ASTM E1820-99a
(Test Method)Standard Test Method for Measurement of Fracture Toughness
Standard Test Method for Measurement of Fracture Toughness
SCOPE
1.1 This test method covers procedures and guidelines for the determination of fracture toughness of metallic materials using the following parameters: K, J, and CTOD. Toughness can be measured in the R-curve format or as a point value. The fracture toughness determined in accordance with this test method is for the opening mode (Mode I) of loading.
1.2 The recommended specimens are single-edge bend, [SE(B)], compact, [C(T)], and disk-shaped compact, [DC(T)]. All specimens contain notches that are sharpened with fatigue cracks.
1.2.1 Specimen dimensional (size) requirements vary according to the fracture toughness analysis applied. The guidelines are established through consideration of material toughness, material flow strength, and the individual qualification requirements of the toughness value per values sought.
1.3 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
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 and health practices and determine the applicability of regulatory limitations prior to use.
Note 1--Other standard methods for the determination of fracture toughness using the parameters K, J, and CTOD are contained in Test Methods E399, E813, E1152, E1290, and E1737. This test method was developed to provide a common method for determining all applicable toughness parameters from a single test.
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Designation: E 1820 – 99a
Standard Test Method for
Measurement of Fracture Toughness
This standard is issued under the fixed designation E 1820; 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 E 813 Test Method for J , A Measure of Fracture Tough-
Ic
ness
1.1 This test method covers procedures and guidelines for
E 1152 Test Method for Determining J-R Curves
the determination of fracture toughness of metallic materials
E 1290 Test Method for Crack-Tip Opening Displacement
using the following parameters: K, J, and CTOD (d). Tough-
(CTOD) Fracture Toughness Measurement
ness can be measured in the R-curve format or as a point value.
E 1737 Test Method for J-Integral Characterization of Frac-
The fracture toughness determined in accordance with this test
ture Toughness
method is for the opening mode (Mode I) of loading.
E 1823 Terminology Relating to Fatigue and Fracture
1.2 The recommended specimens are single-edge bend,
Testing
[SE(B)], compact, [C(T)], and disk-shaped compact, [DC(T)].
All specimens contain notches that are sharpened with fatigue
3. Terminology
cracks.
3.1 Terminology E 1823 is applicable to this test method.
1.2.1 Specimen dimensional (size) requirements vary ac-
3.2 Definitions:
cording to the fracture toughness analysis applied. The guide-
−1
3.2.1 compliance [LF ], n— the ratio of displacement
lines are established through consideration of material tough-
increment to load increment.
ness, material flow strength, and the individual qualification
3.2.2 crack displacement [L], n—the separation vector be-
requirements of the toughness value per values sought.
tween two points (on the surfaces of a deformed crack) that
1.3 The values stated in SI units are to be regarded as the
were coincident on the surfaces of an ideal crack in the
standard. The values given in parentheses are for information
undeformed condition.
only.
3.2.2.1 Discussion—In this practice, displacement, v, is the
1.4 This standard does not purport to address all of the
total displacement measured by clip gages or other devices
safety concerns, if any, associated with its use. It is the
spanning the crack faces.
responsibility of the user of this standard to establish appro-
3.2.3 crack extension, Da [L], n—an increase in crack size.
priate safety and health practices and determine the applica-
−1 −2
3.2.4 crack-extension force, G [FL or FLL ], n—the
bility of regulatory limitations prior to use.
elastic energy per unit of new separation area that is made
NOTE 1—Other standard methods for the determination of fracture
available at the front of an ideal crack in an elastic solid during
toughness using the parameters K, J, and CTOD are contained in Test
a virtual increment of forward crack extension.
Methods E 399, E 813, E 1152, E 1290, and E 1737. This test method was
3.2.5 crack size, a [L], n—a lineal measure of a principal
developed to provide a common method for determining all applicable
planar dimension of a crack. This measure is commonly used
toughness parameters from a single test.
in the calculation of quantities descriptive of the stress and
2. Referenced Documents
displacement fields, and is often also termed crack length or
depth.
2.1 ASTM Standards:
3.2.5.1 Discussion—In practice, the value of a is obtained
E 4 Practices for Force Verification of Testing Machines
from procedures for measurement of physical crack size, a ,
E 8 Test Methods for Tension Testing of Metallic Materials
p
original crack size, a , and effective crack size, a , as appro-
E 21 Test Methods for Elevated Temperature Tension Tests
o e
priate to the situation being considered.
of Metallic Materials
3.2.6 crack-tip opening displacement (CTOD), d [L],
E 399 Test Method for Plane-Strain Fracture Toughness of
n—the crack displacement due to elastic and plastic deforma-
Metallic Materials
tion at variously defined locations near the original (prior to an
application of load) crack tip.
