ASTM D5045-99
(Test Method)Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials
Standard Test Methods for Plane-Strain Fracture Toughness and Strain Energy Release Rate of Plastic Materials
SCOPE
1.1 These test methods are designed to characterize the toughness of plastics in terms of the critical-stress-intensity factor, KIc, and the energy per unit area of crack surface or critical strain energy release rate, GIc, at fracture initiation.
1.2 Two testing geometries are covered by these test methods, single-edge-notch bending (SENB) and compact tension (CT).
1.3 The scheme used assumes linear elastic behavior of the cracked specimen, so certain restrictions on linearity of the load-displacement diagram are imposed.
1.4 A state-of-plane strain at the crack tip is required. Specimen thickness must be sufficient to ensure this stress state.
1.5 The crack must be sufficiently sharp to ensure that a minimum value of toughness is obtained.
1.6 The significance of these test methods and many conditions of testing are identical to those of Test Method E 399, and, therefore, in most cases, appear here with many similarities to the metals standard. However, certain conditions and specifications not covered in Test Method E 399, but important for plastics, are included.
1.7 This protocol covers the determination of GIc as well, which is of particular importance for plastics.
1.8 These test methods give general information concerning the requirements for KIc and GIc testing. As with Test Method E 399, two annexes are provided which give the specific requirements for testing of the SENB and CT geometries.
1.9 Test data obtained by these test methods are relevant and appropriate for use in engineering design.
1.10 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- There is currently no ISO standard that duplicates this test method. Pending ISO/CD 13586 covers similar testing and references this test method for testing conditions.
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Designation: D 5045 – 99
Standard Test Methods for
Plane-Strain Fracture Toughness and Strain Energy Release
Rate of Plastic Materials
This standard is issued under the fixed designation D5045; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
this test method for testing conditions.
1. Scope*
1.1 These test methods are designed to characterize the
2. Referenced Documents
toughness of plastics in terms of the critical-stress-intensity
2.1 ASTM Standards:
factor, K , and the energy per unit area of crack surface or
Ic
D638 Test Method for Tensile Properties of Plastics
critical strain energy release rate, G , at fracture initiation.
Ic
D4000 Classification System for Specifying Plastic Mate-
1.2 Two testing geometries are covered by these test meth-
rials
ods, single-edge-notch bending (SENB) and compact tension
E399 Test Method for Plane-Strain Fracture Toughness of
(CT).
Metallic Materials
1.3 The scheme used assumes linear elastic behavior of the
E691 Practice for Conducting an Interlaboratory Study to
cracked specimen, so certain restrictions on linearity of the
Determine the Precision of a Test Method
load-displacement diagram are imposed.
1.4 A state-of-plane strain at the crack tip is required.
3. Terminology
Specimen thickness must be sufficient to ensure this stress
3.1 Definitions:
state.
3.1.1 compact tension, n—specimengeometry consisting of
1.5 The crack must be sufficiently sharp to ensure that a
single-edge notched plate loaded in tension. See 3.1.5 for
minimum value of toughness is obtained.
reference to additional definition.
1.6 The significance of these test methods and many con-
3.1.2 critical strain energy release rate, G , n—toughness
Ic
ditions of testing are identical to those of Test Method E399,
parameter based on energy required to fracture. See 3.1.5 for
and, therefore, in most cases, appear here with many similari-
reference to additional definition.
ties to the metals standard. However, certain conditions and
3.1.3 plane-strain fracture toughness, K , n—toughness
Ic
specificationsnotcoveredinTestMethodE399,butimportant
parameter indicative of the resistance of a material to fracture.
for plastics, are included.
See 3.1.5 for reference to additional definition.
1.7 This protocol covers the determination of G as well,
Ic
3.1.4 single-edge notched bend, n—specimen geometry
which is of particular importance for plastics.
consisting of center-notched beam loaded in three-point bend-
1.8 Thesetestmethodsgivegeneralinformationconcerning
ing. See 3.1.5 for reference to additional definition.
the requirements for K and G testing.As with Test Method
Ic Ic
3.1.5 ReferenceismadetoTestMethodE399foradditional
E399, two annexes are provided which give the specific
explanation of definitions.
requirements for testing of the SENB and CT geometries.
3.2 Definitions of Terms Specific to This Standard:
1.9 Testdataobtainedbythesetestmethodsarerelevantand
3.2.1 yield stress, n—stress at fracture is used. The slope of
appropriate for use in engineering design.
the stress-strain curve is not required to be zero. See 7.2 for
1.10 This standard does not purport to address all of the
reference to additional definition.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
4. Summary of Test Methods
priate safety and health practices and determine the applica-
4.1 These test methods involve loading a notched specimen
bility of regulatory limitations prior to use.
that has been precracked, in either tension or three-point
NOTE 1—There is currently no ISO standard that duplicates these test bending. The load corresponding to a 2.5% apparent incre-
methods. Pending ISO/CD 13586 covers similar testing and references
ment of crack extension is established by a specified deviation
These test methods are under the jurisdiction of ASTM Committee D-20 on
Plastics and is the direct responsibility of Subcommittee D20.10 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 March 10, 1999. Published June 1999. Originally Standards volume information, refer to the standard’s Document Summary page on
published as D5045–90. Last previous edition D5045–96. the ASTM website.
