ASTM E2472-12(2018)
(Test Method)Standard Test Method for Determination of Resistance to Stable Crack Extension under Low-Constraint Conditions
Standard Test Method for Determination of Resistance to Stable Crack Extension under Low-Constraint Conditions
SIGNIFICANCE AND USE
5.1 This test method characterizes a metallic material’s resistance to stable crack extension in terms of crack-tip-opening angle (CTOA), ψ and/or crack-opening displacement (COD), δ5 under the laboratory or application environment of interest. This method applies specifically to fatigue pre-cracked specimens that exhibit low constraint and that are tested under slowly increasing displacement.
5.2 When conducting fracture tests, the user must consider the influence that the loading rate and laboratory environment may have on the fracture parameters. The user should perform a literature review to determine if loading rate effects have been observed previously in the material at the specific temperature and environment being tested. The user should document specific information pertaining to their material, loading rates, temperature, and environment (relative humidity) for each test.
5.3 The results of this characterization include the determination of a critical, lower-limiting value, of CTOA (ψc) or a resistance curve of δ5, a measure of crack-opening displacement against crack extension, or both.
5.4 The test specimens are the compact, C(T), and middle-crack-tension, M(T), specimens.
5.5 Materials that can be evaluated by this standard are not limited by strength, thickness, or toughness, if the crack-size-to-thickness (a/B) ratio or ligament-to-thickness (b/B) ratio are equal to or greater than 4, which ensures relatively low and similar global crack-front constraint for both the C(T) and M(T) specimens (2, 3).
5.6 The values of CTOA and COD (δ5) determined by this test method may serve the following purposes:
5.6.1 In research and development, CTOA (ψc) or COD (δ5), or both, testing can show the effects of certain parameters on the resistance to stable crack extension of metallic materials significant to service performance. These parameters include, but are not limited to, material thickness, material composition, thermo-mechanical processing,...
SCOPE
1.1 This standard covers the determination of the resistance to stable crack extension in metallic materials in terms of the critical crack-tip-opening angle (CTOA), ψc and/or the crack-opening displacement (COD), δ5 resistance curve (1).2 This method applies specifically to fatigue pre-cracked specimens that exhibit low constraint (crack-size-to-thickness and un-cracked ligament-to-thickness ratios greater than or equal to 4) and that are tested under slowly increasing remote applied displacement. The test specimens are the compact, C(T), and middle-crack-tension, M(T), specimens. The fracture resistance determined in accordance with this standard is measured as ψc (critical CTOA value) and/or δ5 (critical COD resistance curve) as a function of crack extension. Both fracture resistance parameters are characterized using either a single-specimen or multiple-specimen procedures. These fracture quantities are determined under the opening mode (Mode I) of loading. Influences of environment and rapid loading rates are not covered in this standard, but the user must be aware of the effects that the loading rate and laboratory environment may have on the fracture behavior of the material.
1.2 Materials that are evaluated by this standard are not limited by strength, thickness, or toughness, if the crack-size-to-thickness (a/B) ratio and the ligament-to-thickness (b/B) ratio are greater than or equal to 4, which ensures relatively low and similar global crack-front constraint for both the C(T) and M(T) specimens (2, 3).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory lim...
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Designation: E2472 − 12 (Reapproved 2018)
Standard Test Method for
Determination of Resistance to Stable Crack Extension
under Low-Constraint Conditions
This standard is issued under the fixed designation E2472; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
1.1 This standard covers the determination of the resistance
1.5 This international standard was developed in accor-
to stable crack extension in metallic materials in terms of the
dance with internationally recognized principles on standard-
critical crack-tip-opening angle (CTOA), ψ and/or the crack-
c
ization established in the Decision on Principles for the
opening displacement (COD), δ resistance curve (1). This
Development of International Standards, Guides and Recom-
method applies specifically to fatigue pre-cracked specimens
mendations issued by the World Trade Organization Technical
that exhibit low constraint (crack-size-to-thickness and un-
Barriers to Trade (TBT) Committee.
