Critical internal defect size for subsurface crack initiation in heavy haul car wheels

Abstract

Rolling contact fatigue failure is one of the very common causes for the replacement of heavy haul car wheels. There are two crack initiation modes in rolling contact fatigue failures, which are surface and subsurface crack initiation modes. Internal defects such as voids and non–metallic inclusions are known to be the possible origins of subsurface cracks. In this study, torsion and axial fatigue tests are conducted on railway wheel steel with artificial defects, and finite element analyses of heavy haul car wheels are performed to study the subsurface crack initiation due to cyclic rolling contact. The fatigue limits of the wheel steel decrease with an increase in the artificial defect size. The shear and axial fatigue limits with different defect sizes agree well the El–Haddad formula. Based on the finite element analysis considering the multiaxial stress state, the critical defect size for subsurface crack initiation is estimated to be 1.1 mm. This indicates that subsurface cracks might be initiated in service conditions as the critical size is less than 1.6 mm, which is the maximum permissible size of an internal defect in the wheel rim as per Association of American Railroads specifications. Therefore, higher–cleanliness wheels would be required to prevent subsurface cracks.