*A Summary of Changes section appears at the end of this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D5045–99
from the linear portion of the record. The K value is specification before using these test methods. Table 1 of
Ic
calculated from this load by equations that have been estab- Classification System D4000 lists the ASTM materials stan-
lishedonthebasisofelasticstressanalysisonspecimensofthe dards that currently exist.
type described in the test methods. The validity of the
6. Apparatus
determination of the K value by these test methods depends
Ic
upon the establishment of a sharp-crack condition at the tip of 6.1 Testing Machine—A constant displacement-rate device
the crack, in a specimen of adequate size to give linear elastic
shall be used such as an electromechanical, screw-driven
behavior. machine, or a closed loop, feedback-controlled servohydraulic
4.2 Amethod for the determination of G is provided. The
load frame. For SENB, a rig with either stationary or moving
Ic
method requires determination of the energy derived from rollers of sufficiently large diameter to avoid excessive plastic
integrationoftheloadversusload-pointdisplacementdiagram,
indentation is required.Asuitable arrangement for loading the
while making a correction for indentation at the loading points SENB specimen is that shown in Fig. 1. A loading clevis
as well as sample compression and system compliance.
suitable for loading compact tension specimens is shown in
Fig.2.Loadingisbymeansofpinsinthespecimenholes(Fig.
5. Significance and Use
3(b)).
5.1 ThepropertyK (G )determinedbythesetestmethods 6.2 Displacement Measurement—Anaccuratedisplacement
Ic Ic
measurement must be obtained to assure accuracy of the G
characterizestheresistanceofamaterialtofractureinaneutral
Ic
environment in the presence of a sharp crack under severe value.
tensile constraint, such that the state of stress near the crack 6.2.1 InternalDisplacementTransducer—ForeitherSENB
front approaches plane strain, and the crack-tip plastic (or orCTspecimenconfigurations,thedisplacementmeasurement
non-linear viscoelastic) region is small compared with the can be performed using the machine’s stroke (position) trans-
cracksizeandspecimendimensionsintheconstraintdirection. ducer. The fracture-test-displacement data must be corrected
A K value is believed to represent a lower limiting value of for system compliance, loading-pin penetration (brinelling)
Ic
fracture toughness. This value may be used to estimate the and sample compression by performing a calibration of the
relation between failure stress and defect size for a material in testing system as described in 9.2.
service wherein the conditions of high constraint described 6.2.2 External Displacement Transducer— If an internal
abovewouldbeexpected.Backgroundinformationconcerning displacement transducer is not available, or has insufficient
the basis for development of these test methods in terms of precision, then an externally applied displacement-measuring
linear elastic fracture mechanics may be found in Refs (1-5). device may be used as illustrated in Fig. 1 for the SENB
5.1.1 TheK (G )valueofagivenmaterialisafunctionof configuration. For CT specimens, a clip gage can be mounted
Ic Ic
testing speed and temperature. Furthermore, cyclic loads can acrosstheloadingpins.ForboththeSENBandCTspecimens,
cause crack extension at K values less than K (G ). Crack the displacement should be taken at the load point.
Ic Ic
extension under cyclic or sustained load will be increased by
7. Specimen Size, Configurations, and Preparation
the presence of an aggressive environment. Therefore, appli-
cation of K (G ) in the design of service components should 7.1 Specimen Size:
Ic Ic
be made considering differences that may exist between 7.1.1 SENB and CT geometries are recommended over
laboratory tests and field conditions. other configurations because these have predominantly bend-
5.1.2 Plane-strain fracture toughness testing is unusual in
ing stress states which allow smaller specimen sizes to achieve
that there can be no advance assurance that a valid K (G ) plane strain. Specimen dimensions are shown in Fig. 3 (a, b).
Ic Ic
will be determined in a particular test. Therefore it is essential
If the material is supplied in the form of a sheet, the specimen
thatallofthecriteriaconcerningvalidityofresultsbecarefully thickness, B, should be identical with the sheet thickness, in
considered as described herein.
5.1.3 Clearly,itwillnotbepossibletodetermineK (G )if
Ic Ic
any dimension of the available stock of a material is insuffi-
cient to provide a specimen of the required size.
5.2 Inasmuch as the fracture toughness of plastics is often
dependent on specimen process history, that is, injection
molded, extruded, compression molded, etc., the specimen
crack orientation (parallel or perpendicular) relative to any
processing direction should be noted on the report form
discussed in 10.1.
