ASTM D5045-99(2007)e1
(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
p>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.
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.
There is currently no ISO standard that duplicates these test methods. Pending ISO/CD 13586 covers similar testing and references this test method for testing conditions.
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Designation: D5045 − 99(Reapproved 2007)
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 (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—Reapproved with editorial changes in March 2007
1. Scope* 1.10 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 These test methods are designed to characterize the
responsibility of the user of this standard to establish appro-
toughness of plastics in terms of the critical-stress-intensity
priate safety and health practices and determine the applica-
factor, K , and the energy per unit area of crack surface or
Ic
bility of regulatory limitations prior to use.
critical strain energy release rate, G , at fracture initiation.
Ic
NOTE 1—There is currently no ISO standard that duplicates these test
1.2 Two testing geometries are covered by these test
methods. Pending ISO/CD 13586 covers similar testing and references
methods, single-edge-notch bending (SENB) and compact
this test method for testing conditions.
tension (CT).
2. Referenced Documents
1.3 The scheme used assumes linear elastic behavior of the
2.1 ASTM Standards:
cracked specimen, so certain restrictions on linearity of the
D638Test Method for Tensile Properties of Plastics
load-displacement diagram are imposed.
D4000Classification System for Specifying Plastic Materi-
1.4 A state-of-plane strain at the crack tip is required.
als
Specimen thickness must be sufficient to ensure this stress
E399Test Method for Linear-Elastic Plane-Strain Fracture
state.
Toughness K of Metallic Materials
Ic
1.5 The crack must be sufficiently sharp to ensure that a E691Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
minimum value of toughness is obtained.
1.6 The significance of these test methods and many con-
3. Terminology
ditions of testing are identical to those of Test Method E399,
3.1 Definitions:
and, therefore, in most cases, appear here with many similari-
3.1.1 compact tension, n—specimen geometry consisting of
ties to the metals standard. However, certain conditions and
single-edge notched plate loaded in tension. See 3.1.5 for
specifications not covered in Test Method E399, but important
reference to additional definition.
for plastics, are included.
3.1.2 critical strain energy release rate, G ,n—toughness
Ic
1.7 This protocol covers the determination of G as well,
Ic
parameter based on energy required to fracture. See 3.1.5 for
which is of particular importance for plastics.
reference to additional definition.
1.8 Thesetestmethodsgivegeneralinformationconcerning
3.1.3 plane-strain fracture toughness, K ,n—toughness
Ic
the requirements for K and G testing.As with Test Method
Ic Ic parameter indicative of the resistance of a material to fracture.
E399, two annexes are provided which give the specific
See 3.1.5 for reference to additional definition.
requirements for testing of the SENB and CT geometries.
3.1.4 single-edge notched bend, n—specimen geometry
1.9 Testdataobtainedbythesetestmethodsarerelevantand
consisting of center-notched beam loaded in three-point bend-
appropriate for use in engineering design.
ing. See 3.1.5 for reference to additional definition.
3.1.5 Reference is made toTest Method E399 for additional
explanation of definitions.
These test methods are under the jurisdiction of ASTM Committee D20 on
Plastics and is the direct responsibility of Subcommittee D20.10 on Mechanical
Properties. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2007. Published June 2007. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1990. Last previous edition approved in 1999 as D5045-99. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D5045-99R07E01. 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
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D5045 − 99 (2007)
3.2 Definitions of Terms Specific to This Standard: 5.2 Inasmuch as the fracture toughness of plastics is often
3.2.1 yield stress, n—stress at fracture is used. The slope of dependent on specimen process history, that is, injection
the stress-strain curve is not required to be zero. See 7.2 for molded, extruded, compression molded, etc., the specimen
reference to additional definition. crack orientation (parallel or perpendicular) relative to any
processing direction should be noted on the report form
4. Summary of Test Methods
discussed in 10.1.
4.1 These test methods involve loading a notched specimen
5.3 For many materials, there may be a specification that
that has been pre-cracked, in either tension or three-point
requires the use of these test methods, but with some proce-
bending. The load corresponding to a 2.5% apparent incre-
dural modifications that take precedence when adhering to the
ment of crack extension is established by a specified deviation
specification. Therefore, it is advisable to refer to that material
from the linear portion of the record. The K value is
Ic
specification before using these test methods. Table 1 of
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
determination of the K value by these test methods depends 6. Apparatus
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 specimen 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
Ic Ic 6.2 Displacement Measurement—An accurate displacement
characterizestheresistanceofamaterialtofractureinaneutral
measurement must be obtained to assure accuracy of the G
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 Internal Displacement Transducer— For either SENB
front approaches plane strain, and the crack-tip plastic (or
orCTspecimenconfigurations,thedisplacementmeasurement
non-linear viscoelastic) region is small compared with the
shall be performed using the machine’s stroke (position)
cracksizeandspecimendimensionsintheconstraintdirection.
