Analysis of a Power Plant Rotor Made of Tempered Martensitic Steel Based on a Composite Model of Inelastic Deformation

Abstract

Power plant components are subjected to high temperatures up to 903K, which induce creep deformations. Furthermore, power plants are frequently started and shut-down, thus resulting in cyclic loads on the components. Since they provide adequate mechanical and thermal properties, tempered martensitic steels are ideal candidates to withstand these conditions. The contribution at hand presents a phase mixture model for simulating the mechanical behavior of tempered martensitic steels at high temperatures. To provide a unified description of the rate-dependent deformation including hardening and softening, the model makes use of an iso-strain approach including a hard and a soft constituent. The model is implemented into the finite element method, using the implicit Euler method for time integration of the evolution equations. In addition, the consistent tangent operator is derived. As a final step, the behavior of an idealized steam turbine rotor during a cold start and a subsequent hot start is simulated by means of a thermo-mechanical finite element analysis. First, the heat transfer analysis is conducted, while prescribing the instationary steam temperature and the heat transfer coefficients. The resulting temperature fields serve as input for the subsequent structural analysis, which yields the stress and strain fields in the rotor.