ASTM E1290-99
(Test Method)Standard Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement
Standard Test Method for Crack-Tip Opening Displacement (CTOD) Fracture Toughness Measurement
SCOPE
1.1 This test method covers the determination of critical crack-tip opening displacement (CTOD) values at one or more of several crack extension events. These CTOD values can be used as measures of fracture toughness for metallic materials, and are especially appropriate to materials that exhibit a change from ductile to brittle behavior with decreasing temperature. This test method applies specifically to notched specimens sharpened by fatigue cracking. The recommended specimens are three-point bend [SE(B)] or compact [C(T)] specimens. The loading rate is slow and influences of environment (other than temperature) are not covered. The specimens are tested under crosshead or clip gage displacement controlled loading.
1.1.1 The recommended specimen thickness, , is that of the material in thicknesses intended for an application. Superficial surface machining may be used when desired.
1.1.2 For the recommended three-point bend specimens [SE(B)], width, , is either equal to, or twice, the specimen thickness, , depending upon the application of the test. (See 4.3 for applications of the recommended specimens.) For SE(B) specimens the recommended initial normalized crack size is 0.45 [
1.1.3 For the recommended compact specimen [C(T)] the initial normalized crack size is 0.45 [
1.2 This standard does not purport to address all of the safety problems, 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: E 1290 – 99
Standard Test Method for
Crack-Tip Opening Displacement (CTOD) Fracture
Toughness Measurement
This standard is issued under the fixed designation E 1290; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 1.2 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the determination of critical
responsibility of the user of this standard to establish appro-
crack-tip opening displacement (CTOD) values at one or more
priate safety and health practices and determine the applica-
of several crack extension events. These CTOD values can be
bility of regulatory limitations prior to use.
used as measures of fracture toughness for metallic materials,
and are especially appropriate to materials that exhibit a change
2. Referenced Documents
from ductile to brittle behavior with decreasing temperature.
2.1 ASTM Standards:
This test method applies specifically to notched specimens
E 4 Practices for Force Verification of Testing Machines
sharpened by fatigue cracking. The recommended specimens
E 8 Test Methods for Tension Testing of Metallic Materials
are three-point bend [SE(B)] compact [C(T)], or arc-shaped
E 399 Test Method for Plane-Strain Fracture Toughness of
bend [A(B)] specimens. The loading rate is slow and influences
Metallic Materials
of environment (other than temperature) are not covered. The
E 1820 Test Method for Measurement of Fracture Tough-
specimens are tested under crosshead or clip gage displacement
ness
controlled loading.
E 1823 Terminology Relating to Fatigue and Fracture
1.1.1 The recommended specimen thickness, B, for the
Testing
SE(B) and C(T) specimens is that of the material in thicknesses
intended for an application. For the A(B) specimen, the
3. Terminology
recommended depth, W, is the wall thickness of the tube or
3.1 Terminology E 1823 is applicable to this test method.
pipe from which the specimen is obtained. Superficial surface
3.2 Definitions:
machining may be used when desired.
3.2.1 crack tip opening displacement, (CTOD), d[L]—the
1.1.2 For the recommended three-point bend specimens
crack displacement due to elastic and plastic deformation at
[SE(B)], width, W, is either equal to, or twice, the specimen
variously defined locations near the original (prior to an
thickness, B, depending upon the application of the test. (See
application of force) crack tip.
4.3 for applications of the recommended specimens.) For
3.2.1.1 Discussion—In this test method, CTOD is the dis-
SE(B) specimens the recommended initial normalized crack
placement of the crack surfaces normal to the original (un-
size is 0.45 # a /W # 0.70. The span-to-width ratio (S/W)is
o
loaded) crack plane at the tip of the fatigue precrack, a .
o
specified as 4.
In CTOD testing, d [L] is the value of CTOD at the onset of
c
1.1.3 For the recommended compact specimen [C(T)] the
unstable brittle crack extension (see 3.2.13) or pop-in (see
initial normalized crack size is 0.45 # a /W # 0.70. The
o
3.2.7) when Da < 0.2 mm (0.008 in.). The force P and the clip
p c
half-height-to-width ratio (H/W) equals 0.6 and the width to
gage displacement v , for d are indicated in Fig. 1.
c c
thickness ratio W/B is specified to be 2.
