A stochastic simulation model for microcrack initiation in a martensitic steel

Specimens of the martensitic steel F82H-mod were fatigued under strain control. During the tests, crack initiation and growth were monitored on the specimen surface using an optical microscope. The experiments revealed microcrack initiation at the martensitc laths in the grains. These microcracks grew transgranularly until they were stopped at the grain boundaries. Empirical relations for crack initiation could be inferred from a statistical analysis of the microcrack patterns observed on the specimen surface. The probability that a microcrack of a specific length and orientation is initiated in a grain was determined and inserted in a stochastic simulation model based on a random cell structure. The simulation results correlated well with the experimental findings.