Fig. 7. An example of crack growth in a single-edge-notch specimen for cyclic repeated loading at 1 Hz to 0.166 strain. Approximate energy release rate as a function of crack size, calculated as if change in strain energy density with cycling (Eqn 6) were negligible, is shown on the secondary ordinate. Only data points for which crack growth was equal to or greater than 10% of previously used value (filled points) were used in analysis of crack growth rate.