ASTM E2472-12(2018)e3
(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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Standards Content (Sample)
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.
´3
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. 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—Sections 7.4.1, 7.4.2, 9.3.1.4, A1.1.3, A2.1.3, and Fig. 7 were editorially corrected in May 2020.
ε NOTE—Section A2.1.3 was editorially corrected in June 2023.
ε NOTE—Section 3.2.21 was editorially corrected in April 2024.
1. Scope 1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This standard covers the determination of the resistance
responsibility of the user of this standard to establish appro-
to stable crack extension in metallic materials in terms of the
priate safety, health, and environmental practices and deter-
critical crack-tip-opening angle (CTOA), ψ and/or the crack-
c
2 mine the applicability of regulatory limitations prior to use.
opening displacement (COD), δ resistance curve (1). This
1.5 This international standard was developed in accor-
method applies specifically to fatigue pre-cracked specimens
dance with internationally recognized principles on standard-
that exhibit low constraint (crack-size-to-thickness and un-
ization established in the Decision on Principles for the
cracked ligament-to-thickness ratios greater than or equal to 4)
Development of International Standards, Guides and Recom-
and that are tested under slowly increasing remote applied
mendations issued by the World Trade Organization Technical
displacement. The test specimens are the compact, C(T), and
Barriers to Trade (TBT) Committee.
middle-crack-tension, M(T), specimens. The fracture resis-
tance determined in accordance with this standard is measured
2. Referenced Documents
as ψ (critical CTOA value) and/or δ (critical COD resistance
c 5
2.1 ASTM Standards:
curve) as a function of crack extension. Both fracture resis-
E4 Practices for Force Calibration and Verification of Test-
tance parameters are characterized using either a single-
ing Machines
specimen or multiple-specimen procedures. These fracture
E8/E8M Test Methods for Tension Testing of Metallic Ma-
quantities are determined under the opening mode (Mode I) of
terials
loading. Influences of environment and rapid loading rates are
not covered in this standard, but the user must be aware of the E399 Test Method for Linear-Elastic Plane-Strain Fracture
Toughness of Metallic Materials
effects that the loading rate and laboratory environment may
have on the fracture behavior of the material. E561 Test Method for K Curve Determination
R
E647 Test Method for Measurement of Fatigue Crack
1.2 Materials that are evaluated by this standard are not
Growth Rates
limited by strength, thickness, or toughness, if the crack-size-
E1290 Test Method for Crack-Tip Opening Displacement
to-thickness (a/B) ratio and the ligament-to-thickness (b/B)
(CTOD) Fracture Toughness Measurement (Withdrawn
ratio are greater than or equal to 4, which ensures relatively
2013)
low and similar global crack-front constraint for both the C(T)
E1820 Test Method for Measurement of Fracture Toughness
and M(T) specimens (2, 3).
E1823 Terminology Relating to Fatigue and Fracture Testing
1.3 The values stated in SI units are to be regarded as
E2309 Practices for Verification of Displacement Measuring
standard. No other units of measurement are included in this
Systems and Devices Used in Material Testing Machines
standard.
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. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2018. Published December 2018. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ε1
approved in 2006. Last previous edition approved in 2012 as E2472–12 . DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/E2472-12R18E03. the ASTM website.
2 4
The boldface numbers in parentheses refer to the list of references at the end of The last approved version of this historical standard is referenced on
this standard. www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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E2472 − 12 (2018)
2.2 ISO Standards: 3.2.6 crack-tip-opening displacement (CTOD), δ [L],
ISO 22889:2007 Metallic Materials—Method of Test for the n—relative displacement of crack surfaces resulting from the
Determination of Resistance to Stable Crack Extension total deformation (elastic plus plastic) measured (or calculated)
Using Specimens of Low Constraint at 1- mm behind the current crack tip as the crack stably tears.
ISO 12135 Metallic Materials—Unified Method of Test for
3.2.7 critical crack-tip-opening displacement (CTOD ), δ
c 1c
the Determination of Quasistatic Fracture Toughness
[L], n—steady-state relative displacement of crack surfaces
resulting from the total deformation (elastic plus plastic)
3. Terminology
measured (or calculated) at 1-mm behind the current crack tip
3.1 Terminology E1823 is applicable to this test standard.
as the crack stably tears.
