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An article and method for measuring strain using a strain gauge made of a shape memory alloy, and preferably a pseudoelastic alloy, is disclosed. The strain gauge includes an element that preferably is attached to a substrate and mounted on an object, or is woven or stitched to a fabric to measure t

An article and method for measuring strain using a strain gauge made of a shape memory alloy, and preferably a pseudoelastic alloy, is disclosed. The strain gauge includes an element that preferably is attached to a substrate and mounted on an object, or is woven or stitched to a fabric to measure the strain experienced under an applied stress. The preferred pseudoelastic alloy is Nitinol, which in pseudoelastic form can elongate by up to approximately 8% to accommodate strain in an object or fabric. When woven into a fabric, a Nitinol-based strain gauge can measure strains of up to approximately 20% in the fabric. The strain gauge can be used in such applications as automotive and aircraft seatbelts, parachute canopies and static lines, and commercial cargo nets.

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1. A strain gauge comprising:a substrate; and a length of shape memory alloy mounted on the substrate, the alloy reversibly elongating to accommodate an applied stress while exhibiting a change of resistance. 2. The strain gauge of claim 1, wherein the shape memory alloy is a pseudoelastic alloy. 3

1. A strain gauge comprising:a substrate; and a length of shape memory alloy mounted on the substrate, the alloy reversibly elongating to accommodate an applied stress while exhibiting a change of resistance. 2. The strain gauge of claim 1, wherein the shape memory alloy is a pseudoelastic alloy. 3. The strain gauge of claim 1, wherein the strain gauge is attached to an object and measures an elongation of the object. 4. The strain gauge of claim 3, wherein the strain gauge elongates by up to approximately 8% to accommodate the elongation of the object. 5. The strain gauge of claim 4, wherein the elongation of the object is determined by measuring the change of resistance. 6. The strain gauge of claim 1, wherein the length of shape memory alloy is a Nitinol wire. 7. A strain gauge comprising:a length of shape memory alloy attached to a web of material, the alloy reversibly elongating to accommodate an applied stress in the material while exhibiting a change of resistance. 8. The strain gauge of claim 7, wherein the strain gauge elongates by up to approximately 8% to accommodate the elongation of the web of material. 9. The strain gauge of claim 8, wherein the elongation of the web of material is determined by measuring the change of resistance. 10. The strain gauge of claim 8, wherein the web of material is a large-strain material such as a rubber sheet, a rubber diaphragm, a rubber strap, a balloon, or a plastic. 11. The strain gauge of claim 10, wh erein the length of shape memory alloy is embedded into the large-strain material. 12. The strain gauge of claim 7, wherein the strain gauge is stitched to the web of material. 13. The strain gauge of claim 7, wherein the strain gauge is woven into the web of material. 14. The strain gauge of claim 7, wherein the strain gauge measures elongation of up to approximately 20% in the web of material. 15. The strain gauge of claim 7, wherein the web of material is a seat belt. 16. The strain gauge of claim 7, wherein the web of material is a parachute. 17. The strain gauge of claim 7, wherein the length of shape memory alloy is a Nitinol wire. 18. A device for measuring strain in a web which experiences the strain in response to an applied stress, comprising:an elongated element of a shape memory alloy embedded into the web, the element forming an integral part of a strain gauge, wherein the element reversibly elongates to accommodate the applied stress. 19. The device of claim 18, wherein the shape memory alloy element elongates by up to approximately 8% to accommodate the applied stress. 20. The device of claim 18, wherein the strain gauge measures the strain by measuring a change of resistance of the shape memory alloy element. 21. The device of claim 18, wherein the shape memory alloy element is made of a pseudoelastic alloy. 22. The device of claim 18, wherein the shape memory alloy element is made of Nitinol. 23. The device of claim 18, wherein the st rain gauge measures the strain of up to approximately 20% in the web. 24. The device of claim 18, wherein the web is a seat belt. 25. The device of claim 18, wherein the web is a parachute. 26. A method for measuring strain, comprising the steps of:providing a web of material; providing a strain gauge including an elongated element of a shape memory alloy attached to the web of material; subjecting the web of material to an applied stress such that the web elongates to accommodate the applied stress; and applying a current through the element of the shape memory alloy to measure a change of resistance of the element and thereby determine strain in the web of material caused by the applied stress. 27. The method of claim 26, wherein the shape memory alloy element is a pseudoelastic alloy. 28. The method of claim 27, wherein the strain gauge element elongates by up to approximately 8% to accommodate the elongation of the web of material. 29. The method of claim 27, wherein the strain gauge is mounted on an object. 30. The method of claim 29, wherein the strain gauge includes a substrate, and the shape memory alloy element is mounted on the substrate. 31. The method of claim 28, wherein the element is woven into the web of material. 32. The method of claim 28, wherein the element is stitched to the web of material. 33. The method of claim 26, wherein the web of material is a seat belt. 34. The method of claim 26, wherein the web of material is a parachute.