Hygroscopic stresses development in epoxy-metal bonded assemblies under hydrothermal conditions

Epoxy-metal bonded assemblies are widely used in various industrial applications due to their mechanical efficiency and stress distribution capabilities. However, the durability of these assemblies in humid environments remains the subject of extensive research. This study focuses on the development of a numerical hygroelastic model to investigate hygroscopic stresses in a single-lap epoxy-metal bonded assembly exposed to immersion at different temperatures and durations. The model considers a Fickian sorption behavior with hygroscopic swelling and thermal expansion, enabling a detailed analysis of stress development. As input data, experimental measurements were conducted to determine the water diffusion kinetics, the thermal expansion coefficient, the hygroscopic swelling coefficient, and the evolution of the elastic modulus during aging. The impact of temperature is discussed to evaluate the effect and relevance of accelerated aging. The role of interphases, characterized by distinct diffusion properties, is also examined to assess their impact on water content distribution and stress fields. Results highlight the critical influence of water diffusion kinetics, temperature, and interphase properties on stress distribution, emphasizing localized swelling and elevated stress levels at the adhesive-substrate interface.