Simulation of Initiation and Early Propagation of Creep-Fatigue Small Cracks Based on the Model of Random Fracture Resistance of Grain Boundaries

A stochastic model and a method of simulation of the initiation and the early propagation of creep-fatigue small cracks along grain boundaries were proposed. In the model, grain boundaries between two adjacent triple points were projected and linked on a straight line perpendicular to the applied stress axis, and their length was given as random variables of a normal distribution. The grain boundaries had their own fracture resistances, the magnitudes of which were given as uniform random numbers. The fracture resistance of each grain boundary decreased by a constant magnitude corresponding to the driving force of one fatigue cycle. When the resistance became zero or a negative value, the grain boundary was assumed to fracture and to yield an intergranular facet of small crack. Based on this model, a numerical calculation was done for a smooth specimen of 304 stainless steel subjected to the slow-fast strain cycle of 1%-total strain range at 923K in a vacuum. The result of simulation on crack density, cumulative probability of crack length, and crack propagation rates coincided with the experimental results.