From √A to Elliptical Defects: Refining Murakami’s Model for Fatigue Prediction in Sintered Steels

The use of powder metallurgy in the manufacturing of automotive components requires understanding the influence of porosity on fatigue behaviour. The most widely accepted explanation for the impact of porosity on the fatigue limit is Murakami’s “√Area = √A” theory. However, the presence of elongated or irregular pores in sintered steels challenges this simplification. This study analyses the fatigue behaviour of three sintered steels and performs a statistical and geometrical assessment of porosity. Results demonstrate that replacing the √A parameter with the ellipse-fitted major axis (dmax) reduces the average prediction error from nearly 50% to below 6%, markedly improving the predictive accuracy of defect-based fatigue models.