Fig. 4. An example of calculating critical strain energy release rate, T_C, for M. flaccida in single-edge-notch, pull-to-break tests. The inverse of crack length, a, introduced into each sample is plotted against at fracture, where _Wo is calculated as total absorbed strain energy density, W_o,T, and estimated stored strain energy density, W_o,S. Solid circles indicate data points calculated from total strain energy density; solid diamonds indicate data points calculated from stored strain energy density. T_C is the slope of the regression line for each data set: regression line (broken line) for data points calculated from total strain energy density yields an estimate of T_C,T, and regression line (solid line) for data points calculated from estimated stored strain energy density yields an estimate of T_C,S, as defined in the text. Open circles and diamonds indicate data points for un-notched samples, for which effective crack length was estimated.