ASTM D5528-01(2007)e3
(Test Method)Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites
Standard Test Method for Mode I Interlaminar Fracture Toughness of Unidirectional Fiber-Reinforced Polymer Matrix Composites
SIGNIFICANCE AND USE
Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures. Knowledge of a laminated composite material's resistance to interlaminar fracture is useful for product development and material selection. Furthermore, a measurement of the Mode I interlaminar fracture toughness, independent of specimen geometry or method of load introduction, is useful for establishing design allowables used in damage tolerance analyses of composite structures made from these materials.
This test method can serve the following purposes:
To establish quantitatively the effect of fiber surface treatment, local variations in fiber volume fraction, and processing and environmental variables on GIc of a particular composite material.
To compare quantitatively the relative values of GIc for composite materials with different constituents.
To develop delamination failure criteria for composite damage tolerance and durability analyses.
SCOPE
1.1 This test method describes the determination of the opening Mode I interlaminar fracture toughness, GIc, of continuous fiber-reinforced composite materials using the double cantilever beam (DCB) specimen (Fig. 1).
1.2 This test method is limited to use with composites consisting of unidirectional carbon fiber and glass fiber tape laminates with brittle and tough single-phase polymer matrices. This limited scope reflects the experience gained in round-robin testing. This test method may prove useful for other types and classes of composite materials; however, certain interferences have been noted (see 6.5).
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 may involve hazardous materials, operations, and equipment.
1.5 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.
(a) with piano hinges (b) with loading blocksFIG. 1 Double Cantilever Beam Specimen
General Information
Relations
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
´3
Designation: D5528 − 01 (Reapproved2007)
Standard Test Method for
Mode I Interlaminar Fracture Toughness of Unidirectional
Fiber-Reinforced Polymer Matrix Composites
This standard is issued under the fixed designation D5528; 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.
´ NOTE—Added research report reference to Section 14 editorially in March 2008.
´ NOTE—Corrected Eq. 3 in July 2008.
´ NOTE—Eq. 3 was rewritten for clarification in August 2009.
1. Scope D2734TestMethodsforVoidContentofReinforcedPlastics
D3171Test Methods for Constituent Content of Composite
1.1 This test method describes the determination of the
Materials
opening Mode I interlaminar fracture toughness, G , of con-
Ic
D3878Terminology for Composite Materials
tinuous fiber-reinforced composite materials using the double
D5229/D5229MTestMethodforMoistureAbsorptionProp-
cantilever beam (DCB) specimen (Fig. 1).
erties and Equilibrium Conditioning of Polymer Matrix
1.2 This test method is limited to use with composites
Composite Materials
consisting of unidirectional carbon fiber and glass fiber tape
E4Practices for Force Verification of Testing Machines
laminates with brittle and tough single-phase polymer matri-
E6Terminology Relating to Methods of MechanicalTesting
ces. This limited scope reflects the experience gained in
E122PracticeforCalculatingSampleSizetoEstimate,With
round-robin testing. This test method may prove useful for
Specified Precision, the Average for a Characteristic of a
other types and classes of composite materials; however,
Lot or Process
certain interferences have been noted (see 6.5).
E177Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
1.3 The values stated in SI units are to be regarded as the
standard. The values given in parentheses are for information E456Terminology Relating to Quality and Statistics
E691Practice for Conducting an Interlaboratory Study to
only.
Determine the Precision of a Test Method
1.4 This standard may involve hazardous materials,
operations, and equipment.
3. Terminology
1.5 This standard does not purport to address all of the
3.1 Terminology D3878 defines terms relating to high-
safety concerns, if any, associated with its use. It is the
modulus fibers and their composites. Terminology D883 de-
responsibility of the user of this standard to establish appro-
fines terms relating to plastics. Terminology E6 defines terms
priate safety and health practices and determine the applica-
relating to mechanical testing. Terminology E456 and Practice
bility of regulatory limitations prior to use.
E177 define terms relating to statistics. In the event of conflict
between terms, Terminology D3878 shall have precedence
2. Referenced Documents
over the other terminology standards.
2.1 ASTM Standards:
3.2 Definitions of Terms Specific to This Standard:
D883Terminology Relating to Plastics
3.2.1 crack opening mode (Mode I)—fracture mode in
D2651GuideforPreparationofMetalSurfacesforAdhesive
which the delamination faces open away from each other.
Bonding
3.2.2 Mode I interlaminar fracture toughness, G —the
Ic
critical value of G for delamination growth as a result of an
This test method is under the jurisdiction of ASTM Committee D30 on
opening load or displacement.
Composite Materials and is the direct responsibility of Subcommittee D30.06 on
Interlaminar Properties.
