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. 3. (a) Close-up view of the fracture surface of the control rod showing the crack origin, progressive crack zone, and overload fracture zone, and (b) inner surface of the rod showing distinct machining marks on the fillet surface at the crack initiation region (arrow).

3.2. Fractography studies Figure 4(a) shows a low magnification secondary electron (SE) image of the fracture surface. Crack origin region and crack propagation direction are shown in the figure. Examination revealed that the crack originated on the fillet surface over a length (region encircled in Fig.4(b)). Examination did not reveal any external mechanical damage, or unusual fillet profile, or any metallurgical abnormalities at the crack origin. Figure 5(a) shows the fractograph recorded on the progressive crack propagation zone. In this region, the fracture surface showed presence of striations, typical of fatigue crack propagation. Outside the progressive crack propagation zone, the fracture surface showed presence of dimples, typical of overload fracture in ductile metallic materials (refer Fig.5(b)).

Fig. 4. (a) Scanning electron image showing the crack origin region and crack propagation direction, and (b) magnified view of the crack origin region marked by a rectangular box in (a).