A 3D correlation of damage criticality with the defect and life of externally impacted EA4T alloy steel

Abstract Modern railway axles have been frequently observed with various external damages, which induces the deteriorate fatigue performance and then requires careful maintenance. The strengthening behavior and its effect of shot peening (SP) on the fatigue strength of high-speed railway axle EA4T alloy steel due to foreign object damage (FOD) were then elucidated using the electron backscattered diffraction, transmission electron microscopy, X-ray diffraction and nano indentation. Based on improved backward statistical inference method, the probabilistic fatigue S N curves from high cycle fatigue tests were constructed to derive reliable endurance limits of UnFODed and FODed specimens with and without SP treatment, respectively. Eventually, El-Haddad model and Wohler curve along with modified Miner damage accumulation theory were collaborated to develop a three-dimensional (3D) Kitagawa-Takahashi (K-T) diagram in the framework of nominal stress. This 3D K-T fatigue figure can well correlate the fatigue damage accumulation Dcri and critical FOD defect size √areacr of externally impacted railway axles with knee-point life Nfw and slope kw.