PSI - Issue 68

418 4

Akito Tabata et al. / Procedia Structural Integrity 68 (2025) 415–419 A. Tabata et al. / Structural Integrity Procedia 00 (2025) 000–000

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Figure 5. Test setup.

Figure 4. Dimension of test specimen.

3.2 Results and discussion Figure 6 shows an example of a fracture surface. Fatigue cracks initiated from the most stressed part, the transverse-rib intersection. Figure 7 shows the S - N 5% diagram when conventional steel is applied. N 5% was calculated from the strain over time measured by strain gauges near the rib-to-deck welded joints. The nominal stress range Δ σ was extrapolated to the simulated U-rib position by confirming the strain gradient corresponding to the bending moment in the general part where the transverse rib crossing was not affected. The stress range as cut-off threshold, σ w is the average value of the minimum Δ σ at which a crack is generated up to the cut-off threshold and the maximum Δ σ at which a crack is not generated. Linear regression was performed in both logarithms with the slope, m=3. The dashed line in Figure 5 shows the average value, and the solid line shows the lower bound (average life of -2 σ ) using the standard deviation σ . Incidentally, σ w was 22.5 MPa. Figure 8 shows the S - N 5% diagram when developed steel is applied. The fatigue life was more than 1.5 times as long as the lower bound of the conventional steel joint, and the dispersion of the N 5% data was smaller than that of the conventional steel. σ w was 27.5 MPa, which was 22% higher than that of the conventional steel joint, suggesting that the fatigue limit was higher than that of the conventional steel joint. From the above results, it was clarified that the crack initiation life of rib-to-deck welded joint was stably improved by using developed steel which shows high resistance to crack initiation.

Figure 6. Example of fracture surface.