ASTM E2472-12(2018)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´1
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.
1. Scope responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
1.1 This standard covers the determination of the resistance
mine the applicability of regulatory limitations prior to use.
to stable crack extension in metallic materials in terms of the
1.5 This international standard was developed in accor-
critical crack-tip-opening angle (CTOA), ψ and/or the crack-
c
2 dance with internationally recognized principles on standard-
opening displacement (COD), δ resistance curve (1). This
ization established in the Decision on Principles for the
method applies specifically to fatigue pre-cracked specimens
Development of International Standards, Guides and Recom-
that exhibit low constraint (crack-size-to-thickness and un-
mendations issued by the World Trade Organization Technical
cracked ligament-to-thickness ratios greater than or equal to 4)
Barriers to Trade (TBT) Committee.
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-
tance determined in accordance with this standard is measured 2.1 ASTM Standards:
as ψ (critical CTOA value) and/or δ (critical COD resistance E4 Practices for Force Verification of Testing Machines
c 5
curve) as a function of crack extension. Both fracture resis- E8/E8M Test Methods for Tension Testing of Metallic Ma-
tance parameters are characterized using either a single- terials
specimen or multiple-specimen procedures. These fracture E399 Test Method for Linear-Elastic Plane-Strain Fracture
quantities are determined under the opening mode (Mode I) of Toughness of Metallic Materials
loading. Influences of environment and rapid loading rates are E561 Test Method forK Curve Determination
R
not covered in this standard, but the user must be aware of the E647 Test Method for Measurement of Fatigue Crack
effects that the loading rate and laboratory environment may Growth Rates
have on the fracture behavior of the material. E1290 Test Method for Crack-Tip Opening Displacement
(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-
E1820 Test Method for Measurement of Fracture Toughness
to-thickness (a/B) ratio and the ligament-to-thickness (b/B)
E1823 Terminology Relating to Fatigue and Fracture Testing
ratio are greater than or equal to 4, which ensures relatively
E2309 Practices for Verification 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
ISO 22889:2007 Metallic Materials—Method of Test for the
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
safety concerns, if any, associated with its use. It is the
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
This test method is under the jurisdiction of ASTM 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/E2472-12R18E01. Available from International Organization for Standardization (ISO), 1, ch. de
The boldface numbers in parentheses refer to the list of references at the end of 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
ϵ1
E2472 − 12 (2018)
ISO 12135 Metallic Materials—Unified Method of Test for measured (or calculated) at 1-mm behind the current crack tip
the Determination of Quasistatic Fracture Toughness as the crack stably tears.
3.2.8 crack extension resistance curve (R curve),
3. Terminology
n—variation of δ with crack extension, Δa.
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, Δa [L], n—an increase in crack size.
plastic yielding upon fracture test parameters.
3.2.1.1 Discussion—It should be noted that in thin-sheet and
3.2.9.1 Discussion—Effective yield strength is calculated as
thick-plate materials under low constraint conditions, the crack
the average of the 0.2 % offset yield strength σ , and the
extension observed on the surface of the specimen may be
YS
ultimate tensile strength, σ as follows:
significantly less than that in the interior of the specimen due TS
to the effects of crack tunneling. This must be considered if
σ 5 σ 1σ /2 (1)
~ !
Y YS TS
direct optical techniques are used to monitor and measure
NOTE 1—The yield and ultimate tensile strength are determined from
free-surface crack extension. Indirect crack extension measure-
Test Methods E8/E8M.
ment techniques such as unloading compliance and electric-
3.2.9.2 Discussion—In estimating σ , influences of testing
Y
potential drop method may be used in place of (or to comple-
conditions, such as loading rate and temperature, should be
ment) the direct optical techniques to provide a measure of
considered.
average crack extension. (See Test Method E647 for compli-
ance methods for C(T) and M(T) specimens; and ISO 12135
3.2.10 final crack size, a [L], n—crack extension at end of
f
and Test Method E647 for electric potential-drop methods for
stable tearing (a = a + Δa ).
f o f
C(T) specimens.)
3.2.11 final remaining ligament, b [L], n—distance from
f
3.2.2 crack size, a [L], n—principal linear dimension used
the tip of the final crack size to the back edge of the specimen,
in the calculation of fracture mechanics parameters for through
that is b = W – a .
f f
thickness cracks.
3.2.12 force, P [F], n—force applied to a test specimen or to
3.2.2.1 Discussion—A measure of the crack size after the
a component.
fatigue pre-cracking stage is denoted as the original crack size,
a . The value for a may be obtained using surface
o o 3.2.13 minimum crack extension, Δa [L], n—crack exten-
min
measurement, unloading compliance, electric-potential drop or
sion beyond which ψ is nearly constant.
c
other methods where validation procedures for the measure-
3.2.14 maximum crack extension, Δa [L], n—crack ex-
max
ments are available.
tension limit for ψ and δ controlled crack extension.
c 5
3.2.3 crack-tip-opening angle (CTOA), ψ [deg], n—relative
3.2.15 maximum fatigue force, P [F] , n—maximum fatigue
angle of crack surfaces resulting from the total deformation
f
force applied to specimen during pre-cracking stage.
(elastic plus plastic) measured (or calculated) at 1-mm behind
–1
-2
the current crack tip as the crack stably tears, where ψ = 2 tan
3.2.16 modulus of elasticity, E [FL ], n—the ratio of stress
(δ /2).
to corresponding strain below the proportional limit.
