Finite element modeling of debonding failure in CFRP-strengthened steel beam using a ductile adhesive

Carbon fiber-reinforced polymer (CFRP) composites externally bonded to the tensile flange of the steel beam are an effective strengthening technique. Due to the apparent effect of the adhesive toughness on the debonding behavior between the CFRP and steel, this paper focuses on the CFRP-strengthened steel beam using a ductile adhesive and the adhesive selection in the strengthening work. Three-dimensional (3-D) finite element (FE) models were proposed to simulate the mechanical response of the CFRP-strengthened steel beam under a static four-point bending load. The failure of a ductile adhesive was modeled using the trapezoidal mixed-mode cohesive zone model (CZM) coded in the user subroutine (UMAT) of ABAQUS. The effectiveness of the trapezoidal CZM was validated by the experiment in the literature, and the debonding characteristics using different laminate thicknesses and lengths were clarified by the stress and damage analysis. In terms of plate-end debonding failure mode, the ductile adhesive is more appropriate for the CFRP-strengthened steel beam due to its reduced normal stress, increased mixed-mode fracture energy, and more uniform stress distribution.