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Research Papers: Materials and Fabrication

A Unified Viscoplastic Model for High Temperature Low Cycle Fatigue of Service-Aged P91 Steel

[+] Author and Article Information
R. A. Barrett

Mechanical Engineering,
College of Engineering and Informatics,
NUI Galway, Ireland;
Ryan Institute for Environmental,
Marine and Energy Research,
NUI Galway, Ireland,
e-mail: r.barrett2@nuigalway.ie

T. P. Farragher

Mechanical Engineering,
College of Engineering and Informatics,
NUI Galway, Ireland;
Ryan Institute for Environmental,
Marine and Energy Research,
NUI Galway, Ireland

C. J. Hyde

Department of Mechanical,
Materials, and Manufacturing Engineering,
University of Nottingham,
Nottingham NG7 2RD, UK

N. P. O'Dowd

Department of Mechanical,
Aeronautical and Biomedical Engineering,
Materials and Surface Science Institute,
University of Limerick, Ireland

P. E. O'Donoghue

Civil Engineering,
College of Engineering and Informatics,
NUI Galway, Ireland;
Ryan Institute for Environmental,
Marine and Energy Research,
NUI Galway, Ireland

S. B. Leen

Mechanical Engineering,
College of Engineering and Informatics,
NUI Galway, Ireland;
Ryan Institute for Environmental,
Marine, and Energy Research,
NUI Galway, Ireland

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received May 28, 2013; final manuscript received August 25, 2013; published online January 7, 2014. Assoc. Editor: Wolf Reinhardt.

J. Pressure Vessel Technol 136(2), 021402 (Jan 07, 2014) (8 pages) Paper No: PVT-13-1090; doi: 10.1115/1.4025618 History: Received May 28, 2013; Revised August 25, 2013

The finite element (FE) implementation of a hyperbolic sine unified cyclic viscoplasticity model is presented. The hyperbolic sine flow rule facilitates the identification of strain-rate independent material parameters for high temperature applications. This is important for the thermo-mechanical fatigue of power plants where a significant stress range is experienced during operational cycles and at stress concentration features, such as welds and branched connections. The material model is successfully applied to the characterisation of the high temperature low cycle fatigue behavior of a service-aged P91 material, including isotropic (cyclic) softening and nonlinear kinematic hardening effects, across a range of temperatures and strain-rates.

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References

Figures

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Fig. 1

Comparison of the hyperbolic sine material model with experimental data for a 9Cr steel [27,28], illustrating the extrapolation capability of the model

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Fig. 2

Kinematic hardening regions for material parameter identification

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Fig. 3

Comparison of the isotropic hardening model with the experimentally measured softening data for a strain-rate of 0.1%/s and strain range of ±0.5% at 500 °C

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Fig. 4

Kinematic hardening parameter identification for the later stages of strain hardening at a temperature of 500 °C

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Fig. 5

Identification of the cyclic yield stress value at a temperature of 400 °C

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Fig. 6

Calibration of the cyclic viscoplastic material parameters at temperatures of 400 °C and 500 °C via (a) comparison with stress relaxation data and (b) comparison of the FE-predicted plastic strain with the experimental values obtained during the stress relaxation tests

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Fig. 7

Comparison of the model predicted results with experimental data, for the initial cycle and half life at 400 °C and a strain-rate of 0.1%/s

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Fig. 8

Comparison of the model and experimental stress-strain response at a temperature of 500 °C and a strain-rate of 0.1%/s for the initial and 642nd cycles

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Fig. 9

Validation of FE-predicted results with experimental data for the initial and 600th cycles at a temperature of 400 °C and a strain-rate of 0.033%/s

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Fig. 10

Validation of FE-predicted results with experimental data for the initial cycle and the half life at a temperature of 500 °C and a strain-rate of 0.033%/s

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Fig. 11

Validation of FE-predicted results with experimental data for the initial cycle and the half life at a temperature of 500 °C and a strain-rate of 0.025%/s

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Fig. 12

Validation of the FE-predicted and experimental stress–strain response for the half life at strain ranges of ±0.3%, ±0.4%, and ±0.5%, under a strain-rate of 0.033%/s and a temperature of 400 °C

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Fig. 13

Comparison of the Coffin-Manson predicted number of cycles to failure with the number of cycles to failure obtained from HTLCF experiments

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Fig. 14

Effect of varying the value of the cyclic viscoplastic parameter, β, using the analytical model for stress relaxation

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