Fatigue failure mechanisms and probabilistic S-N curves for CFRP–steel adhesively bonded joints

Abstract

In this study, fatigue tests were conducted on a series of carbon fiber reinforced polymer (CFRP)–steel double lap shear joints. The fatigue failure mechanisms were investigated based on the failure modes, load–displacement relationships, and stiffness degradation. Inherent scatter characteristics of the fatigue life were discussed using probabilistic S-N (P-S-N) curves based on four statistical models (ISO 12107, ASTM E739-91, two-parameter Weibull, and Gumber models). The results indicate that the fatigue life decreased dramatically with the increase of the load level, and interface debonding is the primary failure mode of fatigue joints. Stable debonding and accelerated debonding of the bonded interface are initiated when the joint stiffness degrades to approximately 98% and 82–86% of the initial stiffness, respectively. The S-N curve based on the mean bond stress range shows a better fit than that based on the local bond stress. Based on the comprehensive evaluation of the performance of the P-S-N curves, the two-parameter Weibull model is recommended for fatigue life design as it can well-constrain fatigue data without excessive safety redundancy.