selectively reconfigurable between permanent original and manipulated shapes. The manipulated configuration is achievable by thermally activating the SMP material, so that it changes to its softer state, wherein it can be worked. It is appreciated by those of ordinary skill in the art that in fiber form, activated SMP is unable to overcome external forces (including gravity), and therefore does not autonomously cause the change in configuration or otherwise serve as an actuator. Instead, the SMP fabric must be manually reconfigured. Cooling the manipulated material captures the new configuration. Concernedly, however, it is appreciated that SMP based reconfigurable fabrics or coverings require substantial energy input for activation, and due to low thermal conductivity rates, result in large cycle times.
In response to the afore-mentioned concerns, the invention presents a shape memory alloy (SMA) or electroactive polymer (EAP) based conformable protective layer (e.g., fit fabric, uniform coverings, etc.). The invention further presents a method of applying an outer protective layer to an object and increasing the superjacent area of engagement therebetween, after application. As such, the invention in many but not all of its embodiments is useful for reducing wrinkles and other anomalies that may form in the outer layer during application, which results in a smoother finish, and improves appearance. Moreover, in this configuration, enhanced structural stiffness in the protective layer is also provided.
The invention alternatively uses the shape memory and superelastic properties of SMA to create comformable easy-to install fabrics and flexible material coverings that conform either passively or on-demand to the objects upon which they are installed.
Where the SMA element presents a tether (e.g., tie-down, strap, etc.) for use with the protective layer (such as a tent, or automotive/boating covers), the invention is useful for presenting a cover that is more facilely positioned, tightened, and later removed when no longer in use. Moreover, in this configuration, enhanced structural stiffness in the protective layer is also provided.
Finally, the invention is useful for presenting a uniform protective layer that more evenly applies surface pressures and tensions upon the applied object, in comparison to purely elastic coverings.
Generally, the invention concerns a conformable (or reconfigurable) protective layer adapted for overlaying an object or space, so as to present a first condition relative thereto. The layer is formed of at least one SMA or EAP element (e.g., wire for SMA, and roll actuator form for EAP, etc.) operable to undergo a reversible change when exposed to an external signal. The element is configured such that the change is operable to autonomously modify the condition. For example, the condition may be the geometric configuration of the layer, such that modification thereof causes the layer to more tightly and securely overlay the object or space.
Other aspects and advantages of the present invention will be apparent from the following detailed description of the preferred embodiment(s) and the accompanying drawing figures.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
A preferred embodiment(s) of the invention is described in detail below with reference to the attached drawing figures, wherein:
FIG. 1 is an elevation view of a swimmer donning a body suit comprising interlaced SMA wires (either as a parallel or randomly oriented arrangement of individual wires or variously as a woven, knitted, or braided construct of SMA wires) and non-active fibers, wherein the wires have been activated, so as to cause the suit to conform to the body of the swimmer, in accordance with a preferred embodiment of the invention;
FIG. 2 represents progressive elevations of a spherical object being overlaid by a conformable protective layer, and the layer being thermally activated by a radiant/convection heating source, so as to increase the superjacent area of engagement, in accordance with a preferred embodiment of the invention;
FIG. 3a is an elevation of a conformable truck bed covering overlaying a cargo, and employing SMA or EAP tethers (or “tie-downs”), in accordance with a preferred embodiment of the invention; and
FIG. 3b is an elevation of the truck, covering, and cargo, shown in FIG. 3a, wherein the tethers have been activated so as to contract and thereby cause the covering to be pulled down tightly over the cargo.
The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. The present invention may find utility in a wide range of applications; including, for example, in compositions of clothing and apparel (FIG. 1), as coverings for vehicles (FIGS. 3a,b), boats, and furniture, and as reusable shrinkage wrap (FIG. 2). That is to say, the invention is applicable wherever the advantages and benefits of using a selectively conformable fabric or covering is desired.
In general, the invention concerns a fabric, covering, sheath, film, or otherwise thin layer of conformable material configured to overlay the outer surface of an object or form a barrier between two adjacent spaces (collectively referred to herein as “protective layer”). The protective layer 10 employs active material actuation to facilitate application and/or improve function.
Suitable active materials for use with the present invention include but are not limited to shape memory alloys, ferromagnetic shape memory alloys, and other active materials, such as electroactive polymers (EAP), that can function as actuators under fibrous configurations and atmospheric conditions. These types of active materials have the ability to remember their original shape and/or elastic modulus, which can subsequently be recalled by applying an external stimulus. As such, deformation from the original shape is a temporary condition. In this manner, an element composed of these materials can change to the trained shape in response to either the application or removal (depending on the material and the form in which it is used) of an activation signal.
