Abstract: Carbon fiber reinforced polymer (CFRP) is a widely used structural material in advanced aircraft, and its components are often used in important load-bearing areas through bolted joint. These structures need to withstand complex alternating loads during service, which puts high demands on their fatigue performance. However, The structural holes in CFRP components are easily subjected to bolt compression during mechanical connection. This will cause fatigue failure of these components, affecting the long-term service performance of the aircraft. To address the above problems, this work proposes a CFRP hole expansion strengthening process. The influence of expansion deformation on the damage of CFRP hole walls and fatigue performance was studied through a combination of simulation and experiment, and the gain mechanism of hole expansion process on the fatigue life of CFRP/Ti connectors was explained. The results indicate that as the expansion deformation increases, the expansion force continuously increases. The damage to CFRP holes is also more severe. When the expansion deformation exceeds 4%, serious damage occurs to the hole wall. The main forms of damage are fiber compression fracture in the 0 ° layer, fiber compression bending fracture in the 90 ° layer, and matrix compression fracture damage in each layer. The bushing pressed into the hole during the expansion process can reduce the compression effect of the bolt on the CFRP hole during the loading process of the CFRP/Ti connector. It can avoid stress concentration and prevent premature fatigue failure caused by CFRP crushing. When the expansion deformation is 3%, the fatigue life of the specimen is 3.5 times that of the ordinary specimen, and the gain is the most significant. Excessive initial damage will suppress the fatigue life gain of CFRP when the expansion deformation is too large.

Key words: composite materials, hole expansion, deformation, damage, fatigue performance