Numerical Study on Fatigue Behavior of Damaged Steel Beams Strengthened by Film Adhesive‐Bonded CFRP Laminas Under Elevated Temperatures

As a key factor affecting the fatigue performance of damaged steel structures strengthened by adhesive‐bonded carbon fiber‐reinforced polymer (CFRP), the adhesive layer is highly sensitive to elevated temperatures. In this study, a novel film adhesive J‐69E, with great high‐temperature stability, was selected as the adhesive to adhere the strengthening material CFRP laminas to damaged structures. The bond‐slip relationships and interfacial fracture parameters of film adhesive‐bonded CFRP‐steel at room (25°C) and elevated (40/55/70°C) temperatures were obtained. Then, a finite element (FE) model, validated by test results in the open literature, was developed to model the fatigue behavior of damaged steel beams strengthened with CFRPs subjected to four‐point bending loads. Using the validated FE model, the interfacial damage evolution and fatigue behavior of damaged steel beams strengthened with film adhesive‐bonded CFRPs at varied elevated temperatures were analyzed, and the effect of CFRP bond length and width on the fatigue crack growth life of damaged steel beams was investigated. The results show that the CFRP interface damage occurs at the notch in the middle span of the damaged steel beams. The damage area increases with the increase of temperatures, indicating that the elevated temperatures aggravated bonding interfacial damage.