EXPERIMENTAL INVESTIGATION OF FATIGUE BEHAVIOR FOR WELDED JOINT WITH MECHANICAL HETEROGENEITY

Because of material and mechanical heterogeneity in welded joints, exp erimental studies of low-cycle fatigue (LCF) life and fatigue crack in itiation behaviour were performed on weld metal, heat-affected zone (H AZ) and base metal of 16 MnR pressure vessel steel. A fatigue damage t est was carried out by introducing a new damage variable. The fatigue damage evolution laws in each zone of a welded joint were obtained. A circular-notched compact tension specimen was designed and the whole p rocess of fatigue damage, crack initiation and crack growth in each zo ne was investigated. The effect of mechanical heterogeneity in welded joints on the fatigue damage behaviour and fatigue crack initiation li fe was also investigated. The experimental and theoretical results ind icate that the fatigue behaviour is markedly different in three zones of welded joints; there is a trend toward reduction in the fatigue lif e of HAZ as compared with the base metal. The weld metal does not have the same fatigue behaviour as confirmed by LCF life and crack growth rate. This study leads to the conclusion that fairly accurate estimate s of fatigue life for welded joints should include the whole process o f fatigue damage evolution and fatigue crack initiation as well as cra ck growth. Furthermore, a local experimental method should be carried out for weld metal, HAZ and base metal, respectively. Finally, the loc al fatigue failure criterion based on the weakest chain model has been presented.