New Criteria for Self-Loosening of Fasteners Under Vibration

A UNIQUE TEST method and apparatus now make it possible to reproduce conditions of vibration that are not only certain to loosen bolted joints but which also closely simulate actual conditions. It can be shown that properly preloaded fasteners loosen as a result of rotation as soon as relative motion occurs between the mating threads and between the bearing surfaces of the fastener and the clamped material. In addition to fatigue failure, self-loosening is the most frequent cause of failure of dynamically loaded, bolted joints. Goodier and Sweeney, as well as Sauer, Lemmon, and Lynn, have tested only axial dynamically loaded, bolted connections. In spite of their failure to obtain a complete self-loosening of threaded fasteners, they have offered an explanation for partial loosening, which docs contain the basic element of the mechanism of self-loosening of bolted connections. That is, bolted connections are loosened by the relative motion between the thread flanks and other contact surfaces of the clamped and clamping parts. In 1966, Paland precisely formulated and affirmed the prior theory and