Environmental degradation of the interfacial fracture energy in an adhesively bonded joint

The mixed mode flexure and notched coating adhesion tests have been carried out in order to characterise interfacial fracture for a range of environmental exposure conditions and to find a meaningful interfacial strength parameter using a fracture mechanics approach. The moisture uptake of the adhesive was accelerated using an open-faced configuration. The critical loading to cause interfacial fracture was measured and was used in conjunction with finite element analysis (FEA) to determine the fracture energy under various exposure conditions. Moisture dependent material properties were incorporated in the FEA. Scanning electron microscopy was used to characterise the nature of the failure surface. Significant degradation of the fracture energy of the interface was found and this was matched by observed changes to the failure surface. The fracture energies were found to be largely independent of test method, exposure environment and time and was primarily related only to the moisture concentration.