Residual performance of a silyl-modified polymer adhesive for CFRP-steel interface exposed to thermally-induced stress states

This paper presents an experimental program evaluating the residual behavior of carbon fiber reinforced polymer (CFRP)-steel interface bonded with a silyl-modified polymer (SMP) adhesive when subjected to thermally-induced stress states. A total of 40 specimens are prepared and exposed to elevated temperatures from 25 °C to 200 °C. According to test results, interfacial capacity is well maintained up to a temperature of 100 °C; however, thermal hysteresis takes place beyond 100 °C. Exposure temperatures higher than 175 °C result in a phase-transition of the adhesive morphology during heating and influence the adhesion characteristics of the bonding agent. Geometric discontinuities along the interface affect CFRP-strain development and a shear-lag mechanism is noticed, which is virtually independent of the degree of thermal exposure. Fiber disintegration is the primary failure mode of the interface up to 150 °C, including intricate local fiber dislocation and partial CFRP pull-out. The specimens exposed to temperatures higher than 175 °C revealed a simple CFRP-debonding failure mode due to the thermal damage of the SMP. A probabilistic approach is taken to complement the experimental observation. The probability of the CFRP-steel interface tested is found to be normally distributed. The Bayesian updating method probabilistically infers the thermal characteristics of the interface with emphasis on temperature-dependent interfacial fracture energy. Design properties are proposed for practical application of the CFRP-steel interface with SMP.