A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels

Improving the understanding of the long term rate dependent behaviour of materials is of critical importance in many engineering applications. Without this understanding, it is potentially difficult to ensure safe and effective plant operation while simultaneously satisfying requirements for sustain...

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Main Authors:	Benaarbia, Adil, Rouse, James Paul, Sun, Wei
Format:	Article
Language:	English
Published:	Elsevier 2018
Online Access:	http://eprints.nottingham.ac.uk/50897/ http://eprints.nottingham.ac.uk/50897/ http://eprints.nottingham.ac.uk/50897/ http://eprints.nottingham.ac.uk/50897/9/1-s2.0-S0749641917306563-main.pdf

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spelling	nottingham-508972018-07-02T08:30:22Z http://eprints.nottingham.ac.uk/50897/ A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels Benaarbia, Adil Rouse, James Paul Sun, Wei Improving the understanding of the long term rate dependent behaviour of materials is of critical importance in many engineering applications. Without this understanding, it is potentially difficult to ensure safe and effective plant operation while simultaneously satisfying requirements for sustainability and responsible resource management. In the present work, a thermodynamically-based constitutive model is proposed to capture the rate sensitivity, the stress relaxation and the accelerated cyclic softening observed during cyclic deformation of a P91 steel at an elevated temperature (600°C). The model is developed within the framework of Thermodynamics of Irreversible Processes and Generalised Standard Materials formalism, thereby offering a thermodynamically grounded coupling of both viscoelasticity (semi-recoverable strain accumulation at vastly different time scales) and viscoplasticity (irreversible strain observed above stress threshold). The later part combines a hyperbolic sine-power flow rule with non-linear isothermal cyclic evolution of isotropic and kinematic hardening. The applicability of the model to various mechanical loadings (e.g., cyclic tensile-compression tests, fatigue-relaxation tests, anhysteretic tests) is validated by designing a heuristic optimization program based on a nonlinear least-squares function coupled with the Levenberg-Marquardt algorithm. The optimization procedure is informed (through the estimation of initial material parameter estimates and objective function evaluation) by anhysteretic type experiential data only (wherein long term load hold periods are introduced at various points in the waveform). Rate dependency is determined and validated by considering experimental waveforms with different loading (strain) rates (0.1%.s−1, 0.01%.s−1 and 0.001%.s−1) and ranges (0.25%, 0.4% and 0.5%) to highlight most of the deformation mechanisms involved during the fatigue and relaxation processes. By comparing predicted and experimentally observed material responses, it is demonstrated in the present work that the viscoelastic-viscoplastic strain decomposition has the ability to capture the accelerated cyclic softening and the uncoupled stress relaxation behaviour (below and above yielding) for a P91 steel at elevated temperatures. Elsevier 2018-08 Article PeerReviewed application/pdf en cc_by http://eprints.nottingham.ac.uk/50897/9/1-s2.0-S0749641917306563-main.pdf Benaarbia, Adil and Rouse, James Paul and Sun, Wei (2018) A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels. International Journal of Plasticity, 107 . pp. 100-121. ISSN 0749-6419 https://www.sciencedirect.com/science/article/pii/S0749641917306563 doi:10.1016/j.ijplas.2018.03.015 doi:10.1016/j.ijplas.2018.03.015
repository_type	Digital Repository
institution_category	Local University
institution	University of Nottingham Malaysia Campus
building	Nottingham Research Data Repository
collection	Online Access
language	English
description	Improving the understanding of the long term rate dependent behaviour of materials is of critical importance in many engineering applications. Without this understanding, it is potentially difficult to ensure safe and effective plant operation while simultaneously satisfying requirements for sustainability and responsible resource management. In the present work, a thermodynamically-based constitutive model is proposed to capture the rate sensitivity, the stress relaxation and the accelerated cyclic softening observed during cyclic deformation of a P91 steel at an elevated temperature (600°C). The model is developed within the framework of Thermodynamics of Irreversible Processes and Generalised Standard Materials formalism, thereby offering a thermodynamically grounded coupling of both viscoelasticity (semi-recoverable strain accumulation at vastly different time scales) and viscoplasticity (irreversible strain observed above stress threshold). The later part combines a hyperbolic sine-power flow rule with non-linear isothermal cyclic evolution of isotropic and kinematic hardening. The applicability of the model to various mechanical loadings (e.g., cyclic tensile-compression tests, fatigue-relaxation tests, anhysteretic tests) is validated by designing a heuristic optimization program based on a nonlinear least-squares function coupled with the Levenberg-Marquardt algorithm. The optimization procedure is informed (through the estimation of initial material parameter estimates and objective function evaluation) by anhysteretic type experiential data only (wherein long term load hold periods are introduced at various points in the waveform). Rate dependency is determined and validated by considering experimental waveforms with different loading (strain) rates (0.1%.s−1, 0.01%.s−1 and 0.001%.s−1) and ranges (0.25%, 0.4% and 0.5%) to highlight most of the deformation mechanisms involved during the fatigue and relaxation processes. By comparing predicted and experimentally observed material responses, it is demonstrated in the present work that the viscoelastic-viscoplastic strain decomposition has the ability to capture the accelerated cyclic softening and the uncoupled stress relaxation behaviour (below and above yielding) for a P91 steel at elevated temperatures.
format	Article
author	Benaarbia, Adil Rouse, James Paul Sun, Wei
spellingShingle	Benaarbia, Adil Rouse, James Paul Sun, Wei A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
author_facet	Benaarbia, Adil Rouse, James Paul Sun, Wei
author_sort	Benaarbia, Adil
title	A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
title_short	A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
title_full	A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
title_fullStr	A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
title_full_unstemmed	A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels
title_sort	thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% cr steels
publisher	Elsevier
publishDate	2018
url	http://eprints.nottingham.ac.uk/50897/ http://eprints.nottingham.ac.uk/50897/ http://eprints.nottingham.ac.uk/50897/ http://eprints.nottingham.ac.uk/50897/9/1-s2.0-S0749641917306563-main.pdf
first_indexed	2018-09-06T14:16:52Z
last_indexed	2018-09-06T14:16:52Z
_version_	1610867972438491136

A thermodynamically-based viscoelastic-viscoplastic model for the high temperature cyclic behaviour of 9-12% Cr steels

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