Pertinence of Material Constants in Paris Model for Fatigue Crack Propagation Rate of Metallic Materials

Fatigue crack propagation rate of metallic materials is an important index of mechanical property, which is employed for damage tolerance design and fatigue life assessment in engineering application. Paris model is the most popular expression for fatigue crack propagation rate, and the relation of fatigue crack propagation rate and stress intensity factor range at the crack front is believed to meet a power-function rule in the model. The model involves in two material constants of C and m. In this paper, based on some test data published in some literatures, the relationships between material constants of C and m in Paris model for fatigue crack propagation rate of metallic materials of alloy steels, copper alloy, titanium alloy and aluminum alloy were analyzed. The results indicated that the constants of C and m of different types of metallic materials satisfied good linear relationship, namely m=alnC+b, which was not affected by specimen sampling orientation, weld position, and test environment. Stress ratios had great influence on the linear relationship, especially when the stress ratio value was negative. The slopes of the linear models for different metallic materials were not equivalent and the influencing factors should be further researched systematically. The analyzing results would provide reference for fatigue design and application in engineering.