PSI - Issue 36

Ivan Pidgurskyi et al. / Procedia Structural Integrity 36 (2022) 190–196 Ivan Pidgurskyi, Mykola Stashkiv, Mykola Pidgurskyi et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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Analysis of the obtained data shows that with the increase of the crack shape parameters a/c (at the same crack size on the surface), the durability of the coalescence stage N coal decreases despite the increase of the size a coal in this zone.

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Fig. 3. Dependence of the durability N coal during coalescence of identical surface cracks on the shape parameter a/c : a) position 1, 2; b) position 4, 5, 6 in Table 1. 4. Estimation of the effect of the coalescence stage of identical surface cracks on the residual durability of the plates Calculations of the fatigue crack growth life N crack of samples with canonical surface cracks, which were formed after the coalescence of smaller cracks, were performed using a specialized program AFGROW (Harter (2020)). The results of the calculation of N crack are presented in table. 1. Comparing the ratio for the studied geometric parameters of the merging surface cracks (Table 1), it is worth noting the following. Firstly, as the crack length on the surface of the element increases, the ratio increases as well. Analyzing the obtained results, we should note that at the crack surface size 4 c = 5.0… 7.16 mm does not exceed 7.55%; at the length of the main crack 4 c = 22.0 mm the specified ratio varies from 18.1% to 26.8%. Also in Table 1 the experimental data of residual durability (positions 7 and 8) of samples of structural steels HY80 (pos. 7) and 50D BS 4360 (pos. 8) with thickness t = 25 mm is shown. Comparison of modeling results with experimental data (Kishimoto et al. (1989)) (cracks with length 22 mm and 21.04 mm were compared with the shape factors of 0.25 and 0.2, respectively) indicate a satisfactory convergence of ratios with modeling experiment data. In the framework of the conducted researches the influence of another factor such as shape factor of surface cracks on the coalescence process of two identical surface cracks is also analyzed. The influence of this factor is indeterminate (Table 1 and Fig. 4). It is determined that during coalescence of surface cracks with different shape factors a /4 c = 0.1; 0.2; 0.25; 0.39, the ratio was the lowest at a /4 c = 0.25 both for the crack length 4c = 5÷7.16 mm and for the length 4c = 22 mm. The ratio is the largest for small cracks at a /4 c = 0.39, while for larger cracks at a /4 c = 0.1. This nature of the influence of the crack shape factor on the development of cracks is explained by the peculiarities of the stress-strain state in the coalescence zone. Different comparative base of the number of cycles N crack create difficulties for analysis.