Directional development of residual stress and surface fatigue during sliding contact

• Point contact sliding produces tensile stresses in the material.
• Highest stresses are measured transversal to the sliding direction.
• Crack propagation is correlated with the direction of highest stress longitudinal to the sliding direction.

Stresses in the near-surface area can form cracks which join together, propagate and combine, forming pits due to material spall-off. The stresses causing the cracks are not only influenced by external forces, residual stresses stored in the material also play an important role. Moreover, these residual stresses can vary during the lifetime of the sliding components. Cracks are found in the wear tracks of linear oscillating ball contacts on AISI 4140 steel. The crack propagation at the surface is longitudinal to the sliding direction. Residual stress analysis by X-ray diffraction (XRD) shows that normalized samples develop tensile stresses in the near-surface zone of the wear track. Residual stresses are found to be higher transversal to the moving direction than longitudinal.