Releasable fastener system Number:7,146,690 from the United States Patent and Trademark Office (PTO) owispatent A releasable fastener system comprises a loop portion and a hook portion. The loop portion includes a support and a loop material disposed on one side thereof. The hook portion generally includes a support and a plurality of closely spaced upstanding hook elements extending from one side thereof, wherein the plurality of hook elements comprises or incorporates a shape memory alloy fiber. When the hook portion and loop portion are pressed together they interlock to form a releasable engagement. The resulting joint created by the engagement is relatively resistant to shear and pull forces and weak in peel strength forces. Introducing a thermal activation signal to the plurality of hook elements causes a change in shape orientation, flexural modulus property, or a combination thereof that effectively reduces the shear and/or pull off forces in the releasable engagement. In this manner, disengagement of the releasable fastener system provides separation of the hook portion from the loop portion under controlled conditions. Also disclosed herein are processes for operating the releasable fastener system.<H Releasable, fastener, Releasable, fast, 7146690.html, Patent, pto, 7146690

Title: Releasable fastener system

Abstract: A releasable fastener system comprises a loop portion and a hook portion. The loop portion includes a support and a loop material disposed on one side thereof. The hook portion generally includes a support and a plurality of closely spaced upstanding hook elements extending from one side thereof, wherein the plurality of hook elements comprises or incorporates a shape memory alloy fiber. When the hook portion and loop portion are pressed together they interlock to form a releasable engagement. The resulting joint created by the engagement is relatively resistant to shear and pull forces and weak in peel strength forces. Introducing a thermal activation signal to the plurality of hook elements causes a change in shape orientation, flexural modulus property, or a combination thereof that effectively reduces the shear and/or pull off forces in the releasable engagement. In this manner, disengagement of the releasable fastener system provides separation of the hook portion from the loop portion under controlled conditions. Also disclosed herein are processes for operating the releasable fastener system.

Patent Number: 7,146,690 Issued on 12/12/2006 to Stanford, Jr., et al.

Inventors: Stanford, Jr.; Thomas B. (Port Hueneme, CA), Browne; Alan L. (Grosse Pointe, MI), Johnson; Nancy L. (Northville, MI), Momoda; Leslie A. (Los Angeles, CA), Barvosa-Carter; William (Ventura, CA), Powell, Jr.; Bob R. (Birmingham, MI)
Assignee: General Motors Corporation (Detroit, MI)

Appl. No.: 10/305,375

Filed: November 26, 2002

Current U.S. Class: 24/451 ; 428/100

Current International Class: B23P 19/04 (20060101); A44B 21/00 (20060101)

Field of Search: 24/442,446,451,450,452,448,304 428/100

References Cited [Referenced By]

