• effective stress
• fatigue
• weld

Lightweight design is a crucial aspect to consider in order to achieve the reduction of green house gasses emission of vehicles, which will be enforced in the next years. For this reason the use of high strength steel is rapidly increasing for automotive applications. In this prospect fatigue life assessment of thin walled welded structures is one of the field where research is needed. Since fatigue is one of the main causes of failure, and a welded joint is generally a critical spot for fatigue crack nucleation.
In the present work the effective notch stress theory will be applied to a database of experimental tests of thin walled specimens. It will be shown that, by means of a properly defined effective stress, results from very different test series can be brought together in an S-N curve with a tight scatter band. Both the stress averaging approach according to Neuber and the critical distance approach according to Taylor will be applied in order to obtain the desired effective stress. Their application will be optimized for thin walled structures using the scatter of the S-N curve as main decisional parameter.
A reference S-N curve with a survival probability of 97% for both methods will be proposed, which could be utilized in design procedures. The possibility of new more complex kernels for the definition of the effective stresses will be discussed.