Micromechanical investigation of damage processes at composite-adhesive interfaces

A new model of an adhesive bond is presented. The model explicitly considers the microscale heterogeneity of a composite material, when bonded with an epoxy adhesive. Finite element models were generated, consisting of a composite microstructure, joined to an epoxy adhesive, separated by a cohesive zone. Damage is considered through fibre–matrix debonding in the composite and damage of the adhesive–composite interface. Boundary conditions applied to the RVEs reflect the Mode I and Mode II deformations commonly found in adhesive bonds. The elastic response of the models was predicted using a spring stiffness calculation. The strength of the adhesive–composite bondline was found to influence the damage process at the microscale, as low bond strengths promoted damage of the adhesive–composite interface, and high bond strength produced failure within the composite under Mode I deformation. Similarly, under Mode II conditions, damage was confined to the adhesive–composite interface at low bondline strengths, while high bondline strengths produced yielding of the adhesive layer. A region of bondline was weakened, and loaded under Mode I conditions. The resultant combination of composite and bondline failure was attributed to a combination of the fibre positions within the composite region and the presence of a weak region of bondline.