| With the modern industry development into high-speed, high-temperature and high-pressure, fatigue problem is threatening the safety of its equipment. Statistics shows that eighty percent components' failure is caused by fatigue. And because all the components are worked under high-temperature, high-pressure and alternating load condition, the failure is not only related to the fatigue properties of the material, but also to the creep properties, and material properties under creep-fatigue complex condition is not only decided by the damage of creep or fatigue, but also by the creep-fatigue interaction. The damage of creep-fatigue interaction will be the important factor to limit their usage life. So it's necessary to study on the high-temperature low-cycle fatigue and creep-fatigue interaction of material of such equipment. For the other side, with the rapid development of science and technology and the need of chemical equipment, power engine, generator equipment, aerospace and nuclear technology, the study like this is booming, researchers domestic and overseas are strive to be the first to study on it. And the subject is became a integrated rising subject including macro-mechanics (elastic mechanics, plastic mechanics, fracture mechanics, damage mechanics etc.),metal microstructure and so on, there are a lot of phenomena which can't be explained by the uni-axial stress state theory especially under the multi-axial stress state for its complexity. So studying on the high-temperature low-cycle fatigue and creep-fatigue interaction not only has the theory significance but also has the engineering significance.In this paper, the high-temperature low-cycle fatigue life and fatigue crack propagation life tests are carried on the cylindrical axial symmetry specimens having precrack or non-precrack with different types of notches of 2.25Cr-1Mo steel in common use in the petrochemical industry contacting hydrogen equipment, the stress/strain and the range of stress/strain of dangerous points are received through stress analysis of the specimens using finite element program under multi-axial stress state. Using the Von Mises equivalent theory, the equivalent stress Δ , the equivalent plastic strain range Δεp, the equivalent creep strain range A#Cand the equivalent strain range Δε is calculated. On basis of the conception of equivalent theory, the feasibility of characterizing the fatigue life and fatigue crack propagation life of the material by the equivalent plastic strain range Δεp, the equivalent creep strain range Δεc and theequivalent strain range Δε, the influence of the notches and creep-fatigue interaction on fatigue life and fatigue crack propagation life is studied. Atlast, the equations of evaluating the high-temperature low-cycle fatigue life and the fatigue crack propagation life are found through using the least-square regression method.The study on high-temperature low-cycle fatigue life and fatigue crack propagation life under multi-axial stress state shows that the fatigue life and fatigue crack propagation life can be characterized by the equivalent plastic strain range Δεp, the equivalent creep strain range Δεc and the equivalentstrain range Δε , and don't exit notch dependency. The fatigue life can be evaluated by the following non-notch-dependency equations, so they have important engineering significance.The fatigue crack propagation life can be evaluated by the following non-notch-dependency equations.The study on creep-fatigue interaction on fatigue life and fatigue crack propagation life shows that the fatigue life and fatigue crack propagationlife under the strain control without holding time can be characterized by the nonlinear combination of the fatigue component, creep component and creep-fatigue interaction component, that is to say, the creep-fatigue interaction is existent in the course of the failure, and the creep and fatigue interaction is the positive interaction. The fatigue life and fatigue crack propagation life be... |
PDF Full Text Request