ASTM E2472-06
(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
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 (CTOAc), c and/or the crack-opening displacement (COD), 5 resistance curve (). This method applies specifically to fatigue pre-cracked specimens that exhibit low constraint (crack-length-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 recommended specimens are the compact-tension, C(T), and middle-crack-tension, M(T), specimens. The fracture resistance determined in accordance with this standard is measured as c (critical CTOA value) and/or 5 (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-length-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 (, ).
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses (English) are for information purposes only.
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 and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: E2472 – 06
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.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This standard covers the determination of the resistance
to stable crack extension in metallic materials in terms of the E4 Practices for Force Verification of Testing Machines
critical crack-tip-opening angle (CTOA ), c and/or the crack- E8 Test Methods for Tension Testing of Metallic Materials
c c
opening displacement (COD), d resistance curve (1). This E399 Test Method for Linear-Elastic Plane-Strain Fracture
method applies specifically to fatigue pre-cracked specimens Toughness K of Metallic Materials
Ic
that exhibit low constraint (crack-length-to-thickness and un- E561 Test Method for K-R Curve Determination
cracked ligament-to-thickness ratios greater than or equal to 4) E647 Test Method for Measurement of Fatigue Crack
and that are tested under slowly increasing remote applied Growth Rates
displacement. The recommended specimens are the compact- E1290 Test Method for Crack-Tip Opening Displacement
tension, C(T), and middle-crack-tension, M(T), specimens. (CTOD) Fracture Toughness Measurement
The fracture resistance determined in accordance with this E1820 Test Method for Measurement of Fracture Tough-
standard is measured as c (critical CTOA value) and/or ness
c
d (critical COD resistance curve) as a function of crack E1823 Terminology Relating to Fatigue and Fracture Test-
extension. Both fracture resistance parameters are character- ing
ized using either a single-specimen or multiple-specimen E2309 Practices for Verification of Displacement Measur-
procedures. These fracture quantities are determined under the ing Systems and Devices Used in Material Testing Ma-
opening mode (Mode I) of loading. Influences of environment chines
and rapid loading rates are not covered in this standard, but the 2.2 ISO Standards:
user must be aware of the effects that the loading rate and ISO/TC164/SC4-N413.4 Metallic Materials—Method of
laboratory environment may have on the fracture behavior of Test for the Determination of Resistance to Stable Crack
the material. Extension Using Specimens of Low Constraint
1.2 Materials that are evaluated by this standard are not ISO 12135 Metallic Materials—Unified Method of Test for
limited by strength, thickness, or toughness, if the crack- the Determination of Quasistatic Fracture Toughness
length-to-thickness (a/B) ratio and the ligament-to-thickness
3. Terminology
(b/B) ratio are greater than or equal to 4, which ensures
relativelylowandsimilarglobalcrack-frontconstraintforboth 3.1 Terminology E1823 is applicable to this test standard.
3.2 Definitions:
the C(T) and M(T) specimens (2, 3).
1.3 The values stated in SI units are to be regarded as the 3.2.1 crack extension, Da [L], n—an increase in crack
length.
standard. The values given in parentheses (English) are for
information purposes only. 3.2.1.1 Discussion—It should be noted that in thin-sheet
and thick-plate materials under low constraint conditions, the
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the crack extension observed on the surface of the specimen may
be significantly less than that in the interior of the specimen
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- due to the effects of crack tunneling. This must be considered
if direct optical techniques are used to monitor and measure
bility of regulatory limitations prior to use.
This test method is under the jurisdiction ofASTM Committee E08 on Fatigue
and Fracture and is the direct responsibility of Subcommittee E08.07 on Fracture For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Mechanics. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved June 15, 2006. PublishedAugust 2006. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E2472-06. the ASTM website.
2 4
The boldface numbers in parentheses refer to the list of references at the end of Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
this standard. 4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2472 – 06
free-surfacecrackextension.Indirectcrackextensionmeasure- 3.2.11 final remaining ligament, b [L], n—distance from
f
ment techniques such as unloading compliance and electric- the tip of the final crack length to the back edge of the
potential drop method may be used in place of (or to augment) specimen, that is b = W – a.
f f
the direct optical techniques to provide a measure of average 3.2.12 force, P [F], n—force applied to specimen.
crack extension. (See Test Method E647 for compliance
3.2.13 minimum crack extension, Da [L], n—crack ex-
min
methods for C(T) and M(T) specimens; and ISO 12135 for
tension beyond which c is nearly constant.
c
electric potential-drop methods for C(T) specimens.)
