Influence of harsh environmental conditions on CFRP‐aluminum single lap joints

The objective of this paper is to investigate the influence of harsh environmental conditions on the fundamental failure mechanisms of carbon fiber reinforced plastic (CFRP)‐aluminum single lap single‐bolted joints under tensile loading.

CFRP‐aluminum single lap joints were aged under extremely hot (60°C), hot and humid (60°C, 95%RH), and freezing cold (−51°C) environments and tensile‐tested to measure the joint stiffness and ultimate tensile strength (UTS). Finite element studies were performed to design the experiments.

For all composite stacking sequences studied, it was found that hot and humid conditions reduced UTS of the joint by as much as 29 percent. Hot‐humid and freezing conditions also decreased UTS with the exception of the twill 2 × 2 laminate, which slightly increased UTS by 3.7 percent under freezing conditions. The opposite effect was observed for stiffness, where hot‐humid conditions increased the modulus of elasticity in the axial direction.

The results of the study can be used to design hybrid structures comprising CFRP composites and aluminum single lap single‐bolted joints. For example, such joints are found in the fuselage of aircraft and more recently in critical components such as wing boxes and nacelles.

Even though there is much information about temperature and moisture effects on composites materials and the mechanics of hybrid joints, the analysis of environmental condition for hybrid joints, specifically for CFRP‐aluminum bolted joints, is vaguely documented. The paper shows the experimental results for single lap single‐hole bolted joints that have been aged to three different environmental conditions: extreme hot, hot and humid, and extreme cold.