PSI - Issue 66

378 Aditya Khanna et al. / Procedia Structural Integrity 66 (2024) 370–380 Author name / Structural Integrity Procedia 00 (2025) 000–000 9 The residual SIF results shown in Figure 4 can be used to calculate the actual stress ratio at the crack tip using Eq. (8). The results for the opening load ratio, , are plotted against the applied and actual stress ratios is Figure 5 for both crack growth directions. Plotting vs. act significantly reduces the spatial variability in the measured values of opening load ratio at constant values of the applied stress ratio and demonstrates the dominant dependance of the opening load ratio on the stress ratio under small-scale yielding conditions. For comparison, the analytical equation for crack opening stress proposed by Newman Jr. (1984) for center-cracked specimens is plotted on Figures 5b and 5d. The latter equation can be written as 1 − + = � 0 +( 1 +( 2 + 3 ) ) , >0 0 + 1 , 0 (10) where 0 = (0.825 − (0.34 − 0.05 ) ) � cos � 2 max flow �� 1 ⁄ , 1 =(0.415 − 0.071 ) � max flow � , 3 =2 0 + 1 − 1, 2 =2 0 + 1 − 1.

1.00

1.00

0.90

0.90

0.80

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0.70

0.70

S1L

S1L

0.60

0.60

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0

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-0.20

0.00

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0.60

(b)

(a)

1.00

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0.90

0.90

0.80

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0.70

S2T

S2T

0.60

0.60

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0

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-0.20

0.00

0.20

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(d)

(c)

Fig. 5. Opening load ratio vs (a) applied stress ratio ap and crack growth longitudinal to weld deposition, (b) actual stress ratio act and crack growth longitudinal to weld deposition, (c) applied stress ratio ap and crack growth transverse to weld deposition, and (d) actual stress ratio act and crack growth transverse to weld deposition. The fit shown in Figures 5b and 5d is obtained by substituting max flow ⁄ =0.3 and =2.7 into Eq. (10). After residual stress correction, the experimental opening load ratio vs. stress ratio dependance shows excellent correlation with the theoretical prediction within the limitations of the experimental uncertainties and the radical simplifications used in the derivation of Eq. (10). A direct comparison of the vs. act trends for crack growth in the two directions is performed in Figure 6. After residual stress correction using Eq. (8) and the experimentally determined res values,