Characterization of viscoplasticity behaviour of P91 and P92 power plant steels

This paper deals with the determination of material constitutive model for P91 and P92 steels at high temperatures. An isothermal, strain-controlled test programme was conducted for both steels for a temperature range between 400 and 675 °C. The experimental data from these tests were used to obtain the material constants in a viscoplasticity model. The model includes the effects of isotropic and kinematic hardening, as well as time-dependent effects, and has been used to model the cyclic material behaviour of each material. Material constants were initially determined from initial cycle stress–strain data, maximum stress evolution data and stress relaxation data. The material constants were improved by use of a least-squares optimisation algorithm. The constitutive models have been implemented into the ABAQUS finite element (FE) code by using the Z-mat software. The performances of the material models for both steels have been assessed by comparing predictions with experimental data obtained from the tests

FE analysis of a notched bar under thermomechanical fatigue using a unified viscoplasticity model

AbstractZ-mat software is used to implement the multiaxial form of the Chaboche unified viscoplastic constitutive equations into the Abaqus finite element (FE) code. Complex transient stress fields within a grade P91 steel notched bar specimen are investigated in detail for different thermomechanical fatigue (TMF) loading conditions. The results of this work can be used to determine suitable test conditions for notched specimens by providing predictions of the stress-strain history local to the notch. In future, such tests will be used along with the FE analyses to develop and validate multiaxial TMF lifing models