Structural adhesives are being increasingly used for bonding of dissimilar materials, however environmental degradation remains a significant challenge limiting the bonding reliability. A common form of degradation comes from water ingress, regarding which there is limited quantitative understanding of how water diffusion affects the adhesive local mechanical properties. This work proposes a meso-scale approach to characterise the influence of water diffusion on local mechanical properties of structural adhesives at elevated temperature, aiming to develop a model of degradation due to water exposure. Gravimetric study was conducted on adhesives immersed in deionised and 5 wt% NaCl water, to obtain water diffusion characteristics. The immersed specimens were periodically removed from the aqueous environment and precisely cut to expose the internal section. The samples were then indented using nanoindentation to extract the modulus and hardness distribution. SEM observation was conducted to analyse the microscopic morphology and ageing mechanism. Experimental results revealed that water diffusion caused significant local (meso-scale) degradation in adhesive mechanical properties. Increase in local moisture concentration led to greater degradation as moisture gradually diffused inward. Comparing to salt water immersion, the elastic modulus and hardness of adhesive saturated in deionised water decreased by further 5.9% and 11.9%, respectively. The developed degradation model coupled with insights from ageing mechanism provides a detailed understanding of degradation in adhesive property due to water diffusion. The proposed characterisation approach can be readily applied to other adhesives. Furthermore, this model allows for degradation of such adhesives to be reasonably predicted through FE modelling effort.

结构粘合剂越来越多地用于异种材料的粘合，但是环境退化仍然是限制粘合可靠性的重大挑战。降解的常见形式来自进水，对此，关于水扩散如何影响粘合剂局部机械性能的定量理解有限。这项工作提出了一种介观尺度的方法，以表征在高温下水扩散对结构胶粘剂局部机械性能的影响，旨在建立因暴露于水而引起的降解的模型。对浸入去离子水和5 wt％NaCl水中的粘合剂进行重量分析，以获得水扩散特性。定期将浸没的样品从水环境中移出并精确切割以露出内部区域。然后使用纳米压痕对样品进行压痕以提取模量和硬度分布。进行SEM观察以分析微观形态和老化机理。实验结果表明，水的扩散会引起粘合剂机械性能的显着局部（中尺度）下降。随着水分逐渐向内扩散，局部水分浓度的增加导致更大的降解。与盐水浸泡相比，去离子水中饱和的粘合剂的弹性模量和硬度分别分别降低了5.9％和11.9％。所开发的降解模型与老化机理的洞见相结合，可提供对由于水扩散而导致的粘合性能下降的详细了解。所提出的表征方法可以容易地应用于其他粘合剂。此外，该模型允许通过有限元建模工作合理地预测此类粘合剂的降解。