2016 Volume 57 Issue 666 Pages 660-666
In this study, the effects of pre-straining and surface friction on fatigue properties have been investigated. Three grades of 590-MPa-class steel sheets that have different roughnesses and yield ratios were used. At first, the steel sheets were subjected to 10% tension and 10% compression as a pre-straining process. Then, the surfaces of the steel sheets were burnished with a contact force of 19.1 kN. After that, plane-bending fatigue tests were carried out using these specimens. The evaluation by this fatigue test has revealed the following. A low roughness of the steel surface diminishes the effects of pre-straining and surface friction on the fatigue properties. Fatigue strength increases after applying surface friction in the case of complete smoothing of the initial roughness. Otherwise, fatigue strength decreases in the case of residual concavities after applying surface friction. These residual concavities are caused by the work-hardened surface after the tension-compression process. For the fatigue deterioration due to the presence of the residual concavities, finite element simulations have implied that tensile residual stress is generated at the residual-concavity tips after applying surface friction. This residual stress probably deteriorates the fatigue strength.
