白色層を起点とした鉄道車輪鋼の転がり接触下における疲労損傷評価

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Spalling is one of the typical rolling contact fatigue (RCF) failure of railway wheels, initiating at white layers, as the result of unexpected wheel slides. As for spalling, evaluation methods of fatigue strength have not been tried and tested. The purpose of this study is to propose a prediction method of RCF strength for crack initiation at white layers. In this study, 1) RCF tests in order to evaluate spalling behavior of wheel steels, 2) axial fatigue tests to obtain fatigue strength of white layer itself, and 3) elastic-plastic FEM analyses simulating the RCF tests to calculate stress distribution in/around white layers were conducted. As the results, the following facts were clarified. 1) In RCF tests, cracks were initiated at the leading edge of white layers particularly under slip condition. 2) Fatigue strength of the white layer can be evaluated accurately using the endurance limit diagram estimated by a straight line passing the true fracture strength and fully reversed fatigue strength. 3) According to FEM analysis results, the maximum stress at the leading edge of white layer is larger than at the trailing edge, and the maximum stress of the white layer increases by taking into consideration of small surface profile change during RCF test. Moreover, Dang Van model, which is one of the multiaxial fatigue strength evaluation methods, was applied to predict the white layer's fatigue strength in RCF tests. It can be concluded that the present prediction method is reasonably acceptable for crack initiation assessment of spalling and that in case of the existence of relatively apparent surface profile change, stress evaluation has to be done by taking it into consideration.
日本材料学会の論文

白色層を起点とした鉄道車輪鋼の転がり接触下における疲労損傷評価

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