3.2.3 energy release rate, G—the loss of energy, dU, in the
Current edition approved May 1, 2007. Published June 2007. Originally
test specimen per unit of specimen width for an infinitesimal
approved in 1994. Last previous edition approved in 2001 as D5528–01. DOI:
increaseindelaminationlength,da,foradelaminationgrowing
10.1520/D5528-01R07E03.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or under a constant displacement. In mathematical form,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
1 dU
Standards volume information, refer to the standard’s Document Summary page on
G52 (1)
the ASTM website. b da
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
´3
D5528 − 01 (2007)
3.3.31 ∆ —incremental change in Log C.
y
4. Summary of Test Method
4.1 The DCB shown in Fig. 1 consists of a rectangular,
uniform thickness, unidirectional laminated composite speci-
men containing a nonadhesive insert on the midplane that
servesasadelaminationinitiator.Openingforcesareappliedto
(a) with piano hinges (b) with loading blocks
the DCB specimen by means of hinges (Fig. 1a) or loading
FIG. 1 Double Cantilever Beam Specimen
blocks (Fig. 1b) bonded to one end of the specimen. The ends
of the DCB are opened by controlling either the opening
displacement or the crosshead movement, while the load and
where:
delamination length are recorded.
U = total elastic energy in the test specimen,
b = specimen width, and
4.2 A record of the applied load versus opening displace-
a = delamination length.
ment is recorded on an X-Y recorder, or equivalent real-time
3.3 Symbols: plotting device or stored digitally and postprocessed. Instanta-
1/3
3.3.1 A —slope of plot of a/b versus C . neous delamination front locations are marked on the chart at
intervals of delamination growth. The Mode I interlaminar
3.3.2 a—delamination length.
fracture toughness is calculated using a modified beam theory
3.3.3 a —initial delamination length.
or compliance calibration method.
3.3.4 b—width of DCB specimen.
5. Significance and Use
3.3.5 C—compliance, δ/ P, of DCB specimen.
3.3.6 CV—coefficient of variation, %.
5.1 Susceptibility to delamination is one of the major
weaknessesofmanyadvancedlaminatedcompositestructures.
3.3.7 da—differential increase in delamination length.
Knowledge of a laminated composite material’s resistance to
3.3.8 dU—differential increase in strain energy.
interlaminar fracture is useful for product development and
3.3.9 E —modulus of elasticity in the fiber direction.
material selection. Furthermore, a measurement of the Mode I
3.3.10 E —modulus of elasticity in the fiber direction
interlaminar fracture toughness, independent of specimen ge-
1f
measured in flexure.
ometry or method of load introduction, is useful for establish-
ing design allowables used in damage tolerance analyses of
3.3.11 F—large displacement correction factor.
composite structures made from these materials.
3.3.12 G—strain energy release rate.
5.2 This test method can serve the following purposes:
3.3.13 G —opening Mode I interlaminar fracture tough-
Ic
5.2.1 To establish quantitatively the effect of fiber surface
ness.
treatment, local variations in fiber volume fraction, and pro-
3.3.14 h—thickness of DCB specimen.
cessing and environmental variables on G of a particular
Ic
3.3.15 L—length of DCB specimen.
composite material.
3.3.16 L`—half width of loading block.
5.2.2 To compare quantitatively the relative values of G
Ic
for composite materials with different constituents.
3.3.17 m—number of plies in DCB specimen.
5.2.3 To develop delamination failure criteria for composite
3.3.18 N—loading block correction factor.
damage tolerance and durability analyses.
3.3.19 NL—pointatwhichtheloadversusopeningdisplace-
ment curve becomes nonlinear.
6. Interferences
3.3.20 n—slope of plot of Log C versus Log a.
6.1 Linear elastic behavior is assumed in the calculation of
3.3.21 P—applied load.
G used in this test method. This assumption is valid when the
3.3.22 P —maximum applied load during DCB test. zone of damage or nonlinear deformation at the delamination
max
front, or both, is small relative to the smallest specimen
3.3.23 SD—standard deviation.
dimension, which is typically the specimen thickness for the
3.3.24 t—distance from loading block pin to center line of
DCB test.
top specimen arm.
6.2 In the DCB test, as the delamination grows from the
3.3.25 U—strain energy.
insert, a resistance-type fracture behavior typically develops
3.3.26 VIS—point at which delamination is observed visu-
wherethecalculatedG firstincreasesmonotonically,andthen
Ic
ally on specimen edge.
