Effect of outdoor environmental exposure on the mechanical behavior of steel/GFRP single-lap joints

Adhesive joints GFRP/Steel bonded with epoxy adhesive were exposed to the external environment for one year, a tropical environment with temperature variations, humidity, radiation, and salt spray, due to its proximity to the sea. The shear strength of the joint was measured over the exposure time, as well as their chemical and physical changes. Tg of the adhesive was evaluated through DMA, and changes in the composite matrix were studied using FTIR. A significant reduction in joint strength was observed within the first 30 days, but this reduction quickly stabilized. High corrosion of the metal adherend was evident, which was also observed in the bonded region, significantly impacting the adhesive strength of the joints. Changes in the color of the composite were also identified due to exposure to solar radiation, which also affected the chemical bonds, as indicated by FTIR. The Tg of the adhesive decreased in the first 90 days and then gradually increased. These changes may have been related to the humidity, initially decreasing the Tg, and the exposure to higher ambient temperatures, which causes post cure effect. Therefore, the proposed external exposure conditions contain factors capable of causing significant changes in the joint and its components.