Evaluating the Bond Characteristics of Intermediate and Ultra-High Modulus CFRP Laminates Adhered to Steel

Externally bonding Carbon Fiber Reinforced Polymer (CFRP) to steel, as a means of increasing the load carrying capacity of steel and concrete-steel composite beams, has become popular over the last couple of decades. When compared with traditional Intermediate Modulus (IM) CFRP, and due to the elastic modulus being higher than that of steel, high modulus (HM) and ultra-high modulus (UHM) CFRP laminates provide substantial load transfer in steel beams prior to yielding of steel. Several studies have been conducted on the bond between steel and CFRP, addressing the different failure mechanisms. Several bond-slip relations have been proposed, primarily for IM CFRP, based on cohesive failure within the bonding epoxy adhesive. This study aims to develop bond-slip models for both IM and UHM CFRP laminates bonded to steel, focusing on failure due to debonding at the steel-adhesive interface. Double lap shear tests were carried out using both IM and UHM CFRP laminates and the behavior of the specimens are compared with the finite element model results based on the developed bond-slip models. The double-lap shear joint stiffness was found to be higher for the UHM CFRP-steel bond, while the interfacial fracture energy was found to be higher for the IM CFRP-steel bond.