stabilizeswithfurtherdelaminationgrowth.Inthistestmethod,
3.3.27 V—fiber volume fraction, %.
f
a resistance curve (R curve) depicting G as a function of
Ic
3.3.28 δ—load point deflection. delamination length will be generated to characterize the
3.3.29 ∆—effective delamination extension to correct for initiationandpropagationofadelaminationinaunidirectional
rotation of DCB arms at delamination front. specimen (Fig. 2). The principal reason for the observed
3.3.30 ∆ —incremental change in Log a. resistance to delamination is the development of fiber bridging
x
´3
D5528 − 01 (2007)
problem with the insert. For example, the insert may not be
completely disbonded from the laminate, or may be too thick,
resulting in a large neat resin pocket, or may contain a tear or
fold. Furthermore, rapid delamination growth may introduce
dynamic effects in both the test specimen and in the fracture
morphology. Treatment and interpretation of these effects is
beyond the scope of this test method. However, because crack
jumpinghasbeenobservedinatleastonematerialinwhichthe
guidelinesforinserts(see8.2)werenotviolated,thespecimens
are unloaded after the first increment of delamination growth
and reloaded to continue the test. This procedure induces a
natural Mode I precrack in the DCB specimen. The first
propagation G value is referred to as the Mode I precrack
Ic
G .
FIG. 2 Delamination Resistance Curve (RCurve) from DCB Test
Ic
6.5 Application to Other Materials, Layups, and Architec-
tures:
(1-3). Thisfiberbridgingmechanismresultsfromgrowingthe
6.5.1 Toughnessvaluesmeasuredonunidirectionalcompos-
delamination between two 0° unidirectional plies. Because
iteswithmultiple-phasematricesmayvarydependinguponthe
most delaminations that form in multiply laminated composite
tendency for the delamination to wander between various
structures occur between plies of dissimilar orientation, fiber
matrix phases. Brittle matrix composites with tough adhesive
bridging does not occur. Hence, fiber bridging is considered to
interleaves between plies may be particularly sensitive to this
be an artifact of the DCB test on unidirectional materials.
phenomenon resulting in two apparent interlaminar fracture
Therefore, the generic significance of G propagation values
Ic
toughness values: one associated with a cohesive-type failure
calculated beyond the end of the implanted insert is
within the interleaf and one associated with an adhesive-type
questionable, and an initiation value of G measured from the
Ic
failure between the tough polymer film and the more brittle
implantedinsertispreferred.Becauseofthesignificanceofthe
composite matrix.
initiation point, the insert must be properly implanted and
6.5.2 Nonunidirectional DCB configurations may experi-
inspected (8.2).
ence branching of the delamination away from the midplane
6.3 Threedefinitionsforaninitiationvalueof G havebeen
Ic
through matrix cracks in off-axis plies. If the delamination
evaluated during round-robin testing (4). These include G
Ic branches away from the midplane, a pure Mode I fracture may
values determined using the load and deflection measured (1)
not be achieved as a result of the structural coupling that may
atthepointofdeviationfromlinearityintheload-displacement
exist in the asymmetric sublaminates formed as the delamina-
curve (NL), (2) at the point at which delamination is visually
tion grows. In addition, nonunidirectional specimens may
observed on the edge (VIS) measured with a microscope as
experience significant anticlastic bending effects that result in
specified in 7.5, and (3) at the point at which the compliance
nonuniform delamination growth along the specimen width,
hasincreasedby5%ortheloadhasreachedamaximumvalue
particularly affecting the observed initiation values.
(5%/max) (see Section 11). The NL G value, which is
Ic 6.5.3 Woven composites may yield significantly greater
typically the lowest of the three G initiation values, is
Ic scatter and unique R curves associated with varying toughness
recommended for generating delamination failure criteria in
within and away from interlaminar resin pockets as the
durability and damage tolerance analyses of laminated com-
delamination grows. Composites with significant strength or
posite structures (5.2.3). Recommendations for obtaining the
toughness through the laminate thickness, such as composites
NLpointaregiveninAnnexA2.Allthreeinitiationvaluescan
withmetalmatricesor3Dfiberreinforcement,mayexperience
be used for the other purposes cited in the scope (5.2.1 and
failures of the beam arms rather than the intended interlaminar
5.2.2). However, physical evidence indicates that the initiation
failures.
value corresponding to the onset of nonlinearity (NL) in the
load versus opening displacement plot corresponds to the 7. Apparatus
physicalonsetofdelaminationfromtheinsertintheinteriorof
7.1 Testing Machine—A properly calibrated test machine
the specimen width (5). In round-robin testing of AS4/PEEK
shall be used that can be operated in a displacement control
thermoplastic matrix composites, NL G values were 20%
Ic
mode with a constant displacement rate in the range from 0.5
lower than VIS and 5%/max values (4).
to5.0mm/min(0.02to0.20in./min).Thetestingmachineshall
6.4 Delamination growth may proceed in one of two ways:
conform to the requirements of Practices E4. The testing
(1) by a slow stable extension or (2) a run-arrest extension in machine shall be equipped with grips to hold the loading
which the delamination front jumps ahead abruptly. Only the
hinges, or pins to hold the loading blocks, that are bonded to
first type of growth is of interest in this test method. An the specimen.
unstable jump from the insert may be an indication of a
7.2 Load Indicator—The testing machine load-sensing de-
vice shall be capable of indicating the total load carried by the
testspecimen.Thisdeviceshallbeessentiallyfreefrominertia
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this test method. lag at the specified rate of testing and shall indicate the load
´3
D5528 − 01 (2007)
with an accuracy over the load range(s) of interest of within that are manufactured at relatively high temperatures, greater
61% of the indicated value. than 177°C (350°F), a thin polyimide film is recommended.