More particularly, shape memory alloys (SMA's) generally refer to a group of metallic materials that demonstrate the ability to return to some previously defined shape or size when subjected to an appropriate thermal stimulus. Shape memory alloys are capable of undergoing phase transitions in which their yield strength, stiffness, dimension and/or shape are altered as a function of temperature. The term “yield strength” refers to the stress at which a material exhibits a specified deviation from proportionality of stress and strain. Generally, in the low temperature, or martensite phase, shape memory alloys can be pseudo-plastically deformed and upon exposure to some higher temperature will transform to an austenite phase, or parent phase, returning to their shape prior to the deformation. Materials that exhibit this shape memory effect only upon heating are referred to as having one-way shape memory. Those materials that also exhibit shape memory upon re-cooling are referred to as having two-way shape memory behavior.
Shape memory alloys exist in several different temperature-dependent phases. The most commonly utilized of these phases are the so-called Martensite and Austenite phases discussed above. In the following discussion, the martensite phase generally refers to the more deformable, lower temperature phase whereas the austenite phase generally refers to the more rigid, higher temperature phase. When the shape memory alloy is in the martensite phase and is heated, it begins to change into the austenite phase. The temperature at which this phenomenon starts is often referred to as austenite start temperature (As). The temperature at which this phenomenon is complete is called the austenite finish temperature (Af).
When the shape memory alloy is in the austenite phase and is cooled, it begins to change into the martensite phase, and the temperature at which this phenomenon starts is referred to as the martensite start temperature (Ms). The temperature at which austenite finishes transforming to martensite is called the martensite finish temperature (Mf). Generally, the shape memory alloys are softer and more easily deformable in their martensitic phase and are harder, stiffer, and/or more rigid in the austenitic phase. In view of the foregoing, a suitable activation signal for use with shape memory alloys is a thermal activation signal having a magnitude to cause transformations between the martensite and austenite phases.
Shape memory alloys can exhibit a one-way shape memory effect, an intrinsic two-way effect, or an extrinsic two-way shape memory effect depending on the alloy composition and processing history. Annealed shape memory alloys typically only exhibit the one-way shape memory effect. Sufficient heating subsequent to low-temperature deformation of the shape memory material will induce the martensite to austenite type transition, and the material will recover the original, annealed shape. Hence, one-way shape memory effects are only observed upon heating. Active materials comprising shape memory alloy compositions that exhibit one-way memory effects do not automatically reform, and will likely require an external mechanical force to reform the shape that was previously suitable for airflow control.
Intrinsic and extrinsic two-way shape memory materials are characterized by a shape transition both upon heating from the martensite phase to the austenite phase, as well as an additional shape transition upon cooling from the austenite phase back to the martensite phase. Active materials that exhibit an intrinsic shape memory effect are fabricated from a shape memory alloy composition that will cause the active materials to automatically reform themselves as a result of the above noted phase transformations. Intrinsic two-way shape memory behavior must be induced in the shape memory material through processing. Such procedures include extreme deformation of the material while in the martensite phase, heating-cooling under constraint or load, or surface modification such as laser annealing, polishing, or shot-peening. Once the material has been trained to exhibit the two-way shape memory effect, the shape change between the low and high temperature states is generally reversible and persists through a high number of thermal cycles. In contrast, active materials that exhibit the extrinsic two-way shape memory effects are composite or multi-component materials that combine a shape memory alloy composition that exhibits a one-way effect with another element that provides a restoring force to reform the original shape.
The temperature at which the shape memory alloy remembers its high temperature form when heated can be adjusted by slight changes in the composition of the alloy and through heat treatment. In nickel-titanium shape memory alloys, for instance, it can be changed from above about 100° C. to below about −100° C. The shape recovery process occurs over a range of just a few degrees and the start or finish of the transformation can be controlled to within a degree or two depending on the desired application and alloy composition. The mechanical properties of the shape memory alloy vary greatly over the temperature range spanning their transformation, typically providing the system with shape memory effects, superelastic effects, and high damping capacity.