This test method is under the jurisdiction of ASTM Committee E-8 on Fatigue
3.2.6.1 Discussion—In this test method, CTOD is the dis-
and Fracture and is the direct responsibility of Subcommittee E08.08 on Elastic-
Plastic Fracture Mechanics Technology. placement of the crack surfaces normal to the original (un-
Current edition approved December 10, 1999. Published April 2000. Originally
loaded) crack plane at the tip of the fatigue precrack, a . In this
o
published as E 1820 - 96. Last previous edition E 1820 - 99.
test method, CTOD is calculated at the original crack length,
Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
E 1820
a , from observations away from the crack tip.
W 5 loading work per unit volume or, for elastic
o
3.2.6.2 Discussion—In CTOD testing, d [L] is a value of
Ic bodies, strain energy density,
CTOD near the onset of slow stable crack extension, here
G5 path of the integral, that encloses (that is,
defined as occurring at Da 5 0.2 mm (0.008 in.) + 0.7d .
contains) the crack tip,
p Ic
3.2.6.3 Discussion—In CTOD testing, d [L] is the value of
ds 5 increment of the contour path,
c
¯
CTOD at the onset of unstable crack extension (see 3.2.17) or T 5 outward traction vector on ds,
u¯ 5 displacement vector at ds,
pop-in (see 3.2.17) when Da <0.2 mm (0.008 in.) + 0.7d . The
p c
x, y, z 5 rectangular coordinates, and
d corresponds to the load P and clip-gage displacement v .It
c c c
]u¯
5 rate of work input from the stress field into
may be size-dependent and a function of test specimen
¯
T· ds
]x the area enclosed by G.
geometry.
3.2.6.4 Discussion—In CTOD testing, d [L] is the value of 3.2.9.2 Discussion—The value of J obtained from this
u
CTOD at the onset of unstable crack extension (see 3.2.28) or equation is taken to be path-independent in test specimens
pop-in (see 3.2.17) when the event is preceded by D a >0.2 commonly used, but in service components (and perhaps in test
p
mm (0.008 in.) + 0.7d . The d corresponds to the load P and specimens) caution is needed to adequately consider loading
u u u
the clip gage displacement v . It may be sizedependent and a interior to G such as from rapid motion of the crack or the
u
function of test specimen geometry. It can be useful to define service component, and from residual or thermal stress.
limits on ductile fracture behavior.
3.2.9.3 Discussion—In elastic (linear or nonlinear) solids,
3.2.6.5 Discussion—In CTOD testing, d [L] is the value of
m the J-integral equals the crack-extension force, G. (See crack
CTOD at the first attainment of a maximum load plateau for
extension force.)
fully plastic behavior. The d corresponds to the load P and
−1
m m
3.2.10 J [FL ]—The property J determined by this test
c c
the clip gage displacement v . It may be size-dependent and a
m
method characterizes the fracture toughness of materials at
function of test specimen geometry. It can be useful to define
fracture instability prior to the onset of significant stable
limits on ductile fracture behavior.
tearing crack extension. The value of J determined by this test
c
3.2.6.6 Discussion—In CTOD testing, ^d [L] characterizes
c
method represents a measure of fracture toughness at instabil-
the CTOD fracture toughness of materials at fracture instability
ity without significant stable crack extension that is indepen-
prior to the onset of significant stable tearing crack extension.
dent of in-plane dimensions; however, there may be a depen-
The value of ^d determined by this test method represents a
c c
dence of toughness on thickness (length of crack front).
measure of fracture toughness at instability without significant
−1
3.2.11 J [FL ]—The quantity J determined by this test
u u
stable crack extension that is independent of in-plane dimen-
method measures fracture instability after the onset of signifi-
sions. However, there may be a dependence of toughness on
cant stable tearing crack extension. It may be size-dependent
thickness (length of crack front).
and a function of test specimen geometry. It can be useful to
3.2.7 effective thickness, B [L], n—for side-grooved speci-
e
2 define limits on ductile fracture behavior.
mens B 5 B −(B−B ) /B. This is used for the elastic
e N
3.2.12 net thickness, B [L], n—distance between the roots
unloading compliance measurement of crack length. N
of the side grooves in side-grooved specimens.
3.2.7.1 Discussion—This definition is different from the
definition of effective thickness in Test Method E 813. 3.2.13 original crack size, a [L], n—the physical crack size
o
−2
at the start of testing.
3.2.8 effective yield strength, s [FL ], n—an assumed
Y
value of uniaxial yield strength that represents the influence of
3.2.13.1 Discussion—In this test method, a is used to
oq
plastic yielding upon fracture test parameters.
denote original crack size estimated from compliance.
3.2.8.1 Discussion—It is calculated as the average of the
3.2.14 original remaining ligament, b [L], n—distance
o
0.2 % offset yield strength s , and the ultimate tensile
YS
from the original crack front to the back edge of the specimen,
strength, s as follows:
TS
that is (b 5W−a ).
o o
~s 1s !