For materials outside the scope of this test method, different
7.3 O
...
This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´3
Designation:D5528–94a Designation: D 5528 – 01 (Reapproved 2007)
Standard Test Method for
Mode I Interlaminar Fracture Toughness of Unidirectional
Fiber-Reinforced Polymer Matrix Composites
This standard is issued under the fixed designation D 5528; 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.
´ NOTE—Added research report reference to Section 14 editorially in March 2008.
´ NOTE—Corrected Eq. 3 in July 2008.
´ NOTE—Eq. 3 was rewritten for clarification in August 2009.
1. Scope
1.1 This test method describes the determination of the opening Mode I interlaminar fracture toughness, G , of unidirection-
Ic
alcontinuous fiber-reinforced polymer matrix compositescomposite materials using the double cantilever beam (DCB) specimen
(Fig. 1).
1.2 This test method is limited to use with composites consisting of unidirectional carbon fiber and glass fiber tape laminates
with brittle and tough single-phase polymer matrices.This limited scope reflects the experience gained in round-robin testing.This
test method may prove useful for other types and classes of composite materials,; however, certain interferences have been noted
(see 6.5).
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
1.4 This standard may involve hazardous materials, operations, and equipment.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D 883 Terminology Relating to Plastics
D 2651 Guide for Preparation of Metal Surfaces for Adhesive Bonding
D 2734 Test Methods for Void Content of Reinforced Plastics
D 3171 Test Method for Fiber Content of Resin Matrix Composites by Matrix Digestion Test Methods for Constituent Content
of Composite Materials
D 3878 Terminology of High-Modulus Reinforced Fibers and Their Composites Terminology for Composite Materials
D 5229/D 5229M TestMethodforMoistureAbsorptionPropertiesandEquilibriumConditioningofPolymerMatrixComposite
Materials
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E 122 PracticeforChoiceofSampleSizetoEstimateaMeasureofQualityforaLotorProcessPracticeforCalculatingSample
Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot or Process
E 177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E 456 Terminology Relating to Quality and Statistics
E 691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Terminology D 3878 defines terms relating to high-modulus fibers and their composites. Terminology D 883 defines terms
This test method is under the jurisdiction of ASTM Committee D-30 on High Modulus Fibers and Their Composites and is the direct responsibility of Subcommittee
D30 on Composite Materials and is the direct responsibility of Subcommittee D30.06 on Interlaminar Properties.
Current edition approved May 15, 1994. Published July 1994. Originally published as D5528–94. Last previous editions D5528–94.
Current edition approved May 1, 2007. Published June 2007. Originally approved in 1994. Last previous edition approved in 2001 as D 5528 – 01.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book ofASTM Standards
, Vol 08.01.volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
´3
D 5528 – 01 (2007)
(a) with piano hinges (b) with loading blocks
FIG. 1 Double Cantilever Beam Specimen
relating to plastics. Terminology E 6 defines terms relating to mechanical testing. Terminology E 456 and Practice E 177 define
terms relating to statistics. In the event of conflict between terms, Terminology D 3878 shall have precedence over the other
terminology standards.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 crack opening mode (Mode I)—fracture mode in which the delamination faces open away from each other.
3.2.2 Mode I interlaminar fracture toughness, G —the critical value of G for delamination growth due to an opening load or
Ic
displacement. for delamination growth as a result of an opening load or displacement.
3.2.3 strain energy release rate, G—the loss of strain energy, dU, in the test specimen per unit of specimen width for an
infinitesimalincreaseindelaminationlength, da,foradelaminationgrowingunderaconstantdisplacement.Inmathematicalform,
1 dU
G52 (1)
b da
where:
U = total elastic strain energy in the test specimen,
b = specimen width, and
a = delamination length.
3.3 Symbols:
1/3
3.3.1 A —slope of plot of a/b versus C .
3.3.2 a—delamination length.
3.3.3 a —initial delamination length.
3.3.4 b—width of DCB specimen.
3.3.5 C—compliance, d/ P, of DCB specimen.
3.3.6 CV—coefficient of variation, %.
3.3.7 da—differential increase in delamination length.
3.3.8 dU—differential increase in strain energy.
3.3.9 E —modulus of elasticity in the fiber direction.
3.3.10 E —modulus of elasticity in the fiber direction measured in flexure.
1f
3.3.11 F—large displacement correction factor.
3.3.12 FAW—fiber areal weight.
3.3.13FD—fiber density.
