Study On The Subsequent Yield Behavior Of Duplex Stainless Steel

Various valves(such as hydraulic valves)made of duplex stainless steel,which are commonly used in engineering and large ships,are usually in a complex working environment during the working process,and their stress state is greatly different from that of ordinary parts under uniaxial loading.Due to the different mechanical properties of the two phases(ferrite and austenite)that make up duplex stainless steel,there are also certain differences in their performance under complex loads and cyclic loads.At present,some scholars have conducted extensive research on the yield behavior and related yield theories of this material under simple stress states(i.e.,when the material is subjected to unidirectional stress),but there is a lack of theoretical basis for studying its yield under complex stress states.Therefore,further research on the yield behavior and adaptive yield criteria and strengthening theory of duplex stainless steel under complex stress states can provide certain theoretical support for the evaluation of its lifespan and working strength.This article takes duplex stainless steel,a commonly used manufacturing material for engineering structural components,as the research object.Under room temperature and quasi-static conditions,unidirectional tensile tests,unidirectional compression tests,pure shear tests,SCS compression shear tests,SCBS compression shear tests,and STS tensile shear tests were conducted.Analyze the obtained stress-strain curves and summarize the mechanical properties of duplex stainless steel under various stress states.Due to the absence of a yield plateau in the stress-strain curves of each stress state,the initial yield surface of duplex stainless steel was obtained using the offset strain method,and its initial yield behavior was analyzed and summarized.Comparing the initial yield surface obtained from the above multiple sets of experiments with the theoretical initial yield surface derived from the four yield criteria selected in this article(Von Mises,Ellipse,Drucker Prager,and Cazacu Barret),it was found that the theoretical yield surface of the Von Mises yield criterion is relatively close to the experimental yield surface,which can be used to analyze the yield behavior of duplex stainless steel.Subsequently,the subsequent yield point of duplex stainless steel was determined using the offset strain method,and the plastic subsequent yield surface was drawn.According to the Von Mises yield criterion and mixed strengthening model,the evolution function of the plastic subsequent yield surface of duplex stainless steel was defined,and compared with the experimental plastic subsequent yield surface.The high degree of agreement verified the reliability of the derived function.In order to investigate the changes in the plastic subsequent yield surface of duplex stainless steel after undergoing cyclic loading and the influence of cyclic loading parameters,this article first conducted compression unloading cyclic tests on each specimen of duplex stainless steel,and then conducted tests on each loading method to obtain the plastic subsequent yield surface of duplex stainless steel after cyclic loading.The evolution law of the cyclic subsequent yield surface of duplex stainless steel was studied and summarized,Explored the effects of cyclic cycles and peak stress on the shape and position of subsequent yield surfaces,and analyzed the variation patterns and reasons.Finally,finite element analysis of the yield surface after cyclic loading was conducted using the finite element software Abaqus subroutine UMAT and the established constitutive model of duplex stainless steel under cyclic compression unloading,to verify the conclusions obtained from the experiment.