transducer. The fracture-test-displacement data must be cor-
A K value is believed to represent a lower limiting value of
Ic rected for system compliance, loading-pin penetration (brinel-
fracture toughness. This value may be used to estimate the
ling)andspecimencompressionbyperformingacalibrationof
relation between failure stress and defect size for a material in
the 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 can be found in Refs (1-5).
device shall be used as illustrated in Fig. 1 for the SENB
5.1.1 TheK (G )valueofagivenmaterialisafunctionof
Ic Ic
configuration. For CT specimens, a clip gauge shall be
testing speed and temperature. Furthermore, cyclic loads can
cause crack extension at K values less than K (G ). Crack
Ic Ic
extension under cyclic or sustained load will be increased by
the presence of an aggressive environment. Therefore, appli-
cation of K (G ) in the design of service components should
Ic Ic
be made considering differences that may exist between
laboratory tests and field conditions.
5.1.2 Plane-strain fracture toughness testing is unusual in
that there can be no advance assurance that a valid K (G )
Ic Ic
will be determined in a particular test. Therefore it is essential
thatallofthecriteriaconcerningvalidityofresultsbecarefully
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.
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
these test methods. FIG. 1 Bending Rig with Transducer for SENB
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D5045 − 99 (2007)
order to maximize this dimension. The specimen width, W,is
W =2B. In both geometries the crack length, a, should be
selected such that 0.45 < a/W < 0.55.
7.1.2 In order for a result to be considered valid according
to these test methods, the following size criteria must be
satisfied:
B, a, ~W 2 a!.2.5 K /σ (1)
~ !
Q y
where:
K = the conditional or trial K value (see Section 9), and
Q Ic
σ = the yield stress of the material for the temperature and
y
loading rate of the test.
The criteria require that B must be sufficient to ensure plane
strain and that (W−a ) be sufficient to avoid excessive
plasticity 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 shall be permitted for SENB specimens.
7.2 Yield Stress:
7.2.1 The yield stress, σ , is to be taken from the maximum
y
FIG. 2 Tension Testing Clevis Design for CT
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 /σ ) 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
fracture shall 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 /σ ) , 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
FIG. 3 Specimen Configuration as in Test Method E399
geometries are shown in Fig. 3(a) (SENB) and Fig. 3(b) (CT),
whicharetakenfromAnnexesA3andA4,respectively,ofTest
Method E399. The crack length, a (crack pre-notch plus razor
mounted across the loading pins. For both the SENB and CT
notch), is nominally equal to the thickness, B, and is between
specimens, the displacement should be taken at the load point.
0.45 and 0.55 times the width, W. The ratio W/B is nominally
7. Specimen Size, Configurations, and Preparation equal to two.
7.3.2 Alternative Specimens—In certain cases it may be
7.1 Specimen Size:
desirable to use specimens having W/B ratios other than two.
7.1.1 SENB and CT geometries are recommended over
Alternative proportions for bend specimens are 2 < W/B<4.
other configurations because these have predominantly bend-
This alternative shall have the same a/W and S/W ratios as the
ing stress states which allow smaller specimen sizes to achieve
standard specimens (S=support span).
plane strain. Specimen dimensions are shown in Fig. 3 (a, b).
If the material is supplied in the form of a sheet, the specimen 7.3.3 DisplacementCorrectionSpecimens—Separatelypre-
thickness, B, should be identical with the sheet thickness, in paredunnotchedspecimenconfigurationsforthedetermination
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D5045 − 99 (2007)
of the displacement correction mentioned in 9.2 are shown in some tough materials, then a fresh razor blade can be slid in
Fig. 4(a) for SENB and in Fig. 4(b) for CT configurations, one motion, or with a sawing motion across the machined
respectively. notch.
7.4.1.4 Thedepthoftherazornotchgeneratedbyslidingthe
7.4 Specimen Preparation:
razor blade must be two times longer than the width of the
7.4.1 Initially, prepare a sharp notch by machining.
sawed-in slot or of the pre-notch tip radius (the notch diagram
Subsequently, initiate a natural crack by inserting a fresh razor
in Fig. 3 is not to scale).
blade and tapping. If a natural crack cannot be successfully
initiated by tapping, a sufficiently sharp crack shall alterna-
NOTE 2—Pressing the blade into the notch is not recommended for
tively be generated by sliding or sawing a new razor blade moreductileresinsbecauseitmayinduceresidualstressesatthecracktip
which may result in an artificially high value of K .
across the notch root. The procedure is given in 7.4.1.1 – Ic
7.4.1.5.
7.4.1.5 Thetotaldepthofthenotchobtainedbymachining
7.4.1.1 Machine or saw a sharp notch in the specimen and
and generation of the natural crack is the crack length, a.
generate a natural crack by tapping on a fresh razor blade
placed in the notch.
8. General Procedure
7.4.1.2 The depth of the natural crack generated by tapping
8.1 Number of Tests—It is recommended that at least three
mustbea
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