PSI - Issue 28

Giovanni Meneghetti et al. / Procedia Structural Integrity 28 (2020) 1481–1502 Giovanni Meneghetti et al./ Structural Integrity Procedia 00 (2019) 000–000

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the PSM, i.e. a/d =3 → d = a /3. After having calculated the opening peak stress σ θθ,θ=0,peak at the weld toe side, the equivalent peak stress has been calculated from Eq. (5), with f w1 relevant to R 0 = 0.53 mm.

Table 5: Examples of FE analyses for fatigue strength assessment according to the PSM.

d=a/3

a

Δσ θθ,θ=0,peak

Δσ nom

d=a/3

Δσ θθ,θ=0,peak

Δσ nom

a

The experimental results expressed in terms of number of cycles to failure as a function of the equivalent peak stress have been reported in Fig. 14, which includes also a 2.3-97.7% scatter-band calibrated on all considered experimental results and, for comparison purposes, also the PSM-based fatigue curve referred to 97.7% survival probability, as calibrated in (Meneghetti and Lazzarin, 2011) for homogeneous steel welded joints. The resulting fatigue design curve for ADI-to-steel joints exhibiting fatigue failure at weld toe at ADI side is characterised by a fatigue class of Δσ eq,peak,A,97.7% = 160 MPa, an inverse slope k = 8.9 and a scatter index T σ = 2.71, which is significantly reduced with respect to the scatter index obtained in Fig. 11 by synthesizing the same experimental results but in terms of nominal stress range. It is worth noting that the fatigue design curve for ADI-to-steel joints provide almost the same fatigue strength of the curve for homogeneous steel joints at N A = 2 ꞏ 10 6 cycles (160 MPa versus 156 MPa), while the fatigue strength of ADI-to-steel joints is significantly lower than that of homogeneous steel joints at medium cycle fatigue regime. This is due to the different inverse slope k, which equals 8.9 for ADI-to-steel joints, while it is 3 for homogeneous steel joints.