PSI - Issue 36

Petro Yasniy et al. / Procedia Structural Integrity 36 (2022) 197–202 Petro Yasniy, Ihor Okipnyi, Oleksandr Dyvdyk et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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the shape factor on its length on the hole surface a (Fig. 4b). The lowest values of the shape factor are observed for plates with holes 8 and 10 mm in diameter and crack size a ≈ 1.15 mm .

0,0 0,2 0,4 0,6 0,8 1,0 1,2

0,0 0,2 0,4 0,6 0,8 1,0 1,2

a/c

а/ c (8) a/c (10) а/ c (12)

a/c

а/ c (8) a/c (10) а/ c (12)

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N , cycles

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a , mm

a b Fig. 3. The dependences of the shape factor a/c on the number of load cycles (a), the crack length а (b) in plates with holes d = 8 mm, 10 mm and 12 mm in diameter; і = 0. Similar to the specimens in the initial state, the dependence a/c – N for specimens after cold expansion degree 2.4 - 2.8%, can also be divided into three areas: decrease a/c, increase and stabilization (Fig. 4a). Similar dependence of the change in shape factor after cold expansion of hole is observed on the crack length on the hole surface (Fig. 4a). The change of a/c of each area and their duration depend on the specimen hole diameter. In contrast to the specimen without cold expansion, the lowest values of the shape factor is observed for the plates with holes 10 and 12 mm in diameter. Residual lifetime is determined as the number of load cycles at which the angular crack became through thickness, i.e. at a = t . This is due to the fact that through-thickness cracks are more dangerous, because during the transition from angular to through-thickness ones, their growth usually accelerates.

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a/c, i = 2,7 (8) a/c, i = 2,4 (10) a/c, i = 2,8 (12)

a/c

a/c

a/c, i = 2,7 (8) a/c, i = 2,4 (10) a/c, i = 2,8 (12)

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а b Fig. 4. The dependences of the shape factor a/c on the number of load cycles (a) and the crack length а (b) in the plates with cold expansion degree і = (2,4 – 2,8) %; d = 8 mm, 10 mm and 12 mm As the hole diameter increases, the length of the crack c on the surface increases (Fig. 5). Particularly, the value of the crack length on the surface hole with diameter d = 12 mm at a = t is 9 mm, which is much larger than for d = 8 mm ( c = 7.22 mm). This dependence is important for structural elements diagnostics by the methods of non destructive testing and determination of inspection periods. As for non-deformed specimens, with increasing diameter of the strengthened holes, the crack length on the specimen c surface also increases, at the point it becomes through-thickness. Thus, at a = t , the crack length c on the specimen surface with diameter 12 mm is 1.4 times