Influence of K_max and R on Fatigue Crack Growth—A 3D‐Model

Abstract

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 Kmax and the R‐ratio affect the crack growth rate. Consequently, the authors developed a 3D‐model, which describes the dependence of da/dN on Kmax 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 Kmax,th for R‐ratios from −∞ to 1 is presented.

Fatigue crack growth behavior of beta-annealed Ti–6Al–2Sn–4Zr–xMo (x= 2, 4 and 6) alloys: Influence of microstructure and stress ratio

“…Many researchers have pointed out that stress ratio (R, ratio of minimum to maximum stress) had a direct relationship with RICC where a higher stress ratio would make fracture surfaces avoid contact. Until now, most of the research related to stress ratio effect (also called mean stress effect) was based on the mathematical expression descriptions about FCG rates [12,13,16,[32][33][34][35], where stress ratio effect has been taken into account (basically make an amendment to the classic Paris equation [36]). Although crack closure, which induces enhanced shielding effect on FCG, can be rationalized by the effective (∆Keff) rather than by the applied stress intensity factor range (∆K) to some extent, the specific mechanism of stress ratio acting on FCG behavior is complicated [8] and still not fully understood.…”