PSI - Issue 66

7

Aditya Khanna et al. / Procedia Structural Integrity 66 (2024) 370–380 Author name / Structural Integrity Procedia 00 (2025) 000–000

376

R = 0.01 R = 0.1 R = 0.2 R = 0.3 R = 0.5

R = 0.01 R = 0.1 R = 0.2 R = 0.3 R = 0.5

1.00

1.00

0.95

0.95

0.90

0.90

0.85

0.85

0.80

0.80

0.75

0.75

S1L

0.70

S2T

0.70

0.65

0.65

0.2

0.3

0.4

0.5

0.6

0.7

0.2

0.3

0.4

0.5

0.6

0.7

(a)

(b)

Fig. 2. Experimentally determined values of the opening load ratio, , vs. the normalised crack length, ⁄ , for several mean stress ratios, . (a) crack growth is longitudinal (parallel) to the weld deposition direction in Specimen S1L; (b) crack growth is transverse (perpendicular) to the weld deposition direction in Specimen S2T (adapted from Sales et al, 2024). 5. Experimentally measured residual SIF The compliance methods for residual SIF evaluation reviewed in Section 2 become invalid at relatively modest levels of crack tip plasticity. By comparing residual SIF profiles constructed from fatigue crack growth and wire cutting of CT specimens with similar residual stress profiles, Smudde et al. (2023) developed the following empirical limit for the remaining ligament size to ensure the validity of the residual SIF calculation from fatigue crack growth test data: ( ) ≥ 20 � max � 2 . (9) The empirical limit given by Eq. (9) is five times more stringent than the small-scale yielding limit prescribed by ASTM E647 for compact tension specimens, ( ) ASTM ≥ 4 � max � 2 . Bend specimen geometries (e.g. compact tension) are more compliant than tensile specimen geometries (e.g. middle tension). Hence, the crack tip plasticity leads to measurable back-face strain offset upon specimen unload even when the small-scale yielding conditions, as defined by standards, are satisfied. For K-increasing tests, the back-face strain offset due to crack tip plasticity rapidly increases with crack extension once the condition prescribed by Eq. (9) is violated, rendering the compliance method for residual SIF evaluation useless. In Figure 3a, the dotted line shows the empirical limit given by Eq. (9), corresponding to ⁄ =0.54 for the present loading conditions. Figure 3b provides a zoomed view of the data for ⁄ <0.54 . In the following, the compliance method is only applied to strain data