Suitable shape memory alloy materials include, without limitation, nickel-titanium based alloys, indium-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold, and copper-tin alloys), gold-cadmium based alloys, silver-cadmium based alloys, indium-cadmium based alloys, manganese-copper based alloys, iron-platinum based alloys, iron-platinum based alloys, iron-palladium based alloys, and the like. The alloys can be binary, ternary, or any higher order so long as the alloy composition exhibits a shape memory effect, e.g., change in shape orientation, damping capacity, and the like.
It is appreciated that SMA's exhibit a modulus increase of 2.5 times and a dimensional change (recovery of pseudo-plastic deformation induced when in the Martensitic phase) of up to 8% (depending on the amount of pre-strain) when heated above their Martensite to Austenite phase transition temperature. It is appreciated that thermally induced SMA phase changes are one-way so that a biasing force return mechanism (such as a spring) would be required to return the SMA to its starting configuration once the applied field is removed. Joule heating can be used to make the entire system electronically controllable.
Stress induced phase changes in SMA, caused by loading and unloading of SMA (when at temperatures above Af), are, however, two way by nature. That is to say, application of sufficient stress when an SMA is in its austenitic phase will cause it to change to its lower modulus martensitic phase in which it can exhibit up to 8% of “superelastic” deformation. Removal of the applied stress will cause the SMA to switch back to its austenitic phase in so doing recovering its starting shape and higher modulus.
Next, ferromagnetic SMA's (FSMA's) are a sub-class of SMAs. These materials behave like conventional SMA materials that have a stress or thermally induced phase transformation between martensite and austenite. Additionally FSMA's are ferromagnetic and have strong magnetocrystalline anisotropy, which permit an external magnetic field to influence the orientation/fraction of field aligned martensitic variants. When the magnetic field is removed, the material may exhibit complete two-way, partial two-way or one-way shape memory. For partial or one-way shape memory, an external stimulus, temperature, magnetic field or stress may permit the material to return to its starting state. Perfect two-way shape memory may be used for proportional control with continuous power supplied. One-way shape memory is most useful for rail filling applications. External magnetic fields are generally produced via soft-magnetic core electromagnets in automotive applications, though a pair of Helmholtz coils may also be used for fast response.
Finally, as previously mentioned, electroactive polymers may be used in lieu of SMA. This type of active material includes those polymeric materials that exhibit piezoelectric, pyroelectric, or electrostrictive properties in response to electrical or mechanical fields. An example of an electrostrictive-grafted elastomer with a piezoelectric poly(vinylidene fluoride-trifluoro-ethylene) copolymer. This combination has the ability to produce a varied amount of ferroelectric-electrostrictive, molecular composite systems. These may be operated as a piezoelectric sensor or even an electrostrictive actuator.
Materials suitable for use as an electroactive polymer may include any substantially insulating polymer or rubber (or combination thereof) that deforms in response to an electrostatic force or whose deformation results in a change in electric field. Exemplary materials suitable for use as a pre-strained polymer include silicone elastomers, acrylic elastomers, polyurethanes, thermoplastic elastomers, copolymers comprising PVDF, pressure-sensitive adhesives, fluoroelastomers, polymers comprising silicone and acrylic moieties, and the like. Polymers comprising silicone and acrylic moieties may include copolymers comprising silicone and acrylic moieties, polymer blends comprising a silicone elastomer and an acrylic elastomer, for example.
Materials used as an electroactive polymer may be selected based on one or more material properties such as a high electrical breakdown strength, a low modulus of elasticity—(for large deformations), a high dielectric constant, and the like. In one embodiment, the polymer is selected such that is has an elastic modulus at most about 100 MPa. In another embodiment, the polymer is selected such that is has a maximum actuation pressure between about 0.05 MPa and about 10 MPa, and preferably between about 0.3 MPa and about 3 MPa. In another embodiment, the polymer is selected such that is has a dielectric constant between about 2 and about 20, and preferably between about 2.5 and about 12. The present disclosure is not intended to be limited to these ranges. Ideally, materials with a higher dielectric constant than the ranges given above would be desirable if the materials had both a high dielectric constant and a high dielectric strength. With respect to the present invention, it is appreciated that electroactive polymers may be fabricated and implemented as a thin film defining a preferred thickness below 50 micrometers.
