PSI - Issue 28

Vera Petrova et al. / Procedia Structural Integrity 28 (2020) 608–618 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 6a shows the critical loads for edge cracks from the system of cracks in Fig. 4a. The largest value for p cr / p 0 is for crack 2 and the smallest one for crack 1. Thus, the weakest edge crack is the large crack 1.

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Fig. 6. Critical loads as function of angles β for the geometry in Fig. 4a: (a) for edge cracks, (b) for edge cracks and internal cracks, (c) artificial results for edge cracks and internal cracks without taking into account the variation of fracture toughness for the FGC. The critical loads for other internal cracks show similar values as for crack 4 and are not shown here. In Fig. 6b, the results for p cr / p 0 for edge cracks and internal cracks are depicted for cracks in Fig. 4a. The critical loads for other internal cracks have similar values as for crack 4 and are not shown here. The largest value for p cr / p 0 is for internal crack 4. The weakest crack has the smallest p cr / p 0 , and this is crack 1. Thus, the fracture starts from the large edge crack. The results in Fig. 6a and 6b take into account the variation of fracture toughness in accordance with the law in Eq. (4). Artificial results for p cr / p 0 without taking into account the fracture toughness variation are shown in Fig. 6c. These results contrast with those in Fig. 6b, thus, in Fig. 6c, the lowest values for p cr / p 0 are for crack 1 (the weakest crack) and for internals cracks, as was also defined in the comparison of the SIFs k I in Section 4.1.

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Fig. 7. Critical loads as function of angles β for the geometry in Fig. 4b: (a) for edge cracks, (b) for edge cracks and internal cracks, (c) artificial results for edge cracks and internal cracks without taking into account the variation of fracture toughness for the FGC. The critical loads for other internal cracks have similar values as for crack 4 and are not shown here. Fig. 7 shows p cr / p 0 versus β for the geometry in Fig. 4b, i.e. for the cracks of the same length. As in the previous case Fig. 6a, the largest value of critical load is for edge crack 2 (Fig. 7a), but this time its value is about 50% smaller than those for crack 2 in Fig. 6a. At the same time, all values p cr / p 0 for edge cracks 1, 2 and 3 are nearly the same. In Fig. 7b, the results p cr / p 0 for edge cracks and internal cracks are presented, and, as in the previous case in Fig. 6b, the lowest values of critical loads are for edge cracks, that is, these edge cracks are weakest cracks. Artificial results for p cr / p 0 without taking into account the fracture toughness variation are shown in Fig. 7c, where all values do not much differ from each other. The crack order with the smallest and lowest values for p cr / p 0 is completely different from that shown in Fig. 7b and also different from the case of Fig. 6c. It should be noted that the effect of the inclination angle β on critical loads is very small, Fig. 6 and 7.