Fatigue-Based Severity Factors for Shear-Loaded Fastener Joints

Abstract

Using Hi-Lok fasteners and Universal rivets, we experimentally investigated the fatigue behavior of fastener joints under constant-amplitude loading. The study generated fatigue-based stress severity factors for fastener joints at two different load transfer and mean stress levels. Fatigue tests on open-hole, filled-hole, and load transfer specimens were conducted at mean stress levels of 20.68 and 41.37 MPa, with varying stress ratios to achieve lives ranging between 10 3 and 10 6 cycles. The regression-based mean life curves were used to generate the fatigue-based correction factors for hole filling and bearing load transfer as a function of the maximum stress level. The fatigue life of load transfer specimens fell between those of the open-hole and filled-hole configurations. With increasing load transfer and mean stress levels, the fatigue life approached that of the open-hole case. In addition, at stress levels corresponding to fatigue lives in excess of 10 5 cycles, the failure modes of load transfer specimens transitioned from a net-section failure to a clamp-up-induced fretting failure occurring away from the fastener hole. The stress severity factor associated with the mean life of fastener joints and Hi-Lok filled-hole coupons increased with the maximum fatigue stress level. However, different trends were observed with respect to load transfer at the two mean stress levels used in the study.