Experimental development of fatigue delamination threshold criterion

The aim of this study was to develop a semi-empirical criterion capable of predicting the fatigue threshold delamination under varying mixed-mode ratio. To validate this criterion, a series of fatigue delamination tests in a unidirectional glass/epoxy composite were carried out at pure mode I, pure mode II, and different mixed modes. These tests were conducted using DCB (mode I), ENF (mode II), and MMB (mixed mode (I + II)) specimens. The experimental results have been expressed in terms of the total strain energy release rate thresholds GTth which correspond to no delamination growth after 106 cycles. They were correlated with the semi-empirical fatigue criterion through the plot of the total strain release rate thresholds ΔGTth versus the GIIGT modal ratio.