A two-state hysteresis model for bolted joints, with minor loops from partial unloading

Abstract

Bolted lap joints can show hysteretic dissipation via small-scale frictional sliding between contacting surfaces. Here we study lap joints connecting two plates, with a single bolt and with two bolts, loaded cyclically in the transverse direction. Initial computational solutions in ABAQUS show hysteresis in force-displacement responses. We first normalize the computationally obtained hysteresis loops to obtain new ones with standardized slopes and widths. We then adapt a recently developed, unconventional, two-state hysteresis model to capture these normalized hysteresis loops. An excellent match is obtained with the reduced order model, using two free parameters. Interestingly, for single-bolted lap joints, the same hysteresis model fit works well over a range of friction coefficients and bolt preloads. For the double-bolted lap joint, there are two friction coefficients and two preloads; and the fitted parameters are not constant over different combinations thereof. The main advantages of the proposed two-state model are (a) its simplicity, and (b) its ability to capture minor loops formed by partial unloadings.