Study on the preload loss mechanisms of CFRP-steel hybrid bolted joint under transverse cyclic loading

There is bolt preload loss under vibration in the aircraft rudder, of which the connected parts are steel beam and CFRP panel, and the fastener is bolts and self-lock jet nuts. Based on the above phenomenon, this paper analyzes rotational loosening, washer wear, composite progressive damage, and plastic deformation condition of CFRP-steel hybrid self-lock bolted joint under transverse cyclic loading by experiments and finite element simulations, and subsequently analyzes the preload loss mechanisms. The results showed that washer wear was the main factor leading to the preload loss under long-term loading, and even this factor accounted for 70% of the total preload loss when the aluminum washer was used. During short-term loading, local slip and stress redistribution among threads, plastic deformation, and composite damage accounted for 30%, 50%, and 20% of the total preload loss respectively. To prevent preload loss, the wear-resistance of the washer should be improved, and the plastic deformation on the bolt and the damage in the composite material should be reduced.