PSI - Issue 19

Jennifer Hrabowski et al. / Procedia Structural Integrity 19 (2019) 259–266 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Before the fatigue tests, each sample is measured. As the height of the weld convexity is between 10 and 20% for almost all samples, the FAT 80 is valid. During the measuring of the samples, the angular misalignment was identified as significant imperfection. Especially within the series 50d-8-96Q-Hand, the permissible limit of  < 2 ° according to ISO 5817 (2006) is far exceeded for most samples. Hobbacher (2016) gives formulas for taking into account the influence of the angular misalignment  on specimens. With it, the additional bending stresses can be considered by a magnification factor k m for each sample based on the stress range applied during the test. In the FAT-classes a magnification factor for misalignment k m = 1,15 is already covered for butt joints made in shop in flat position. For the samples investigated, this corresponds to an angular misalignment of  = 0.5°. Therefore, in Figure 3, an evaluation of the test results taking into account corrected nominal stress ranges  corr for samples with an angular misalignment of  > 0.5° is carried out. This evaluation leads to a low scattering with a standard deviation of S = 0.23. The fatigue strength at 2 million load cycles with freely calculated inverse slope of m = 3.5 at 95% survival probability is  C,corr = 121.9 N/mm². An evaluation with a lower envelope and a fixed inverse slope of m = 3.0 gives a value for the fatigue strength of  C,corr = 96.8 N/mm².

Fig. 2. Evaluation for very high-strength butt welded plates considering the corrected stress range for samples with angular misalignment  > 0.5°

Since the test points are all within a scattering range, in the evaluation in Figure 2 no influence of the steel grade is obvious, which allows a joint evaluation of the tests. The test results obtained show between 4,000 and 2 million load cycles a linear course of the S-N-curve.

3.5. Plates with transverse attachments

For the specimens with transverse attachments, a thickness of t = 8 mm is selected for the base plate and stiffener, too. The design throat thickness of the fillet weld is 4 mm and the stiffeners are 60 mm high on both sides. The specimens are made of S960QL, S960M and S1100QL, see Table 1. The detail classification for welded transverse attachments is given in EN 1993-1-9 (2010) as a function of the value l, which is the sum of the thickness of the stiffeners including the weld leg lengths on both sides. For l ≤ 50 mm, the detail category 80 and for 50 < l ≤ 80 mm detail category 71 applies. According to IIW (Hobbacher 2016), the FAT 80 applies to transverse non-load-carrying attachment, not thicker than main plate in as