Welding Residual Stress Evaluation Optimization And Fatigue Performance Research Of Square Steel Frame

Agricultural vehicles are mainly driven in rugged mountain roads,which requires higher comprehensive performance of vehicles.In the process of vehicle use,the frame is the main load-bearing structure,and the joint formed by welding is prone to stress concentration when carrying,which will lead to the change of vehicle performance when combined with the residual stress generated during welding.Therefore,based on the elastic-plastic theory,the static analysis of the whole frame of tricycle is carried out by numerical simulation method;The hazardous location areas(T-joint)were identified.The welding process was simulated with and without considering the solid phase transition;And the distribution law of temperature and stress filed was analyzed.On this basis,the welding residual stress is decreased by optimizing the welding path.Finally,the fatigue life of the T-joint under the condition of considering and not considering the welding residual stress is assessed,and the fatigue life of the joint under different welding schemes is compared and analyzed.The following conclusions were reached:(1)Under the full load condition,the danger of the frame lies in the joint between the third beam and the longitudinal beam and the joint between the main beam and the sub beam,but it is still within the range of the material strength.(2)The peak value of welding temperature field appears in the center of heat source,and the distribution of isothermal lines in the vicinity is dense,but he distribution of isothermal lines in other regions is sparse;The longitudinal residual stress of the weld and its adjacent area is higher tensile stress,and the area far away from the weld is compressive stress.After considering the solid phase transition,the transverse residual stress of the second and fourth welding section is reduced by about10%.(3)Under the four welding schemes,secondary heating may occur at both ends of the welding section.The longer the interval time between the two heating processes is,the faster the reduction of the longitudinal residual stress along the weld direction at both ends of the weld segment is;For X direction stress distribution,different welding sequence is similar;For the Y direction stress distribution,there are two obvious compressive stress distribution areas in the reverse symmetrical welding sequence,and there are smaller compressive stress distribution areas in the reverse welding sequence.The longitudinal residual stress perpendicular to the weld direction is small,and the reasonable welding sequence can reduce the transverse residual stress.In the case of giving priority to reducing longitudinal residual stress,the back welding sequence is the optimal welding sequence.(4)Without the welding residual stress,the shortest actual fatigue life of T-joint is at the corner of the weld,and its value is about 5.3×10~5.After considering the welding residual stress,the most dangerous areas of the four welding schemes are mainly distributed in the weld area,and the fatigue life is about 3.0×10~4.It is found that the fatigue life is more than 10 times smaller than that without the residual stress,and the area of the dangerous area in the welding sequence is the smallest,indicating that the fatigue life will be shorter when considering the welding residual stress.