PSI - Issue 60

V. Venkatesh et al. / Procedia Structural Integrity 60 (2024) 372–381 V Venkatesh et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. (a) Scanning electron fractograph recorded on the progressive crack propagation zone showing fatigue striations, and (b) the final fracture region showing dimple rupture, typical of overload failure. Figure 6(a) shows a fractograph recorded at the crack origin region. Examination revealed that there was multiple fatigue crack initiation over a length and after initiation, all these cracks propagated into the material simultaneously. It was also found that the fatigue cracks had initiated at a step originated from machining. Figure 6(b) shows a typical fatigue crack origin at the step and its propagation into the bulk of the material.

Fig. 6. (a) Fractograph recorded at crack origin region, and (b) magnified view of the region marked in (a) showing a typical fatigue crack initiation at a step and its propagation.

3.3. Fatigue crack origin

Figure 7(a) shows SE image of the fillet surface adjacent to the fracture. Fracture origin region is shown in Fig.7(b). At the central region, fracture was found to have followed a deep circular machining mark over a length followed by deviation along a straight path on either side. Examination revealed presence of incipient cracks along the rest of this machining mark (refer Fig.8(a-c)). The incipient cracks along the machining mark were found to be the extension of the crack that resulted in fracture in the bearing housing. Figure 8(d) shows a part of the machining mark close to the fracture. Initiation of multiple fatigue cracks and their simultaneous propagation can be seen.