Influence of Kmax and R on Fatigue Crack Growth-A 3D-Model

To study the influence of the stress intensity factor and the R-ratio on the fatigue crack growth rate different kind of crack propagation experiment have been carried out on the steels X5CrNi18-10 and C45E. The experiments show that both parameters the maximum stress intensity K-max and the R-ratio affect the crack growth rate. Consequently, the authors developed a 3D-model, which describes the dependence of da/dN on K-max and the R-ratio. Discussing the experiments, special attention has been paid to the threshold behavior of the investigated materials. Finally, a new model to describe the influence of the R-ratio on the threshold K-max,K-th for R-ratios from -infinity to 1 is presented.