3.3.14G—strain energy release rate.
3.3.15G
3.3.13 G —opening Mode I interlaminar fracture toughness.
Ic
3.3.16
3.3.14 h—thickness of DCB specimen.
3.3.17
3.3.15 L—length of DCB specimen.
3.3.18
3.3.16 L8—half-width of loading block.
3.3.19—half width of loading block.
3.3.17 m—number of plies in DCB specimen.
3.3.20
3.3.18 N—loading block correction factor.
3.3.21
3.3.19 NL—point at which the load versus opening displacement curve becomes non-linear.
3.3.223.3.20 n—slope of plot of Log C versus Log a.
3.3.23
3.3.21 P—applied load.
3.3.24
´3
D 5528 – 01 (2007)
3.3.22 P —maximum applied load during DCB test.
max
3.3.25
3.3.23 SD—standard deviation.
3.3.26
3.3.24 t—distance from loading block pin to center line of top specimen arm.
3.3.27
3.3.25 U—strain energy.
3.3.28
3.3.26 VIS—point at which delamination is observed visually on specimen edge.
3.3.29
3.3.27 V—fiber volume fraction, %.
f
3.3.30d—load3.3.28 d—load point deflection.
3.3.31D—effective3.3.29 D—effective delamination extension to correct for rotation of DCB arms at delamination front.
3.3.32D3.3.30 D —incremental change in Log a.
x
3.3.33D
3.3.31 D—incremental change in Log C.
y
4. Summary of Test Method
4.1 The DCB shown in Fig. 1 consists of a rectangular, uniform thickness, unidirectional laminated composite specimen,speci-
men containing a nonadhesive insert on the midplane whichthat serves as a delamination initiator. Opening forces are applied to
the DCB specimen by means of hinges (Fig. 1a) or loading blocks (Fig. 1b) bonded to one end of the specimen. The ends of the
DCB are opened by controlling either the opening displacement, or the crosshead movement, while the load and delamination
length are recorded.
4.2 A record of the applied load versus opening displacement is recorded on an X-Y recorder, or equivalent real-time plotting
device or stored digitally and postprocessed. Instantaneous delamination front locations are marked on the chart at intervals of
delamination growth. The Mode I interlaminar fracture toughness is calculated using a modified beam theory or compliance
calibration method.
5. Significance and Use
5.1 Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures.
Knowledge of a laminated composite material’s resistance to interlaminar fracture is useful for product development and material
selection. Furthermore, a measurement of the Mode I interlaminar fracture toughness, independent of specimen geometry or
methodofloadintroduction,isusefulforestablishingdesignallowablesusedindamagetoleranceanalysesofcompositestructures
made from these materials.
5.2 This test method can serve the following purposes:
5.2.1 To establish quantitatively the effect of fiber surface treatment, local variations in fiber volume fraction, and processing
and environmental variables on G of a particular composite material.
Ic
5.2.2 To compare quantitatively the relative values of G for composite materials with different constituents.
Ic
5.2.3 To develop delamination failure criteria for composite damage tolerance and durability analyses.
6. Interferences
6.1 Linear elastic behavior is assumed in the calculation of G used in this test method. This assumption is valid when the zone
of damage or nonlinear deformation at the delamination front, or both, is small relative to the smallest specimen dimension, which
is typically the specimen thickness for the DCB test.
6.2 In the DCB test, as the delamination grows from the insert, a resistance-type fracture behavior typically develops where the
calculated G first increases monotonically, and then stabilizes with further delamination growth. In this test method, a resistance
Ic
curve (R-curve) (R curve) depicting G as a function of delamination length,length will be generated to characterize the initiation
Ic
and propagation of a delamination in a unidirectional specimen (Fig. 2). The principal reason for the observed resistance to
delamination is the development of fiber bridging (1-3). This fiber bridging mechanism results from growing the delamination
between two zero-degree0° unidirectional plies. Because most delaminations that form in multi-plymultiply laminated composite
structures occur between plies of dissimilar orientation, fiber bridging does not occur. Hence, fiber bridging is considered to be an
artifactoftheDCBtestonunidirectionalmaterials.Therefore,thegenericsignificanceofG propagationvaluescalculatedbeyond
Ic
the end of the implanted insert is questionable, and an initiation value of G measured from the implanted insert is preferred.
Ic
Because of the significance of the initiation point, the insert must be properly implanted and inspected (8.2).
6.3 Three definitions for an initiation value of G have been evaluated during round-robin testing (4). These include G values
Ic Ic
determinedusingtheloadanddeflectionmeasured(1)atthepointofdeviationfromlinearityintheload-displacementcurve(NL),
Annual Book of ASTM Standards, Vol 15.06.
