Influence of hygrothermal aging on the lifetime and mechanical properties of GFRP/Al adhesive joints

The study aimed to investigate the impact of hygrothermal aging on the degradation of mechanical properties and predict the lifetime of adhesive joints between aluminum alloy (AA6061) and glass fiber-reinforced epoxy (GFRP) composites. The adhesive joints were prepared in a single lap joint (SLJ) configuration and subjected to hygrothermal conditions to induce aging. Immersion tests were conducted at a water temperature of 70 °C with varying aging periods (10, 18, 40, 54, 60, and 75 days) to assess the long-term performance and predict the lifetime of the joints. The tensile and shear strength of the adhesive joints were evaluated using a tensile test. The test was performed at room temperature (RT) with a speed rate of 1.3 mm/min. Among the different methods available for lifetime prediction, a semi-empirical approach was selected to analyze the changes in the mechanical properties of the adhesive joints. A comprehensive comparison was made between aged and unaged specimens. The experimental results revealed a reduction in the ultimate tensile and shear strength of the adhesive bonds over the 75-day aging period. The semi-empirical relationship used for long-term durability prediction of adhesive joint structures indicated a 78 % decrease in ultimate tensile strength for the adhesive joints over a one-year aging period. This highlights the significant influence of hygrothermal aging on the mechanical properties of the investigated adhesive joints. During the aged periods, various failure modes were observed, including adhesive failure, cohesive failure, and structural failure.