13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- 3. Results and Discussions 3.1. Hardness and residual stress Vickers hardness of the SUP7 specimens in the respective series was measured and the results are indicated in Fig.5. The hardness of T-386 series is higher than that of T-450 series due to the lower tempering temperature. It is found that the hardness is a little improved by performing the shot-peening. Residual stress distributions are plotted in Fig.6. The residual stress on the specimen surface caused by grinding is in a range of 500 400 MPa, and the residual stress is induced in surface layer within a thickness less than 20 m. Another typical finding is that distinct compressive residual stress higher than 1000MPa was caused by shot-peening and the depth of the surface layer having such a distinct high residual stress is around 40 m. (a) Rotating bending Figure 5. Vickers hardness of the respective series (b) Axial loading Figure 6. Distributions of residual stress Vickers hardness of the individual series for SWOSC-V steel is as follows; T-395G series: 584HV, T-363G series: 630HV, T-363EP series: 630HV and T-363SP series: 641HV, respectively. Resulting trend for tempering temperature and shot-peening is quite similar to the results for SUP7 steel. Residual stress for the respective series measured on the specimen surface is as follows; T-395G series: -376MPa, T-363G series: -378MPa, T-363EP series: -31MPa and T-363SP series: -1205MPa, respectively. Thus, residual stress caused by grinding is around 380MPa and this stress is almost entirely removed by electrochemical polishing. However, a distinct compressive residual stress of -1205MPa is produced by performing the shot-peening. This trend is corresponding to the results in Fig.6. 3.2. S-N characteristics Fatigue test results of T-450G and T-386G series for SUP7 steel obtained in rotating bending are plotted as an S-N diagram in Fig.7(a). Every S-N curve was determined by accepting the bilinear
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