3.2 Definitions:
3.2.8 crack extension resistance curve (R curve),
3.2.1 crack extension, Δa [L], n—an increase in crack size.
n—variation of δ with crack extension, Δa.
3.2.1.1 Discussion—It should be noted that in thin-sheet and
-2
3.2.9 effective yield strength, σ [FL ], n—an assumed
Y
thick-plate materials under low constraint conditions, the crack
value of uniaxial yield strength that represents the influence of
extension observed on the surface of the specimen may be
plastic yielding upon fracture test parameters.
significantly less than that in the interior of the specimen due
3.2.9.1 Discussion—Effective yield strength is calculated as
to the effects of crack tunneling. This must be considered if
the average of the 0.2 % offset yield strength σ , and the
direct optical techniques are used to monitor and measure YS
ultimate tensile strength, σ as follows:
free-surface crack extension. Indirect crack extension measure-
TS
ment techniques such as unloading compliance and electric-
σ 5 ~σ 1σ !/2 (1)
Y YS TS
potential drop method may be used in place of (or to comple-
NOTE 1—The yield and ultimate tensile strength are determined from
ment) the direct optical techniques to provide a measure of Test Methods E8/E8M.
average crack extension. (See Test Method E647 for compli-
3.2.9.2 Discussion—In estimating σ , influences of testing
Y
ance methods for C(T) and M(T) specimens; and ISO 12135
conditions, such as loading rate and temperature, should be
and Test Method E647 for electric potential-drop methods for
considered.
C(T) specimens.)
3.2.10 final crack size, a [L], n—crack extension at end of
f
3.2.2 crack size, a [L], n—principal linear dimension used
stable tearing (a = a + Δa ).
f o f
in the calculation of fracture mechanics parameters for through
3.2.11 final remaining ligament, b [L], n—distance from
thickness cracks.
f
the tip of the final crack size to the back edge of the specimen,
3.2.2.1 Discussion—A measure of the crack size after the
that is b = W – a .
fatigue pre-cracking stage is denoted as the original crack size,
f f
a . The value for a may be obtained using surface
o o
3.2.12 force, P [F], n—force applied to a test specimen or to
measurement, unloading compliance, electric-potential drop or
a component.
other methods where validation procedures for the measure-
3.2.13 minimum crack extension, Δa [L], n—crack exten-
min
ments are available.
sion beyond which ψ is nearly constant.
c
3.2.3 crack-tip-opening angle (CTOA), ψ [deg], n—relative
3.2.14 maximum crack extension, Δa [L], n—crack ex-
max
angle of crack surfaces resulting from the total deformation
tension limit for ψ and δ controlled crack extension.
c 5
(elastic plus plastic) measured (or calculated) at 1-mm behind
–1
the current crack tip as the crack stably tears, where ψ = 2 tan
3.2.15 maximum fatigue force, P [F] , n—maximum fatigue
f
(δ /2). force applied to specimen during pre-cracking stage.
-2
3.2.4 critical crack-tip-opening angle (CTOA ), ψ [deg],
3.2.16 modulus of elasticity, E [FL ], n—the ratio of stress
c c
n—steady-state relative angle of crack surfaces resulting from
to corresponding strain below the proportional limit.
the total deformation (elastic plus plastic) measured (or calcu-
3.2.17 notch size, a [L], n—distance from a reference plane
n
lated) at 1-mm behind the current crack tip as the crack stably
to the front of the machined notch, such as the force line in the
–1
tears, where ψ = 2 tan (δ /2).
c 1c
compact specimen to the notch front or from the center line in
3.2.4.1 Discussion—Critical CTOA value tends to approach
the middle-crack-tension specimen to the notch front.
a constant, steady-state value after a small amount of crack
3.2.18 original crack size, a [L], n—the physical crack size
extension (associated with crack tunneling and transition from o
at the start of testing.
flat-to-slant crack extension).
3.2.19 original ligament, b [L], n—distance from the origi-
3.2.5 crack-opening displacement, (COD) δ [L]—force-
o
nal crack front to the back edge of the specimen, that is b = W
induced separation vector between two points. The direction of
o
– a .
the vector is normal to the crack plane (normal to the facing o
surfaces of a crack) at a specified gage length. In this standard,
3.2.20 remaining ligament, b [L], n—distance from the
δ is measured at the fatigue precrack tip location over a gage
5 physical crack front to the back edge of the specimen, that is b
length of 5-mm as the crack stably tears.
