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This study investigates the effect of the fasteners threads dimensional variation within the conformance tolerance limits on the self-loosening of threaded fasteners that are subjected to cyclic transverse service loads. A test setup is developed in order to simulate cyclic transverse service loads, and monitor the fastener clamp load loss and rotation in real-time during the test. The tested fasteners are used in one of the critical safety joints in a DaimlerChrysler vehicle. The tested thread dimensional parameters are the major diameter, the minor diameter, the pitch diameter, thread pitch, and thread profile angle. These parameters are measured optically. A set of conforming fasteners are selected and tested for self loosening. The self-loosening results are used to construct a model that fits the data points that are obtained experimentally. After that, the developed model is used to estimate the effect of each factor and its interaction with other factors on the self-loosening.

This paper investigates the reliability of tightening automotive weld studs, using experimental techniques. During the nut installation on weld studs, only a small amount of the applied torque is used to produce the required clamp load in the joint. While a large amount of the input torque is lost in overcoming friction between the sliding surfaces. Large scatter in the stud tension often results from the normal friction variations. As a result, the weld stud becomes more susceptible to a pull-through failure mode especially in thin sheet metal applications. The torque-angle signature during stud tightening is analyzed to assess the strength and quality of the weld stud joint. The effect of the weld stud thread type, stud coating, sheet metal thickness and stud material on the torque-tension relationship of weld studs is investigated. An experimental procedure and test set up are proposed to test weld studs.