The boldface numbers in parentheses refer to the list of references at the end of this test method.
´3
D 5528 – 01 (2007)
FIG. 2 Delamination Resistance Curve (R-cCurve) F from DCB
Test
(2) at the point where at which delamination is visually observed on the edge (VIS) measured with a microscope as specified in
7.5, and (3) at the point where at which the compliance has increased by 5 % or where the load has reached a maximum value
(5 %/max) (see Section 11). The NL G value, which is typically the lowest of the three G initiation values, is recommended
Ic Ic
for generating delamination failure criteria in durability and damage tolerance analyses of laminated composite structures (5.2.3).
All three initiation values can be used for the other purposes cited in the scope (). Recommendations for obtaining the NL point
are given inAnnexA2.All three initiation values can be used for the other purposes cited in the scope (5.2.1 and 5.2.2). However,
physical evidence indicates that the initiation value corresponding to the onset of non-linearity (NL) in the load versus opening
displacement plot corresponds to the physical onset of delamination from the insert in the interior of the specimen width (5).In
round-robin testing ofAS4/PEEK thermoplastic matrix composites, NLG values were 20 % lower thanVIS and 5 %/max values
Ic
(4).
6.4Delamination growth may proceed in one of two ways: (1) by a slow stable extension, or (2) by a run-arrest extension, where
the delamination front jumps ahead abruptly. Only the first type of growth is of interest in this test method.An unstable jump from
the insert may be an indication of a problem with the insert. For example, the insert may not be completely disbonded from the
laminate, or may be too thick resulting in a large neat resin pocket, or may contain a tear or fold. Furthermore, rapid delamination
growth may introduce dynamic effects in both the test specimen and in the fracture morphology. Treatment and interpretation of
these effects is beyond the scope of this test method.
6.5
6.4 Delamination growth may proceed in one of two ways: (1) by a slow stable extension or (2) a run-arrest extension in which
the delamination front jumps ahead abruptly. Only the first type of growth is of interest in this test method.An unstable jump from
the insert may be an indication of a problem with the insert. For example, the insert may not be completely disbonded from the
laminate, or may be too thick, resulting in a large neat resin pocket, or may contain a tear or fold. Furthermore, rapid delamination
growth may introduce dynamic effects in both the test specimen and in the fracture morphology. Treatment and interpretation of
these effects is beyond the scope of this test method. However, because crack jumping has been observed in at least one material
in which the guidelines for inserts (see 8.2) were not violated, the specimens are unloaded after the first increment of delamination
growth and reloaded to continue the test. This procedure induces a natural Mode I precrack in the DCB specimen. The first
propagation G value is referred to as the Mode I precrack G .
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6.5 Application to Other Materials, Layups, and Architectures:
6.5.1The DCB test has been used extensively for unidirectional glass fiber reinforced tape laminates with single-phase polymer
matrices, but corrections may be needed for anticlastic bending effects. Toughness 6.5.1 Toughness values measured on
unidirectional composites with multiple-phase matrices may vary depending upon the tendency for the delamination to wander
between various matrix phases. Brittle matrix composites
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This document is not anASTM standard and is intended only to provide the user of anASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
´2 ´2
Designation: D 5528 – 01 (Reapproved 2007) D 5528 – 01 (2007) ´3
Standard Test Method for
Mode I Interlaminar Fracture Toughness of Unidirectional
Fiber-Reinforced Polymer Matrix Composites
This standard is issued under the fixed designation D 5528; 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.
´ NOTE—Added research report reference to Section 14 editorially in March 2008.
´ NOTE—Corrected Eq. 3 in July 2008.
—Corrected Eq. 3 in July 2008.
´ NOTE—Eq. 3 was rewritten for clarification in August 2009.
1. Scope
1.1 This test method describes the determination of the opening Mode I interlaminar fracture toughness, G , of continuous
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fiber-reinforced composite materials using the double cantilever beam (DCB) specimen (Fig. 1).
1.2 This test method is limited to use with composites consisting of unidirectional carbon fiber and glass fiber tape laminates
with brittle and tough single-phase polymer matrices.This limited scope reflects the experience gained in round-robin testing.This
test method may prove useful for other types and classes of composite materials; however, certain interferences have been noted
(see 6.5).
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 may involve hazardous materials, operations, and equipment.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
D 883 Terminology Relating to Plastics
D 2651 Guide for Preparation of Metal Surfaces for Adhesive Bonding
D 2734 Test Methods for Void Content of Reinforced Plastics
D 3171 Test Methods for Constituent Content of Composite Materials
D 3878 Terminology for Composite Materials
D 5229/D 5229M TestMethodforMoistureAbsorptionPropertiesandEquilibriumConditioningofPolymerMatrixComposite
Materials
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E 122 Practice for Calculating Sample Size to Estimate, With Specified Precision, theAverage for a Characteristic of a Lot or
Process
E 177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E 456 Terminology Relating to Quality and Statistics
E 691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 Terminology D 3878 defines terms relating to high-modulus fibers and their composites. Terminology D 883 defines terms
relating to plastics. Terminology E 6 defines terms relating to mechanical testing. Terminology E 456 and Practice E 177 define
terms relating to statistics. In the event of conflict between terms, Terminology D 3878 shall have precedence over the other
terminology standards.