3.2.14 maximum crack extension, Da [L], n—crack ex-
max
3.2.2 crack length, a [L], n—a linear measure of a principal
tension limit for c and d controlled crack extension.
c 5
planar dimension of a crack. This measure is commonly used
3.2.15 maximum fatigue force, P [F], n—maximum fatigue
f
in the calculation of quantities descriptive of the stress and
force applied to specimen during pre-cracking stage.
-2
displacement fields of cracked specimens.
3.2.16 modulus of elasticity, E [FL ], n—Young’s modulus
3.2.2.1 Discussion—Ameasure of the crack length after the
of elasticity.
fatigue pre-cracking stage is denoted as the original crack
3.2.17 notch length, a [L], n—the distance from a refer-
n
length, a . The value for a may be obtained using surface
ence plane to the tip of the machined notch, such as the load
o o
measurement, unloading compliance, electric-potential drop or
line in the compact-tension specimen to the notch tip or from
other methods where validation procedures for the measure-
the center line in the middle-crack tension specimen to the
ments are available.
notch tip.
3.2.3 crack-tip-opening angle (CTOA), c [deg], n—relative
3.2.18 original crack length, a [L], n—the physical crack
o
angle of the crack surfaces measured (or calculated) at 1-mm
length at the start of testing.
-1
behind current crack tip, where c = 2 tan (CTOD/2).
3.2.19 original remaining ligament, b [L], n—distance
o
3.2.4 critical crack-tip-opening angle (CTOA ), c [deg],
from the original crack front to the back edge of the specimen,
c c
n—steady-state value of CTOA measured (or calculated) at
that is b = W – a .
o o
1-mm behind the current crack tip, where CTOA =2
3.2.20 remaining ligament, b [L], n—distance from the
c
–1
tan (CTOD /2).
c crack front to the back edge of the specimen, that is b = W – a.
3.2.4.1 Discussion—The critical CTOA value tends to ap-
3.2.21 specimen thickness, B [L], n—the side-to-side di-
proach a constant, steady-state value after a small amount of
mension of the specimen being tested (side grooving is not
crack extension (associated with crack tunneling and transition
allowed).
from flat-to-slant crack extension).
3.2.22 specimen width, W [L], n—a physical dimension on
3.2.5 crack-opening displacement, d [L], n—relative dis-
atestspecimenmeasuredfromareferenceposition,suchasthe
placement of the crack surfaces normal to the original (un-
load line in the compact-tension specimen or the center line in
deformed)crackplaneatthetipofthefatiguepre-cracklength,
themiddle-cracktensionspecimentotheedgeofthespecimen.
a . In this standard, d is measured at the original crack length
(Note that the total width of the M(T) specimen is defined as
o 5
location over a gage length of 5-mm as the crack stably tears.
2W.)
3.2.6 crack-tip-opening displacement (CTOD), d [L],
n—relative displacement resulting from the total deformation
4. Summary of Test Method
(elastic plus plastic) at variously defined locations near the
4.1 The objective of this standard is to induce stable crack
original (prior to force application) crack tip.
extension in a fatigue pre-cracked, low-constraint test speci-
3.2.7 critical crack-tip-opening displacement (CTOD ),
c
men while monitoring and measuring the COD at the original
d [L], n—steady-state value of CTOD resulting from the total
c
fatigue pre-crack tip location (4, 5) or the CTOA(or CTOD) at
deformation (elastic plus plastic) measured (or calculated) at
1-mm behind the stably tearing crack tip (6, 7), or both. The
1-mm behind current crack-tip location.
resistance curve associated with the d measurements and the
3.2.8 crack extension resistance curve (R curve),
critical limiting value of the CTOA measurements are used to
n—variation of d with crack extension, Da.
