Approach Of Life Prediction Under Cyclic Creep

In industry, many of the engineering components are working at high temperature conditions, which suffered both high temperature creep and the cyclic loading, and both of two factors will affect the lifetime of the engineering components. It should be noted that the two mechanisms do not damage on the material individually, the interaction of two mechanisms should be taken into account in the calculation of damage and life-estimation. As we know, once these components sudden breaks or failure, it will cause severe property loss and casualties. Therefore, the study of the life-estimation of those materials which suffered cyclic loading at high temperature is urgently conducted.Through analysis of P91 steel cyclic creep test results and the microscopic observation of the fracture of several kinds of materials, the evolution of damage is revealed in this paper, that is the material suffers creep damage,fatigue damage and interaction damage under cyclic loading at high temperature. According to the micro mechanism and the linear cumulative damage law, a new "damage" concept is proposed, which replenish the defect of boundary conditions inconsistent with engineering when applying the existing "damage" concept solving the cyclic creep problem, superposition of the three damage mechanisms is constructed by this model. Taking advantage of "Strain Recovery Theory" and "Metallography Theory" microscopic explanation for interaction damage, the interaction damage items is defined, a cyclic creep life prediction model is proposed:It was used to life prediction that Gray mathematical theory's superiority in dealing with systems which has incomplete information and unclear operating mechanism, achieving fully guaranteed of model prediction accuracy in the case of complex cyclic creep mechanism and less test data.The lifetime of the P91 steel,12Cr1MoV steel and 316L stainless steel were calculated by this model, and then the results were compared with the experimental results, also the calculated results were also compared with some other models proposed by other researchers. The comparison shows that this model has high accuracy in predicting cyclic creep life under different loading conditions (i.e. different amplitude holding time). Meanwhile, this model is simple in form, and requires less parameter than other models in simulation. On the whole, the lifetime of material under cyclic creep at high temperature can be precisely calculated by this model; also this model is convenient for the engineering application.