cracked ligament-to-thickness ratios greater than or equal to 4)
and that are tested under slowly increasing remote applied
displacement. The test specimens are the compact, C(T), and 2. Referenced Documents
middle-crack-tension, M(T), specimens. The fracture resis-
2.1 ASTM Standards:
tance determined in accordance with this standard is measured
E4Practices for Force Verification of Testing Machines
as ψ (critical CTOAvalue) and/or δ (critical COD resistance
c 5
E8/E8MTest Methods for Tension Testing of Metallic Ma-
curve) as a function of crack extension. Both fracture resis-
terials
tance parameters are characterized using either a single-
E399Test Method for Linear-Elastic Plane-Strain Fracture
specimen or multiple-specimen procedures. These fracture
Toughness K of Metallic Materials
Ic
quantities are determined under the opening mode (Mode I) of
E561Test Method forK Curve Determination
R
loading. Influences of environment and rapid loading rates are
E647Test Method for Measurement of Fatigue Crack
not covered in this standard, but the user must be aware of the
Growth Rates
effects that the loading rate and laboratory environment may
E1290Test Method for Crack-Tip Opening Displacement
have on the fracture behavior of the material.
(CTOD) Fracture Toughness Measurement (Withdrawn
1.2 Materials that are evaluated by this standard are not
2013)
limited by strength, thickness, or toughness, if the crack-size-
E1820Test Method for Measurement of FractureToughness
to-thickness (a/B) ratio and the ligament-to-thickness (b/B)
E1823TerminologyRelatingtoFatigueandFractureTesting
ratio are greater than or equal to 4, which ensures relatively
E2309Practices forVerification of Displacement Measuring
low and similar global crack-front constraint for both the C(T)
Systems and Devices Used in Material Testing Machines
and M(T) specimens (2, 3).
2.2 ISO Standards:
1.3 The values stated in SI units are to be regarded as
ISO22889:2007 MetallicMaterials—MethodofTestforthe
standard. No other units of measurement are included in this
Determination of Resistance to Stable Crack Extension
standard.
Using Specimens of Low Constraint
1.4 This standard does not purport to address all of the ISO 12135Metallic Materials—Unified Method of Test for
safety concerns, if any, associated with its use. It is the the Determination of Quasistatic Fracture Toughness
responsibility of the user of this standard to establish appro-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
and Fracture and is the direct responsibility of Subcommittee E08.07 on Fracture Standards volume information, refer to the standard’s Document Summary page on
Mechanics. the ASTM website.
Current edition approved Nov. 1, 2018. Published December 2018. Originally The last approved version of this historical standard is referenced on
ε1
approved in 2006. Last previous edition approved in 2012 as E2472–12 . DOI: www.astm.org.
10.1520/E2472-12R18. Available from International Organization for Standardization (ISO), 1, ch. de
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
this standard. www.iso.ch.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2472 − 12 (2018)
3. Terminology 3.2.8 crack extension resistance curve (R curve),
n—variation of δ with crack extension, ∆a.
3.1 Terminology E1823 is applicable to this test standard.
-2
3.2.9 effective yield strength, σ [FL ], n—an assumed
Y
3.2 Definitions:
value of uniaxial yield strength that represents the influence of
3.2.1 crack extension, ∆a [L], n—an increase in crack size.
plastic yielding upon fracture test parameters.
3.2.1.1 Discussion—Itshouldbenotedthatinthin-sheetand
3.2.9.1 Discussion—Effective yield strength is calculated as
thick-platematerialsunderlowconstraintconditions,thecrack
the average of the 0.2% offset yield strength σ , and the
YS
extension observed on the surface of the specimen may be
ultimate tensile strength, σ as follows:
TS
significantly less than that in the interior of the specimen due
σ 5 σ 1σ /2 (1)
~ !
