PSI - Issue 19

Jennifer Hrabowski et al. / Procedia Structural Integrity 19 (2019) 259–266 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 7 For the validity of the elastic design as a function of the deformation limit R ∗e based on the load cycle number N LCF , equation (3) applies. = { (∆ ∗ ⁄ ) ∙ 2.000.000 1.000 (3) Butt weld specimens with sealing run and grinded root made of the highest strength steels S960QL, S960M and S1100QL, which comply with evaluation group B according to ISO 5817 (2006) and have an angular misalignment of  < 2 °, meet FAT 80. For specimens with angular misalignment  ≤ 0.5 ° a classification into the FAT 90 is given. The samples with welded-on transverse stiffeners made of S960QL, S960M and S1100QL also satisfy FAT 80 according to the statistical evaluation. This corresponds to the classification according to EN 1993-1-9 (2010) for steels with yield strengths up to 700 N/mm². 4.3. Effective notch stress approach Within the effective notch stress approach, the local weld geometry is considered. For this, each sample is numerically modeled with existing local weld geometry, such as weld width, flank angle and height of the weld convexity. Also, misalignments are explicitly considered within the model. But the actual radius at the weld toe is replaced by an effective one. For structural steels with plate thicknesses t ≥ 5 mm, an effective notch root radius of r = 1.0 mm is used (Hobbacher 2016, Radaj et al. 2009). For the meshing of the notch radius, it is recommended to use 0.25 mm edge length, quadratic elements with mid-side nodes (Hobbacher 2016). The maximum stress  k occurring in the notch is compared with the effective botch fatigue resistance for steel, the FAT class 225 with m = 3 (Hobbacher 2016). 265

Fig. 5. Evaluation of effective not stresses for all specimens

All butt welded plates and plated with transverse stiffeners fulfill the FAT 225 in the range of 1,000 to 2 million load cycles, see Fig. 5. Setting the numerically calculated notch stress  k in relation to the nominal stress  n gives the notch intensity factor K t , which can be further used as a multiplier of the nominal stress range for equal components.