Hygrothermal effect on mechanical behaviours and failure mechanisms of single-lap countersunk-screwed CFRPI-metal joint

Abstract

This paper seeks to probe experimentally and numerically hygrothermal effect on mechanical behaviors and failure mechanisms of single-lap countersunk-screwed CFRPI (carbon fiber reinforced polyimide composite)-metal joints. Accelerated moisture absorption tests were conducted on CCF300/AC721 plate until effective moisture equilibrium, and quasi-static tension tests were performed on single-lap countersunk-screwed CCF300/AC721-30CrMnSiA joints in RD (room temperature and dry), RW (room temperature and wet) and EW (elevated temperature +55 °C and wet) environments, respectively. From the experiment results, moisture and temperature impacts were analyzed and discussed. By considering hygrothermal-mechanical interaction, non-linear shear constitutive relationship and complicated failure modes, an improved PDM (progressive damage model) was devised to simulate mechanical behaviors and failure mechanisms of single-lap countersunk-screwed CCF300/AC721-30CrMnSiA joints. Predictions agree well with the experimental results, demonstrating the effective use of new PDM. It is shown from experimental and numerical results that delamination around screw hole is likely the primary reason for final failure of joint, and the negative hygrothermal effect on joint performance mainly contributes to the decrease in inter-laminar properties of composite laminate with the increase in moisture and temperature. HIGHLIGHTS Accelerated moisture absorption tests were conducted on CCF300/AC721 plate, followed by quasi-static tension tests on single-lap countersunk-screwed CCF300/AC721-30CrMnSiA joints in the RD, RW and EW environments. An improved PDM was devised to simulate mechanical behaviours and failure mechanisms of single-lap countersunk-screwed CCF300/AC721-30CrMnSiA joints, and the predictions agree well with the experimental results. Research results demonstrate that hygrothermal effect likely contributes to the decrease in inter-laminar properties of composite laminate with moisture and temperature, ultimately deteriorating joint performance.