In CTOD testing, d [L] is the value of CTOD at the onset of
u
1.1.4 For the recommended arc-shaped bend [A(B)] speci-
unstable brittle crack extension (see 3.2.13) or pop-in (see
men, B is one-half the specimen depth, W. The initial normal-
3.2.7) when the event is preceded by Da > 0.2 mm (0.008 in.).
p
ized crack size is 0.45 < a /W< 0.55. The span to width ratio,
o
The force P and the clip gage displacement v , for d are
u u u
S/W, may be either 3 or 4 depending on the ratio of the inner
indicated in Fig. 1.
to outer tube radius. For an inner radius, r , to an outer radius,
In CTOD testing, d [L] is the value of CTOD at the first
m
r , ratio of > 0.6 to 1.0, a span to width ratio, S/W, of 4 may be
attainment of a maximum force plateau for fully plastic
used. For r /r ratios from 0.4 to 0.6, an S/W of 3 may be used.
1 2
behavior. The force P and the clip gage displacement v , for
m m
d are indicated in Fig. 1.
m
−2
3.2.2 effective yield strength, s [FL ]—an assumed value
Y
This test method is under the jurisdiction of ASTM Committee E-8 on Fatigue
of uniaxial yield strength that represents the influence of plastic
and Fracture and is the direct responsibility of Subcommittee E08.08 on Elastic-
Plastic Fracture Mechanics Technology.
Current edition approved June 10, 1999. Published September 1999. Originally
published as E 1290 – 89. Last previous edition E 1290 – 93. Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1290
NOTE 1—Construction lines drawn parallel to the elastic loading slope to give v , the plastic component of total displacement, v .
p g
NOTE 2—In curves b and d, the behavior after pop-in is a function of machine/specimen compliance, instrument response, etc.
FIG. 1 Types of Force Versus Clip Gage Displacement Records
yielding upon fracture test parameters. CTOD at one or more of several crack extension events. The
3.2.2.1 Discussion—The calculation of s is the average of values of CTOD may correspond to: d , the onset of unstable
Y c
the 0.2 % offset yield strength (s ), and the tensile strength brittle crack extension with no significant prior slow stable
YS
(s ), that is (s + s )/2. Both s and s are determined in crack extension (see 3.2.1); d , the onset of unstable brittle
TS YS TS YS TS u
accordance with Test Methods E 8. crack extension following prior slow stable crack extension;
3.2.3 original crack size, a [L]—see Terminology E 1823. d , at the first attainment of a maximum force plateau for fully
o m
3.2.4 original uncracked ligament, b [L]—the distance plastic behavior.
o
from the original crack front to the back surface of the
4.2 The test method involves crosshead or clip gage dis-
specimen at the start of testing, b 5 W − a .
placement controlled three-point bend loading or pin loading of
o o
3.2.5 physical crack extension, Da [L]—an increase in
p fatigue precracked specimens. Force versus clip gage crack
physical crack size, Da 5 a − a .
opening displacement is recorded, for example, Fig. 1. The
p p o
3.2.6 physical crack size, a [L]—see Terminology E 1823.
p forces and displacements corresponding to the specific events
3.2.6.1 Discussion—In CTOD testing, a 5 a + Da .
in the crack initiation and extension process are used to
p o p
3.2.7 pop-in—a discontinuity in the force versus clip gage
determine the corresponding CTOD values. For values of d , d
c u
displacement record. The record of a pop-in shows a sudden
and d , the corresponding force and clip gage displacements
m
increase in displacement and, generally, a decrease in force.
are obtained directly from the test records.
Subsequently, the displacement and force increase to above
4.3 The rectangular section bend specimen and the compact
their respective values at pop-in.
specimen are intended to maximize constraint and these are
3.2.8 slow stable crack extension [L]—a displacement con-
generally recommended for those through-thickness crack
trolled crack extension beyond the stretch zone width (see
types and orientations for which such geometries are feasible.
3.2.12). The extension stops when the applied displacement is
For the evaluation of surface cracks in structural applications
held constant.
for example, orientations T-S or L-S (Terminology E 1823), the
3.2.9 specimen span, S [L]—the distance between specimen
square section bend specimen is recommended. Also for
supports in a bend specimen.
certain situations in curved geometry source material or welded
3.2.10 specimen thickness, B[L]—see Terminology E 1823.
joints, the square section bend specimen may be preferred.
3.2.11 specimen width, W [L]—see Terminology E 1823.
Square section bend specimens may be necessary in order to
3.2.12 stretch zone width, SZW [L]—the length of crack
sample an acceptable volume of a discrete microstructure.
extension that occurs during crack-tip blunting, for example,
4.4 The arc-shaped bend specimen permits toughness test-
prior to the onset of unstable brittle crack extension, pop-in, or
ing in the C-R orientation (Terminology E 1823), for pipe or
slow stable crack extension. The SZW is in the same plane as
tube. This orientation is of interest since pipes and tubes under
the original (unloaded) fatigue precrack and refers to an
pressure often fail with longitudinal cracks. The specimen
extension beyond the original crack size.
geometry is convenient for obtaining samples with minimal use
3.2.13 unstable brittle crack extension [L]—an abrupt crack
of material.
extension that occurs with or without prior stable crack
extension in a standard test specimen under crosshead or clip
5. Significance and Use
gage displacement control.