U.S. Patent Documents


2717437	September 1955	DeMestral
2994117	August 1961	McMullin
3101517	August 1963	Fox et al.
3128514	April 1964	Parker et al.
3138749	June 1964	Slibitz
3176364	April 1965	Dritz
3292019	December 1966	Hsu et al.
3365757	January 1968	Billarant
3469289	September 1969	Whitacre
3490107	January 1970	Brumlik
3808648	May 1974	Billarant et al.
4169303	October 1979	Lemelson
4382243	May 1983	Babitzka et al.
4391147	July 1983	Krempl et al.
4634636	January 1987	Yoshino et al.
4637944	January 1987	Walker
4642254	February 1987	Walker
4693921	September 1987	Billarant et al.
4752537	June 1988	Das
4775310	October 1988	Fischer
4794028	December 1988	Fischer
4931344	June 1990	Ogawa et al.
5037178	August 1991	Stoy et al.
5071363	December 1991	Reylek et al.
5133112	July 1992	Gomez-Acevedo
5136201	August 1992	Culp
5182484	January 1993	Culp
5191166	March 1993	Smirlock et al.
5212855	May 1993	McGanty
5284330	February 1994	Carlson et al.
5312456	May 1994	Reed et al.
5319257	June 1994	McIntyre
5328337	July 1994	Kunta
5474227	December 1995	Krengel et al.
5486676	January 1996	Aleshin
5492534	February 1996	Athayde et al.
5497861	March 1996	Brotz
5547049	August 1996	Weiss et al.
5611122	March 1997	Torigoe et al.
5656351	August 1997	Donaruma
5657516	August 1997	Berg et al.
5669120	September 1997	Wessels et al.
5671498	September 1997	Martin et al.
5712524	January 1998	Suga
5725928	March 1998	Kenney et al.
5797170	August 1998	Akeno
5798188	August 1998	Mukohyama et al.
5814999	September 1998	Elie et al.
5816587	October 1998	Stewart et al.
5817380	October 1998	Tanaka
5885652	March 1999	Abbott et al.
5945193	August 1999	Pollard et al.
5969518	October 1999	Merklein et al.
5974856	November 1999	Elie et al.
5979744	November 1999	Brigleb
5983467	November 1999	Duffy
6029783	February 2000	Wirthlin
6086599	July 2000	Lee et al.
6102912	August 2000	Cazin et al.
6102933	August 2000	Lee et al.
6129970	October 2000	Kenney et al.
6148487	November 2000	Billarant
6156842	December 2000	Hoenig et al.
6203717	March 2001	Munoz et al.
6257133	July 2001	Anderson
6388043	May 2002	Langer et al.
6454923	September 2002	Dodgson et al.
6460230	October 2002	Shimamura et al.
6502290	January 2003	Tseng
6544245	April 2003	Neeb et al.
6546602	April 2003	Eipper et al.
6593540	July 2003	Baker et al.
6598274	July 2003	Marmaropoulos
6605795	August 2003	Arcella et al.
6628542	September 2003	Hayashi et al.
6681849	January 2004	Goodson
6740094	May 2004	Maitland et al.
6742227	June 2004	Ulicny et al.
6766566	July 2004	Cheng et al.
6797914	September 2004	Speranza et al.
6815873	November 2004	Johnson et al.
2002/0007884	January 2002	Schuster et al.
2002/0050045	May 2002	Chiodo
2002/0062547	May 2002	Chiodo et al.
2002/0076520	June 2002	Neeb et al.
2002/0142119	October 2002	Seward et al.
2003/0120300	June 2003	Porter
2004/0025639	February 2004	Shahinpoor et al.
2004/0033336	February 2004	Schulte
2004/0074061	April 2004	Ottaviani et al.
2004/0074062	April 2004	Stanford et al.
2004/0074063	April 2004	Golden et al.
2004/0074064	April 2004	Powell et al.
2004/0074067	April 2004	Browne et al.
2004/0074068	April 2004	Browne et al.
2004/0074069	April 2004	Browne et al.
2004/0074070	April 2004	Momoda et al.
2004/0074071	April 2004	Golden et al.
2004/0117955	June 2004	Barvosa-Carter et al.

Foreign Patent Documents


199 56 011	Jun., 2001	DE
0385443	Sep., 1990	EP
0673709	Sep., 1995	EP
401162587	Jun., 1989	JP
4-314446	Apr., 1992	JP
4-266970	Sep., 1992	JP
08260748	Oct., 1996	JP
WO 99/42528	Aug., 1999	WO
WO 00/62637	Oct., 2000	WO
WO 01/84002	Nov., 2001	WO
WO 02/45536	Jun., 2002	WO

Primary Examiner: Lavinder; Jack W.
Attorney, Agent or Firm: Marra; Kathryn A.

Parent Case Text

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 10/273,691 filed Oct. 19, 2002, which is fully incorporated herein by reference.

