Interfacial bonding performance of CFRP sheet reinforced corroded steel plates under fatigue loading

Crucial research gaps remain in understanding the bonding performance of the CFRP-corroded steel interface under fatigue loading. This study investigated the interfacial bonding performance of Carbon Fiber Reinforced Polymer (CFRP)sheets and corroded steel plates under fatigue loading using double shear specimen tests. The analysis focused on the effects of multiple factors, including the steel plate corrosion rate and the ratio of the upper bound value (P_max) and lower bound value (P_min) of the fatigue loading to the debonding load (P_u). Specifically, P_min/P_u ranged from 0.1 to 0.3, while P_max/P_u ranged from 0.45 to 0.65. Notable findings include: (i) Under fatigue loading, the displacement at the tested end of the specimen increased progressively with more fatigue cycles,showing a nonlinear trend. This reflects cumulative interface degradation caused by adhesive plastic slip and micro-crack propagation, particularly at higher stress levels; (ii) The interfacial stiffness of CFRP sheet-corroded steel plate specimens weakened progressively during fatigue loading, particularly under high corrosion rates. A 15 % widening of the load-slip curve envelope at P_max/P_u = 0.45 indicated reduced load transfer efficiency and increased energy dissipation capacity as interface degradation accumulated.; (iii) Fatigue life was highly sensitive to load limits, particularly under high corrosion rates (15 %). Increasing P_max/P_u from 0.45 to 0.65 reduced fatigue life by 97 %, while increasing P_min/P_u from 0.1 to 0.3 extended fatigue life by 17 times, highlighting the critical role of stress amplitude control in fatigue performance.; (iv) At the same corrosion rate, the interface exhibited a reduced fatigue life as stress levels increased, and specimens with different corrosion rates demonstrated a shorter fatigue life compared to uncorroded ones. A method for predicting the fatigue life of the CFRP-steel interface was proposed, taking into account the influence of corrosion rate and load level, with a prediction equation derived using Lagrange polynomial fitting for corrosion rates ranging from 0 % to 15 %,with a prediction error below 8 %. Rarely seen in previous studies, this method offers valuable insights for evaluating the durability of CFRP-reinforced structures and guiding the maintenance of aging infrastructure in corrosive environments.