PSI - Issue 39

Keke Tang et al. / Procedia Structural Integrity 39 (2022) 387–392 Author name / Structural Integrity Procedia 00 (2021) 000–000

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4. Results and Discussions 4.1. Influence of lamellar structure distribution

Strain diagrams for 9 cases after certain cycles of fatigue loading is graphically displayed in Fig. 3. At the RVE level, strain distribution is approximately the same. At the local level, strain distribution around elliptical notches turn out to be vastly different. For one designated notch size presented in Fig3(a)-Fig3(c), influence of lamellar structure distribution is red-outlined and turns out to be appreciable. Indirectly impacted area of lamellar structure is black outlined. Strain distribution in this black-outlined area is slightly changed from Fig3(a) to Fig3(c). If the elliptical notch is varied from ‘Defect III’ to ‘Defect I’, it is clear that strain distribution in lamellar structure remains stable, while strain distribution in single phase grain around elliptical notches is increasing as depicted in the red-outlined area. Based on the numerical results, it can be concluded that lamellar structure is more stable under fatigue loading compared to single phase grains. There is a slight change of strain distribution in black-outlined area from Fig3(a)- Fig3(c), but almost remain the same for different notch sizes from ‘Defect III’ to ‘Defect I’ as shown in Fig.3(a), Fig3(d) and Fig3(g). It is fair to conclude that impact of notch size on whole RVE model is negligible.

Fig.3 Strain diagrams of 9 cases with different lamellar structure distribution and notch sizes

4.2. Strain accumulation along radial path According to Fig.4(a) - Fig4(c), it is easily observed that the high strain accumulation tends to occur around the elliptical notch, strain accumulation afar is relatively trivial. Single phase grains are set at one side of the notch, it seems that strain peak in lamellar structure around the notch is prominent. Strain concentration around the notch are relieved to a certain degree. Strain accumulation in lamellar structure is much higher than that in single phase grain. Oscillation of strain causes the decrease of strain continuity. However, it is noticed that with the increase of aspect ratio, high strain in lamellar structure tend to be close to the strain in single phase grain. It is concluded that adjusting