13th International Conference on Fracture June 16–21, 2013, Beijing, China -5- Both the increase of the transition zone width and the decrease of the hardness in the transformed phase are desired effects of the pre-heating strategy, but will lead to a variation in the fatigue behavior of the flange shaft. So, a comparison of the fatigue crack propagation in the flange shafts for all four pre-heating temperatures is necessary. 3. Experimental set-up For analyzing the fatigue behavior of the transition zone micro-specimens were cut out from the flange using high precision spark erosion. A dog-bone shaped micro-specimen (32.5 mm long and about 2.4 mm thick), shown in Fig. 8, was developed with the purpose of performing microstructure specific fatigue tests. As shown in Fig. 8, the center of the specimen consists of martensite (dark) while the white areas mark the transition zone and the deformed base material is in grey again. The preparation of the specimens consisted of mechanical polishing and mechanical-chemical polishing with OPS in the final step. Figure 7. Micrograph taken from a flange shaft to determine the exact specimen position, etched Figure 8. Micro specimen, etched Figure 9. Experimental setup with two long distances microscopes in front of the micro-specimen All fatigue tests were carried out as uniaxial tests at room temperature on a servo-hydraulic testing machine. The stress ratio was set to R = -1 (i.e. fully reversed) with 500 MPa were chosen as load amplitude. Tests with smooth specimens were monitored using one travelling long distance
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