Sleeve deformation effects on installation damage in CFRP countersunk interference-fit joints

Countersunk sleeved interference-fit joints achieve excellent mechanical strength and lightning strike resistance in carbon fiber reinforced polymer (CFRP) structures. However, non-uniform sleeve deformation during installation can cause interface damage and degrade joint performance. Therefore, a three-dimensional progressive damage model incorporating a stiffness degradation correction algorithm was developed to accurately reveal the initiation and progression of interface damage caused by sleeve deformation. Installation experiments were conducted to validate the simulation results, focusing on mechanical response, damage modes, and sleeve deformation. The influence of key structural parameters, including theoretical interference-fit size, sleeve thickness, and taper, on sleeve deformation and interface damage was systematically investigated. The results show that in the fillet region, the bottom of the sleeve's countersunk section wedges into the CFRP straight-wall region, leading to significant radial deformation and local damage. In the straight-wall region, plastic deformation of the sleeve causes axial material flow and accumulation, resulting in gradual radial expansion of the hole wall and progressive damage. Within the study's scope, maintaining the theoretical interference-fit size below 3.0 % and moderately increasing sleeve thickness effectively suppresses non-uniform sleeve deformation and damage propagation. These findings provide a theoretical basis for the design of countersunk sleeved interference-fit joints.