Fatigue life assessment of Q345 steel fillet welded joints with competitive failure modes

An accurate description of the relationship between fatigue lifetime, applied loading and fracture location has great engineering significance. In the present work, failure competition mechanism and fatigue life assessment of Q345 steel fillet welded joints under the cyclic force-controlled mode were investigated by fatigue testing, structural stress analysis, hardness measurement, microstructure and fractural surface morphology observation. Results revealed that the fatigue fracture location of Q345 steel fillet welded joints was changed from the base plate to the attached plate with the increase of load level. Though the two types of failure had similar fracture surface morphology, the fatigue crack initiation mode differed due to combined effects of load level and weld flaws. Based on the structural stress method, a new probability model was developed to establish a qualitative relationship between the structural stress level and the likelihood at each failure location. The prediction result agreed well with the experimental data.