Fatigue Crack Propagation on Uniaxial Loading of Biaxially Predeformed Pearlitic Rail Steel

Rolling contact fatigue loading causes the surface material in the top of the rail to severely deform. The microstructure aligns along the shear direction and the mechanical behavior in terms of plastic flow becomes anisotropic. Cracks are initiated in the severely deformed surface region and propagates along the direction of microstructure flow lines. However, the effect of large shear deformation on fatigue crack growth is not yet well understood. In this study, uniaxial fatigue crack propagation of undeformed and biaxially predeformed pearlitic rail steel R260 has been investigated. The material was predeformed to different deformation states using combined axial compression and shear deformation, corresponding to material found at different depths in the severely deformed surface layer of rails. Fatigue crack propagation rate was dependent on the material state and influenced by both work hardening and microstructural anisotropy. It was found that predeformed material exhibited lower crack growth rates than undeformed material under this loading condition. The influence of predeformation on the crack growth direction was limited.