A Study On The High-cycle Fatigue Failure Behavior Of Q345 Steel Welded Structure Under Combined Tension-torsion Loading

With the rapid development of society and economy,cranes,as a large-scale lifting equipment,are widely used in many areas of the national economy.It is a key issue in the field of crane fatigue research to ensure the long-term safe use of crane main beam structures.Due to the large number of welded structures in the main girder,it is more difficult to predict the fatigue life of the crane main girder structure.Currently,the commonly used research method is to study according to uniaxial fatigue;in the face of increasingly complex load environments,the crane,especially the crane main girder The safety of the welded structure puts forward more stringent requirements.Combined with the actual load conditions,it is of great engineering significance to carry out the fatigue behavior research of the crane main girder welded structure under multi-axial loading.Based on the actual working conditions of the crane main girder welding structure,this paper takes the commonly used material of the crane main girder Q345 steel welding structure as the research object.The influence of phase difference,average tensile stress and average torsional stress on the failure behavior of multiaxial fatigue,and the failure modes under different loading parameters are analyzed.The main work and results of this paper are as follows:1)The effects of loading parameters such as stress-amplitude ratio,phase difference and average stress on the fatigue of multiaxial fatigue failure of welded specimens are studied.The multiaxial fatigue test was carried out under the constant equivalent stress amplitude,and the influence of the stress amplitude ratio on the multiaxial fatigue life of the welded specimen under proportional loading was studied.The influence of the phase difference on the multiaxial fatigue life of the welded specimen under the constant stress amplitude ratio was studied.The influence law of fatigue life;the influence law of average stress on the multi-axial fatigue life of welded specimens is studied.2)The maximum shear stress amplitude and plane direction,maximum normal stress and plane direction under different loading parameters are theoretically analyzed.According to the theory of multiaxial fatigue formula,the influence law of different stress amplitude ratio on the maximum shear stress amplitude and direction and the maximum normal stress and direction under proportional loading is obtained;The influence law of stress amplitude and direction and maximum normal stress and direction.3)The fatigue fracture of the welded specimen was analyzed macroscopically and microscopically,and the influence of different loading parameters on the failure mode of the welded specimen was studied.A macroscopic analysis of the fracture of the welded specimen was carried out,and it was found that the failure mode of the welded specimen under the combined tensile and torsion loading was a mixed mode of type I and type II;with the change of the loading parameters,the failure modes were not the same,and the overall pattern was regular.Sexual change.A microscopic analysis of the fatigue source area,expansion area and instantaneous failure area of the welding fracture was carried out by scanning electron microscope,and it was found that the loading parameters had a significant effect on the microscopic characteristics of the fracture.