SHEAR MODE CRACK-GROWTH AND ROLLING-CONTACT FATIGUE

Mixed mode crack growth direction criteria have been applied to calculations of the loading experienced by surface-initiated rolling contact fatigue cracks growing at a shallow angle to the surface. It was demonstrated that the cracks grow on the plane of the maximum shear stress rather than perpendicular to the maximum tangential stress as occurs during conventional fatigue testing. Mixed mode fatigue crack growth tests were then performed on rail steel specimens in an investigation of the effect of loading cracks in shear. It was demonstrated that while conventional mixed mode testing always produces cracks that either arrest after at most a millimetre of coplanar growth or branch to grow perpendicular to the tensile stress, under certain conditions similar to those experienced by rolling contact fatigue cracks, growth on the plane of the maximum shear stress range does occur. Additionally, under these conditions the cracks can grow up to 10 times faster than would be predicted by conventional fatigue testing.