PSI - Issue 66

Slobodanka Boljanović et al. / Procedia Structural Integrity 66 (2024) 535– 542 S. Boljanovi ć and A. Carpinteri/ Structural Integrity Procedia 00 (2025) 000–000

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Safety-critical performance of the plate with surface elliptical flaw is assessed here through the computational design strategy employing Eq.11 coupled with Eq.1 to 9. Estimated numbers of loading cycles, as a function of crack length in depth and surface direction, are shown in Fig.3a and b in the case of two different shapes of the elliptical flaw. Further, through relevant experiments discussed by Hall et al. (1974), the predictive capability of theoretical outcomes is verified, as is shown in Table 1. From different comparisons it can be concluded that life assessments adequately correlate with experimental life results for the plate with a semi-elliptical flaw. Table 1. Evaluated fatigue life for a plate (Fig.1a) and corresponding applied maximum stresses ( R = 0.1 and 0.5). Experiments are discussed by Hall et al. (1974), and relevant calculations are the present research results ( N cal ).

a 0 (mm)

b 0 (mm)

S max (MPa)

exp.. (cycles)

N cal. (cycles)

R

N

4.98 6.22 6.17

8.46 7.06 7.21

207 207

0.1 0.1 0.5

27,300 21,900 15,000

22,560 16,960 12,490

310.5

Fig. 3. Fatigue degradation analysis: a vs. N and b vs. N (a) a = 4.98 mm and (b) a = 6.17 mm), experiments discussed by Hall et al. (1974) and calculated curves are the present research results.

Moreover, the fatigue response of a pipe with a surface elliptical flaw (Fig. 1b) is assessed through the residual life. External loading is characterized by two values of maximum stress ( S max = 257.15 MPa and 325.90 MPa) with stress ratio equal to R = 0.1. Damage tolerance-based evaluations are performed, considering the pipe with surface part through damage as the plate with semi-elliptical flaw. The pipe made of carbon steel is subjected to bending, and the geometrical sizes are equal to R 0 = 51 mm and t = 8.5 mm. The material parameters are C A = C B = 3.2 10 -13, , m A = m B = 3.72, respectively. Initial crack length sizes and corresponding loading parameters are presented in Table 2. Stress raiser phenomenon caused by a semi-elliptical flaw is analyzed here using Eq.11 and Eq.1 to 9 through two critical crack growth directions. Generated number of loading cycles is plotted in Fig 4a and b, for two different shapes of elliptical flaw. In order to estimate the predictive capability of the developed computational design model, experimentally tested life by Ahn et al. (1997) for the above pipe with semi-elliptical flaw are listed in Table 2. From different life results it can be inferred that the computational strategy developed is able to generate the interactions between stress ratio effect and stress raiser impacts simultaneously for the pipe with surface semi-elliptical flaw and the plate with the same part-through damage according to damage tolerance-based requirements.