5.3 For many materials, there may be a specification that
requires the use of these test methods, but with some proce-
dural modifications that take precedence when adhering to the
specification. Therefore, it is advisable to refer to that material
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
these test methods. FIG. 1 Bending Rig with Transducer for SENB
D5045–99
The criteria require that B must be sufficient to ensure plane
strain and that (W−a) be sufficient to avoid excessive plas-
ticity in the ligament. If (W−a) is too small and non-linearity
in loading occurs, then increasing the W/B ratio to a maximum
of 4 can be attempted for SENB specimens.
7.2 Yield Stress:
7.2.1 The yield stress, s , is to be taken from the maximum
y
load in a uniaxial tensile test. The yield-stress test can be
performed in a constant stroke-rate uniaxial tensile test where
the loading time to yield is within 620% of the actual loading
time observed in the fracture test.The definition of yield stress
is not identical to that found in Test Method D638 which
requires a zero slope to the stress-strain curve. If it is
established that 2.5 (K /s ) is substantially less than
Q y
the specimen thickness employed, then a correspondingly
smaller specimen can be used.
7.2.2 Yielding in tensile tests in most polymers can be
achieved by carefully polishing the specimen sides. If yielding
does not occur and brittle fracture is observed, the stress at
FIG. 2 Tension Testing Clevis Design for CT fracture may be used in the criteria to give a conservative size
value.
7.2.3 If a tensile test cannot be performed, then an alterna-
tive method is to use 0.7 times the compressive yield stress.
7.2.4 If the form of the available material is such that it is
not possible to obtain a specimen with both crack length and
thickness greater than 2.5 (K /s ) , it is not possible to make
Ic y
a valid K (G ) measurement according to these test methods.
Ic Ic
7.2.5 The test method employed for determining yield
stress, as mentioned in 7.2.1-7.2.4, must be reported.
7.3 Specimen Configurations:
7.3.1 Standard Specimens—The configurations of the two
geometries are shown in Fig. 3(a) (SENB) and Fig. 3(b) (CT),
whicharetakenfromAnnexesA3andA4,respectively,ofTest
Method E399. The crack length, a (crack prenotch plus razor
notch), is nominally equal to the thickness, B, and is between
0.45 and 0.55 times the width, W. The ratio W/B is nominally
equal to two.
7.3.2 Alternative Specimens—In certain cases it may be
desirable to use specimens having W/B ratios other than two.
Alternative proportions for bend specimens are 2 < W/B<4.
This alternative shall have the same a/W and S/W ratios as the
standard specimens (S=support span).
7.3.3 Displacement Correction Specimens— Separately
FIG. 3 Specimen Configuration as in Test Method E 399
prepared unnotched specimen configurations for the determi-
nation of the displacement correction mentioned in 9.2 are
order to maximize this dimension. The sample width, W,is W shown in Fig. 4(a) for SENB and in Fig. 4(b) for CT
configurations, respectively.
=2B. In both geometries the crack length, a, should be
selected such that 0.45 < a/W < 0.55.
7.4 Specimen Preparation:
7.1.2 In order for a result to be considered valid according
7.4.1 Initially, prepare a sharp notch by machining. Subse-
to these test methods, the following size criteria must be
quently, initiate a natural crack by inserting a fresh razor blade
satisfied:
and tapping. If a natural crack cannot be successfully initiated
by tapping, a sufficiently sharp crack can alternatively be
B,a, ~W 2a! .2.5 ~K /s ! (1)
Q y
generated by sliding or sawing a new razor blade across the
where:
notch root. The procedure is given in 7.4.1.1-7.4.1.5.
K = the conditional or trial K value (see Section 9), and
Q Ic
7.4.1.1 Machine or saw a sharp notch in the specimen and
s = the yield stress of the material for the temperature
y
generate a natural crack by tapping on a fresh razor blade
and loading rate of the test.
placed in the notch.
D5045–99
8.2 Specimen Measurement—Specimen dimensions shall
conform to those shown in Fig. 3(a, b). Three fundamental
measurements are necessary for the calculation of K and G ,
Ic Ic
namely, the thickness, B, the crack length, a, and the width W.
8.2.1 Measurethethickness,B,to0.1%accuracyatnotless
than three positions. The average of these three measurements
should be recorded as B.
8.2.2 Measure the crack length a, after fracture to the
nearest 0.5% accuracy at the following three positions: at the
centerofthecrackfront,andtheendofthecrackfrontoneach
surface of the specimen. Use the average of these three
measurements as the crack length, a.
8.2.3 Measure the width, W, to within 0.1% as described in
the annex appropriate to the specimen type being tested.
8.3 Loading Rate:
8.3.1 Sinceplasticsareviscoelasticmaterials,itisnecessary
to specify both the temperature and time scale under which the
result was obtained. As a basic test condition it is recom-
mended that a temperatu
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