Effects of Spring Washer on Self-loosening of Threaded Fasteners under Transverse Vibration

Abstract

Self-loosening of threaded fasteners sometimes occurs under dynamic loads such as vibration and shock. For mechanical structures, the self-loosening with rotation of threaded fasteners under transversely repeated load is particularly important. Although many parts preventing the loosening of bolt joint are being evaluated the locking performance of self-loosening, there are not clear about the locking performance of the spring washer. In this paper, using bolted joint with the spring washer, we have examined the influence of the lubrication state of the seating surface on the self-loosening under transverse cyclic loading. As a result, when lubricating oil is applied to the seating surface, the bolt joint with the spring washer is self-loosening even under the amplitude that does not cause slippage on the seating surface, and is easier to loosen than the fastening of the bolt alone. On the other hand, when the seating surface is degreased, the bolt tension gradually decreases without causing slippage on the seating surface. Using bolted joint with a spring washer, there is a case that it is harder to loosen than fastening of a bolt alone because the frictional resistance of the seating surface increases as the transverse amplitude increases.