| Creep-fatigue has become one of the main failure modes of new-generation nuclear reactors and their key components with the increasing service temperature of new nuclear power systems.At present,the multiaxial stress state caused by the discontinuous position of the structure brings new challenges to the prediction of the strength and life of the reactor components.It is urgent to carry out research on the creep-fatigue failure damage behavior and life prediction methods of the high-temperature discontinuous components of the fourthgeneration reactor research.Therefore,this paper takes 316H stainless steel which is the preferred material for the fourth-generation nuclear reactor as the research object,and carries out creep-fatigue tests on smooth and notched specimens of 316H stainless steel at 600 ℃,and analyzes the effect of multiaxial stress on its creep-fatigue life.The influence of different factors on the creep-fatigue life of 316H stainless steel notched specimen and the microstructure failure and damage evolution behavior were discussed.Based on the test data,a multiaxial creepfatigue life prediction method for 316H stainless steel notched specimens was established.The main research work and conclusions of this paper are as follows:(1)The creep,fatigue and creep-fatigue tests of 316H stainless steel smooth samples and notched samples at 600℃ were carried out.The results show that the material exhibits notched strengthening effect under creep conditions;in creep-fatigue test,when the dwell time is short,the notch weakening effect is exhibited,and the notch strengthening effect is exhibited when the dwell time reaches 1 min.With the increase of the dwell time,the notch creep-fatigue life decreases and gradually becomes stable.With the increase of the nominal maximum stress and the stress concentration factor,the creep-fatigue life of the notched specimen showed a linear decreasing trend in the logarithmic coordinate.(2)In order to analyze the causes of notch strengthening and weakening of 316H stainless steel and the damage evolution law of microstructure of notched specimens under different influencing factors,numerical simulations of notch creep-fatigue specimens and fracture microstructure observations were carried out.The numerical simulation results show that the maximum equivalent stress of the notch specimen will occur near the edge of the notch,and there is a significant stress concentration phenomenon.With the increase of the dwell time,the maximum equivalent stress at the notch edge of 0.15 mm will undergo stress redistribution and stress relaxation phenomenon,creep strain increases in this region.Throughing observation of the fracture microstructure of the notched sample,it is found that with the increase of the dwell time,the fracture microstructure shows that the crack propagation zone has more pits and protrusions,and the size of the dimples in the transient fracture zone become larger and deeper.With the increase of the maximum stress,the fracture becomes smoother and the spacing of the striations in the crack propagation zone is larger.The higher the temperature is,the more obvious the plastic deformation in the fracture propagation zone and the enhanced creep effect are.(3)Based on the test data of smooth and notched specimens of 316H stainless steel,the Sakane-Ohnami creep-fatigue life prediction method is revised considering the strong correlation between its uniaxial creep-fatigue life and multiaxial creep-fatigue life.Using this method to predict the creep-fatigue life of 316H notched specimens,the prediction accuracy is within ± 1.75 times the error range,and the prediction accuracy is high.Compared with other methods,this method is simpler to determine parameters and more convenient for practical engineering applications. |
PDF Full Text Request