As electroactive polymers may deflect at high strains, electrodes attached to the polymers should also deflect without compromising mechanical or electrical performance. Generally, electrodes suitable for use may be of any shape and material provided that they are able to supply a suitable voltage to, or receive a suitable voltage from, an electroactive polymer. The voltage may be either constant or varying over time. In one embodiment, the electrodes adhere to a surface of the polymer. Electrodes adhering to the polymer are preferably compliant and conform to the changing shape of the polymer. Correspondingly, the present disclosure may include compliant electrodes that conform to the shape of an electroactive polymer to which they are attached. The electrodes may be only applied to a portion of an electroactive polymer and define an active area according to their geometry. Various types of electrodes suitable for use with the present disclosure include structured electrodes comprising metal traces and charge distribution layers, textured electrodes comprising varying out of plane dimensions, conductive greases such as carbon greases or silver greases, colloidal suspensions, high aspect ratio conductive materials such as carbon fibrils and carbon nanotubes, and mixtures of ionically conductive materials.
Materials used for electrodes of the present disclosure may vary. Suitable materials used in an electrode may include graphite, carbon black, colloidal suspensions, thin metals including silver and gold, silver filled and carbon filled gels and polymers, and ionically or electronically conductive polymers. It is understood that certain electrode materials may work well with particular polymers and may not work as well for others. By way of example, carbon fibrils work well with acrylic elastomer polymers while not as well with silicone polymers.
Turning to FIGS. 1-3b, a conformable protective layer 10 (e.g., a fit fabric (FIG. 1), flexible covering (FIGS. 3a,b), etc.) is adapted for overlaying an object (or space) 12, such as a human body (FIG. 1), inanimate object (FIG. 2), or automotive (e.g., truck bed) cargo/space (FIGS. 3a,b). Moreover, the protective layer 10 may be used with boating coverings, roofing tarps, coverings for stock-piles of materials (e.g., salt), coverings for furniture, or where ever it is desired to hold down object(s) more securely, so as to prevent, for example, their being blown away; to apply a reusable form-fitting covering, such as for example, with respect to furniture; or to more securely retain irregularly shaped or fragile objects 12 that benefit from the more uniform stress distribution and load limiting capabilities of a covering 10 comprising SMA in either the martensitic or superelastic form. With respect to the latter, it is appreciated that stress experienced by the object 12 due to stretching the active covering 10 will be more uniform than conventional elastic covers; that is to say, the active covering 10 will give/stretch at specific constant non-increasing stress levels corresponding to either the martensitic plateau or austenitic superelastic stress level rather than stretching with a linearly increasing force level as is the case, for example, with bungy cords.
Once applied, the layer 10 presents a first condition relative to the object 12. The layer 10 includes at least one shape memory alloy or electroactive polymer element 14 operable to undergo a reversible change when either exposed to or removed from an external signal, as discussed above. The element 14 is configured such that the change is operable to autonomously modify the condition. For example, the condition may be the geometric configuration and/or stiffness of the layer 10.
In FIG. 1, a conformable fabric 10 composes a full body swim suit, wherein the advantages of donning a protective, wrinkle-free, and preferably thermally insulative layer are appreciated, for example, in endurance events. Here, the fabric 10 is operable to encircle at least a portion of a human body 12, and is formed of suitable non-active and preferably elastic material 16 that enables it to be stretched to apply compression to the body 12. The fabric 10 may be weft knitted in almost one entire piece on a circular rib-knit machine (not shown), and formed in a one-by-one rib stitch knitting pattern.
More particularly, the fabric 10 may be knitted in connected loops of substantially uniform pattern and number per square inch throughout the fabric. It is appreciated that such a uniform pattern results in generally uniform compression against the body 12 over a wide range of stretch. It is also appreciated, however, that the fabric 10 can be formed in varying patterns and densities, so as to present areas of different compressive forces under equal stretches. More preferably, to effect a more uniform compressive force, the fabric 10 comprises four-way stretchable material that is at least capable of stretching approximately 150% in one direction and 145% in a transverse direction.
In a preferred embodiment, the material 16 comprises core-spun yarn and elastic filaments laid in at least every fourth course of knitted yarn. The core-spun yam further comprises a spandex core and fiber sheathing. In the present invention, a shape memory or electroactive polymer element (e.g., wire) 14 is periodically juxtaposed for an elastic filament; for example, every fourth elastic filament may be replaced by an SMA wire or EAP strand or strip 14, laterally and vertically. When at least a portion of the wires 14 are activated, they are caused to contract, further causing the fabric 10 to contract in-plane, so as to increase the superjacent area of engagement between the fabric 10 and body 12. When removal of the suit 10 is desired, the wires 14 can be deactivated (in the case of SMA) or deactivated (in the case of EAP) to return them to their softer state (martensitic in the case of SMA). More preferably, the wires 14 are trained to exhibit two-way shape memory, such that deactivation causes the fabric 10 to return to its original configuration.
