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