Durability of adhesively-bonded single lap–shear joints in accelerated hygrothermal exposure for automotive applications

Structural adhesives offer unique advantages in joining mixed lightweight materials in vehicle applications. One of the concerns is the potential aging during the service life, especially under exposure of hygrothermal conditions. In this study, adhesively-bonded single lap–shear (SLS) joints with thin panel sheets were exposed under various designed accelerated constant and cyclic hygrothermal environments. The residual strengths of SLS joints with different adherends were compared to assess their durability. It has been observed that the electro-galvanized steel (EGS) joints have a significant loss of the bonding strength at 80 °C constant exposure, and the aluminum alloy (AL) joints exhibit a relatively stable durability in the same scenario. Moreover, the aging of SLS joints with dissimilar substrates is determined by the weaker adhesive–substrate interface, which is the adhesive–zinc interface of the EGS/AL joint under hot-wet condition. The history effect of temperature-path on residual strengths of SLS joints was also investigated. It is deduced that the durability of SLS joints under long-term exposure may be estimated by some short-term hygrothermal aging with appropriate scenarios.