PSI - Issue 60

Prakash Bharadwaj et al. / Procedia Structural Integrity 60 (2024) 655–664 Prakash Bharadwaj / Structural Integrity Procedia 00 (2019) 000 – 000

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5. Results and discussion The measured FCG by both methods, namely the unloading compliance method and DIC system are found in good agreement with each other. For load maxima, 8.5 kN, and load ratio, 0.1, crack size versus the number of cycles is shown in Fig. 5(a), where the crack is measured by the unloading compliance method. Crack growth at different cycles by the DIC system is shown in Fig. 5(b)

Fig. 5. Crack growth vs number of cycles by; (a) unloading compliance method; (b) DIC system

Fig. 6, depicts the contours of the plastic zone that was obtained by the DIC technique for a number of different cycles. These are butterfly-like curves with an asymmetrical shape. As the size of the crack increases, the value of the stain does as well since large driving forces contribute to this. This results in a rise in the size of the contours, which is measured as the plastically deformed area, as the number of cycles increases ahead of the crack.

Fig. 6. Plastic zone contours of growing crack at different numbers of cycles obtained using the DIC system

For a cycle no 575472, von-Mises strain and load are plotted at four distinct locations ahead of the crack tip as shown in Fig. 7(a). The plot clearly demonstrates the opening of hysteresis of load-strain at a point which fall inside the cyclic plastic zone (CPZ). While the point, which is inside the MPZ but out of CPZ, the opening of the hysteresis