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High-R Fatigue Crack Growth Threshold Stress Intensity Factors at High Temperatures

  • Stuart R. HoldsworthEmail author
  • Zhen Chen
Conference paper
  • 728 Downloads

Abstract

While knowledge relating to the determination and practical application of fatigue crack growth threshold stress intensity factors for defect assessment is relatively well established for many circumstances, this is not the case for materials and conditions which are sensitive to time-dependent mechanisms. There are two well-established international standard procedures for the determination of this fracture mechanics parameter, although their respective crack growth rate criteria differ by an order of magnitude. Unfortunately neither specifically addresses determination of the property for very high-R (K min/K max) ratios, under conditions when the environment can be influential, and Δ K th can be even more sensitive to the da/dNK) criterion adopted for its determination. In addition to a general state of knowledge review, particular attention is paid to circumstances concerning high-R Δ K th in power plant steels at high temperatures for which oxide-induced crack closure and creep cracking can be influential. Evidence for low-alloy 1%Cr, martensitic 9%Cr and austenitic 17%Cr steels is examined.

Keywords

High-R High temperature ΔKth Oxide-induced crack closure Creep cracking 

Nomenclature

a

Crack depth

A

Constant in Paris mid-K regime power law

B

Specimen thickness

CT

Compact tension (specimen)

CTOD

Crack opening displacement

da/dN

Fatigue crack growth rate

DCPD

Direct current potential drop (electrical crack monitoring instrumentation)

f

Frequency

FIB

Focussed ion beam

HCFCG

High-cycle fatigue crack growth (typically for 80 < f < 100 Hz)

TDFAD

Time-dependent failure assessment diagram

kp

Oxidation parabolic growth constant

k′

Inelastic strain constant in ε(σ) relationship

K, ΔK

Stress intensity factor, range of stress intensity factor

Kc

Critical stress intensity factor responsible for unstable fracture

\(K_{\text{mat}}^{\text{C}}\)

Material creep toughness (for a given temperature and time)

Kmax

Maximum stress intensity factor (in cycle)

Kmin

Minimum stress intensity factor (in cycle)

Kr

K Ratio representing proximity to fracture

ΔKth

Fatigue crack growth threshold stress intensity factor

\({\text{d}}\Delta K_{\text{th}}^{\text{ox}}\)

Enhancement to ΔK th due to oxide-induced crack closure

Lr

Stress ratio representing proximity to plastic collapse or creep rupture

m

Exponent in Paris mid-K regime power law

N

Number of cycles

R

Load ratio (K min/K max)

Rp0.2

0.2% proof strength

Rm

Ultimate tensile strength

RR

Creep-rupture strength

\(R_{ 0. 2}^{\text{C}}\)

0.2% creep strength (stress responsible for 0.2% inelastic strain for a given temperature and time)

RT

Room temperature

SEM

Scanning electron microscope

t

Time

W

Specimen width

x

Oxide thickness

β

Inelastic strain exponent in ε(σ) relationship

ε, εref

Strain, Reference strain

σ, σref

Stress, Reference stress

\(\sigma_{\text{ref}}^{ \hbox{max} }\)

Maximum reference stress (in cycle)

υ

Poisson’s ratio

References

  1. 1.
    P.C. Paris, F. Erdogan, A critical examination of crack propagation laws. J. Basic Eng. 85(4), 528–533 (1963)CrossRefGoogle Scholar
  2. 2.
    S.R. Holdsworth, in High Temperature Fatigue Crack Growth, ed. by J.B. Marriott. High Temperature Crack Growth in Steam Turbine Materials, (Commission European Communities, COST Monograph EUR 14678en, 1994), pp. 129–176Google Scholar
  3. 3.
    E 647, in Standard Test Method for Measurement of Fatigue Crack Growth Rates, (ASTM Standard, ASTM International, West Conshohocken, PA, US)Google Scholar
  4. 4.
    ISO 12108, in Metallic Materials—Fatigue Testing—Fatigue Crack Growth Method, International StandardGoogle Scholar
  5. 5.
    R.P. Skelton, J.R. Haigh, Fatigue crack growth rates and thresholds in steels under oxidising conditions. Mat. Sci. Eng. 36, 17–25 (1978)CrossRefGoogle Scholar
  6. 6.
    BS 7910, in Guide to Methods for Assessing the Acceptability of Flaws in Metallic Structures, (British Standards Institution, 2013)Google Scholar
  7. 7.
    S.R. Holdsworth, in Review of Air Oxidation Kinetics for a Range of Low and High Alloy Steels, unpublished (2000)Google Scholar
  8. 8.
    P.J. Ennis, W.J. Quadakkers, Mechanisms of steam oxidation in high strength martensitic steels. Int. J. Pres. Ves. Pip. 84, 75–81 (2007)CrossRefGoogle Scholar
  9. 9.
    J.R. Rice, in The Mechanics of Crack Tip Deformation and Extension by Fatigue. Fatigue Crack Propagation, vol. 415 (ASTM STP 1967), pp. 247–311Google Scholar
  10. 10.
    A.T. Stewart, The influence of environment and stress ratio on fatigue crack growth at near threshold stress intensities in low alloy steels. Eng. Fract. Mech. 13(3), 463–478 (1980)CrossRefGoogle Scholar
  11. 11.
    D.W. Dean, R.D. Patel, A. Klenk, F. Mueller, Comparison of procedures for the assessment of creep crack initiation. OMMI 3(3), (2004)Google Scholar
  12. 12.
    R5, An Assessment Procedure for the High Temperature Response of Structures, EDF Energy, 3 (2003)Google Scholar
  13. 13.
    ASME, in Boiler and Pressure Vessel Code III, Rules for construction of nuclear facility components, Class 1 components in elevated temperature service, Division 1—Subsection NH, ASME (2004)Google Scholar

Copyright information

© Springer Nature Singapore Pte Ltd. 2018

Authors and Affiliations

  1. 1.Swiss Federal Laboratories for Materials Science and Technology (EMPA)Dubendorf, ZurichSwitzerland

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