Blind fasteners
Fasteners for producing double blind joints where the fastener is not visible or accessible are provided. The fasteners comprise a shape memory polymer that may be used to fasten workpieces by heating the fasteners, inducing recovery of the original, permanent shape of the fasteners.
1. A fastener comprising a thermoplastic polyurethane shape memory polymer having a transition temperature (T trans ) of at least 50° C.; the fastener comprising a length, a width, and no head; wherein the fastener is axially oriented at least 50% in the longitudinal direction.
2. The fastener of claim 1 , wherein the thermoplastic polyurethane shape memory polymer comprises a thermoplastic polyurethane with a hard segment as a permanent shape and a soft segment as a switching temporary shape.
3. The fastener of claim 1 , wherein the thermoplastic polyurethane shape memory polymer is partly derived from methylene diphenyl diisocyanate.
4. The fastener of claim 1 , wherein the fastener is axially oriented at least 100% in the longitudinal direction.
5. The fastener of claim 4 , wherein the fastener is axially oriented 150% in the longitudinal direction.
6. The fastener of claim 4 , wherein the fastener is axially oriented at least 200% in the longitudinal direction.
7. The fastener of claim 1 , wherein the thermoplastic polyurethane shape memory polymer has a transition temperature (T trans ) of at least 100° C.
8. The fastener of claim 7 , wherein the thermoplastic polyurethane shape memory polymer has a transition temperature (T trans ) of at least 125° C.
9. The fastener of claim 1 , wherein the fastener has a rod shape.
10. The fastener of claim 9 , wherein the fastener is a rivet.
11. The fastener of claim 1 , wherein the fastener has a solid cross-section.
12. The fastener of claim 11 , wherein the fastener has a cross-section selected from the group consisting of cylindrical, ovoid, square, rectangular, and higher polygonal.
13. The fastener of claim 12 , wherein the fastener has a cylindrical cross-section.
14. The fastener of claim 13 , wherein an outer surface of the fastener comprises grooves or ridges.
15. The fastener of claim 1 , wherein the transition temperature (T trans ) is a glass transition temperature (T g ).
16. The fastener of claim 15 , wherein the thermoplastic polyurethane shape memory polymer has a glass transition temperature (T g ) of at least 100° C.
17. The fastener of claim 16 , wherein the thermoplastic polyurethane shape memory polymer has a glass transition temperature (T g ) of at least 125° C.