Effects of stress ratio on crack growth rate and fatigue strength for high cycle and very-high-cycle fatigue of metallic materials

• da/dN versus stress ratio from near-threshold region to Paris region is investigated.
• Proposed model is able to predict da/dN from near-threshold region to Paris region.
• da/dN values by experiments and predictions range from 10−13 m/cycle to 10−4 m/cycle.
• A relationship is derived to describe the effect of stress ratio on fatigue strength.
• Predicted da/dN and fatigue strength are in good agreement with experimental data.

This paper studies the effects of stress ratio R on crack growth rate and fatigue strength for high cycle and very-high-cycle fatigue of metallic materials. First, the effect of R on fatigue crack growth rate is analyzed, and the result shows that the effect of R on crack growth rate at near-threshold region and on Paris region is well expressed by a unified relation. Then, a model is developed for describing the fatigue crack growth rate with the effect of R in near-threshold region and Paris region. The model is verified by experimental data of metallic materials in literature. Finally, a formula is derived for the effect of R on fatigue strength. The estimated results are in good agreement with the experimental data for high cycle and very-high-cycle fatigue regime in literature. The comparison of the present result with Goodman diagram is also discussed.