5.1 This test method characterizes the fracture toughness of
4. Summary of Test Method
materials through the determination of crack-tip opening dis-
4.1 The objective of the test is to determine the value of placement (CTOD) at one of three events: (a) onset of unstable
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1290
crack extension without significant prior stable crack exten- displacement is autographically recorded on an x-y plotter for
sion, (b) onset of unstable crack extension with significant visual display, or converted to digital form for accumulation in
prior stable crack extension, or (c) achievement of plastic limit
a computer information storage facility and subsequent pro-
load with or without significant stable crack extension. This cessing. Testing is performed under crosshead or clip gage
test method may also be used to characterize the toughness of
displacement control in a compression or tension testing
materials for which the properties and thickness of interest
machine, or both, that conforms to the requirements of Prac-
preclude the determination of K fracture toughness in accor-
tices E 4.
lc
dance with Test Method E 399.
6.2 Fixturing for Three-Point Bend Specimens—A recom-
5.2 The different values of CTOD determined by this test
mended SE(B) or A(B) specimen fixture is shown in Fig. 2.
method characterize the resistance of a material to crack
Friction effects between the support rollers and specimen are
initiation and early crack extension at a given temperature.
reduced by allowing the rollers to rotate during the test. The
5.3 The values of CTOD may be affected by specimen
use of high hardness steel of the order of 40 HRC or more is
dimensions. It has been shown that values of CTOD deter-
recommended for the fixture and rollers to prevent indentation
mined on SE(B) specimens using the square section geometry
of the platen surfaces.
may not be the same as those using the rectangular section
6.3 Tension Testing Clevis—A loading clevis suitable for
geometry, and may differ from those obtained with either the
testing C(T) specimens is shown in Fig. 3. Each leg of the
(C)T or (A)B specimens.
specimen is held by such a clevis and loaded through pins, in
5.4 The values of CTOD determined by this test method
order to allow rotation of the specimen during testing. To
may serve the following purposes:
provide rolling contact between the loading pins and the clevis
5.4.1 In research and development, CTOD testing can show
holes, these holes are produced with small flats on the loading
the effects of certain parameters on the fracture toughness of
surfaces. Other clevis designs may be used if it can be
metallic materials significant to service performance. These
demonstrated that they will accomplish the same result as the
parameters include material composition, thermo-mechanical
design shown. Clevises and pins should be fabricated from
processing, welding, and thermal stress relief.
steels of sufficient strength and hardness (greater than 40 HRC)
5.4.2 For specifications of acceptance and manufacturing
to elastically resist indentation forces. The critical tolerances
quality control of base materials, weld metals, and weld heat
and suggested proportions of the clevis and pins are given in
affected zones.
Fig. 3. These proportions are based on specimens having W/B
5.4.3 For inspection and flaw assessment criteria, when used
5 2 for B > 12.7 mm (0.5 in.) and W/B 5 4 for B #12.7 mm
in conjunction with fracture mechanics analyses. Awareness of
(0.5 in.). If a 1930-MPa (280 000-psi) yield strength maraging
differences that may exist between laboratory test and field
steel is used for the clevis and pins, adequate strength will be
conditions is required to make proper flaw assessment (see 4.3
obtained. If lower strength grip material is used, or if substan-
and 4.4).
tially larger specimens are required at a given s /E ratio, then
YS
6. Apparatus
heavier grips will be required. As indicated in Fig. 3, the clevis
corners may be cut off sufficiently to accommodate seating of
6.1 This procedure involves measurement of applied force,
P, and clip gage crack opening displacement, v. Force versus the clip gage in specimens less than 9.5 mm (0.375 in.) thick.
NOTE 1—Roller pins and specimen contact surface of loading ram must be parallel to each other within 0.002W.
NOTE 2— 0.10 in. 5 2.54 mm; 0.15 in. 5 3.81 mm.
FIG. 2 SE(B) Test Fixture Design
NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
E 1290
NOTE 1—Corners of the clevis may be removed as necessary to accommodate the clip gage.
FIG. 3 Clevis for C(T) Specimen Testing
Attention should be given to achieving good alignment through 6.5 Force Measurement—The sensitivity of the force sens-
careful machining of all auxiliary gripping fixtures. ing device shall be sufficient to avoid distortion caused by over
6.4 Displacement Measuring Devices: amplification and the device shall have a linearity identical to
6.4.1 Displacement measuring gages are used to measure that for the displace
...
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