YS TS 3.2.15 physical crack size, a [L], n—the distance from a
p
s 5 (1)
Y
reference plane to the observed crack front. This distance may
represent an average of several measurements along the crack
3.2.8.2 Discussion—In estimating s , influences of testing
Y
conditions, such as loading rate and temperature, should be front. The reference plane depends on the specimen form, and
it is normally taken to be either the boundary, or a plane
considered.
−1
3.2.9 J-integral, J [FL ], n—a mathematical expression, a containing either the load line or the centerline of a specimen
or plate. The reference plane is defined prior to specimen
line or surface integral that encloses the crack front from one
deformation.
crack surface to the other, used to characterize the local
−3/2
stress-strain field around the crack front.
3.2.16 plane-strain fracture toughness, K [FL ], J
Ic Ic
−1 −3/2
3.2.9.1 Discussion—The J-integral expression for a two-
[FL ], K [FL ] , n—the crack-extension resistance under
JIc
dimensional crack, in the x-z plane with the crack front parallel
conditions of crack-tip plane strain.
to the z-axis, is the line integral as follows:
3.2.16.1 Discussion—For example, in Mode I for slow rates
]¯u
of loading and negligible plastic-zone adjustment, plane-strain
¯
J 5 Wdy 2 T · ds (2)
S D
*
]x
G fracture toughness is the value of the stress-intensity factor
−3/2
designated K [FL ] as measured using the operational
Ic
where:
procedure (and satisfying all of the qualification requirements)
E 1820
lim 1/2
specified in this test method, which provides for the measure-
K 5 s 2pr! (3)
@ ~ #
1 r→0 yy
ment of crack-extension resistance at the start of crack exten-
lim 1/2
K 5 @t ~2pr! # (4)
2 r→0 xy
sion and provides operational definitions of crack-tip sharp-
lim 1/2
K 5 @t ~2pr! # (5)
ness, start of crack extension, and crack-tip plane-strain. 3 r→0 yz
3.2.16.2 Discussion—For example, in Mode I for slow rates
where r 5 distance directly forward from the crack tip to a location
of loading and substantial plastic deformation, plane-strain
where the significant stress is calculated.
fracture toughness is the value of the J-integral designated J
Ic 3.2.26.2 Discussion—In this test method, Mode 1 or Mode
−1
[FL ] as measured using the operational procedure (and
I is assumed. See Terminology E 1823 for definition of mode.
satisfying all of the qualification requirements) specified in this
3.2.27 stretch-zone width, SZW [L], n—the length of crack
test method, that provides for the measurement of crack-
extension that occurs during crack-tip blunting, for example,
extension resistance near the onset of stable crack extension.
prior to the onset of unstable brittle crack extension, pop-in, or
3.2.16.3 Discussion—For example, in Mode I for slow rates
slow stable crack extension. The SZW is in the same plane as
of loading, plane-strain fracture toughness is the value of the
the original (unloaded) fatigue precrack and refers to an
−3/2
stress intensity designated K [FL ] calculated from J
JIc Ic extension beyond the original crack size.
using the equation (and satisfying all of the qualification
3.2.28 unstable crack extension [L], n—an abrupt crack
requirements) specified in this test method, that provides for
extension that occurs with or without prior stable crack
the measurement of crack-extension reistance near the onset of
extension in a standard test specimen under crosshead or clip
stable crack extension under dominant elastic conditions.(1)
gage displacement control.
3.2.17 pop-in, n—a discontinuity in the load versus clip
4. Summary of Test Method
gage displacement record. The record of a pop-in shows a
4.1 The objective of this test method is to load a fatigue
sudden increase in displacement and, generally a decrease in
precracked test specimen to induce either or both of the
load. Subsequently, the displacement and load increase to
following responses (1) unstable crack extension, including
above their respective values at pop-in.
significant pop-in, referred to as “fracture instability” in this
3.2.18 R-curve or J-R curve, n—a plot of crack extension
test method; (2) stable crack extension, referred to as “stable
resistance as a function of stable crack extension, Da or Da .
p e
tearing” in this test method. Fracture instability results in a
3.2.18.1 Discussion—In this test method, the J-R curve is a
single point-value of fracture toughness determined at the point
plot of the far-field J-integral versus the physical crack
of instability. Stable tearing results in a continuous fracture
extension, Da . It is recognized that the far-field value of J may
p
toughness versus crack-extension relationship (R-curve) from
not represent the stress-strain field local to a growing crack.
which significant point-values may be determined. Stable
3.2.19 remaining ligament, b [L], n—distance from the
tearing interrupted by fracture instability results in an R-curve
physical crack front to the back edge of the specimen, that is
up to the point of instability.
(b 5W−a ).
p
4.2 This test method requires continuous measurement of
3.2.20 specimen center of pin hole distance, H* [L], n—the
load versus load-line displacement and crack mouth opening
distance between the center of the pin holes on a pin-loaded
displacement. If any stable tearing respon
...
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