Fatigue Life Dependence on Non-uniform Hardening Effect After Surface Rolling

Fatigue failure of high strength steel shafts in different mechanisms leads to expensive replacement of shaft or the entire mechanism. Fatigue failure usually takes place in stress concentration areas. One of the effective methods to improve shafts fatigue characteristics is surface hardening by rolling [1]. In order to reach maximum fatigue life of the shaft the process of calibration, selection of rolling parameters (roller section radius, curvature, rolling force, etc.) [2] and non-uniform rolling influence are described in this article. The task was to design a bolted joint that has to fail by shear under specified load conditions. To ensure these requirements two grooves with certain geometry are made on bolt’s surface. Grooves decreased fatigue life of the bolted joint several times. In order to repair fatigue characteristics, groove areas were hardened by surface rolling. Several computer models were made in order to select optimal hardening parameters and understand how non-uniform hardening effects fatigue life. Numerical results were verified by experimental data. As a result necessary rolling parameters were selected and fatigue life of shafts with stress concentrations (grooves) increased no less than 3 times.