Effects of moisture ingress on the mesoscale mechanical properties of epoxy adhesives under elevated temperature
Yuxiang Zhang, Jianli Ma, Chengwei Wu, Xiao Han, Wei Zhang, Wei Zhang
Abstract
This paper aims to investigate the relationship between local moisture concentration and mesoscale mechanical properties of epoxy adhesive under elevated temperature. Araldite® 2015 was chosen as the target adhesive due to its curing stability and possible validation with previously published literatures. The specimens were aged at 60 °C in deionised water and 5%wt NaCl solution, separately, with the water ingress evaluated by Fickian diffusion model. Nanoindentation was utilised to characterise the mesoscale modulus and hardness distribution along the water diffusion path. Then Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were conducted to investigate the variation of functional groups and microstructure, respectively. The results show that mechanical properties degrade as ageing duration increases, with higher degradation observed in the edge region where higher moisture concentration exists. Besides, higher ageing temperature leads to larger decrease in mechanical properties of saturated specimens. An empirical relation between local mechanical properties and moisture concentration was established. Chemical and morphology performance of adhesives also exhibited variations when saturated. The obtained local moisture-mechanical relationship can then be used to improve the accuracy of numerical simulation on the environmental durability of structural adhesive in future work.