Short Fatigue Crack Propagation Threshold of Railway LZ50 Axle Steel

Collective short fatigue behaviour nearby material micro-structural barrier threshold is experimentally observed for the smooth specimens of Chinese railway LZ50 axle steel. Effective micro-cracks which result in the specimens' failure were initiated from the material ferrite particles on the surfaces of the specimens. Four elements i.e. crack size, orientation angle, and the two crack tip orientation angles should be contained for each micro-crack. The collective micro-crack behaviour should be described by an equivalent dominant effective short fatigue crack (ESFC) concept using an ESFC theory. And an equivalent method is then developed with an equivalent growth driving energy concept. A random modeling of the equivalent dominant ESFC growth rates is further constructed for describing the random behaviour of the collective ESFCs nearby the material micro-structure barrier threshold. And the kinetic threshold is subsequently conducted from the modeling.