Most dismantlable assemblies are integrated using threaded joints where bolts are used in the clearance hole. The integrity of such assemblies critically depends on the preload induced by an initial tightening of fasteners. Preload decreases over service time and is known as bolt self-loosening. Bolt self-loosening causes more than 20% of catastrophic failures in mechanical systems and more than 80% of required maintenance in the automobile industry.

Two parts are held together with a pretention load in the bolt shank. The preload induces pre-elongation in the bolt shank. A reduction/relaxation in the pre-elongation results in a reduction of the preload. Change in the pre-elongation can occur in several ways: free rotation of the nut, mismatched thermal expansion, plastic deformation, stress relaxation, or creep and fretting wear. This example problem focuses on the effect of wear on non-rotational bolt self-loosening.

Bolt pretention load and small relative oscillatory motion between mating parts induces fretting wear that erodes material at the interfaces. The fretting wear depends on pretention load, amplitude, frequency, and direction of the external excitation. Erosion of material at the mating interfaces continually reduces the pre-elongation that results in bolt self-loosening [1]. A simple literature problem [2] is examined here for demonstration purposes. The effects of amplitude, frequency, and direction of an external excitation are discussed for a simple lap joint. The numerical results reported here are consistent with experimental observations from the literature [3].