ABSTRACT
A metallic part subjected to cyclic tensile loads can suddenly and unexpectedly fail—even if those loads are well below the yield strength of the material. Fatigue failure of a single bolt means a reduction in clamping force. Fatigue failures are called high-cycle or low-cycle failures, depending on the number of load cycles required to break the part. Shear stress, for example, would rob a portion of the strength of the fastener, making it more susceptible to tension fatigue. A bolt is a very poor shape when it comes to fatigue resistance. Although the average stress levels in the body may be well below the endurance limit of the material, stress levels in unavoidable stress concentration points such as thread roots, and head-to-body fillets can be well over the endurance limit. Increasing the preload in an eccentric prying joint will increase the mean tension seen by the bolt.
