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Research Papers

On the Determination of Material Creep Constants Using Miniature Creep Test Specimens

[+] Author and Article Information
Tom H. Hyde, Wei Sun

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

Balhassn S. M. Ali

Department of Mechanical, Materials and
Manufacturing Engineering,
University of Nottingham,
Nottingham NG7 2RD, UK
e-mail: eaxba@nottingham.ac.uk

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received September 16, 2013; final manuscript received January 23, 2014; published online February 12, 2014. Assoc. Editor: Tetsuya Ohashi.

J. Eng. Mater. Technol 136(2), 021006 (Feb 12, 2014) (10 pages) Paper No: MATS-13-1171; doi: 10.1115/1.4026596 History: Received September 16, 2013; Revised January 23, 2014

Full size creep test specimens, i.e., conventional uniaxial creep test specimen and Bridgman notch specimens are usually used to determine the full set of material constants for any creep model. However, in many situations, sufficient material is not available for theses specimens to be manufactured from it. Therefore, small creep test specimens have been introduced and used to determine (i) creep constants and (ii) the remaining life time for engineering components. Two commonly used small creep specimen types, i.e., the impression and the small ring creep tests, are used in this paper to determine the steady state creep constants. However, these specimen types are limited for use in determining the secondary creep properties, i.e., they are unable to determine the full set of material creep constants for creep damage models. In this paper the recently developed small two-bar creep test specimen and the newly developed small notched specimen test are described and used to determine a full set of material constants for Kachanov and Liu-Murakami creep damage models. The small notched specimen manufacturing, loading and testing procedures are described in this paper. P91 steel at 600 °C and (Bar-257) P91 steel at 650 °C have been used to compare the material constants obtained from the small two-bar and the small notched creep test specimens with those obtained from the conventional uniaxial creep test specimens and Bridgman notch specimens. The results show remarkably good agreement between the two sets of results.

Copyright © 2014 by ASME
Topics: Creep , Steel , Testing
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References

Figures

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Fig. 1

Conventional uniaxial creep test specimen [14]

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Fig. 2

Conventional notched bar specimen [14]

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Fig. 3

Small ring specimen dimensions and loading arrangement (R ∼ 3–10 mm, d ∼ b ∼ 1–2 mm)

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Fig. 4

Minimum creep test strain rate data for (Bar-257) P91 steel at 650 °C [9]

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Fig. 5

Impression creep test specimen (a) and loading arrangement (b), (w ≈ b ≈ 10 mm, di ≈ 1 mm, h ≈ 2.5 mm), loading area is bdi

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Fig. 6

(a) Minimum creep strain rate data obtained from uniaxial and impression creep tests for a 2-1/4Cr1Mo weld metal at 640 °C [20]. (b) Minimum creep strain rate data obtained from uniaxial and impression creep tests for 316 stainless steel at 600 °C [20].

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Fig. 7

The small two-bar specimen dimensions and loading arrangement, (Lo ∼ 13 mm, k ∼ 6.5 mm, Di ∼ 5 mm, and d ∼ b ∼ 2 mm)

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Fig. 8

Converted TBS creep strain curves together with the corresponding uniaxial creep strain curves for P91 steel at 600 °C [16]

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Fig. 9

Converted TBS creep strain curves together with the corresponding uniaxial creep strain curves for (Bar-257) P91 steel at 650 °C

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Fig. 10

Minimum creep strain rates for P91 steel at 600 °C, uniaxial and TBS tests [16]

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Fig. 11

Minimum creep strain rates for (Bar-257) P91 steel at 650 °C, for the uniaxial and the TBS tests

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Fig. 12

Creep rupture data obtained from TBS and uniaxial specimens for P91 steel at 600 °C [16]

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Fig. 13

Creep rupture data obtained from TBS and uniaxial specimens for (Bar-257) P91 steel at 650 °C [28]

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Fig. 14

The experimental converted TBS creep strain curves, for (Bar-257) P91 steel at 650 °C and the fitted creep strain curves using Kachanov model with Ø = 9.5 and Liu–Murakami model with q2 = 4.00

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Fig. 15

The experimental converted TBS creep strain curves, for P91 steel at 600 °C and the fitted creep strain curves using Kachanov model with Ø = 19.00 and Liu–Murakami model with q2 = 7.00

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Fig. 16

Small notched specimen dimensions and loading application

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Fig. 17

Finite element mesh and the boundary conditions

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Fig. 18

Contour plot of damage parameter, ω, in the small notched specimen for (Bar-257) P91 steel at 650 °C

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Fig. 19

The effect of α value on uniaxial specimen, Bridgman notch specimens and small notched specimens with varies R/w ratio, w = 1 for all small notched cases

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Fig. 20

A photo of the small notched specimens manufactured using EDM machine

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Fig. 21

Determining α value for (Bar-257) P91 steel at 650 °C using small notched specimen

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Fig. 22

Comparison between (i) the converted TBS creep strain versus time curves obtained from the FE analyses, using the Liu–Murakami model and the material constants obtained from the TBS creep tests and (ii) the corresponding uniaxial experimental creep strain versus time curves, for (Bar-257) P91 steel at 650 °C

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