Effect of installation and preloading on tensile failure mechanism of composite countersunk sleeved interference-fit joints

Countersunk sleeved interference-fit joints are increasingly utilized in high-performance composite structures due to their superior lightning strike resistance and load-bearing capacity. However, the coupling effects of radial interference and axial preload on the tensile failure behavior remain insufficiently understood. This study develops a high-fidelity multi-stage damage analysis method to investigate the progressive damage evolution and mechanical response of the joints throughout interference installation, bolt preloading, and subsequent tensile loading. By incorporating detailed thread geometry and a 3D progressive damage model with modified stiffness degradation, this method ensures a consistent transfer of damage states across loading stages and is rigorously validated by experimental results. This study revealed the preload conversion mechanism under various interference levels and clarified the tensile failure mechanism. The coupled effects of interference-fit size and preload on joint stiffness and ultimate load were also investigated. The results indicated that preload conversion efficiency is restricted by radial contact pressure and decreases with increasing interference level. Appropriately increasing the preload can effectively inhibit the non-uniform propagation of interface damage. The joint load-bearing performance is governed by the synergistic interaction between radial interference and axial preload. These findings can provide a basis for strength optimization of composite bolted joints.