Technical Brief

Cyclic Viscoplasticity Testing and Modeling of a Service-Aged P91 Steel

[+] Author and Article Information
C. J. Hyde, W. Sun, T. H. Hyde, J. P. Rouse

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

T. Farragher, S. B. Leen

Mechanical and Biomedical Engineering,
College of Engineering and Informatics,
NUI Galway,
Galway, Ireland

Noel P. O'Dowd

Materials and Surface Science Institute,
University of Limerick,
Limerick, Ireland

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received August 23, 2012; final manuscript received February 14, 2014; published online April 16, 2014. Assoc. Editor: Osamu Watanabe.

J. Pressure Vessel Technol 136(4), 044501 (Apr 16, 2014) (5 pages) Paper No: PVT-12-1136; doi: 10.1115/1.4026865 History: Received August 23, 2012; Revised February 14, 2014

A service-aged P91 steel was used to perform an experimental program of cyclic mechanical testing in the temperature range of 400 °C–600 °C, under isothermal conditions, using both saw-tooth and dwell (inclusion of a constant strain dwell period at the maximum (tensile) strain within the cycle) waveforms. The results of this testing were used to identify the material constants for a modified Chaboche, unified viscoplasticity model, which can deal with rate-dependant cyclic effects, such as combined isotropic and kinematic hardening, and time-dependent effects, such as creep, associated with viscoplasticity. The model has been modified in order that the two-stage (nonlinear primary and linear secondary) softening which occurs within the cyclic response of the service-aged P91 material is accounted for and accurately predicted. The characterization of the cyclic viscoplasticity behavior of the service-aged P91 material at 500 °C is presented and compared to experimental stress–strain loops, cyclic softening and creep relaxation, obtained from the cyclic isothermal tests.

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Fig. 1

Schematic representation of the (a) saw-tooth and (b) dwell waveforms

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Fig. 2

Schematic representation of the cyclic primary (nonlinear) and the secondary (linear) softening as well as the material failure behavior

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Fig. 3

Schematic representations of (a) kinematic and (b) isotropic cyclic hardening behavior

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Fig. 4

Model predictions to experimental data comparisons for the saw-tooth waveform (a) 1st σ-ε loop, (b) 575th σ-ε loop, (c) 1100th σ-ε loop, and (d) cyclic softening behavior

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Fig. 5

Model predictions to experimental data comparisons for the dwell waveform (a) 1st σ-ε loop, (b) 525th σ-ε loop, (c) 975th σ-ε loop, (d) 1st relaxation period, (e) 525th relaxation period, (f) 975th relaxation period, and (g) cyclic softening behavior




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