Effect mechanisms of hygrothermal environments on failure of single-lap and double-lap CFRP-aluminum bolted joints

The high demands for load-carrying capability and structural efficiency of composite-metal bolted joints trigger in-depth investigations on failure mechanisms of the joints in hygrothermal environments. However, few studies have been presented to exhaustively reveal hygrothermal effects on the failure of CFRP-metal bolted joints, which differ from CFRP-CFRP or metal-metal bolted joints because of the remarkably different material properties of CFRPs and metals. In this paper, hygrothermal effects on tensile failures of single-lap and double-lap CFRP-aluminum bolted joints were experimentally and numerically investigated. A novel numerical model, in which a hygrothermal-included progressive damage model of composites was established and elastic-plastic models of metals were built, was proposed to predict the failures of the CFRP-metal bolted joints in hygrothermal environments and validated by corresponding experiments. Different failure mechanisms of single-lap and double-lap CFRP-aluminum bolted joints, under 23°C/Dry and 70°C/Wet conditions, were revealed, respectively. It follows that both the collapse failures of the single-lap and double-lap bolted joints were dominated by the bearing failure of the CFRP hole laminate in the two conditions, indicating that the hygrothermal environment did not change the macro failure modes of the joints. However, the hygrothermal environment considerably shortened the damage propagation processes and reduced the strength of the joints. Besides, the hygrothermal environment weakened the load-transfer capability of the single-lap joint more severely than the double-lap joint because it aggravated the secondary bending effects of the single-lap joint obviously.