DOE Investigation on the Effect of Dimensional Thread Tolerance on the Vibration-Induced Loosening of Fasteners

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.