Y YS TS
to the effects of crack tunneling. This must be considered if
NOTE 1—The yield and ultimate tensile strength are determined from
direct optical techniques are used to monitor and measure
Test Methods E8/E8M.
free-surfacecrackextension.Indirectcrackextensionmeasure-
ment techniques such as unloading compliance and electric- 3.2.9.2 Discussion—In estimating σ , influences of testing
Y
conditions, such as loading rate and temperature, should be
potential drop method may be used in place of (or to comple-
ment) the direct optical techniques to provide a measure of considered.
average crack extension. (See Test Method E647 for compli-
3.2.10 final crack size, a [L], n—crack extension at end of
f
ance methods for C(T) and M(T) specimens; and ISO 12135
stable tearing (a = a + ∆a).
f o f
and Test Method E647 for electric potential-drop methods for
3.2.11 final remaining ligament, b [L], n—distance from
f
C(T) specimens.)
the tip of the final crack size to the back edge of the specimen,
3.2.2 crack size, a [L], n—principal linear dimension used
that is b = W – a.
f f
inthecalculationoffracturemechanicsparametersforthrough
3.2.12 force, P[F], n—forceappliedtoatestspecimenorto
thickness cracks.
a component.
3.2.2.1 Discussion—A measure of the crack size after the
3.2.13 minimumcrackextension,∆a [L],n—crackexten-
min
fatiguepre-crackingstageisdenotedastheoriginalcracksize,
sion beyond which ψ is nearly constant.
c
a . The value for a may be obtained using surface
o o
3.2.14 maximum crack extension, ∆a [L], n—crack ex-
measurement, unloading compliance, electric-potential drop or
max
other methods where validation procedures for the measure- tension limit for ψ and δ controlled crack extension.
c 5
ments are available.
3.2.15 maximum fatigue force, P [F],n—maximumfatigue
f
force applied to specimen during pre-cracking stage.
3.2.3 crack-tip-opening angle (CTOA), ψ [deg], n—relative
-2
angle of crack surfaces resulting from the total deformation
3.2.16 modulus of elasticity, E [FL ], n—the ratio of stress
(elastic plus plastic) measured (or calculated) at 1-mm behind
to corresponding strain below the proportional limit.
–1
thecurrentcracktipasthecrackstablytears,whereψ=2tan
3.2.17 notch size, a [L], n—distancefromareferenceplane
n
(δ /2).
to the front of the machined notch, such as the force line in the
3.2.4 critical crack-tip-opening angle (CTOA ), ψ [deg],
c c compact specimen to the notch front or from the center line in
n—steady-state relative angle of crack surfaces resulting from
the middle-crack-tension specimen to the notch front.
the total deformation (elastic plus plastic) measured (or calcu-
3.2.18 original crack size, a [L], n—thephysicalcracksize
o
lated) at 1-mm behind the current crack tip as the crack stably
at the start of testing.
–1
tears, where ψ = 2 tan (δ /2).
c 1c
3.2.19 original ligament, b [L], n—distancefromtheorigi-
o
3.2.4.1 Discussion—Critical CTOAvalue tends to approach
nalcrackfronttothebackedgeofthespecimen,thatis b = W
o
a constant, steady-state value after a small amount of crack
– a .
o
extension (associated with crack tunneling and transition from
flat-to-slant crack extension). 3.2.20 remaining ligament, b [L], n—distance from the
physical crack front to the back edge of the specimen, that is b
3.2.5 crack-opening displacement, (COD) δ [L]—force-
= W – a.
inducedseparationvectorbetweentwopoints.Thedirectionof
3.2.21 specimen thickness, B [L], n—distance between the
the vector is normal to the crack plane (normal to the facing
parallel sides of a test specimen or component. Side grooving
surfacesofacrack)ataspecifiedgagelength.Inthisstandard,
is not allowed.
δ is measured at the fatigue precrack tip location over a gage
length of 5-mm as the crack stably tears.
3.2.22 specimen width, W [L], n—distance from a reference
position (for example, the force line of a compact specimen or
3.2.6 crack-tip-opening displacement (CTOD), δ [L],
center line in the middle-crack-tension specimen) to the rear
n—relative displacement of crack surfaces resulting from the
surface of the specimen. (Note that the total width of the M(T)
totaldeformation(elasticplusplastic)measured(orcalculated)
specimen is defined as 2W.)
at 1- mm behind the current crack tip as the crack stably tears.
