Study On Creep-fatigue Mechanical Behavior Of 316L Stainless Steel Welded Joints

With the development of pressure equipment in chemical industry toward high temperature,high pressure,high speed and other high parameters,creep-fatigue has gradually become an important factor leading to the failure of such equipment.Residual stress will inevitably occur in the welding process of equipment.Studying creep-fatigue behavior of welded joints can provide important theoretical basis for its use under complex loads.Based on creep-fatigue constitutive model,damage evolution and welding residual stress calculation,the mechanical evolution behavior and life of 316 L stainless steel welded joints under creep-fatigue were studied.The effects of holding time,fatigue amplitude and loading form on the life of welded joints under creep-fatigue were analyzed.The main work and related conclusions are as follows:(1)The traditional creep-fatigue constitutive model is modified and a new creep-fatigue constitutive model related to the holding time is established.Based on the creep-fatigue test of uniaxial strain control,the time-dependent fatigue interaction factor and creep interaction factor are added to the traditional creep-fatigue constitutive model,and then a new constitutive model related to the holding time is established.The accuracy of the new constitutive model is verified by the creep-fatigue test of stress control.(2)The creep-fatigue mechanics evolution law of welded joints was studied by numerical analysis method,and the influence of various factors on creep-fatigue behavior of welded joints was analyzed.The residual stresses of welded joints were calculated by finite element method,and the accuracy of simulation calculation of residual stresses of welded joints was verified by X-ray tester.It is found that welding residual stress gradually releases with the increase of cycle number under creep-fatigue load.The release of residual stress is compared with that of welding residual stress under creep or fatigue load.It is found that the release of residual stress is not only a simple superposition of the release amount of the two,but also the release mechanism of the residual stress under creep-fatigue.(3)In this paper,the creep-fatigue damage and life of welded joints are analyzed.The creep-fatigue damage model subroutine for 316 L stainless steel was written.The accuracy of creep-fatigue damage model and subroutine was verified by comparison with stress control and strain control uniaxial creep-fatigue test.In the numerical analysis of the creep-fatigue damage subroutine introduced into the welded joint under creep-fatigue,the influence of welding residual stress on the creep-fatigue life of the welded joint was studied by combining experiments.