Effects of hygrothermal aging on the mechanical properties of aluminum alloy adhesive joints for high-speed train applications

Abstract

ABSTRACT The mechanical properties of adhesives are sensitive to both temperature and humidity. A modified Arcan device was proposed to characterize the failures of adhesive joints under mixed mode loading. Aluminum alloy butt joints (BJs), 45°scarf joints (45°SJs) and thick-adherend shear joints (TASJs) were manufactured to investigate the effects of loading conditions. Moreover, these joints were subjected to various durations of high-temperature aging (80°C) and hygrothermal aging (80°C/95% RH): 0 (unaged), 6, 12, 18, 24, and 30 days. The adhesive joints were analyzed by Fourier transform infrared (FTIR) spectroscopy, and the load–displacement curves, failure strengths, failure modes were analyzed. The results showed under high-temperature conditions, humidity can accelerate the rate of decrease in the failure strength of the adhesive joints, which resulted from the fracture of the polymer chains and the influence of internal stresses. As the hygrothermal aging duration increased, the fracture surfaces of the joints changed significantly. The number of cracks and cavities in the fracture surface increased as the aging duration increased. After aging, the failure strength values of the adhesive joints conformed to the quadratic stress failure criterion. Two curved surface equations reflecting the relationship between the quadratic stress criterion and the aging duration were established.