PSI - Issue 57

Luca Vecchiato et al. / Procedia Structural Integrity 57 (2024) 518–523 Vecchiato L et al./ Structural Integrity Procedia 00 (2023) 000 – 000

522

5

0.4

0.3

0.2

n i / L s [-]

0.1

0.0

0.000

0.200

0.400

0.600

0.800

1.000

Δσ / Δσ max [-]

Figure 2. Normalized stress range spectra applied during VA tests.

Then, FE results have been used to convert the original experimental data from nominal stress ranges to equivalent peak stress ranges (Eq. (1)) at the crack initiation point (see Figure 1). Thereafter, experimental results have been compared with the proper PSM-based design scatter band according to Table 1: endurable stress range Δσ eq,peak,A,50% = 123 MPa, inverse slope k = 3.8 and scatter index referred to survival probabilities of 2.3%-97.7% (mean value ± two standard deviations) T σ = 1.80. Figure 3 shows that the PSM estimations are in good agreement with experimental data, with a certain underestimation of the fatigue strength both for CA and VA data.

1000

Δσ A,50% = 123 MPa N A = 2 ∙10 6 cycles Scatter Index (2.3%-97.7%): T σ = 166/92 = 1.80 Slope k = 3.8

PSM design scatter band for aluminium joints under pure mode I loading , λ = 0 (NOT FITTED)

92 166 123

D 2.3% = 3.12 D 50% = 1.00 D 97.7% = 0.33

100

Δσ eq,peak [MPa]

k = 3.8

Run-out

CA VA

10

1E+5

1E+6

1E+7

1E+8

2E+8

N A

N 0 [Cycles]

Figure 3. Fatigue strength assessment adopting the PSM: comparison between the PSM design scatter band for aluminium arc-welded joints under pure mode I (λ = 0) loadings and experimental data from Smith and Hirt (1992).