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SPIRALOCK TEST STUDIES

Dynamic and Static Testing
By: Goddard Space Flight Center

Dynamic Test (Sine: 24.7 Hz - 2G and Random 20-400 Hz - 2G RMS)
¼ -28 x 2, 180 KSI alloy steel bolt, with alloy steel and A286 hex nuts
Withstood 10X sine and random vibration Space Shuttle requirements without loosening.

Static Test (Tinius Olsen tensile test)
More consistent pattern of friction (K) factors
Non-Lubricated: 0.12 min., 0.36 max. Lubricated: 0.08 min., 0.13 max.
Friction characteristics of SPL nuts with lubrication considerably increases the accuracy of the preload due to torquing, measured on strain gaged bolts when discarding the first three readings.
This test was repeated 60 times on the same bolt.
Suggested tightening method: Torque at or near full torque (3) times before service.

Finite Element Analysis
By: Lawrence Livermore National Laboratory

SPL requires approximately 20% greater assembly torque to achieve same axial preload as 60° threads
FEA shows the first thread supports 12.5% of total load, and no thread less than 8% of total load. Very even load distribution.
Shows graphically the loading characteristics of SPL threads compared to 60° threads.
Shows reduced areas of stress concentration in bolt due to even thread loading of SPL threads.

Vibration Resistance and Stress Distribution
By: Massachusetts Institute of Technology
For: Chrysler Corporation

Very detailed with formulae calculating thread deflections and loading.
Conclusions show greater than 3:1 improvement is resistance to vibration loosening, empirically and proven in testing.
More even thread loading over 8 engaged threads.

Vibration Testing of Spiralock Wire Thread Inserts
By: British Aerospace: Naval Warfare Division

Vibration testing on an Unbrako Fastener Vibration Machine SV-102-71
M6 x 25 mm grade 8 bolts with wire inserts in L168 aluminum, 20 samples of both Spiralock wire inserts and standard (60 degree UN thread) wire inserts
Tested at 13.6 Hz, tightened to 1800 pounds of preload
Results showed that Spiralock wire inserts yielded consistent vibration resistant performance with an average preload loss of 15%
Standard wire inserts yielded erratic results, losing from 22% to 95% preload given the same test parameters
Spiralock wire inserts averaged 120% off-torque, compared with on-torque