Degradation mechanism of steel/CFRP plate interface subjected to overloading fatigue and wetting/drying cycles

The bond strength of the interface between carbon fiber-reinforced polymer (CFRP) and steel is crucial for CFRP-reinforced steel structures. However, the influence of fatigue loading and the service environment on the bond durability of strengthened steel structures requires further investigation. This work focused on the bond degradation mechanism of the steel/CFRP interface subjected to overloading fatigue damage (OFD) and wetting/drying cycles (WDCs). A total of 12 CFRP/steel joints subjected to OFD and/or WDCs was tensioned to failure. Samples were collected from the debonding zone near the loading end for scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The SEM results revealed that cracks induced by OFD, and microcracks and hydrolysis caused by WDCs in the adhesive were the main reasons for interfacial bonding degradation. OFD introduced localized cracks in the adhesive, whereas WDCs caused widely distributed and staggered microcracks in the adhesive. OFD-induced cracks accelerated moisture intrusion and subsequently enhanced the generation of microcracks, leading to a further decrease in the interfacial bond strength. In addition, the EDS results demonstrated a content change in interfacial chemical elements and precipitates at different sampling locations, which also confirmed the above mechanical degradation mechanism. Furthermore, changes in the load capacity, interfacial stiffness, and failure mode were examined, and the aforementioned degradation mechanism was verified. • The characteristics of fatigue- and/or moisture-induced cracks in adhesive were revealed. • The crack formation was examined from physical and chemical aspects. • Changes in mechanical behavior and failure mode were explained based on microscopic tests.