Mechanical Behavior and Failure Mechanisms of Composite Bolted Joints Subjected to Static Pull-Through Loading

This study explores the mechanical performance and failure mechanisms of composite bolted joints under static pull-through loading by integrating experimental tests and numerical analyses. Three configurations, including the asymmetrical composite joint (ABJ), symmetrical composite joint (SBJ), and shim-reinforced symmetrical composite joint (RSBJ), are designed and examined via a custom-designed fixture. The out-of-plane bearing strength and damage characteristics of these joints are comparatively analyzed. Test results demonstrate that the stiffness and ultimate bearing load of ABJ are notably inferior to those of SBJ, with respective reductions of 22.27% and 35.62% in these two key parameters. A three-dimensional numerical model was established via ABAQUS/Explicit 2024 and validated with high accuracy for predicting both the mechanical response and failure modes of joints with all configurations. The intralaminar and interlaminar damage mechanisms were further explored through numerical analyses, indicating that matrix damage and delamination serve as the primary failure modes of the tested joints. The bolt stress distribution patterns across different joint configurations are predicted and analyzed. The findings demonstrate that the symmetrical composite lap joint enhances stress distribution uniformity in the bolt under out-of-plane pull-through loading, and the addition of shims leads to stress concentration near the bolt head, increasing the risk of joint failure.