Stable Crack Growth Based on the Resistance Curve Method

The crack growth resistance curve of a certain material at a thickness 2 mm is expressed by $$ R = \frac{{K_k^2}}{E} + \frac{1}{2}{\left( {\Delta a} \right)^{0.5}}{{MJ} \mathord{\left/ {\vphantom {{MJ} {{m^2}}}} \right. \kern-\nulldelimiterspace} {{m^2}}},{K_k} = 95MPa\sqrt m ,E = 210 \times {10^3}MPa. $$ (1) Consider a center cracked plate of width 10 cm and thickness 2 mm with a crack of length 4 cm. Calculate the length of stable crack growth, the critical crack length, and the critical stress at instability.