Implementation of a Phase Mixture Model for Rate‐Dependent Inelasticity

Abstract

AbstractPower plant components have to withstand complex thermo‐mechanical loads, i.e. frequent start‐ups and shut‐downs in combination with long holding times at high temperatures induce creep‐fatigue loads. Tempered martensitic steels with high chromium content feature high creep strength and corrosion resistance among other properties such that these alloys are often used for power plant components.This contribution focuses on the simulation of the complex mechanical behavior of the alloy X20CrMoV12‐1 based on a multi‐axial phase mixture model. Within this model, we distinguish two phases: a hard and a soft phase. Both phases are connected via an iso‐strain approach, and nonlinear kinematic hardening as well as microstructural softening effects are taken into account by introducing a backstress and a softening variable as internal variables. The model is implemented into the commercial finite element code ABAQUS with a user material subroutine. For this purpose, the stress update algorithm and the consistent tangent operator are implemented based on the backward EULER method in combination with NEWTON‐RAPHSON iteration. Next, a wide range of benchmarks for uni‐axial as well as multi‐axial stress states is taken into account in order to verify the numerical implementation. Furthermore, a thermo‐mechanical fatigue test based on a typical sequence of start‐ups and shut‐downs of power plants is simulated.