This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.06 on Interlaminar
Properties.
Current edition approved May 1, 2007. Published June 2007. Originally approved in 1994. Last previous edition approved in 2001 as D 5528 – 01.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
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(a) with piano hinges (b) with loading blocks
FIG. 1 Double Cantilever Beam Specimen
3.2 Definitions of Terms Specific to This Standard:
3.2.1 crack opening mode (Mode I)—fracture mode in which the delamination faces open away from each other.
3.2.2 Mode I interlaminar fracture toughness, G —the critical value of G for delamination growth as a result of an opening
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load or displacement.
3.2.3 energyreleaserate,G—thelossofenergy,dU,inthetestspecimenperunitofspecimenwidthforaninfinitesimalincrease
in delamination length, da, for a delamination growing under a constant displacement. In mathematical form,
1 dU
G52 (1)
b da
where:
U = total elastic energy in the test specimen,
b = specimen width, and
a = delamination length.
3.3 Symbols:
1/3
3.3.1 A —slope of plot of a/b versus C .
3.3.2 a—delamination length.
3.3.3 a —initial delamination length.
3.3.4 b—width of DCB specimen.
3.3.5 C—compliance, d/ P, of DCB specimen.
3.3.6 CV—coefficient of variation, %.
3.3.7 da—differential increase in delamination length.
3.3.8 dU—differential increase in strain energy.
3.3.9 E —modulus of elasticity in the fiber direction.
3.3.10 E —modulus of elasticity in the fiber direction measured in flexure.
1f
3.3.11 F—large displacement correction factor.
3.3.12 G—strain energy release rate.
3.3.13 G —opening Mode I interlaminar fracture toughness.
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3.3.14 h—thickness of DCB specimen.
3.3.15 L—length of DCB specimen.
3.3.16 L8—half width of loading block.
3.3.17 m—number of plies in DCB specimen.
3.3.18 N—loading block correction factor.
3.3.19 NL—point at which the load versus opening displacement curve becomes nonlinear.
3.3.20 n—slope of plot of Log C versus Log a.
3.3.21 P—applied load.
3.3.22 P —maximum applied load during DCB test.
max
3.3.23 SD—standard deviation.
3.3.24 t—distance from loading block pin to center line of top specimen arm.
3.3.25 U—strain energy.
3.3.26 VIS—point at which delamination is observed visually on specimen edge.
3.3.27 V—fiber volume fraction, %.
f
3.3.28 d—load point deflection.
3.3.29 D—effective delamination extension to correct for rotation of DCB arms at delamination front.
3.3.30 D —incremental change in Log a.
x
3.3.31 D —incremental change in Log C.
y
4. Summary of Test Method
4.1 The DCB shown in Fig. 1 consists of a rectangular, uniform thickness, unidirectional laminated composite specimen
containing a nonadhesive insert on the midplane that serves as a delamination initiator. Opening forces are applied to the DCB
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specimen by means of hinges (Fig. 1a) or loading blocks (Fig. 1b) bonded to one end of the specimen. The ends of the DCB are
opened by controlling either the opening displacement or the crosshead movement, while the load and delamination length are
recorded.
4.2 A record of the applied load versus opening displacement is recorded on an X-Y recorder, or equivalent real-time plotting
device or stored digitally and postprocessed. Instantaneous delamination front locations are marked on the chart at intervals of
delamination growth. The Mode I interlaminar fracture toughness is calculated using a modified beam theory or compliance
calibration method.
5. Significance and Use
5.1 Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures.
Knowledge of a laminated composite material’s resistance to interlaminar fracture is useful for product development and material
selection. Furthermore, a measurement of the Mode I interlaminar fracture toughness, independent of specimen geometry or
methodofloadintroduction,isusefulforestablishingdesignallowablesusedindamagetoleranceanalysesofcompositestructures
made from these materials.
5.2 This test method can serve the following purposes:
5.2.1 To establish quantitatively the effect of fiber surface treatment, local variations in fiber volume fraction, and processing
and environmental variables on G of a particular composite material.
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5.2.2 To compare quantitatively the relative values of G for composite materials with different constituents.
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5.2.3 To develop delamination failure criteria for composite damage tolerance and durability analyses.
6. Interferences
6.1 Linear elastic behavior is assumed in the calculation of G used in this test method. This assumption is valid when the zone
of damage or nonlinear deformation at the delamination front, or both, is small relative to the smallest specimen dimension, which
is typically the specimen thickness for the DCB test.
