Use of a dislocation-based boundary element model to extract crack growth rates from depth distributions of intergranular stress corrosion cracks

A dislocation-based boundary element model was used to simulate intergranular stress corrosion crack propagation in virtual microstructures. A Monte Carlo approach was used in which the propagation of approximately 100 cracks was calculated for different Voronoi generated microstructures. At every simulation step the model gave the position of the crack tip together with stress intensity factors K_I and K_II. Using a simple power-law-type crack growth rate $\mathit{da}/\mathit{dt}=D_p{K}^{m_p}$, the depth of each particular crack can be calculated knowing the time the samples were exposed to the stress and corrosive environment. Existing experimental data giving crack depth distributions for Alloy 600, and XM-19 and 304 stainless steel are investigated and the best-fit crack growth law established. Alloy 600 in a light water reactor environment and XM-19 in high-temperature water both lead to m_p = 3. While for 304 stainless steel in the more aggressive K₂S₄O₆/H₂SO₄ (pH 2) an exponent m_p = 0.8 was found.