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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5

larger than the size с in comparison with 8 mm diameter. The length of corner crack from which it becomes through thickness for cold expanded hole is greater than non-deformed ones regardless of the hole diameter. As the hole diameter increases, this difference increases as well.

10 12 14

c(a=t) ,mm

2

1

4 6 8

8

10

12

d , mm

Fig. 5. The dependence of the crack length c from the notch top on the surface on the hole diameter at a = t, і = 0 (1) and і = 2,4 – 2,8 (2)

The increase in the crack length c during its transition to the through-thickness one is caused by slowing down its growth along the specimen thickness due to the action of residual compressive stresses after cold expansion holes with preexisting crack alloys (Yasnii et al. (2020)). The dependence of residual lifetime on the initial crack length а 0 of the non-deformed specimen with the hole 8 mm in diameter and after cold expansion holes with tension і = 2,7 % is presented in Fig. 6. The residual lifetime for non-deformed specimen with initial crack length а 0 = 1 mm is N r = 12500 cycles, and increases up to N r = 77000 cycles after cold expansion degree і = 2,7 % The cold expansion holes impact on the residual lifetime is determined by formula: ̅ = / , (2) where , are respectively, the residual lifetime of the plate without and after cold expansion holes. It is determined that the greatest effect is achieved during cold expansion holes of aluminum plates with diameter of functional holes 8 mm. 4. Conclusions The main impact factors of cold expansion holes with preexisting corner crack on residual lifetime of the aluminum alloy plates are determined. The number of cycles of the crack growth delay after cold expansion holes increases with the hole diameter increase. This is due to the strengthening of the material in its plastic zone after cold expansion of the holes and the induce of residual compressive stresses near the hole and crack tip, which action width zone increases with the hole diameter increase. The critical crack length on the plate surface, at which the crack becomes through-thickness, increases significantly with the hole diameter increase from 8 mm to 12 mm after cold expansion of the holes. Cold expansion of the holes significantly increases the residual lifetime of the aluminum alloy plates in comparison with those without cold expansion. The greatest effect of increasing the residual lifetime by 6,6 times ( i = 2.7 %) is after cold expansion of the holes at the initial crack length on the ho le surface а 0 = 1 mm. References

Amrouche, A., Su, M., Aid, A., Mesmacque, G., 2008. Numerical study of the optimum degree of cold expansion: Application for the pre