This study is investigating how the effective notch method can be used for fatigue assessment of welded joints. The effective notch method is based on a finite element analysis where the joint is modeled with all notches fictitiously rounded with a radius of 1 mm.
Analyses are performed on a cruciform fillet welded joint where parameters such as, load case, steel plate thickness and weld size, are varied. The achieved lifetime estimations are then compared to calculations with other fatigue assessment methods, linear elastic fracture mechanics and the nominal method.
The goal is to draw conclusions about pros and cons of the effective notch method. The results are also compared to experimental fatigue tests performed on the same geometry.
The results indicates that the effective notch method tends overestimating the lifetime, especially when the steel plate thickness is small. This leads to a non conservative method that is dangerous to use as guidance when designing. The estimations are though better when considering a toe crack then when considering a root crack.
Due to a large scatter in experimental test results, it is hard to validate a fatigue assessment method in an absolute sense. That is also the case for the effective notch method, and more results from experimental fatigue tests are needed before the effective notch method can be fully used.
For relative analysis, when variations of the same design needs to be compared, the effective notch can be a very powerful tool. This is because of the flexibility for different geometries that this method grants.
Source: Uppsala University
Author: Nielsen, Kristin