PSI - Issue 57

Magnus Andersson et al. / Procedia Structural Integrity 57 (2024) 307–315 M. Andersson et al. / Structural Integrity Procedia 00 (2023) 000–000

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done with the e ff ective notch method. Hobbacher (2007) gives a threshold for the stress intensity factor, ∆ K th = 2MPa · √ m . In the SFM method this threshold may be taken into account. The fatigue life without the threshold is 4.5 times longer for SFM, using varying crack angle than the fatigue life for e ff ective notch method. This fatigue life ratio increases to 6.5 if the threshold is taken into account. The fatigue life ratio for SFM using constant crack angle is 3.8 (with a minimum at v = 35 ◦ ).

Fig. 11. (a) Position of the weld; (b) the weld cross section i2a5.

Fig. 12. (a) Structural stress for a typical load case; (b) normalized life.

6. Conclusions

The Simplified Fracture Mechanics (SFM) method for weld roots:

• predicts fatigue life well when comparing to ”real” LEFM, • predicts more realistic life compared to the e ff ective notch method when the dominating stress is parallel to the weld, • is much faster than using ”real” LEFM analyses since the geometry factor is pre-calculated and stored in a database, and only the structural stress is needed to be extracted from FE analyses, • is also much faster than using the e ff ective notch method since the element size can be much larger, • is suitable for complex industrial applications.

7. Future work

The SFM method will be validated with fatigue testing of realistic weld geometries. An ongoing master thesis work deals with calculating the weld residual stress in fillet welds. This stress is expected to often be beneficial for the fatigue life on the weld root side. However since welds often are subjected to high variable amplitude stresses,