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. 2. Radial mesh around – crack tip (left); left corner of steel inclusion (middle); top corner of steel inclusion (right).

3.2. Crack initiation from the notch Distance d was considered as the length between the crack tip and bottom corner of the inclusion, which are both potential stress concentrators. According to the theories of finite fracture mechanics, see Taylor et al. (2005), Cornetti et al. (2006), Taylor (2017), we suppose, that this distance d corresponds to current crack increment of final length. We suppose that the bridge between the initial crack (edge notch) and the inclusion breaks at once. The stress concentration ahead of the crack tip and the inclusion is shown in Fig. 3.

Fig. 3. Isosurfaces of the first principal stress for the specimen with the steel inclusion (left) and the homogeneous reference specimen (right).

Various notch depths would lead to different stress distributions as shown in Vyhlídal and Klusák (2019), where it was found that the diamond blade of the saw can damage the specimen more than expected. Here in the study of the notch with the depth 12 mm, the critical applied force was determined as crack propagation in the matrix: F crit (STE) = 1.36 kN. Similarly, the critical forces were calculated for the reference specimens: F crit (REF) = 1.14 kN. 3.3. Crack propagation from the bottom corner of the inclusion In this stage, we analyzed the crack propagation in the bottom corner of the inclusion. The distribution of the first principal stress can be seen in Fig. 4 (left), while a graph describing the development of the critical force F crit in dependence on the distance d is shown in Fig. 4 (right). It should be noted that the critical force F crit was determined for the crack propagation along the interface, whose fracture toughness was equal to 70 % of the fracture toughness of the matrix in the numerical model. The critical forces for reference specimen are also shown in Fig. 4 (right). Although the crack propagation along the interface is not natural, in contrast to the vertical crack propagation in the case of reference specimens, the F crit (STE) reaches lower values in comparison to the F crit (REF). It is caused by the lower fracture toughness of the interface K Ic, ITZ compared to the K Ic, MTX .