= W – a.
3.2.21 specimen thickness, B [L], n—the distance between
Available from International Organization for Standardization (ISO), 1, ch. de
the parallel sides of a test specimen as depicted in Fig. 1, Fig.
la Voie-Creuse, Case postale 56, CH-1211, Geneva 20, Switzerland, http://
www.iso.ch. 2, and Fig. 3.
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E2472 − 12 (2018)
FIG. 1 Clevis for Compact, C(T), Specimen Testing
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E2472 − 12 (2018)
FIG. 2 Compact, C(T), Specimen with Anti-Buckling Guides
3.2.21.1 Discussion—for side-grooved specimens, the net terized using either a single-specimen or multiple-specimen
thickness, B , is the distance between the roots of the side- procedure. In all cases, tests are performed by applying slowly
N
grooves. increasing displacements to the test specimen and measuring
the forces, displacements, crack extension and angles realized
3.2.22 specimen width, W [L], n—distance from a reference
during the test. The forces, displacements and angles are then
position (for example, the force line of a compact specimen or
used in conjunction with certain pre-test and post-test specimen
center line in the middle-crack-tension specimen) to the rear
measurements to determine the material’s resistance to stable
surface of the specimen. (Note that the total width of the M(T)
crack extension.
specimen is defined as 2W.)
4.3 Four procedures for measuring crack extension are:
4. Summary of Test Method
surface visual, unloading compliance, electrical potential, and
4.1 The objective of this standard is to induce stable crack multiple specimens.
extension in a fatigue pre-cracked, low-constraint test speci-
4.4 Two techniques are presented for measuring CTOA:
men while monitoring and measuring the COD at the original
optical microscopy (OM) (8) and digital image correlation
fatigue pre-crack-tip location (4, 5) or the CTOA (or CTOD) at
(DIC) (9).
1-mm behind the stably tearing crack tip (6, 7), or both. The
4.5 Three techniques are presented for measuring COD: δ
resistance curve associated with the δ measurements and the
clip gage (5), optical microscopy (OM) (8), and digital image
critical limiting value of the CTOA measurements are used to
correlation (DIC) (9).
characterize the corresponding resistance to stable crack ex-
tension. In contrast, the CTOD values determined from Test 4.6 Data generated following the procedures and guidelines
Method E1290 (high-constraint bend specimens) are values at
contained in this standard are labeled qualified data and are
one or more crack extension events, such as the CTOD at the insensitive to in-plane dimensions and specimen type (tension
onset of brittle crack extension with no significant stable crack
or bending forces), but are dependent upon sheet or plate
extension. thickness.
4.2 Either of the fatigue pre-cracked, low-constraint test
5. Significance and Use
specimen configurations specified in this standard [C(T) or
M(T)] may be used to measure or calculate either of the 5.1 This test method characterizes a metallic material’s
fracture resistance parameters considered. The fracture resis- resistance to stable crack extension in terms of crack-tip-
tance parameters, CTOA (or CTOD) and δ , may be charac- opening angle (CTOA), ψ and/or crack-opening displacement
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E2472 − 12 (2018)
FIG. 3 Middle-Crack-Tension, M(T), Specimen with Anti-Buckling Guides
(COD), δ under the laboratory or application environment of 5.6 The values of CTOA and COD (δ ) determined by this
5 5
interest. This method applies specifically to fatigue pre-cracked test method may serve the following purposes:
specimens that exhibit low constraint and that are tested under 5.6.1 In research and development, CTOA (ψ ) or COD
c
slowly increasing displacement.
(δ ), or both, testing can show the effects of certain parameters
on the resistance to stable crack extension of metallic materials
5.2 When conducting fracture tests, the user must consider
significant to service performance. These parameters include,
the influence that the loading rate and laboratory environment
but are not limited to, material thickness, material composition,
may have on the fracture parameters. The user should perform
thermo-mechanical processing, welding, and thermal stress
a literature review to determine if loading rate effects have
relief.
been observed previously in the material at the specific
5.6.2 For specifications of acceptance
...
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