On the physical interpretation of the R-ratio effect and the LEFM parameters used for fatigue crack growth in adhesive bonds

The available models for the prediction of fatigue crack growth in adhesive bonds rely on the similitude principle. In most cases, one of three similitude parameters based on the strain energy release rate (SERR) is used; i.e. Gmax,(ΔG)2, or ΔG. In all cases it is usually observed that keeping the similitude parameter constant, and changing the R-ratio, results in a different crack growth rate. In this paper it is shown that this apparent...