Claims

The invention claimed is:

1. A releasable fastener system comprising: a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support, and a plurality of hook elements attached to the support, wherein the plurality of hook elements comprise a first portion fabricated from a shape memory alloy and a second portion fabricated from a different shape memory alloy; and an activation device coupled to the plurality of hook elements, the activation device being operable to selectively provide an activation signal to the plurality of hook elements to change a shape orientation, a yield strength property, a flexural modulus property, or a combination thereof to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

2. The releasable fastener system of claim 1, wherein the shape memory alloy comprises nickel-titanium based alloys, indium-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, copper based alloys, gold-cadmium based alloys, iron -platinum based alloys, iron-palladium based alloys, silver-cadmium based alloys, indium-cadmium based alloys, manganese-copper based alloys, or combinations comprising at least one of the foregoing alloys.

3. The releasable fastener system of claim 1, wherein the shape memory alloy comprises an alloy composition selected to exhibit an austenite phase at an environmental temperature in which the fastener system is disposed and a martensite phase at about a temperature lower than the environmental temperature.

4. The releasable fastener system of claim 1, wherein the shape memory alloy comprises an alloy composition selected to exhibit a martensite phase at an environmental temperature in which the fastener system is disposed and an austenite phase at a temperature greater than the environmental temperature.

5. The releasable fastener system of claim 1, wherein the loop material comprises a shape memory alloy fiber comprising a spiral shape orientation at a martensite temperature condition and a substantially straightened orientation at an austenite temperature condition, and wherein the plurality of hook elements comprise a spiral shape orientation at the martensite temperature condition and a substantially straightened orientation at the austenite temperature condition.

6. The releasable fastener system of claim 1, wherein the plurality of hook elements comprise a shape orientation comprising a J-shaped orientation, a mushroom shape, a knob shape, a multi-timed anchor shape, a T-shape, a spiral shape, or combinations comprising at least one of the foregoing shapes.

7. The releasable fastener system of claim 1, wherein the plurality of hook elements further comprises a polymer coating about the shape memory alloy.

8. The releasable fastener system of claim 7, wherein the polymer comprises an elastomer or a shape memory polymer.

9. The releasable fastener system of claim 7, wherein the hook portion support and the loop portion support comprise an inflexible material.

10. The releasable fastener system of claim 7, wherein the shape memory alloy exhibits a one-way shape memory effect.

11. The releasable fastener system of claim 7, wherein the shape memory alloy exhibits a two-way shape memory effect.

Description

BACKGROUND

This disclosure relates to releasable attachment devices of the type used to fasten, retain, or latch together components of an apparatus or a structure that are to be separated or released under controlled conditions.

Hook and loop type separable fasteners are well known and are used to join two members detachably to each other. These types of fasteners generally have two components disposed on opposing member surfaces. One component typically includes a plurality of resilient hooks while the other component typically includes a plurality of loops. When the two components are pressed together they interlock to form a releasable engagement. The resulting joint created by the releasable engagement is relatively resistant to shear and pull forces, and weak in peel strength forces. As such, peeling one component from the other component can be used to separate the components with a minimal applied force. As used herein, the term "shear" refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction parallel to their plane of contact. The term "pull force" refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction perpendicular to their plane of contact.

Shape memory alloys 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 flexural modulus, yield strength, and shape orientation is altered as a function of temperature. Generally, in the low temperature, or martensite phase, shape memory alloys can be plastically deformed and upon exposure to some higher temperature will transform to an austenitic 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.

BRIEF SUMMARY

Disclosed herein is a releasable fastener system a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support and a plurality of hook elements disposed on a surface thereon, wherein the plurality of hook elements comprises a shape memory alloy fiber; and a thermal activation device coupled to the plurality of hook elements, the thermal activation device being operable to selectively provide a thermal activation signal to the shape memory alloy fiber and change a shape orientation, a yield strength property, a flexural modulus property, or a combination thereof to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

In another embodiment, the releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon, wherein the loop portion comprises shape memory alloy fibers in a spiral shape orientation at a martensite phase temperature and a substantially straightened orientation at an austenite phase temperature; a hook portion comprising a support and a plurality of hook elements disposed on a surface, wherein the plurality of hook elements comprises shape memory alloy fibers in the spiral shape orientation at the martensite phase temperature and a substantially straightened orientation at the austenite phase temperature; and means for changing the shape orientation, the yield strength property, the flexural modulus property, or the combination thereof of the hook elements to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

