13th International Conference on Fracture June 16–21, 2013, Beijing, China -3- 25 fatigue test specimens as received (non-nitrided) and 25 plasma nitrided specimens with a nitriding layer of 0.3mm, were tested in a rotating bending fatigue machine and the results were plotted and compared by Wöhler’s curve for both types of steel specimens. Besides, the surface hardness of non-nitrided and plasma nitrided specimens and the limit strength were obtained by hardness and tensile tests respectively. Photographs by SEM of the fractured surface specimens were obtained and provided a visual analysis of fracture of nitrided and non-nitrided specimens in tensile and fatigue tests. The fatigue test specimens were machined from one bar, according to the dimensions seen in Fig.2. Each specimen were polished to surface average roughness of Ra = 0.11µm in the useful region which had lower specimen diameter of 7.0mm. Figure 2. Geometry dimensions of rotating bending fatigue test specimens. Figure 3 shows a photo of a non-nitrided specimen employed in the rotating bending fatigue test which attained a fatigue life over 106 cycles. Figure 3. Photo of a rotating bending fatigue test specimen which attained fatigue life over 106 cycles. 2.1. Fatigue Tests Fatigue tests were carried out in the rotating bending fatigue machine, type TYP RM 506, Budapeste/Hungary, seen in Fig. 4. The specimen bending load was applied by a load arm existing in the machine. The true bending load applied on the fatigue specimen corresponds to 10 times the load applied on the plate situated at the opposite arm end. Figure 4. Photo of the rotating bending fatigue machine, type TYP RM 506, utilized in the fatigue tests. Ф7.0 R = 15.0 Ф10 49 45 49
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