PSI - Issue 54

Naveen Kumar Kanna et al. / Procedia Structural Integrity 54 (2024) 196–203 Author name / Structural Integrity Procedia 00 (2019) 000–000

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The fracture surface analysis has been carried out with an image analysis program, Imagic IMS client, on the scanning electron microscope (SEM) images. The crack size measurement has been carried out by measuring the crack depth a perpendicular to the specimen surface, crack width c parallel to the specimen surface as well as area of the crack as depicted in Fig. 6. All the semi-elliptical cracks on the fracture surface have been measured in the similar manner.

Fig. 6. Scanning Electron Microscope image of the fracture surface. The crack depth a, the crack width c as well as the fractured area A were measured at the traces produced by the overloads using an image analysis program. 3. Results and discussion 3.1. Aspect ratio The aspect ratio is defined as the ratio between crack depth a and crack width c, which changes with the crack size as shown in Fig. 7. Under fatigue loading conditions, the crack size increases with the cycling but there was no linear relation between the crack depth and crack width. It tends to a constant value at an aspect ratio of around 0.35 but it is increasing sharply in the beginning. This is because the a/c value of the produced laser notch is rectangular in shape with an a/c ratio of 0.035. The a/c value of the laser notch is not an equilibrium value making the aspect ratio increase sharply at the beginning until it reaches an equilibrium range.

0.35

0.30

0.25

0.20

0.15

0.10 aspect ratio a/c

0.05

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.00

relative crack depth a/t

Fig. 7. The aspect ratio a/c increasing nonlinearly during the propagation of the fatigue cracks.