In another embodiment, the releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon, wherein the loop portion comprises shape memory alloy fibers in a spiral shape orientation at an austenite phase temperature and a reduction in yield strength and/or flexural modulus properties at a martensite phase temperature; a hook portion comprising a support and a plurality of hook elements disposed on a surface, wherein the plurality of hook elements comprises shape memory alloy fibers in the spiral shape orientation at the austenite phase temperature whose yield strength and/or flexural modulus properties are reduced at the martensite phase temperature; and means for changing a temperature of the plurality of hook elements and the loop material upon demand to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

In another embodiment, the releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support and a plurality of hook elements disposed on a surface thereon, wherein the plurality of hook elements comprises a shape memory alloy sleeve coupled to an elastic core material; and a thermal activation device coupled to the plurality of hook elements, the thermal activation device being operable to selectively provide a thermal activation signal to the shape memory alloy fiber and change a shape orientation, a yield strength property, a flexural modulus property, or a combination thereof to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

In another embodiment, a releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support and a plurality of hook elements disposed on a surface thereon, wherein the plurality of hook elements comprises an elastic sleeve coupled to a shape memory alloy fiber; and a thermal activation device coupled to the plurality of hook elements, the thermal activation device being operable to selectively provide a thermal activation signal to the shape memory alloy fiber and change a shape orientation, a yield strength property, a flexural modulus property, or a combination thereof to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

In another embodiment, a releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support and a plurality of hook elements disposed on a surface thereon, wherein the plurality of hook elements comprises an inflexible sleeve and a shape memory alloy fiber disposed within the sleeve, wherein one end of the shape memory alloy fiber is fixedly attached to the support surface and an other end is fixedly attached to an elastic hook, wherein the elastic hook extends from the sleeve in an amount effective to engage the loop material; and a thermal activation device coupled to the plurality of hook elements, the thermal activation device being operable to selectively provide a thermal activation signal to the shape memory alloy fiber and change a length dimension and retract the elastic hook into the sleeve and disengage the elastic hook from the loop material.

In another embodiment, a releasable fastener system comprises a loop portion comprising a support and a loop material disposed on a surface thereon; a hook portion comprising a support and a plurality of hook elements disposed on a surface thereon, wherein each one of the plurality of hook elements comprises one or more shape memory alloy fibers combined with one or more elastic fibers or elements; and a thermal activation device coupled to the plurality of hook elements, the thermal activation device being operable to selectively provide a thermal activation signal to the shape memory alloy fiber and change a shape orientation, a yield strength and/or flexural modulus property, or a combination of these properties of the plurality of hook elements to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.

A hook portion for a releasable fastener system comprises a support; and a plurality of hook elements disposed on a surface of the support, wherein the plurality of hook elements comprise a shape memory alloy fiber adapted to change a shape orientation, a yield strength property, a flexural modulus property, or a combination thereof, upon receipt of an activation signal.

A process for operating a releasable fastener system comprises contacting a loop portion with a hook portion to form a releasable engagement, wherein the loop portion comprises a support and a loop material disposed on a surface thereon, and wherein the hook portion comprises a support and a plurality of hook elements disposed on a surface, wherein the plurality of hook elements comprises a shape memory alloy fiber; maintaining constant shear and pull-off forces in the releasable engagement without introducing an energy signal; selectively introducing the energy signal to the hook elements, wherein the energy signal is effective to change a shape orientation, a yield strength property, a flexural modulus property, or a combination thereof to the plurality of hook elements; and reducing the shear and/or pull off forces in the releasable engagement.