5 characterize the corresponding resistance to stable crack ex-
-2
3.2.9 effective yield strength, s [FL ], n—an assumed
Y tension. In contrast, the CTOD values determined from Test
value of uniaxial yield strength that represents the influence of
Method E1290 (high-constraint bend specimens) are values at
plastic yielding upon fracture test parameters.
one or more crack extension events, such as the CTOD at the
3.2.9.1 Discussion—Effective yield strength is calculated as
onset of brittle crack extension with no significant stable crack
the average of the 0.2 % offset yield strength s , and the
extension.
YS
ultimate tensile strength, s as follows:
TS 4.2 Either of the fatigue pre-cracked, low-constraint test
specimen configurations specified in this standard (C(T) or
s 5 ~s 1s !/ 2 (1)
Y YS TS
M(T)) may be used to measure or calculate either of the
NOTE 1—The yield and ultimate tensile strength are determined from
fracture resistance parameters considered. The fracture resis-
Test Methods E8.
tance parameters, CTOA (or CTOD) and d , may be charac-
3.2.9.2 Discussion—In estimating s , influences of testing
terized using either a single-specimen or multiple-specimen
Y
conditions, such as loading rate and temperature, should be
procedure. In all cases, tests are performed by applying slowly
considered.
increasing displacements to the test specimen and measuring
3.2.10 final crack length, a [L], n—crack extension at end the forces, displacements, crack extension and angles realized
f
of stable tearing (a = a + Da). during the test. The forces, displacements and angles are then
f o f
E2472 – 06
usedinconjunctionwithcertainpre-testandpost-testspecimen 5.6.3 Forinspectionandflawassessmentcriteria,whenused
measurements to determine the material’s resistance to stable in conjunction with fracture mechanics analyses.Awareness of
crack extension. differences that may exist between laboratory test and field
4.3 Four procedures for measuring crack extension are: conditions is required to make proper flaw assessment.
surface visual, unloading compliance, electrical potential, and 5.6.4 The critical CTOA (c ) has been used with the
c
multiple specimens.
elastic-plastic finite-element method to accurately predict
4.4 Two techniques are presented for measuring CTOA: structural response and force carrying capacity of simple and
optical microscopy (OM) (8) and digital image correlation complex cracked structural components, see Appendix X1.
(DIC) (9).
5.6.5 The d parameter has been related to the J-integral by
4.5 Three techniques are presented for measuring COD: d
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
the d -resistance curve, in that, the concept has been applied to
or bending forces), but are dependent upon sheet or plate
both C(T) and M(T) specimens (under low-constraint condi-
thickness.
tions) and the K-R curve concept has been used successfully in
industry (11). However, the d parameter has been related to
5. Significance and Use
the J-integral and the parameter incorporates the material
non-linear effects in its measurement. Comparisons have also
5.1 This test method characterizes a metallic material’s
been made among various fracture criteria on fracture of C(T),
resistance to stable crack extension in terms of crack-tip-
M(T) and a structurally configured crack configuration (12)
opening angle (CTOA), c and/or crack-opening displacement
that were made of several different materials (two aluminum
(COD), d under the laboratory or application environment of
alloys and a very ductile steel), and the K-R curve concept was
interest.Thismethodappliesspecificallytofatiguepre-cracked
found to have limited application, in comparison to the critical
specimens that exhibit low constraint and that are tested under
CTOA (c ) concept.
slowly increasing displacement. c c
5.2 When conducting fracture tests, the user must consider
6. Apparatus
the influence that the loading rate and laboratory environment
may have on the fracture parameters. The user should perform
6.1 This procedure involves measurement of applied force,
a literature review to determine if loading rate effects have
P, crack extension, Da, and crack-opening displacement at the
been observed previously in the material at the specific
original fatigue crack tip location or crack-tip-opening angle at
temperature and environment being tested. The user should
the current crack tip, or both. Testing is performed under
document specific information pertaining to their material,
crosshead displacement control in a tension-testing machine
loading rates, temperature, and environment (relative humid-
that conforms to the requirements of Practice E4.
ity) for each test.
6.1.1 Calibration—Calibration of all measuring apparatus
5.3 The results of this characterization include the determi-
shall be traceable either directly or indirectly via a hierarchical
nation of a critical, lower-limiting value, of CTOA (c)ora
chain to an accredited calib
...
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