A new semi-empirical law for variable stress-ratio and mixed-mode fatigue delamination growth

A new semi-empirical equation that describes the fatigue delamination growth in fibre reinforced toughened epoxies is presented and validated against data available in the literature. The new law accounts for the simultaneous effects of the stress-ratio and mode-mixity on the interlaminar crack propagation. If delamination propagation thresholds are ignored, the proposed semi-empirical equation allows describing interlaminar crack propagation employing only three material dependent parameters, whereas alternative models presented in the literature require four. If reliable threshold data are available from experimental tests, the new semi-empirical law can be extended to a unified description of stress-ratio, mode-mixity and thresholds effects using six material dependent parameters.