3.2.7 critical crack-tip-opening displacement (CTOD ), δ
c 1c
4. Summary of Test Method
[L], n—steady-state relative displacement of crack surfaces
resulting from the total deformation (elastic plus plastic) 4.1 The objective of this standard is to induce stable crack
measured (or calculated) at 1-mm behind the current crack tip extension in a fatigue pre-cracked, low-constraint test speci-
as the crack stably tears. men while monitoring and measuring the COD at the original
E2472 − 12 (2018)
fatiguepre-crack-tiplocation (4, 5)ortheCTOA(orCTOD)at resistance curve of δ , a measure of crack-opening displace-
1-mm behind the stably tearing crack tip (6, 7), or both. The ment against crack extension, or both.
resistance curve associated with the δ measurements and the
5.4 The test specimens are the compact, C(T), and middle-
critical limiting value of the CTOAmeasurements are used to
crack-tension, M(T), specimens.
characterize the corresponding resistance to stable crack ex-
5.5 Materials that can be evaluated by this standard are not
tension. In contrast, the CTOD values determined from Test
limited by strength, thickness, or toughness, if the crack-size-
Method E1290 (high-constraint bend specimens) are values at
to-thickness (a/B) ratio or ligament-to-thickness (b/B) ratio are
one or more crack extension events, such as the CTOD at the
equal to or greater than 4, which ensures relatively low and
onset of brittle crack extension with no significant stable crack
similar global crack-front constraint for both the C(T) and
extension.
M(T) specimens (2, 3).
4.2 Either of the fatigue pre-cracked, low-constraint test
5.6 The values of CTOA and COD (δ ) determined by this
specimen configurations specified in this standard [C(T) or
test method may serve the following purposes:
M(T)] may be used to measure or calculate either of the
5.6.1 In research and development, CTOA (ψ)orCOD
c
fracture resistance parameters considered. The fracture resis-
(δ ), or both, testing can show the effects of certain parameters
tance parameters, CTOA (or CTOD) and δ , may be charac-
ontheresistancetostablecrackextensionofmetallicmaterials
terized using either a single-specimen or multiple-specimen
significant to service performance. These parameters include,
procedure. In all cases, tests are performed by applying slowly
butarenotlimitedto,materialthickness,materialcomposition,
increasing displacements to the test specimen and measuring
thermo-mechanical processing, welding, and thermal stress
the forces, displacements, crack extension and angles realized
relief.
during the test. The forces, displacements and angles are then
5.6.2 For specifications of acceptance and manufacturing
usedinconjunctionwithcertainpre-testandpost-testspecimen
quality control of base materials.
measurements to determine the material’s resistance to stable
5.6.3 Forinspectionandflawassessmentcriteria,whenused
crack extension.
in conjunction with fracture mechanics analyses.Awareness of
4.3 Four procedures for measuring crack extension are:
differences that may exist between laboratory test and field
surface visual, unloading compliance, electrical potential, and
conditions is required to make proper flaw assessment.
multiple specimens.
5.6.4 The critical CTOA (ψ ) has been used with the
c
4.4 Two techniques are presented for measuring CTOA:
elastic-plastic finite-element method to accurately predict
optical microscopy (OM) (8) and digital image correlation
structural response and force carrying capacity of simple and
(DIC) (9).
complex cracked structural components, see Appendix X1.
5.6.5 The δ parameter has been related to the J-integral by
4.5 Three techniques are presented for measuring COD: δ 5
means of the Engineering Treatment Model (ETM) (10) and
clip gage (5), optical microscopy (OM) (8), and digital image
provides an engineering approach to predict the structural
correlation (DIC) (9).
response and force carrying capacity of cracked structural
4.6 Data generated following the procedures and guidelines
components.
contained in this standard are labeled qualified data and are
5.6.6 The K-R curve method (Practice E561) is similar to
insensitive to in-plane dimensions and specimen type (tension
theδ -resistancecurve,inthat,theconcepthasbeenappliedto
or bending forces), but are dependent upon sheet or plate
both C(T) and M(T) specimens (under low-constraint condi-
thickness.
