Characterization of Wear and Fatigue Damage in CFRP/Ti Single-Lap Bolted Joints Under Cyclic Loading: X-ray Tomography and Finite Element Simulation

The single-lap bolted joints composed of carbon fiber reinforced polymer (CFRP) and titanium alloy (Ti) exhibit interfacial wear and hole-edge fatigue damage under cyclic loading, which constitute the primary forms of structural failure. However, accurately quantifying the fatigue accumulation and understanding its spatial relationship with interfacial wear remains challenging due to the opacity and heterogeneity of composite laminates. The present study employed tension–tension fatigue loading to simulate service mechanical conditions, investigating the effects of ply sequence ([0°/±45°/90°]2s vs. [45°/0°/-45°/90°]2s) and tightening torque (3, 6, 9 N·m) on interfacial wear and hole-edge fatigue damage accumulation. The wear depth and fatigue damage volume fraction were quantitatively characterized through a super-depth-of-field microscope and X-ray computed tomography (X-ray CT). Subsequently, a finite element model integrating interfacial wear and structural fatigue degradation was developed. The results show that the CFRP ply sequence primarily influences the interfacial wear and hole-edge fatigue damage mechanisms through the fiber-dominated orientation effect. Axial fatigue fracture of carbon fibers in loading-aligned plies generates interface-migrating third-body debris, while 45° orientations induce shear-dominated stepped delamination. Notably, the ±45° plies in both sequences exhibit pronounced fatigue damage with a maximum damage volume fraction of 17%. Furthermore, tightening torque induces a stress partitioning effect that propagates wear inward through matrix crushing as torque increases. This inward progression physically merges with internal fatigue damage zones, ultimately reaching a maximum wear depth of 23 μm.