Load Interaction Effects On Fatigue Crack Growth In Structure Steel Under Constant Amplitude Loading

There have been many researches on the structure steel welded joints. However, thecurrent study is not enough due to the complexity of fatigue and the heterogeneity of thewelded joints. In this paper fatigue test were carried out for Q345B welded joint. And thefatigue crack growth behavior of Q345B welded joint was described by a new driving forcemodel with two parameters. The result of the researches provides a test basis for the correctassessment of the fatigue life of Q345B welded joint and the structural design.The main results of research works can be summarized as follows:(1) The base metal and Q345B welded joint show cycle softening properties and cyclicloading can enhance the strength of the materials. Weld metal show clearnon-Massing features(2) The fatigue endurance limits of the base metal and weld metal are similar, and higherthan the overheated zone(3) The base metal along the rolling direction on crack propagation shows no effect ofstress ratio, but the base metal along vertical to the rolling direction shows someeffects of stress ratio at low average stress. The weld metal shows some effects ofstress ratio and overheating zone shows obvious effects of stress ratio. Base metal oncrack propagation shows no significant effect of thickness. Rolling direction has nosignificant effect to the crack propagation rate of base metal.(4) Comparing the other three models, the new model can more effectively describe thestress ratio effect on crack propagation.(5) Fatigue crack growth behavior for the base metal and weld zone were explained fromthe microscopic point of view, and how the crack closure, crack branching and crack interlocking phenomena affect on fatigue crack propagation rate was discussed inperspective of the variation of crack propagation driving force.