In a preferred embodiment, the element 14 presents a suitable gauge and cylindrical wire configuration that results in stress and strain values of 170 MPa and 2.5%, respectively. In this example configuration, it is appreciated that an SMA wire produces an actuating force of 2N, when activated, and requires between 2.5 to 12 V, and 2 amps of current for actuation. Actuation times less than five seconds, an approximate lifetime of 100,000 actuations, and a working environment between −40 to 90° C. is also appreciated. The wires 14 may be employed singularly or in bundles; or in other configurations, such as weaves, knits, cables and braids.
Thus, a signal source (or power supply) 18 is in operative communication with the elements 14 and operable to provide a suitable activation signal (FIG. 2) thereto. The source 18 may be automatically demanded via user input, and regulated by a PWM, regulator, or power resistor in-series (not shown). For example, in the case of thermally activated SMA elements 14, a current can be supplied by the source 18 to effect Joule heating. Alternatively, the source 18 may come from the ambient environment, such as, for example, radiation from the Sun (also not shown), such that the element 14 is passively activated.
In a first mode of operation, SMA wires 14 in either the martensitic or austenitic state may be incorporated in a flexible fabric 10 made from non-active fibers 16 with limited extensibility (e.g., presenting less than 5% elastic strain capability). In the martensitic state, if the fabric 10 is extensible or contractible in-plane through for example pantographing of its interlaced fibers 16 then the SMA wires 14 can be stretched prior to being incorporated therein. When activated (by applying a thermal activation signal) the wires 14 and fabric 10 are caused to contract, thereby, pulling the layer down tightly over the applied object (or space) 12. As a result, it is appreciated that wrinkles are minimized within the fabric 10. Alternatively, if the fabric 10 is extensible or contractible in plane, then the SMA wires 14 and fabric 10 can be stretched prior to or during the application process (FIG. 2).
Where the SMA wires 14 are in the deactivated austenitic state, if the fabric is extensible or contractible in-plane, then the SMA wires 14 and fabric 10 can again be stretched prior to or during the application process. When the stress is released, the superelastic property of the SMA material will cause the wires 14 to revert back to their shorter and stiffer austenitic states. Consequently, the fabric 10 will be pulled down tightly over the applied object 12, while eliminating or minimizing wrinkling and increasing the in-plane stiffness of the protective layer. It is appreciated that SMA in superelastic form provides a constant force holding effect independent (over a 10% range of variation) of the size of the object being covered.
In a second mode of operation, the SMA elements 14 are incorporated in a flexible fabric 10 made from elastic fibers 16 with significant extensibility. In the martensitic state, the elements 14 and fabric 16 can be congruently stretched prior to or during the process of being applied as a covering. The elements 14 are then activated to pull the fabric 10 down tight without inducing wrinkling and with an accompanying increase in in-plane stiffness.
Alternatively, where the fabric 10 is flexible and comprised of elastic fibers 16 exhibiting significant extensibility, the SMA elements 14 can be pre-stretched prior to incorporation into the fabric 10. The fabric 10 presents an excess in size (e.g., presents linear dimensions up to 8% greater and a surface area up to 16% greater than the targeted area of engagement) relative to the object 12, so as to ease application as a covering. Once applied, the elements 14 are activated to pull the fabric 10 down tight over the object 12. In this embodiment, however, it is appreciated that significant wrinkling may be produced.
In the austenitic state, where the fabric 10 is flexible and comprised of elastic fibers 16 exhibiting significant extensibility, the SMA elements 14 and fabric 10 can again be stretched prior to or during the process of being applied as a covering. When the stress load is ceased, the superelastic property of the SMA material plus the elasticity of the fabric 10, causes it to contract and be pulled down tightly over the object 12, without inducing wrinkling and with an accompanying increase in in-plane stiffness. It is appreciated that this configuration utilizes the work (e.g., manually) performed in placing the fabric 10 to store potential energy for later actuation, and therefore does not require an external signal source 18.
In a third mode, SMA elements 14 may be incorporated in an inextensible in-plane but flexible in-bending covering 10. Here, in the martensitic state, the SMA elements 14 can be stretched prior to embedding in the covering 10. The covering 10 is again oversized relative to the object 12. The SMA elements 14 are then activated, and configured to bend the covering 10 downward. It is appreciated that significant wrinkling in the covering 10 may occur.
