PSI - Issue 57

Inge Lotsberg et al. / Procedia Structural Integrity 57 (2024) 569–580 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

572

4

Thickness of main plate: t = 20 mm Thicknes of doubler plates t D =10mm

Hot spot locations

Fig. 2. Test specimen with doubling plates.

2.2. Target stress concentration factors from strain measurements and fatigue testing

From the strain measurements a hot spot stress equal to 1.480 is derived. Number of test cycles is close to that of the mean F1 curve. This S-N curve includes a stress concentration factor 1.41 relative to the hot spot S-N curve in DNV-RP-C203 (2019). A more exact calculation of a stress concentration factor based on 150 800 cycles tested to failure gives a factor 1.448. As this is only one failed hot spot out of 6 hot spots (where the others have not failed) it is assessed that the mean value of the stress concentration factor for all 6 hot spot locations in Fig. 1 should be less than this value. Based on this there is no good reason to deviate from the design standard when selecting a target hot spot stress value which is equal to 1.41. In addition to include this value as a target value also ± 10% are shown for comparison with derived hot spot stresses using different methods. This gives a range 1.27 – 1.55 which is included for illustration in Fig. 9. When using a quadratic extrapolation of the measured values in Fig. 3 a slightly larger stress concentration factor equal to 1.560 is derived. This value might be used as target value when analyzing finite element analysis results in a similar way to derive hot spot stress by using quadratic extrapolation.

Fig. 3. Stresses from measured strains at the hot spot areas in the as-welded specimen no 1.