Collaborative crack initiation mechanism of 25CrMo4 alloy steels subjected to foreign object damages. (15th February 2020)

• Record Type: Journal Article
• Authors: Wu, S.C.; Luo, Y.; Shen, Z.; Zhou, L.C.; Zhang, W.H.; Kang, G.Z.
• Is Part Of: Engineering fracture mechanics. Volume 225(2020)
• Publication Date: 2020-02-15
• Subjects: Probabilistic fatigue assessment -- Kitagawa-Takahashi diagram -- Compressive residual stress -- Fatigue crack initiation and growth -- High-speed railway axles; Fracture mechanics -- Periodicals; Rupture, Mécanique de la -- Périodiques; Fracture mechanics; Periodicals; 620.112605
• DOI: 10.1016/j.engfracmech.2019.106844
• Languages: English
• ISSNs: 0013-7944

Abstract

Highlights: The microstructure and micro-damage were investigated at the FOD crater. The residual stress was depicted by Johnson-Cook model and failure criterions. The conditional probability density distributions were plotted in three dimensions. The modified Kitagawa-Takahashi diagram was established with FOD defects. Abstract: High-speed railway axles are seriously threaten by external flying objects. Foreign object damage (FOD) on 25CrMo4 or EA4T axle steel specimens was then prepared by a compressed-gas gun. The microstructure and micro-damage at the crater were investigated by scanning electron microscopy, electron backscattered diffraction, transmission electron microscopy and nano-indentation. To correlate the FOD to the fatigue crack resistance, residual stress distribution due to FOD was also simulated by calibrating the Johnson-Cook constitutive equation and associated failure criterion in experiments. Besides the significant uncertainty of fatigue crack initiations from the FOD-induced micro-damage, residual stress and microstructure change, those FODed specimens also present a significantly lower fatigue strength than those at the absence of FOD. Furthermore, a higher impact velocity on the specimens appears to produce lower fatigue endurance. Finally, a modified Kitagawa-Takahashi diagram was established to combine the fatigue strength with FOD defects, which can be used in the fatigue resistance evaluation of high-speed railway axles.