Full range S–N curves for fatigue life evaluation of steels using hardness measurements

• A hardness based method is proposed for predicting full range S–N curves of steels.
• Proposed formula is a single function which describes the entire S–N range from 1 to 109 cycles.
• Procedure is given for life evaluations of components with different geometries and stress ratios.
• Hardness measurements are nondestructive; hence the procedure proposed is nondestructive.

A simplified formula for deriving full range S–N curves of steels with ultimate tensile strength <1400 N/mm2 is proposed by combining empirical formulae and a mathematical function. The salient features of the formula proposed are that it describes the fatigue S–N curve from the first cycle up to the gigacycle region in a single function and that the monotonic test based material parameter needed in this formula is only the Brinell hardness. Fatigue life predictability of the proposed formula is verified using experimental data of smooth and notched specimens tested under various stress ratios.