FATIGUE CRACK PROPAGATION IN HSS S690QL WELDED CONNECTIONS IN BRIDGES

The fatigue and crack study of HSS S690QL steel welded pieces is first experimentally analyzed by fatigue tests on small samples of Base Material (BM), Heat Affected Zone (HAZ) and Weld Metal (WM) separately for several stress ratios, stress levels, on smooth and notched samples. The Lemaître-Chaboche fatigue model combined with the stress gradient method and the three sets of parameters are found to accurately describe the behavior of each material. Another experimental campaign with larger pieces (closer to the scale of the bridge connections) called "small scale samples", with/without welded stiffeners, with several geometries and with/without post-treatment has shown each effect separately: the scale and machining effects, residual stresses due to the welding, geometrical and post-treatments effects. Numerical simulations of these experiments are used to improve and validate the material data, with a study in real context and size. Then, the characterized fatigue damage model is coupled with the element deletion method to model the propagation of cracks along the welded samples and the numerical predictions are compared with experimental results in order to validate the approach.