Fatigue life prediction method of Q235 steel single lap thin-walled bolted connections under shear loading

In this study, a large number of shear fatigue tests were conducted on Q235 steel single lap thin-walled bolted connections to investigate the influence of different geometric and load parameters on the dispersion of fitting data for load amplitude-life (Fa-N) curves. Due to the large dispersion of fitting data, the Fa-N curves were unable to meet engineering requirements. In order to standardize these Fa-N curves, an equivalent structural stress model for single lap thin-walled bolted connections was established based on a mechanical model with a strict physical definition. The shell equivalent model of the Q235 steel single lap thin-walled bolted connection was developed using the Rupp structural stress calculation method, and the equivalent structural stress was determined by considering the node loads coupled by the beam element. Subsequently, a normalized fatigue characteristic curve (Ss-N curve) was created to standardize the Fa-N curves. However, differences in external load, pre-tightening force, bolt diameter, and plate thickness resulted in a relatively low correlation across the entire Ss-N curve. To address this, four quasi-Newton optimization algorithms (C1-C4) were employed to optimize the equivalent structural stress model. This approach yielded the best optimization model for equivalent structural stress and an Ss-N curve with a higher correlation. These findings offer valuable insights for optimizing single lap thin-walled bolted connection parameters and predicting fatigue life.