tions)andtheK-Rcurveconcepthasbeenusedsuccessfullyin
5. Significance and Use industry (11). However, the δ parameter has been related to
the J-integral and the parameter incorporates the material
5.1 This test method characterizes a metallic material’s
non-linear effects in its measurement. Comparisons have also
resistance to stable crack exte
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´1
Designation: E2472 − 12 E2472 − 12 (Reapproved 2018)
Standard Test Method for
Determination of Resistance to Stable Crack Extension
under Low-Constraint Conditions
This standard is issued under the fixed designation E2472; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—3.2.5 and 3.2.6 were editorially revised in March 2013.
1. Scope
1.1 This standard covers the determination of the resistance to stable crack extension in metallic materials in terms of the critical
crack-tip-opening angle (CTOA), ψ and/or the crack-opening displacement (COD), δ resistance curve (1). This method applies
c 5
specifically to fatigue pre-cracked specimens that exhibit low constraint (crack-size-to-thickness and un-cracked ligament-to-
thickness ratios greater than or equal to 4) and that are tested under slowly increasing remote applied displacement. The test
specimens are the compact, C(T), and middle-crack-tension, M(T), specimens. The fracture resistance determined in accordance
with this standard is measured as ψ (critical CTOA value) and/or δ (critical COD resistance curve) as a function of crack
c 5
extension. Both fracture resistance parameters are characterized using either a single-specimen or multiple-specimen procedures.
These fracture quantities are determined under the opening mode (Mode I) of loading. Influences of environment and rapid loading
rates are not covered in this standard, but the user must be aware of the effects that the loading rate and laboratory environment
may have on the fracture behavior of the material.
1.2 Materials that are evaluated by this standard are not limited by strength, thickness, or toughness, if the crack-size-to-
thickness (a/B) ratio and the ligament-to-thickness (b/B) ratio are greater than or equal to 4, which ensures relatively low and
similar global crack-front constraint for both the C(T) and M(T) specimens (2, 3).
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
E4 Practices for Force Verification of Testing Machines
E8/E8M Test Methods for Tension Testing of Metallic Materials
E399 Test Method for Linear-Elastic Plane-Strain Fracture Toughness K of Metallic Materials
Ic
E561 Test Method forK Curve Determination
R
E647 Test Method for Measurement of Fatigue Crack Growth Rates
E1290 Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement (Withdrawn 2013)
E1820 Test Method for Measurement of Fracture Toughness
E1823 Terminology Relating to Fatigue and Fracture Testing
E2309 Practices for Verification of Displacement Measuring Systems and Devices Used in Material Testing Machines
This test method is under the jurisdiction of ASTM Committee E08 on Fatigue and Fracture and is the direct responsibility of Subcommittee E08.07 on Fracture
Mechanics.
Current edition approved July 1, 2012Nov. 1, 2018. Published January 2013December 2018. Originally approved in 2006. Last previous edition approved in 20062012
ε1
as E2472–06–12 . DOI: 10.1520/E2472-12E01.10.1520/E2472-12R18.
The boldface numbers in parentheses refer to the list of references at the end of this standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2472 − 12 (2018)
2.2 ISO Standards:
ISO 22889:2007 Metallic Materials—Method of Test for the Determination of Resistance to Stable Crack Extension Using
Specimens of Low Constraint
ISO 12135 Metallic Materials—Unified Method of Test for the Determination of Quasistatic Fracture Toughness
3. Terminology
3.1 Terminology E1823 is applicable to this test standard.
3.2 Definitions:
3.2.1 crack extension, Δa [L],n—an increase in crack size.
3.2.1.1 Discussion—
It should be noted that in thin-sheet and thick-plate materials under low constraint conditions, the crack extension observed on the
surface of the specimen may be significantly less than that in the interior of the specimen due to the effects of crack tunneling.
