Influence of hygrothermal aging on the mechanical strength of an Aluminum/Aluminum bonded assembly

The adhesive bonding technique has become widely prevalent in recent years, especially in fields such as engineering, aerospace, and sports. During operational service, adhesives are subjected to severe environmental conditions, including temperature variations, humidity, and UV radiation, which can impact their performance. In this study, we utilized the mechanical properties of the aged epoxy adhesive Adekit A140 in a finite element model to assess the impact of temperature and water absorption on the degradation of mechanical properties in metal-metal adhesive joints used in aeronautical structures. Our primary objective was to analyze, using the finite element method, the influence of these environmental factors on the joint's strength by evaluating the distribution of Von Mises stresses. The adhesive's mechanical properties, such as Young's modulus (E), were measured at different immersion periods and then integrated into the numerical modeling. The results revealed that water absorption leads to a significant degradation of the adhesive's mechanical properties, primarily manifested as a reduction in Young's modulus. Despite this degradation, an increase in plasticity was observed, which surprisingly improved the overall strength of the bonded assembly under certain conditions. Notably, after 90 days of immersion, the joint's strength demonstrated a 15% reduction in stiffness but exhibited enhanced durability due to plastic deformation, indicating a potential trade-off between stiffness and durability in long-term service. This provides valuable insight into the design of adhesive joints under varying environmental conditions.