Environmental durability of epoxy-bonded CFRP-to-steel joints in mode I fracture

Abstract Exposure to environmental stresses can weaken the connection of epoxy-bonded CFRP-strengthened steel elements. As a result, designers often express concern about possible premature delamination arising from combined peel and shear effects at the CFRP-steel interface. This study was undertaken to further knowledge in relation to the peel failure of epoxy-bonded CFRP-to-steel joints subjected to hygrothermal conditioning. The effect of the bond-line thickness on the bond strength was also examined in this study. A total of 54 specimens were tested including 30 adhesive CFRP-to-steel specimens and 24 adhesive coupons. Two commercially available structural epoxy adhesives were examined. Hygrothermal conditioning may cause the adhesion failure near to the edges of the adhesive joints. The load-carrying capacity and strain energy release rate of adhesive joints depend on the adhesive and hygrothermal environment, and can be degraded up to 15%. The statistical analysis using two-way ANOVA method was applied and showed that the wet conditioning has a significant effect on the maximum failure load of CFRP-to-steel bonded specimens. Reducing the bond-line thickness to less than 1 mm can result in a major reduction in load-carrying capacity and strain energy release rate of CFRP-to-steel bonded specimens. Humid and wet conditioning cause up to 44% and 63% drop in elastic modulus, 31% and 55% reduction in tensile strength, and 32% and 44% increase in average maximum strain of adhesive materials, respectively.