PSI - Issue 75

Xiru Wang et al. / Procedia Structural Integrity 75 (2025) 85–93 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

89 5

1.8

=0.0025 ( 2 0 68 )

(2) Baumgartner et al. (2022) proposed a linear correlation of and based on the best fit from fatigue tests of notched specimen representing base material and heat effected zone of S235, S355, QStE380, S690 and S960QL: = −0.00026 +0.216 (3) Based on all three equations the value of was estimated: For equation (1) ∆ 0 was estimated according to the FKM guideline from the HAZ hardness of 210 HV, that lead to = 675 MPa, according to ISO 18265. Based on a ∆ ℎ ( =−1) of 12.53 MPa (m) -1/2 from the NASGRO database a value of = 0.129 mm is estimated according to equation (1), while according to equation (2) a value of = 0.187 mm and according to equation (3) a value of = 0.162 mm is estimated. A simple evaluation of the stress trough thickness in a distance of is point method with ( /2) . All three values are in the range of common initial crack sizes of 0.05 mm to 0.10 mm for linear elastic fracture mechanics analysis. 4.2. Linear elastic fracture mechanics (LEFM) In addition to the critical distance approach, a crack propagation analysis was conducted. As data input the gradients of the directional ( ) perpendicular to the plate have been used. The starting point of the paths that have been used for the extraction of stress gradients are positioned at the location of maximum principal stress. For the 2D- and 3D modell, stress gradients have been extracted for an equidistant spacing of 1 mm for the 3D- and 5 mm for the 2D model that leads to 120 resp. to 24 paths. To cover the stress gradient from the surface, this spacing is sufficient. The crack growth and with it the fatigue life was calculated using the weight function approach (Shen, Plumtree and Glinka, 1991) as described in the IIW-recommendations (Hobbacher and Baumgartner, 2024). The NASGRO crack growth model was applied, with the material data shown in Table 1 . A starting crack depth of = 0.1 mm , a width of = 0.5 mm and an end crack depth of =5 mm were used to evaluate cycles in crack propagation. Table 1: Parameters of the NASGRO equation 0 ℎ, ℎ, 0 0.8 0.8 5 233.4 1 -0.5 0 3 0.3 378 2.2 5. Results As a result from the numerical analysis and fatigue analyses, three scalar values were derived for every of the 24 evaluated cross sections: The maximum principal stress 1 , the effective stress according to TCD eff = 1 ( = 0.1 mm) and the number of cycles spend in crack propagation , Fig. 3. To plot both stresses and cycles to failure in one diagram, the logarithm of was evaluated and subtracted by a factor of 4 to avoid unnecessary space. The calculated number of cycles is subsequently in the range between 10 6 ≤ ≤10 7 cycles. As mentioned, the element edge length in both the 2D- and 3D-models was similar. One main result that can be taken from Fig. 3 is the local 3D-influence. In the 3D-model, one large stress peak can be identified at coordinate 55, see in addition Fig. 3. This location is the area in which the main body of the weld end is positioned. Quite interestingly, the 2D-model assumes the highest location of stress concentration at coordinate 60. This is an area that is slightly set back but has a sharp weld toe angle beyond 90° at which the 3D-model shows only