This must be considered if direct optical techniques are used to monitor and measure free-surface crack extension. Indirect crack
extension measurement techniques such as unloading compliance and electric-potential drop method may be used in place of (or
to complement) the direct optical techniques to provide a measure of average crack extension. (See Test Method E647 for
compliance methods for C(T) and M(T) specimens; and ISO 12135 and Test Method E647 for electric potential-drop methods for
C(T) specimens.)
3.2.2 crack size, a [L], n—principal linear dimension used in the calculation of fracture mechanics parameters for through
thickness cracks.
3.2.2.1 Discussion—
A measure of the crack size after the fatigue pre-cracking stage is denoted as the original crack size, a . The value for a may be
o o
obtained using surface measurement, unloading compliance, electric-potential drop or other methods where validation procedures
for the measurements are available.
3.2.3 crack-tip-opening angle (CTOA), ψ [deg],n—relative angle of crack surfaces resulting from the total deformation (elastic
–1
plus plastic) measured (or calculated) at 1-mm behind the current crack tip as the crack stably tears, where ψ = 2 tan (δ /2).
3.2.4 critical crack-tip-opening angle (CTOA ),ψ [deg],n—steady-state relative angle of crack surfaces resulting from the total
c c
deformation (elastic plus plastic) measured (or calculated) at 1-mm behind the current crack tip as the crack stably tears, where
–1
ψ = 2 tan (δ /2).
c 1c
3.2.4.1 Discussion—
Critical CTOA value tends to approach a constant, steady-state value after a small amount of crack extension (associated with crack
tunneling and transition from flat-to-slant crack extension).
3.2.5 crack-opening displacement, (COD) δ [L]—force-induced separation vector between two points. The direction of the
vector is normal to the crack plane (normal to the facing surfaces of a crack) at a specified gage length. In this standard, δ is
measured at the fatigue precrack tip location over a gage length of 5-mm as the crack stably tears.
3.2.6 crack-tip-opening displacement (CTOD), δ [L],n—relative displacement of crack surfaces resulting from the total
deformation (elastic plus plastic) measured (or calculated) at 1- mm behind the current crack tip as the crack stably tears.
3.2.7 critical crack-tip-opening displacement (CTOD ), δ [L], n—steady-state relative displacement of crack surfaces
c 1c
resulting from the total deformation (elastic plus plastic) measured (or calculated) at 1-mm behind the current crack tip as the crack
stably tears.
3.2.8 crack extension resistance curve (R curve), n—variation of δ with crack extension, Δa.
-2
3.2.9 effective yield strength, σ [FL ],n—an assumed value of uniaxial yield strength that represents the influence of plastic
Y
yielding upon fracture test parameters.
3.2.9.1 Discussion—
Effective yield strength is calculated as the average of the 0.2 % offset yield strength σ , and the ultimate tensile strength, σ as
YS TS
follows:
Available from International Organization for Standardization (ISO), 1, ch. de la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://www.iso.ch.
E2472 − 12 (2018)
σ 5 σ 1σ /2 (1)
~ !
Y YS TS
NOTE 1—The yield and ultimate tensile strength are determined from Test Methods E8/E8M.
3.2.9.2 Discussion—
In estimating σ , influences of testing conditions, such as loading rate and temperature, should be considered.
Y
3.2.10 final crack size, a [L],n—crack extension at end of stable tearing (a = a + Δa ).
f f o f
3.2.11 final remaining ligament, b [L],n—distance from the tip of the final crack size to the back edge of the specimen, that is
f
b = W – a .
f f
3.2.12 force, P [F], n—force applied to a test specimen or to a component.
3.2.13 minimum crack extension, Δa [L],n—crack extension beyond which ψ is nearly constant.
min c
3.2.14 maximum crack extension, Δa [L],n—crack extension limit for ψ and δ controlled crack extension.
max c 5
3.2.15 maximum fatigue force, P [F] , n—maximum fatigue force applied to specimen during pre-cracking stage.
f
-2
3.2.16 modulus of elasticity, E [FL ],n—the ratio of stress to corresponding strain below the proportional limit.
3.2.17 notch size, a [L],n—distance from a reference plane to the front of the machined notch, such as the force line in the
n
compact specimen to the notch front or from the center line in the middle-crack-tension specimen to the notch front.
