Experimental assessment of the evolution of mode II parameters of an adhesively bonded assembly subjected to physical, humid, creep, and hygro-mechanical aging conditions

Structural bonding is increasingly used for the repair and reinforcement of some metallic structures in offshore environments. However, the durability of structural bonding under various aging conditions remains poorly understood, particularly under coupled aging conditions, for which few studies are available. This study aims to investigate the evolution of mode II mechanical properties of steel-to-steel bonded assemblies subjected to severe environmental conditions, including uncoupled (physical aging, humid aging, and creep aging) and coupled hygro-mechanical aging. This work focuses specifically on the mechanical properties under shear loading. To evaluate the mode II mechanical behavior of the bonded joints before and after aging, an approach combining fracture mechanics and cohesive zone modeling is adopted. Mode II mechanical characterization tests, particularly the End-Loaded Split (ELS) test, are conducted on specimens instrumented with continuous optical fibers for crack propagation monitoring. Digital Image Correlation (DIC) is also employed to directly determine, via the J-integral, the cohesive laws of the interface at various stages of aging. First, a new bonded assembly geometry was designed and validated to be compatible with both the different aging condition setups and the mechanical characterization test requirements. Then, four aging conditions were investigated at three aging periods of 49, 147 and 245 days:(1) physical aging at 50°C, (2) humid aging by immersion in demineralized water at 50°C, (3) mechanical aging via a four-point bending creep frame, and (4) coupled hygro-mechanical aging, where samples were subjected to creep loading while immersed in demineralized water at 50°C. The results reveal a significant degradation in mechanical properties after immersion in water, whereas creep aging appears to enhance the mechanical performance.