The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the FIGURES, which are exemplary embodiments and wherein like elements are numbered alike:

FIG. 1 is a cross sectional view of a releasable fastening system of a first embodiment;

FIG. 2 is a cross sectional view of the releasable fastening system of FIG. 1, wherein the releasable fastening system is engaged;

FIG. 3 is a cross sectional view of the releasable fastening system of FIG. 1, wherein the releasable fastening system is disengaged;

FIG. 4 is a cross sectional view of an engaged releasable fastener system in accordance with another embodiment;

FIG. 5 is a cross sectional view of the engaged releasable fastener system, wherein a loop material and a plurality of hook elements are in a shape orientation suitable for providing the engaged releasable fastener system of FIG. 6 with a reduction in shear and/or pull-off forces;

FIG. 6 is a perspective view of a hybrid hook element comprised of a fiber and sleeve, and support;

FIG. 7 is a perspective view of a hybrid hook element comprised of a fiber and sleeve, and support, in accordance with another embodiment;

FIGS. 8A and 8B are cross sectional views of a retractable hook element; and

FIG. 9A is a cross sectional view of hook element in accordance with another embodiment and FIG. 9B is an enlarged perpective view of hook element.

DETAILED DESCRIPTION

As shown in FIG. 1, a releasable fastener system, generally indicated as 10, comprises a loop portion 12 and a hook portion 14. The loop portion 12 includes a support 16 and a loop material 18 disposed on one side thereof whereas the hook portion 14 includes a support 20 and a plurality of closely spaced upstanding hook elements 22 extending from one side thereof. The hook elements 22 generally comprise or incorporate a fiber, coating, or sheath fabricated from a shape memory alloy, or a fiber, coating, or sheath (i.e., sleeve) of superelastic shape memory alloy. As used herein, the term "fiber" refers to and is interchangeable with a filament or a wire, which fiber may comprise a single strand or multiple strands.

The shape memory alloy provides the hook element 22 with a shape changing capability, a yield strength changing capability, and/or a flexural modulus property change capability to the hook elements 22, as will be described in greater detail. Coupled to and in operative communication with the hook elements 22 is an activation device 24. The activation device 24, on demand, provides a thermal activation signal to the hook elements 22 to cause a change in the shape orientation, yield strength, and/or flexural modulus properties of the hook elements 22. The change in shape orientation, yield strength and/or flexural modulus property generally remains for the duration of the applied thermal activation signal. Upon discontinuation of the thermal activation signal, the hook elements 22 revert to an unpowered state. The illustrated releasable fastener system 10 is exemplary only and is not intended to be limited to any particular shape, size, configuration, number or shape of hook elements 22, shape of loop material 18, or the like. Moreover, the orientation of each hook element may be randomly arranged on the support or may be aligned in the same direction (as shown in FIG. 1).

During engagement, the two portions 12, 14 are pressed together to create a joint that is relatively strong in shear and/or pull-off directions, and weak in a peel direction. For example, as shown in FIG. 2, when the two portions 12, 14 are pressed into face-to-face engagement, the hook elements 22 become engaged with the loop material 18 and the close spacing of the hook elements 22 resist substantial lateral movement when subjected to shearing forces in the plane of engagement. Similarly, when the engaged joint is subjected to a force substantially perpendicular to this plane, (i.e., pull-off forces), the hook elements 22 resist substantial separation of the two portions 12, 14. However, when the hook elements 22 are subjected to a peeling force, the hook elements 22 can become more readily disengaged from the loop material 18, thereby separating the hook portion 12 from the loop portion 14. It should be noted that separating the two portions 12, 14 using the peeling force generally requires that one or both of the supports forming the hook portion and loop portion to be flexible.

