Numerical assessment of power plant components by use of mechanism-based material models for deformation and lifetime

The present work describes an approach to evaluate the expected fatigue damage of power plant components under thermo mechanical fatigue loading by use of finite element simulations in conjunction with mechanism based material models. The material is described with two models: A Chaboche type model that describes cyclic plastic deformation as well as time dependent deformation (creep) under non-isothermal conditions. Creep fatigue damage is modeled by a mechanism based fatigue crack growth model based on the damage parameter D(TMF). Both these models can be calibrated with lab experiments. With a finite element model of the component, temperature time fields are calculated by means of an energy transfer from steam to the component. The component deformation under cyclic load is then calculated taking into account both the primary load and the thermal stresses, which are based on the temperature time fields. Calculating the creep fatigue damage (and hence component lifetime) can be difficult since due to delaying effects, such as heat transports through thick walls and stress redistribution, each part of the component experiences an individual cycle, often shifted in time to the cycle of exterior conditions. An automatic and user friendly post processing procedure is introduced, that gives a lifetime assessment based on the deformation calculation.