Probabilistic Fracture Mechanics Simulation of Stress Corrosion Cracking Using Accelerated Laboratory Testing and Multi-Scale Modeling

A propagation approach to manage stress corrosion cracking (SCC) is justified for modern high-strength alloys that exhibit low-subcritical crack growth rates, and is enabled by maturing probabilistic fracture mechanics and mechanism-based hydrogen damage modeling. A computer program, SCCrack, is developed based on stress intensity (K) similitude and fast Monte Carlo analysis to predict SCC life distributions from input distributions of variable material crack growth rate (da/dt vs. K), starting crack size, environment, and stress. Growth rates are obtained using an accelerated experiment that exploits precision electrical potential measurement of crack propagation, small crack size, and slow-rising K loading. Data are leveraged by fundamental models of SCC threshold (K_TH) and H-diffusion limited Stage II da/dt, built on the hydrogen environment assisted cracking mechanism. With these inputs, SCCrack enables multi-scale “What if?” simulations of the effects of alloy-environment-precorrosion-stress variables on component cracking. Examples are presented for SCC in modern ultra-high strength martensitic steel (AerMet™100 [UNS K92580] and Ferrium™M54 [UNS K91973]), a Ni-Cu superalloy (Monel K-500 [UNS N05500]), and a sensitized Al-Mg alloy (Alloy 5083-H131 [UNS A95083]), each stressed in chloride solution with varying cathodic polarization. Research is required to enhance accelerated measurement of very low da/dt, to capture the effects of atmospheric-environment spectra, to advance mechanism modeling, and to validate the approach for field-specific components.