Research On Creep-Fatigue Interation Damage Model And Life Assessments Of P91 Steel

With the rapid development of modern industry, the impact of creep/fatigue and their interaction on the material must be taken into consideration in order to ensure the safety and reliability of equipments which operate under high temperature conditions. Thus, the prediction of material life under creep/fatigue and their interaction is of great importance to the design, selection and safety evaluation of high temperature resistant components.This paper analyzes and researches the test results of the creep/fatigue and their interaction , using P91 steel, and finds out that the fatigue life increased while the creep life decreased under the creep/fatigue interaction. It is concluded, therefore, that the creep damage and fatigue damage do not necessarily enhance and accelerate each other under the interaction. They may inhibit each other as well. With meso damage mechanics analysis, it is discovered that when material is damaged to a certain degree, cavity may result in. Then, some of the cavities are tensile-deformed during the process of cyclic loading, which causes the micro cracks in turn. In other words, some of the cavities caused by the creep damage are consumed and then transformed into micro cracks resulted form the fatigue damage during each cyclic process. So, the creep damage is inhibited and the creep life increases while the fatigue damage is enhanced and the fatigue life decreases under the interaction.The creep damage index and fatigue damage index is introduced into the creep/fatigue interaction damage model when the linear damage accumulation method and correction method are studied in this paper. Also, the interaction influence quantity, which means the influence that the cyclic loading has on the creep strain during each cyclic process according to the features of the material, is presented. The fatigue equivalent stress is introduced into the control parameter of fatigue damage model.The creep/fatigue interaction life prediction model, which is based on the creep and fatigue damage index, is established. This paper further applies the life prediction model to compare the test results and life index of P91 steel under creep/fatigue interaction and those data obtained by using other models. Finally, this paper predicts the life of 2.25Cr-1Mo steel under strain controlling mode by adopting the methods put forward by the author.