A new semi-empirical model for stress ratio effect on mode II fatigue delamination growth

A new semi-empirical law for mode II delamination growth in moderately tough fibre reinforced epoxies at various stress ratios is introduced and validated. The new semi-empirical law is valid for positive stress ratios. The quality of the data fit obtained using the new semi-empirical equation is comparable to that achieved using alternative models from the literature, but the model presented here requires only two material parameters to represent the fatigue behaviour for the whole positive stress ratio range.The first validation data set comprises tension–tension fatigue tests performed by the authors on IM7/8552 using central cut ply specimens. Further validation cases have been considered from the literature; these include end-notch flexure fatigue tests on T800H/#3631 and E-glass/913 central cut ply samples tested in alternate tension.