Full and partial compression fatigue tests on welded specimens of steel St 52-3. Effects of the stress ratio on the probabilistic fatigue life estimation

The fatigue strength of structures subjected to cyclic loading depends strongly on the stress ratio. Particularly, in case of welded steel structures this fact is not considered in the corresponding standards nor in the guidelines. Experimentally, two approaches are used to study the effect of stress ratio on the fatigue life. On the one hand, based on the S-N curves obtained from tests performed at different stress ratios, the fatigue life under a particular stress range is estimated. On the other hand, the stress amplitude corresponding to a constant fatigue life is estimated by applying the failure criteria for fluctuating stress like the Goodman-Haigh relationship. This paper presents a general probabilistic model, which estimates the S-N and Goodman-Haigh curves for any stress ratio. Afterwards, this model is applied on data obtained from full and partial cyclic compression loading tests performed on welded specimens made of steel St 52-3. The tested details correspond to the permissible notch condition limit occurred in highly stressed structures used to build ships.