New Test Data for Self Locking Threaded Fasteners Offers Resolution for Toughest Engineering Challenges

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

British Aerospace: Naval Warfare Division confirmed Spiralock’s self locking threaded fasteners resistance to vibration. Testing was done 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 also known as Helicoil Screwlock wire thread inserts. These were tested at 13.6 Hz and tightened to 1800 pounds of preload.

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

Resistance to Axial-Torsional Loading
A Finite Element Analysis report prepared for Lawrence Livermore National Laboratory compared a spacecraft node to strut threaded connection using 10-32 UNF to Spiralock female thread. In analyzing axial thread load distribution, separate analysis was done to compare the load distribution for each thread of Spiralock’s self locking fasteners and 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 localized 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 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.

Spiralock Corporation
Kate Turowska
KTurowska@spiralock.com
Phone: (248) 543-7800
Fax: (248) 543-1403
http://www.spiralock.com