3.2.4 critical crack-tip-opening angle (CTOA ), ψ [deg],
c c
3.2.17 notch size, a [L], n—distance from a reference plane
n
n—steady-state relative angle of crack surfaces resulting from
to the front of the machined notch, such as the force line in the
the total deformation (elastic plus plastic) measured (or calcu-
compact specimen to the notch front or from the center line in
lated) at 1-mm behind the current crack tip as the crack stably
the middle-crack-tension specimen to the notch front.
–1
tears, where ψ = 2 tan (δ /2).
c 1c
3.2.4.1 Discussion—Critical CTOA value tends to approach 3.2.18 original crack size, a [L], n—the physical crack size
o
at the start of testing.
a constant, steady-state value after a small amount of crack
extension (associated with crack tunneling and transition from
3.2.19 original ligament, b [L], n—distance from the origi-
o
flat-to-slant crack extension).
nal crack front to the back edge of the specimen, that is b = W
o
3.2.5 crack-opening displacement, (COD) δ [L]—force-
5 – a .
o
induced separation vector between two points. The direction of
3.2.20 remaining ligament, b [L], n—distance from the
the vector is normal to the crack plane (normal to the facing
physical crack front to the back edge of the specimen, that is b
surfaces of a crack) at a specified gage length. In this standard,
= W – a.
δ is measured at the fatigue precrack tip location over a gage
length of 5-mm as the crack stably tears.
3.2.21 specimen thickness, B [L], n—distance between the
parallel sides of a test specimen or component. Side grooving
3.2.6 crack-tip-opening displacement (CTOD), δ [L],
is not allowed.
n—relative displacement of crack surfaces resulting from the
total deformation (elastic plus plastic) measured (or calculated)
3.2.22 specimen width, W [L], n—distance from a reference
at 1- mm behind the current crack tip as the crack stably tears.
position (for example, the force line of a compact specimen or
3.2.7 critical crack-tip-opening displacement (CTOD ), δ center line in the middle-crack-tension specimen) to the rear
c 1c
[L], n—steady-state relative displacement of crack surfaces surface of the specimen. (Note that the total width of the M(T)
resulting from the total deformation (elastic plus plastic) specimen is defined as 2W.)
ϵ1
E2472 − 12 (2018)
4. Summary of Test Method document specific information pertaining to their material,
loading rates, temperature, and environment (relative humid-
4.1 The objective of this standard is to induce stable crack
ity) for each test.
extension in a fatigue pre-cracked, low-constraint test speci-
men while monitoring and measuring the COD at the original 5.3 The results of this characterization include the determi-
fatigue pre-crack-tip location (4, 5) or the CTOA (or CTOD) at nation of a critical, lower-limiting value, of CTOA (ψ ) or a
c
1-mm behind the stably tearing crack tip (6, 7), or both. The resistance curve of δ , a measure of crack-opening displace-
resistance curve associated with the δ measurements and the ment against crack extension, or both.
critical limiting value of the CTOA measurements are used to
5.4 The test specimens are the compact, C(T), and middle-
characterize the corresponding resistance to stable crack ex-
crack-tension, M(T), specimens.
tension. In contrast, the CTOD values determined from Test
5.5 Materials that can be evaluated by this standard are not
Method E1290 (high-constraint bend specimens) are values at
limited by strength, thickness, or toughness, if the crack-size-
one or more crack extension events, such as the CTOD at the
to-thickness (a/B) ratio or ligament-to-thickness (b/B) ratio are
onset of brittle crack extension with no significant stable crack
equal to or greater than 4, which ensures relatively low and
extension.
similar global crack-front constraint for both the C(T) and
4.2 Either of the fatigue pre-cracked, low-constraint test
M(T) specimens (2, 3).
specimen configurations specified in this standard [C(T) or
5.6 The values of CTOA and COD (δ ) determined by this
M(T)] may be used to measure or calculate either of the
test method may serve the following purposes:
fracture resistance parameters considered. The fracture resis-
5.6.1 In research and development, CTOA (ψ ) or COD
c
tance parameters, CTOA (or CTOD) and δ , may be charac-
(δ ), or both, testing can show the effects of certain parameters
terized using either a single-specimen or multiple-specimen
on the resistance to stable crack extension of metallic materials
procedure. In all cases, tests are performed by applying slowly
significant to service performance. These parameters include,
increasing displacements to the test specimen and measuring
but are not limited to, material thickness, material composition,
the forces, displacements, crack extension and angles realized
thermo-mechanical processing, welding, and thermal stress
during the test. The forces, displacements and angles are then
relief.
used in conjunction with certain pre-test and post-test specimen
5.6.2 For specifications of acceptance and manufacturing
measurements to determine the material’s resistance to stable
quality control of base materials.
crack extension.
5.6.3 For inspection and flaw assessment criteria, when used
4.3 Four procedures for measuring crack extension are:
in conjunction with fracture mechanics analyses. Awareness of
surface visual, unloading compliance, electrical potential, and
differences that may exist between laboratory test and field
multiple specimens.
conditions is required to make proper flaw assessment.
4.4 Two techniques are presented for measuring CTOA: 5.6.4 The critical CTOA (ψ ) has been used with the
c
optical microscopy (OM) (8) and digital image correlation elastic-plastic finite-element method to accurately predict
(DIC) (9). structural response and force carrying capacity of simple and
complex cracked structural components, see Appendix X1.
4.5 Three techniques are presented for measuring COD: δ
5.6.5 The δ parameter has been related to the J-integral by
clip gage (5), optical microscopy (OM) (8), and digital image
means of the Engineering Treatment Model (ETM) (10) and
correlation (DIC) (9).
provides an engineering approach to predict the structural
4.6 Data generated following the procedures and guidelines
response and force carrying capacity of cracked structural
contained in this standard are labeled qualified data and are
components.
insensitive to in-plane dimensions a
...