Three dimensional Finite Element model is used to investigate the loosening behavior of countersunk threaded fasteners subjected to cyclic shear loading applied through prescribed transverse excitation to the fastener head. Fasteners with conical head profile require precision machining of both the fastener head and the mating joint hole. Any mismatch between the head and the joint conical angles affects the torque tension relationship as well as the loosening performance. Investigation focuses on the loosening behavior in its early stages. Factors investigated include the effect of the bolt head/joint hole contact location, joint elastic modulus, and tapped hole clearance for different combinations of thread fit, on the loosening performance of preloaded countersunk-head bolts. The FEA model prediction of the self-loosening behavior is experimentally validated.

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