To reduce the shear and pull-off forces resulting from the engagement, the shape orientation, yield strength, and/or flexural modulus properties of the hook elements 22 are altered upon receipt of the thermal activation signal from the activation device 24 to provide a remote releasing mechanism of the engaged joint. That is, the change in shape orientation, yield strength, and/or flexural modulus of the hook elements reduces the shearing forces in the plane of engagement, and/or reduces the pull off forces perpendicular to the plane of engagement. However, depending on the hook geometry and direction of shear, the reduction in pull off forces is generally expected to be greater than the reduction in shear forces. For example, as shown in FIGS. 2 and 3, the plurality of hook elements can have inverted J-shaped orientations that are changed, upon demand, to substantially straightened shape orientations upon receiving the thermal activation signal from the activation device 24. The substantially straightened shape relative to the J-shaped orientation provides the joint with marked reductions in shear and/or pull-off forces. Similarly, a reduction in shear and/or pull off forces can be observed by changing the yield strength, and/or flexural modulus of the hook elements. The change in yield strength and/or flexural modulus properties can be made independently, or in combination with the change in shape orientation. For example, changing the flexural modulus properties of the hook elements to provide an increase in flexibility will reduce the shear and/or pull-off forces. Conversely, changing the flexural modulus properties of the hook elements to decrease flexibility (i.e., increase stiffness) can be used to increase the shear and pull-off forces when engaged. Similarly, changing the yield strength properties of the hook elements to increase the yield strength can be used to increase the shear and pull-off forces when engaged. In both cases, the holding force is increased, thereby providing a stronger joint.

Shape memory alloys typically exist in several different temperature-dependent phases. The most commonly utilized of these phases are the so-called martensite and austenite phases. 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 (A.sub.s). The temperature at which this phenomenon is complete is called the austenite finish temperature (A.sub.f). 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 (M.sub.s). The temperature at which martensite finishes transforming to martensite is called the martensite finish temperature (M.sub.f). Generally, the shape memory alloys are soft and easily deformable in their martensitic phase and are hard, stiff, and/or rigid in the austenitic phase.

Depending on the phase transformation temperatures for the particular shape memory alloy composition, the releasable fastener system can be configured with a variety of capabilities. For example, in a so-called "hot-hold" configuration, the hook elements may be fabricated from shape memory alloys that exhibit an austenite phase at an ambient environmental temperature in which the releasable fastener system is disposed and with a shape effective for engagement with the loop material. Thermal activation would thus require cooling the hook elements to a temperature below the austenite temperature to the martensite phase transformation temperature to cause disengagement. Alternatively, in a so-called "cold-hold" configuration, the hook elements may be fabricated and engaged with the loop portion in a martensite phase, wherein the martensite phase transformation is at or above the ambient environmental conditions in which the releasable fastener system is disposed. Thus, heating the hook elements to an austenite finish temperature would, given the proper materials processing, preferably cause the hook elements to straighten and cause disengagement.

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. Hook elements formed from shape memory alloy compositions that exhibit one-way memory effects do not automatically reform, and depending on the hook element design, will likely require an external mechanical force to reform the shape orientation that was previously suitable for engagement with the loop portion.

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 martensite phase back to the austenite phase. Hook elements that exhibit an intrinsic shape memory effect are fabricated from a shape memory alloy composition that will 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, hook elements 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 hook-like shape.

In one embodiment, as shown in FIGS. 2 and 3, the hook elements 22 are fabricated from shape memory alloys that exhibit one-way shape memory effects. The hook elements are fixedly attached to support 20 or may be integrally formed with the support 20. The mechanical engagement of the hook portion 14 with the loop portion 12 (as shown in FIG. 1) can be achieved by interaction of the hook elements 22 with the loop material 18 or through physical deformation of suitably arranged hook elements 22 during the face-to-face engagement. That is, each hook element 22 preferably maintains a shape orientation conducive for contact engagement with the loop material 18. Physical deformation may also be employed to provide a shape orientation suitable for the engagement with the loop portion 18. FIG. 2 illustrates the hook element 22 in one such exemplary engagement position. In this position, the shape memory alloy is preferably in the martensite phase. However, upon heating the hook element 22 to a temperature greater than the austenite finish temperature (A.sub.f), the hook elements 22 change to substantially straightened shape orientations as shown in FIG. 3. As a result, a marked reduction in shear and pull-off forces can be provided to the releasable fastener system 10 through application of a thermal activation signal. As previously noted, the marked reduction in shear and pull-off forces may also be effected by changes in the yield strength, and/or flexural modulus properties of the hook elements 22.

