The influence of moisture on the strength and durability of adhesively bonded joints

摘要

The influence of moisture on the strength and durability of adhesively bonded joints has been studied. Dielectric relaxation spectroscopy was used as a non-destructive tool to characterize the molecular level changes in the adhesive when exposed to hygrothermal environments. Adhesively bonded specimens in double notch shear (DNS) and wedge test configurations were exposed to various temperatures at 95% relative humidity for various times in an environmental chamber. The wedge test specimen was periodically removed from the test chamber and crack length was measured and recorded as a function of time. At the end of the environmental conditioning, the DNS specimen was subjected to axial compression load to determine the shear strength. The main finding is that the shear strength decreases with the increase in duration of the exposure time at constant temperature. The bonded joint fails increasingly in the metal/adhesive interface (interfacial failure) as the exposure temperature and duration is increased. The interfacial failure starts along the edge of the bonded DNS specimen and move towards the center of the bonded area as the exposure temperature and duration is increased. The durability of bonded joints decreases with the increase in temperature. The durability of FM-73U/aluminum joints in 95% relative humidity at various temperatures follows the order: 40°C>50°C > 60°C> 80°C.