Effect of functionalized nano-SiO2 addition on bond behavior of adhesively bonded CFRP-steel double-lap joint

The mechanical properties of adhesives significantly influence the bond behavior of steel structures strengthened by carbon fiber-reinforced polymer (CFRP) composites. In order to improve the toughness of the adhesive and the ductile behavior of adhesively bonded CRFP-steel joint, functionalized nano-sized silica (hereafter refer as nano-SiO2) toughening agent were added into the adhesive. Firstly, the effects of functionalized nano-SiO2 toughening agent on the mechanical properties of the adhesives after curing at room temperature were tested and analyzed. Then, a total of 19 adhesively bonded CFRP-steel double-lap joints were fabricated and tested under shear loading to investigate the effect of functionalized nano-SiO2 on the bonding behaviors, including the failure modes, bond–slip relationships, bond strength and so on. The test results indicate that tensile stress–strain relationship of the adhesive changes from linear to nonlinear with the increase of functionalized nano-SiO2 toughening agent, the elongation at break, strain energy and shear strength of functionalized nano-SiO2-toughened adhesive (ZR14-weight ratio of 1% functionalized nano-SiO2) was improved by 202.88%, 292.10% and 133.12% respectively in comparison to the adhesive without functionalized nano- SiO2 toughening agent. Moreover, the tensile strength, elongation at break, and strain energy of functionalized nano-SiO2-toughened adhesive ZR14 are much higher than those of commercial adhesives (e.g. Sika30, 330) without Nano-SiO2. In addition, the failure mode of CFRP-steel joints changed from interface failure to CFRP plate delamination, when the weight ratio of functionalized nano-SiO2 to adhesive increasing from 0 to 1%. The bond-slip curves could be simplified into a bilinear model (triangle-shape) for CFRP-steel joints without and with only weight ratio of 0.5% functionalized nano-SiO2, however, the bond-slip curves change to simplified trilinear model (trapezoidal shape) for the joints with 1% functionalized nano-SiO2 and the toughness of bonding interface is significantly improved. In all, the CFRP-steel lap joints bonded by adhesive with appropriate amount functionalized nano-SiO2 (i.e., wt. of 1%) shows superior interfacial performance.