PSI - Issue 68

Swastik Soni et al. / Procedia Structural Integrity 68 (2025) 513–519 S. Soni et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 6. Fractographs of the Mod P91 specimen at (a) -20 0 C & 6.7x10 -3 s -1 Strain rate having fractal dimension 1.899 and (b) -40 0 C & 6.7x10 -3 s -1 Strain rate having fractal dimension 1.9 The behavior of fractal dimension and dimple diameter with respect to temperature and strain rate is illustrated in Figure 7. The experimental results indicate that, as the strain rate increases, the dimple diameter also increases (at - 20 o C), while a decrease in testing temperature leads to an increase in dimple diameter. However, it is not very conclusive between -30°C and -40°C, where this trend reverses, however, it can just be an experimental scatter because these are locally calculated parameters. For fractal dimension, an increase in strain rate results in a decrease in fractal dimension, and similarly, a decrease in testing temperature reduces the fractal dimension. Yet, in the same transition region between -30°C and -40°C, the trend of the curve reverses.

Fig. 7. Behaviour of dimple diameter and fractal dimension

4. Conclusion This study provides a comprehensive investigation into the fracture behavior of 9Cr-1Mo ferritic/martensitic steel in the DBT regime using quantitative fractography techniques. The key findings are: • Fractal dimension shows an inverse behavior in comparison to dimple diameter. • The material transitions from brittle to ductile behavior with increasing temperature, showing a decrease in yield strength and ultimate tensile strength, while with increasing the strain rates stabilize tensile strength across the temperature range.