3.2.18 original crack size, a [L],n—the physical crack size at the start of testing.
o
3.2.19 original ligament, b [L],n—distance from the original crack front to the back edge of the specimen, that is b = W – a .
o o o
3.2.20 remaining ligament, b [L], n—distance from the physical crack front to the back edge of the specimen, that is b = W –
a.
3.2.21 specimen thickness, B [L], n—distance between the parallel sides of a test specimen or component. Side grooving is not
allowed.
3.2.22 specimen width, W [L], n—distance from a reference position (for example, the force line of a compact specimen or
center line in the middle-crack-tension specimen) to the rear surface of the specimen. (Note that the total width of the M(T)
specimen is defined as 2W.)
4. Summary of Test Method
4.1 The objective of this standard is to induce stable crack extension in a fatigue pre-cracked, low-constraint test specimen while
monitoring and measuring the COD at the original fatigue pre-crack-tip location (4, 5) or the CTOA (or CTOD) at 1-mm behind
the stably tearing crack tip (6, 7), or both. The resistance curve associated with the δ measurements and the critical limiting value
of the CTOA measurements are used to characterize the corresponding resistance to stable crack extension. In contrast, the CTOD
values determined from Test Method E1290 (high-constraint bend specimens) are values at one or more crack extension events,
such as the CTOD at the onset of brittle crack extension with no significant stable crack extension.
4.2 Either of the fatigue pre-cracked, low-constraint test specimen configurations specified in this standard [C(T) or M(T)] may
be used to measure or calculate either of the fracture resistance parameters considered. The fracture resistance parameters, CTOA
(or CTOD) and δ , may be characterized using either a single-specimen or multiple-specimen procedure. In all cases, tests are
performed by applying slowly increasing displacements to the test specimen and measuring the forces, displacements, crack
extension and angles realized during the test. The forces, displacements and angles are then used in conjunction with certain
pre-test and post-test specimen measurements to determine the material’s resistance to stable crack extension.
4.3 Four procedures for measuring crack extension are: surface visual, unloading compliance, electrical potential, and multiple
specimens.
4.4 Two techniques are presented for measuring CTOA: optical microscopy (OM) (8) and digital image correlation (DIC) (9).
4.5 Three techniques are presented for measuring COD: δ clip gage (5), optical microscopy (OM) (8), and digital image
correlation (DIC) (9).
4.6 Data generated following the procedures and guidelines contained in this standard are labeled qualified data and are
insensitive to in-plane dimensions and specimen type (tension or bending forces), but are dependent upon sheet or plate thickness.
5. Significance and Use
5.1 This test method characterizes a metallic material’s resistance to stable crack extension in terms of crack-tip-opening angle
(CTOA), ψ and/or crack-opening displacement (COD), δ under the laboratory or application environment of interest. This method
applies specifically to fatigue pre-cracked specimens that exhibit low constraint and that are tested under slowly increasing
displacement.
E2472 − 12 (2018)
5.2 When conducting fracture tests, the user must consider the influence that the loading rate and laboratory environment may
have on the fracture parameters. The user should perform a literature review to determine if loading rate effects have been observed
previously in the material at the specific temperature and environment being tested. The user should document specific information
pertaining to their material, loading rates, temperature, and environment (relative humidity) for each test.
5.3 The results of this characterization include the determination of a critical, lower-limiting value, of CTOA (ψ ) or a resistance
c
curve of δ , a measure of crack-opening displacement against crack extension, or both.
5.4 The test specimens are the compact, C(T), and middle-crack-tension, M(T), specimens.
5.5 Materials that can be evaluated by this standard are not limited by strength, thickness, or toughness, if the crack-size-to-
thickness (a/B) ratio or ligament-to-thickness (b/B) ratio are equal to or greater than 4, which ensures relatively low and similar
global crack-front constraint for both the C(T) and M(T) specimens (2, 3).
5.6 The values of CTOA and COD (δ ) determined by this test method may serve the following purposes:
5.6.1 In research
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