Effect of moderately elevated temperatures on bond behaviour of CFRP-to-steel bonded joints using different adhesives

The bond behaviour of CFRP-to-steel bonded joint considerably depends on the properties of adhesives, and is significantly influenced by temperature. Meanwhile, different adhesives behave differently at elevated temperatures. Therefore, an in-depth understanding of the effect of temperature on CFRP-to-steel bonded joints with different adhesives is crucial. In this study, a total of 24 single-lap shear joints with four different types of adhesives, were investigated to examine the bond behaviour of CFRP-to-steel bonded joints at a temperature of 23 °C, at 15 °C below the glass transition temperature Tg-15 °C, and at 15 °C above the glass transition temperature Tg + 15 °C. The results indicate that 1) the failure mode of specimens was transformed from cohesive failure or CFRP delamination failure at room temperature to adhesive-steel interface failure with an increase in temperature, 2) the bond strength of all specimens was reduced by approximately 10% at Tg-15 °C, and 70% at Tg + 15 °C. Based on a literature review, an analytical model was proposed to predict the bond strength of the CFRP-to-steel bonded joints at elevated temperatures, 3) the bond-slip relationship of the joints with linear adhesive was changed from a trapezoidal to a triangular with an increase in temperature; However, the bond-slip relationship of the joints with a nonlinear adhesive didn't change, and 4) the stiffness of the joints decreased with temperature owning to the degradation of the elastic modulus of adhesive.