Alternatively, the shape memory alloy hook elements are coated with a polymer, an elastomer, or a shape memory polymer to increase the stiffness of the hook elements and as such, its hold force at martensite temperature states. The applied polymer or elastomer serves to maintain a nearly constant strain level to the hook element. The polymer or elastomer is preferably selected to provide reversible strains to the hook elements such that upon cooling, the shape memory alloy transforms to the martensite phase, and the elastic strains extant in the polymer or elastomer coating are sufficient to reset the shape of the shape memory alloy element back into the hook shape that existed prior to release. Similar to the behavior of a shape memory alloy, when the temperature is raised through its transition temperature, a shape memory polymer also undergoes a rapid and reversible decrease in yield strength/flexural modulus and change in shape orientation. By coating a shape memory alloy with a shape memory polymer whose transition temperature is below that of the shape memory alloy, it is also possible to reversibly form and reform the hook shape. In this instance, the straightened shape is set by the shape memory alloy above its (higher) transition temperature while the (reformed) hook shape is set by the shape memory polymer above its (lower) transition temperature. Heating therefore causes hook release and as the straightened hook is cooled below the higher temperature, the shape orientation defined by the shape memory alloy reestablishes the hook orientation.

In another embodiment, the superelastic properties of the shape memory alloys can be employed. Superelastic behavior results if the shape memory alloy is deformed at a temperature that is slightly above its transformation temperatures. The superelastic effect is caused by a stress-induced formation of some martensite above its normal temperature. Because it has been formed above its normal temperature, the martensite reverts immediately to an undeformed austenite as soon as the stress is removed. This process provides a very springy, "rubberlike" elasticity in these alloys. In this alternative embodiment, the hook elements 22 are fabricated from a selected shape memory alloy composition that maintains the austenite phase at environmental temperature conditions in which the fastener is to be employed. The shape of the hook elements 22 in the austenite phase would be suitable for engagement with the loop material 18 (e.g., similar to the shape shown in FIG. 2). Cooling the hook elements 22 to a temperature below the austenite phase (i.e., to the martensite phase) reduces the yield strength and/or the flexural modulus of the hook elements, hence reducing the shear and pull off forces relative to those present while the hook elements 22 are engaged with the loop material 18 while in the austenite phase. For example, the shape memory alloy composition can be selected to exhibit an austenite phase at about room temperature. Lowering the temperature of the hook elements 22 below room temperature would cause the hook elements 22 to transform from the stiffer austenite phase to the weaker martensite phase, thereby permitting separation in the shear and/or pull off directions at significantly lower force levels.

In another embodiment, the hook elements 22 and/or loop material 18 are fabricated from shape memory alloys that preferably exhibit two-way shape memory effects. In this embodiment, both the hook and loop elements receive processing ("training") suitable to produce a reversible shape change that occurs as the hook elements (and/or loop material) transition from the martensite phase to the austenite phase, and vice versa. In this manner, the reversible shape change can be manipulated back and forth between shape orientations suitable for engagement and disengagement. For example, as shown in FIGS. 4 and 5, both the hook elements 22 and the loop material 18 are selected to have a spiral shape orientation, which when pressed together result in an engagement that is relatively strong in shear and pull-off forces and weak in peel forces. Preferably, the hook elements and the loop material are mated together in a straightened shape orientation (FIG. 5), and then allowed to cool to the spiral shape orientation (FIG. 4). As such, instead of being passive, the loop material 18 in this embodiment can be made active upon receipt of an appropriate thermal activation signal. Thermally activating the hook elements 22 and/or loop material 18 can cause a change in shape orientation, yield strength, and/or flexural modulus to provide a marked reduction in shear and pull-off forces required for separation.

Alternatively, the superelastic properties of the shape memory alloy can be employed in a manner similar to that previously described, except that proc