Self-locking threaded fasteners assessed by institutions

Engineers are successfully attacking vibrational loosening, axial-torsional loading, joint fatigue, and thermal extremes with Spiralock's innovative self-locking threaded fasteners whose effectiveness has been validated in published test studies at leading institutions including MIT, the Goddard Space Flight Center, Lawrence Livermore National Laboratory, and British Aerospace, as well as at noted corporations such as Mack Truck and Dana Corporation.

Resistance to vibration

Tests undertaken by the Goddard Space Flight Center subjected Spiralock nuts (stainless alloy A-286 and alloy steel) to vibration and static load conditions. The most severe vibration tests (sine: 24.7Hz - 2G and random 20-400Hz - 2G RMS) did not loosen the nuts when subjected to both high amplitude and sine random testing.

British Aerospace: Naval Warfare Division also confirmed Spiralock's self-locking threaded fasteners' resistance to vibration. Testing was performed on an Unbrako Fastener Vibration Machine using M6 x 25mm grade 8 bolts with wire inserts in L168 aluminum, and 20 samples of both Spiralock wire inserts and standard (60 degree UN thread) wire inserts. These were tested at 13.6Hz and tightened to 1800 pounds of preload.

Results showed that Spiralock wire inserts delivered consistent vibration-resistant performance with an average preload loss of 15 per cent, while the standard wire inserts gave erratic results, losing from 22 to 95 per cent preload given the same test parameters.

Resistance to axial-torsional loading

A finite element analysis (FES) report prepared for Lawrence Livermore National Laboratory compared a spacecraft node-to-strut threaded connection using 10-32 UNF-to-Spiralock female thread. In analysing axial thread load distribution, separate analyses were performed to compare the load distribution for each thread of Spiralock's self-locking fasteners and the UNF. The boundary condition on both nuts was changed to constrain the face of the nut in the axial direction, but free to move in the radial direction.

The report explains how the design of Spiralock's self-locking fasteners allows for more uniform load distribution on each thread: "The thread bearing stresses in the Spiralock threads are concentrated at the sharp points of contact where there is localised yielding in compression. These high local compressive stresses do not cause a strength problem, but the local yielding allows a more uniform load distribution on each thread."

Similar studies published in a report by the Massachusetts Institute of Technology (MIT) for Chrysler Corporation compares Spiralock's self-locking threaded fasteners (on the nut) and standard 60 degree thread forms.

According to the report, calculations show: the total bolt load is more evenly distributed over the engaged threads for Spiralock thread locking form than the 60 degree thread form; the maximum stresses at the root of the bolt thread are of the same order of magnitude in both cases; and the movement required for relative rotation is significantly higher for Spiralock.

Visit Spiralock's website for complete reports on the self locking threaded fasteners, including comparative graphic loading characteristics or photoelastic analysis/load vector comparison animation, as well as test data from Mack Truck and Dana Corporation about the thread locking form.