PSI - Issue 66

Akash Shit et al. / Procedia Structural Integrity 66 (2024) 247–255 Shit and Prakash/ Structural Integrity Procedia 00 (2025) 000–000

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Fig. 6 illustrates the percentage decrement of the effective SIF at H1 for load ratios 0.75, 0.5, and 0.25 relative to load ratio 1 (i.e. equi-biaxial loading). At a load ratio of 0.75, the maximum reduction in effective SIF is 47% for 38 mm and 40 mm crack lengths. At a load ratio of 0.5, the maximum reduction in effective SIF is 67% at a crack length of 38 mm. At a load ratio of 0.25, the maximum reduction is 78% at the same crack length. In all three cases,

the maximum decrement in effective SIF occurs at a crack length of 38 mm. 3.3. Variation of Effective SIF under Different Biaxial Load Ratio at Hole-13

Considering the plate's symmetry, the behavior of the rivet holes on the right side of the plate in the X-direction is identical to that on the left side. To study the effective SIF of cracks at the rivets in the Y-direction, either the top or bottom part of the plate can be analyzed. In this study, H13, located at the upper portion of the plate in the Y direction, is evaluated. At a load ratio of 1, the effective SIF at H13, due to overall specimen symmetry, matches that at H1, as shown in Figs. 7(a) and 7(b). Fig. 7(a) suggests that the effective SIF under equi-biaxial loading is identical for both crack tips due to symmetry. Further studies were conducted to characterize the effect of load ratios 1, 0.75, 0.5, and 0.25, as depicted in Fig. 7(b). At H13, no significant impact is observed at either crack tip under varying load ratios. Since there is no reduction in SIF by decreasing the load ratio at the most critical location, other holes location is not examined in further analysis. a b

Crack tip ‐ 1 Crack tip ‐ 2

Load ratio ‐ 1 Load ratio ‐ 0.5

Load ratio ‐ 0.75 Load ratio ‐ 0.25

1000 1200 1400

1000 1200 1400

0 200 400 600 800 K_effective, MPa.mm^0.5 30

0 200 400 600 800 K_effective, MPa.mm^0.5 30

40

50

40

50

Crack length (2a), mm

Crack length (2a), mm

Fig. 7 - Variation of K_effective (a) under equi-biaxial loading (b) under different load ratio at Hole-13.

3.4. Crack Shadowing Effect under Equi-biaxial Loading This study reveals that an initial crack at the H1 location is more critical than at other locations in the left part of the strap plate connected with the lozenge pattern riveted joints, as discussed in Section 3.1. To study the effect of crack shadowing, the primary crack is considered at the H1 location, with shadow cracks placed at H2 and H3 in row 2. Two different shadow crack configurations are considered, and the study is conducted on the left part of the strap under equi-biaxial loading as marked in Fig. 8(c). The crack propagation at all tips of the primary and shadow cracks is allowed simultaneously according to the Maximum Energy Release Rate (MERR) criteria, with increments of up to 5 mm beyond the rivet holes for each crack tip. Case-1 involves a shadow crack at the top of Hole-2 and the bottom of Hole-3, while Case-2 considers a shadow crack at the bottom of Hole-2 and the top of Hole-3, as shown in Figs. 8 (a) and (b) respectively. The study is conducted with an initial through-the-thickness crack of 1 mm in all cases, oriented in the direction of maximum principal stress. The comparison of effective SIF at different crack lengths for crack tip 1 and crack tip 2 of the primary crack at H1 is illustrated in the bar charts shown in Fig. 9(a) and Fig. 10(a), respectively. The effect of the shadow crack in both cases is inconsistent in either increasing or decreasing the effective SIF at both crack tips of the primary crack. In Case-2 configuration, there is a reduction in effective SIF at crack tip 1 of H1 in all five crack lengths except at