Study On Residual Stress Redistribution In Welded Joints Of High-strength Steel Under Fatigue Loading

The residual stress has a serious effect on the fatigue behavior of welded structures,and stress relaxation and redistribution occur frequently during the fatigue process.In this paper,the redistribution of residual stress and the effect of fatigue crack propagation on the welded joint of high strength steel with buffer layer are studied.The main contents are as follows:(1)Through the stress analysis of the crack tip of the welded joint specimen under the fatigue load,according to the formula for calculating the stress intensity factor of the expanded compact specimen(E-CT specimen),based on the theory of linear elastic fracture mechanics,a mathematical model of residual stress true value of crack tip during fatigue crack growth is established.Based on the above theory,the redistribution of residual stress in parent metal zone of three groups of different welded joint specimens was studied,and the results of the initial distribution of residual stress obtained by X-ray diffraction test and finite element simulation were compared,and the release law of the residual stress of welding with the increase of fatigue cycle and the change of crack length was explained.(2)The microhardness,microstructure and Paris curve of the three groups of welded joints before and after annealing were compared.It is found that the mechanical properties such as micro hardness and metallographic microstructure are basically unchanged at 600 degrees centigrade and 4 hours after heat preservation,and the residual stress of welding is basically eliminated.The redistribution of residual stress in the heat affected zone and the fusion zone of three groups of welded joint specimens is further studied.(3)The results show that the residual stress is no longer relaxed in the stage of the crack entering the stable expansion stage;the three groups of specimens have the same relaxation and stability points,and the size of the initial welding residual stress affects the size of the relaxation.The residual compressive stress of NO BL and 10 mm BL joint specimens increases with the increase of crack growth due to the stress balance of tension and pressure,the width of the compressive stress is reduced,and the amplitude of the compressive stress will gradually increase to reach the new equilibrium.There is no such phenomenon in the 4mm BL joint specimen because the initial welding residual tensile stress of the 4 mm BL joint specimen is mainly based on the pressure stress and balance in the weld zone.The stress change point of tension and pressure after redistribution is changed.When the initial stress is large,the change point lag behind,and the greater the initial stress,the higher the lag degree of the transition point;the initial stress is small,and the transition point is ahead of time.