Modelling prediction on the degradation in mode II fracture energy of structural adhesive subjected to hygrothermal ageing

In this work, the effect of hot-humid environment on the mode II fracture energy (GIIc) of the selected structural adhesive was experimentally evaluated through End-Notched Flexure (ENF) testing as well as corresponding finite element (FE) modelling approach. The ready-cured ENF samples were first immersed in distilled water and 5% NaCl solution under 50°C for different durations, and then removed from the hot-wet environment for mode II loading up to failure. Degradation was observed in the experimentally measured GIIc for adhesives immersed in both aqueous environments, while a further decrease was found in the samples immersed in distilled water, possibly due to the fact that more water was absorbed than saltwater immersion. A two-step FE modelling approach was developed to simulate the water absorption process under-elevated temperature (Step 1) and subsequent mode II loading test after hygrothermal ageing (Step 2) of ENF specimens. User subroutines were developed to accurately simulate the water ingress process in the adhesive layer and properly transfer the moisture distribution data between the two FE models. The feasibility of the established FE modelling was then successfully validated through comparison between the experimental and numerical results.