Stress ratio dependence of fibre bridging significance in mode I fatigue delamination growth of composite laminates

Abstract

This paper aims to investigate stress ratio effect on fibre bridging significance in mode I fatigue delamination growth of composite materials. Fatigue resistance curves (R-curves) of different stress ratios are determined and compared with the quasi-static R-curve. The fatigue R-curve of a high stress ratio is similar to the quasi-static results. However, fatigue resistance of a low stress ratio is smaller than quasi-static resistance. These indicate that fibre bridging significance is stress ratio dependent. More bridging fibres can be generated in delamination of a high stress ratio, as compared to that of a low stress ratio. This can lead to fatigue bridging laws are stress ratio dependent and fatigue delamination is block load sequence dependent.

Thickness effects on fibre-bridged fatigue delamination growth in composites

“…The results also demonstrated that fibre bridging can decrease fatigue crack growth. Yao et al [14][15][16] experimentally examined FDG with different amounts of fibre bridging and proposed empirical power law relations to determine fibre-bridged FDG behaviors. Furthermore, it was reported that the significance of fibre bridging was related to loading regime.…”

“…As a result, one can reason that the resistance curve (R-curve) obtained in quasi-static delamination cannot well represent resistance increase in fatigue delamination. In addition, it has been proven that stress ratio also affected the significance of fibre bridging, due to crack closure or other unknown reasons [16,18]. Particularly, fibre bridging of a high stress ratio delamination was much more significant than that of a low stress ratio.…”

“…Particularly, in the studies of Murri et al [3] and Hwang et al [13], they used quasi-static R-curve to normalize G max in fatigue data analysis. However, it is questionable to directly use quasi-static data in FDG studies, as there was difference in the amount of fibre bridging generated in quasi-static and fatigue loading [14,16,17]. To address this problem, in the studies of Zhao et al [7,19], the resistance increase in fatigue delamination was determined via a compliance method and subsequently used in FDG study.…”

Fibre-bridged fatigue delamination in multidirectional composite laminates

“…Obvious differences in the amount of fibre bridging in quasi-static and fatigue delamination were also observed in an experimental study conducted by Yao et al [20]. Furthermore, it was recently reported that the significance of fibre bridging in fatigue delamination was dependent on stress ratio [27]. More fibre bridging can be present in a higher stress ratio fatigue delamination.…”

“…(1). According to previous studies [20,27], the use of this relation was an effective way to qualitatively evaluate the significance of fibre bridging in fatigue delamination in composite laminates.…”