Alternatively, the SMA elements 14 are not pre-stretched prior to embedding in the covering 10, and the covering 10 is correctly sized relative to the object 12. In this configuration, the SMA elements 14 when activated, either passively or on-demand, are unable to contract, but significantly increase in tension. Therefore the stiffness of the covering 10 is increased, so as to change the modulus of bending. Activation is discontinued to re-soften the covering 10.
In the deactivated austenitic state, the SMA elements 14 are stretched to effect transition to the martensitic state prior to embedding in the inextensible covering 10; and the covering 10 is applied while the elements 14 are held under tensile load. Once applied, the load is released, so that the elements 14 revert back to the austenitic state due to the super-elasticity effect in SMA. The covering 10 is caused to tighten to a point of even wrinkling in otherwise unstressed regions.
In another exemplary mode, especially applicable to tents, and automotive/boating cargo covers, the SMA elements 14 may comprise tethers (e.g., ties, tie-down, etc.) 20 adapted for use with an otherwise conventional cover 22. For example, in the illustrated embodiment shown in FIGS. 3a,b, a plurality of looped tethers 20 are offset along the lateral sides of a tarp 22; said tarp 22 being used to secure, for example, the cargo 12 of a truck bed 24. The tethers 20 are manually caused to engage a plurality of anchor prongs 26 attached to or defined by the truck bed 24. In one configuration, the SMA tethers 20 are in the austenitic deactivated state, and activated by causing them to super-elastically stretch. Once secured, the tensile load applied to the SMA tethers 20 is ceased so as to cause the tethers 20 to revert back to their austenitic state and contract in dimension. To remove the cover 22 after use, a tensile load is again applied to the tethers 20 causing them to first soften then stretch.
Alternatively, where shape memory activation is utilized, the tethers 20 comprise SMA in the martensitic deactivated state, and are activated, passively or on-demand, by exposing them to a thermal activation signal, as is known in the art. In this application, the tethers 20, when deactivated, present the elongated configuration (FIG. 3a) that facilitates the application process; that is to say, in this configuration the tethers 20 enable the cover 22 to be more facilely positioned by increasing the size of the loop openings defined thereby and increasing the slack in the cover 22. When activated, the tethers 20 are caused to contract, so as to pull down the cover 22 and apply tension at the attachment points.
More preferably, to hold the cover in tight relationship with the cargo 12, at least one latching mechanism 28, such as a second non-active tether (FIG. 3b) or strap, may be configured so as to be selectively caused to also engage the respective prong 26. The second tether 28 is preferably elastic, and presents a modulus of elasticity greater than the return force produced by the active tether 20. As such, the mechanism 28 presents a zero-power hold that retains the cover 22 in tight relationship with the cargo 12 when the tethers 20 are deactivated. When removal of the cover 22 is desired, the tethers 20,28 are de-activated and the latching mechanisms 28 are disengaged.
Other applications include skate boot covers, wherein the SMA element 14 may utilize either its superelastic or shape memory characteristic to snuggly engage a skate boot (not shown) with the foot of a wearer. Head covers for golf clubs (also not shown) that preferably utilize the superelastic characteristic of SMA. Here, the covering 10 is pulled over the club head and then released, so as to snap back and form an exterior protective and/or decorative layer. Finally, it is appreciated that SMA elements 14 may also be utilized in the construction of shower caps.
This invention has been described with reference to exemplary embodiments; it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to a particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
Ranges disclosed herein are inclusive and combinable (e.g., ranges of “up to about 25 wt %, or, more specifically, about 5 wt % to about 20 wt %”, is inclusive of the endpoints and all intermediate values of the ranges of “about 5 wt % to about 25 wt %,” etc.). “Combination” is inclusive of blends, mixtures, alloys, reaction products, and the like. Furthermore, the terms “first,” “second,” and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another, and the terms “a” and “an” herein do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. The modifier “about” used in connection with a quantity is inclusive of the state value and has the meaning dictated by context, (e.g., includes the degree of error associated with measurement of the particular quantity). The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the colorant(s) includes one or more colorants). Reference throughout the specification to “one embodiment”, “another embodiment”, “an embodiment”, and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the embodiment is included in at least one embodiment described herein, and may or may not be present in other embodiments. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various embodiments.