Characterization of viscoplasticity behaviour of P91 and P92 power plant steels

Abstract

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 temperatre 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, 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.

Determination of material parameters for a unified viscoplasticity-damage model for a P91 power plant steel

“…Using these initial estimates of parameters and using the optimisation procedure described in the work of Saad et al [1], material parameters for the Chaboche model were obtained for P91 at 600°C for different strain ranges. Optimisation was conducted using LSQNONLIN within MATLAB (the Chaboche model ordinary differential equations (ODEs) were solved using ODE45).…”

“…In the present work, a continuum damage model has been coupled with a Chaboche unified viscoplastic constitutive model in order to predict stress-strain behaviour of a P91 martensitic steel (a material used for power plant steam pipes) due to cyclic plasticity and damage accumulation. The experimental data used here are from the previous work [1]. Cyclic fully reversed strain controlled experiments (±0.4%, ±0.25% and ±0.2% strain ranges) and cyclic test with a dwell period (±0.5% strain ranges) for a P91 martensitic steel under isothermal conditions (600°C) are utilised.…”

“…Tong et al [5] used uniaxial Chaboche model to model cyclic inelastic behaviour of a nickel based alloy. Saad et al [1] and Hyde et al [17] used the similar model to analyse evolutions of initial stress range of P91 steel and 316 stainless steel under strain controlled TMF load. The model was modified by Barrett et al [2] for multiaxial TMF problems which are independent of applied strain rate using a hyperbolic sine viscoplastic model.…”

“…The physically relevant material parameters are determined and optimised using experimental results. Although many material parameter identification procedures can be found in the literature [1][2][3][4][5][6], there are uncertainties in determining the limits for the parameters used in the optimisation procedure. This could result in unrealistic parameters while optimising using experimental data.…”

Determination of the material constants of creep damage constitutive equations using Matlab optimization procedure

“…Methods were developed for the creep damage [1,4], and viscoplasticity model [7,8]. The optimization routines of these approaches need a set of careful chosen starting values in order to achieve global convergence.…”