Alarm limits for wheel–rail impact loads – part 2: analysis of crack growth and fracture
The crack growth and subsequent fracture of rails is governed by the imposed rolling contact load from operational vehicles. This study focuses on the growth of longer cracks. In contrast to shorter cracks that are mainly driven by the influence of the contact stress field in combination with the effect of trapped liquid, these cracks are mainly driven by the global bending of the rail. In addition there is, for all-welded rails, a major influence of the rail temperature.
The aim of the study is to find a scientific basis for regulations regarding allowed wheel de- fects. These defects generate wheel–rail impact loads that in severe cases may promote fracture from pre-existing cracks in the rail. Present wheel removal criteria relate wheel defect alarm limits to the size (length) of a wheel flat. This is not an optimal situation since it may be both difficult and dangerous to locate and measure the length of a wheel flat. Further, a given size of a wheel flat will result in different impact loads if present on different types of vehicles due to differences in train speed, axle load, etc, and on different tracks with differences in track proper- ties. In this study, the focus is instead on the wheel–rail impact load magnitude and its influence on the risk of rail breaks.