Reusable Locknuts Using Shape Memory Alloy Inserts for Providing the Prevail ing Torque

Period of Performance: 12/10/1993 - 12/15/1995


Phase 2 SBIR

Recipient Firm

Memry Technologies, Inc.
57 Commerce Drive
Brookfield, CT 06804
Principal Investigator


Fastener improvement was identified in the Air Force Advisory Board's study fo subsystem and component reliability needs, FACTS. Nylon insert locknuts cannot be reused with confidence and alternative insert materials are required. Phase I studies of polymeric and metallic insert materials demonstratred that shape memory alloys will provide the necessary prevailing and breakaway torque specified in MIL-N-25027-Amendment for 250 degrees F improved locknut, and prior Memry Technologies research rpovides data whch clearly identified the Copper-Aluminum-Nickel system as the best insert candidate. The design of a shape memory alloy insert locknut system requires extremely careful measurement and control of thread dimensions in order to assure that it meets performance goals over the entire range of ANSI thread tolerance. After choosing with ALC personnel a series of locknut sizes best suited to AF field trials and demonstrations, the design and testing of prototype locknuts will be carried out. This will include shape memory alloy optimization and the establishment of dimensional tolerance levels. Industrial applications will be identified for the Air Force locknut design or for a modified design for commercial demonstration.