The interrelation of the parameters in the Paris equation of fatigue crack growth

The majority of the models describing the fatigue crack growth under high cycle fatigue loading has being formulated as the form of Paris equation, da/dN = C(ΔK)n, in which n is a constant and C varies with the load ratio R, as such to interpret the effect of mean stress on the fatigue crack growth behavior of materials. In this paper a modified Walker equation was developed by which the interrelation between C and n, in terms of ratio R, was established. The original equations of Paris’s and Walker’s are the special cases of the new equation. The regression results of the new equation for fatigue crack growth data correlate well with testing results of four kinds of materials.