Multi-layer continuum model for adhesive films with knitted carrier

Film adhesives are a form of composite consisting of two constituents i.e. fibrous carrier and matrix. The fracture surfaces are usually dominated by the carrier-matrix de-bonding, but it also co-exists with a minor failure related to resin closer to the adhesive–adherend interface. This investigation aims at a realistic representation of the failure modes. For this, a 3D multi-layer approach of a FM 300-2 adhesive is defined where a non-local Continuum Damage Model (CDM) is developed accounting for the proper matrix mechanism defined with lower fracture energies. The carrier-matrix de-bonding was implemented by an in-built Cohesive Zone Model (CZM) at the interfaces of the matrix-carrier layers. For the characterization and validation, the modelling was tested with the Mode I fracture response of the adhesive in joints (butt joint, BJ, and double cantilever beam specimen, DCB) and bulk form (tensile tests). Numerical results with CZM-CDM implementation agreed with the experimental data in terms of load response and representation of the failure mechanisms, when correct material constants are applied. The multi-layer damage model was able to define strength and fracture properties of the matrix phase by the prediction of failure initiation in the BJ test. Consequently, the mechanism was able to reproduce the local damage path that occurred close to the adhesive–adherend interface.