Failure behaviours of steel/aluminium threaded connections under impact fatigue

Threaded connections work as essential components in engineering structures, covering multiple industries such as aerospace and construction. However, they are frequently exposed to complex loadings of dynamic and impact loads, which even result in unexpected fatigue failure. In this study, we modify Hopkinson tension bar technique by guiding stress wave reflection, to achieve controllable cyclically loading threaded fasteners under impact fatigue. Specimen of steel-aluminum threaded connection is specifically designed for focusing on mere aluminum thread failure. Impact fatigue of 1 kHz around are successfully conducted, enabling to precisely determine mechanical behaviors of each cyclic and impact fatigue life under varying tensile loads. It is demonstrated that, its impact fatigue life is strongly dependent on loading stress amplitude. More importantly, irreversible damage occurring in threads, presents in the overall linear-elastic phase of the connection under impact fatigue loading, leading to progressive degradation of mechanical properties and eventual failure. Failure mode is predicted experimentally and verified by finite element simulated results, of uneven load/stress distribution across threads where higher stress concentrations occur near thread root, making them more susceptible to failure and progressive degradation.