PSI - Issue 42

Michal Vyhlídal et al. / Procedia Structural Integrity 42 (2022) 1000–1007 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 6. Distribution of critical force F crit in dependence on the polar coordinate  , and in dependence on the distance d (on the left); minimum value of critical force F crit in dependence on the distance d (on the right).

3.5. Crack propagation from the top corner of the inclusion The graph in Fig. 7 shows the distribution of average tangential stress for the crack with its tip at the top corner of steel inclusion in dependence on the polar coordinate and distance d . Crack propagation in the almost vertical direction (about 215°) is expected. Further, the crack will turn in vertical direction. The dependences of critical forces F crit on the distance d are shown in Fig. 7 (right) for the specimens both with and without the inclusion. Similarly to the section 3.4, the values of F crit (REF) are calculated for the crack tip in the position which corresponds to the top corner of the inclusion. The differences between F crit (REF) and F crit (STE) are due to the different directions of crack propagation for both specimens (STE and REF) but are negligible in this case.

Fig. 7. Distribution of average values of tangential stress ̅ in dependence on polar angle (potential crack propagation direction), critical force F crit in dependence on the distance d, respectively. 4. Conclusions The numerical study in the previous paragraphs estimated potential crack propagation paths and the critical applied forces during crack propagation stages: crack initiation in the central edge notch, and propagation in the bottom, left, and upper corners of the inclusion. The Fig. 8 shows the evolution of the critical force F crit in the crack stages. The results of critical forces for crack propagation around the inclusion are compared to the crack propagation in homogeneous material (the reference specimen). Although the dependence on the distance d is often discussed, it is apparent, that it is very weak. Crack propagation path depends mainly on the fracture properties of ITZ, see the section 3.4. The comparison of the specimens with and without the inclusion shows that the central inclusion works as an obstacle to crack propagation only in the beginning stage – the crack initiation in the notch tip, where F crit (STE) is higher than F crit (REF). The mechanical fracture parameters of the ITZ strongly influence the overall fracture behavior of test specimens, as we reported in previous papers, see e.g. Vyhlídal et al. (2022), Vyhlídal and Klusák (2020) or Zacharda et al. (2018).