Tensile behaviour of three-dimensional carbon-epoxy adhesively bonded single- and double-strap repairs

An experimental and numerical study of the tensile behaviour of three-dimensional carbon-epoxy adhesively bonded strap repairs is presented. Experimentally, the failure mode, elastic stiffness and strength were evaluated for different overlap lengths and patch thicknesses. The numerical simulations, performed in ABAQUS®, allowed obtaining the elastic stiffness and the patch debonding load, used to understand the repairs behaviour. The adhesive layer was simulated with cohesive elements including a mixed-mode cohesive damage model with trapezoidal traction-separation laws in pure modes I and II, to account for the ductile behaviour of the adhesive used. These laws were determined by an inverse method, which consists on the estimation of the cohesive parameters with a fitting procedure of the experimental and numerical load–displacement curves of the respective fracture characterization test. The pure mode III cohesive law was equalled to the pure mode II one. This numerical methodology was found adequate to reproduce the experimentally observed behaviour of these repairs.