6.2 In the DCB test, as the delamination grows from the insert, a resistance-type fracture behavior typically develops where the
calculated G first increases monotonically, and then stabilizes with further delamination growth. In this test method, a resistance
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curve (R curve) depicting G as a function of delamination length will be generated to characterize the initiation and propagation
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of a delamination in a unidirectional specimen (Fig. 2). The principal reason for the observed resistance to delamination is the
development of fiber bridging (1-3). This fiber bridging mechanism results from growing the delamination between two 0°
unidirectional plies. Because most delaminations that form in multiply laminated composite structures occur between plies of
dissimilar orientation, fiber bridging does not occur. Hence, fiber bridging is considered to be an artifact of the DCB test on
unidirectional materials. Therefore, the generic significance of G propagation values calculated beyond the end of the implanted
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insert is questionable, and an initiation value of G measured from the implanted insert is preferred. Because of the significance
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of the initiation point, the insert must be properly implanted and inspected (8.2).
6.3 Three definitions for an initiation value of G have been evaluated during round-robin testing (4). These include G values
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determinedusingtheloadanddeflectionmeasured(1)atthepointofdeviationfromlinearityintheload-displacementcurve(NL),
(2) at the point at which delamination is visually observed on the edge (VIS) measured with a microscope as specified in 7.5, and
(3) at the point at which the compliance has increased by 5 % or the load has reached a maximum value (5 %/max) (see Section
11).TheNLG value,whichistypicallythelowestofthethree G initiationvalues,isrecommendedforgeneratingdelamination
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failure criteria in durability and damage tolerance analyses of laminated composite structures (5.2.3). Recommendations for
The boldface numbers in parentheses refer to the list of references at the end of this test method.
FIG. 2 Delamination Resistance Curve (R Curve) from DCB Test
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obtainingtheNLpointaregiveninAnnexA2.Allthreeinitiationvaluescanbeusedfortheotherpurposescitedinthescope(5.2.1
and 5.2.2). However, physical evidence indicates that the initiation value corresponding to the onset of nonlinearity (NL) in the
load versus opening displacement plot corresponds to the physical onset of delamination from the insert in the interior of the
specimen width (5). In round-robin testing of AS4/PEEK thermoplastic matrix composites, NL G values were 20 % lower than
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VIS and 5 %/max values (4).
6.4 Delamination growth may proceed in one of two ways: (1) by a slow stable extension or (2) a run-arrest extension in which
the delamination front jumps ahead abruptly. Only the first type of growth is of interest in this test method.An unstable jump from
the insert may be an indication of a problem with the insert. For example, the insert may not be completely disbonded from the
laminate, or may be too thick, resulting in a large neat resin pocket, or may contain a tear or fold. Furthermore, rapid delamination
growth may introduce dynamic effects in both the test specimen and in the fracture morphology. Treatment and interpretation of
these effects is beyond the scope of this test method. However, because crack jumping has been observed in at least one material
in which the guidelines for inserts (see 8.2) were not violated, the specimens are unloaded after the first increment of delamination
growth and reloaded to continue the test. This procedure induces a natural Mode I precrack in the DCB specimen. The first
propagation G value is referred to as the Mode I precrack G .
Ic Ic
6.5 Application to Other Materials, Layups, and Architectures:
6.5.1 Toughness values measured on unidirectional composites with multiple-phase matrices may vary depending upon the
tendency for the delamination to wander between various matrix phases. Brittle matrix composites with tough adhesive interleaves
between plies may be particularly sensitive to this phenomenon resulting in two apparent interlaminar fracture toughness values:
one associated with a cohesive-type failure within the interleaf and one associated with an adhesive-type failure between the tough
polymer film and the more brittle composite matrix.
6.5.2 Nonunidirectional DCB configurations may experience branching of the delamination away from the midplane through
matrix cracks in off-axis plies. If the delamination branches away from the midplane, a pure Mode I fracture may not be achieved
as a result of the structural coupling that may exist in the asymmetric sublaminates formed as the delamination grows. In addition,
nonunidirectional specimens may experience significant anticlastic bending effects that result in nonuniform delamination growth
along the specimen width, particularly affecting the observed initiation values.
6.5.3 Woven composites may yield significantly greater scatter and unique R curves associated with varying toughness within
and away from interlaminar resin pockets as the delamination grows. Composites with significant strength or toughness through
the laminate thickness, such as composites with metal matrices or 3D fiber reinforcement, may experience failures of the beam
arms rather than the intended interlaminar failures.
7. Apparatus
7.1 Testing Machine—Aproperlycalibratedtestmachineshallbeusedthatcanbeoperatedinadisplacementcontrolmodewith
a constant displacement rate in the range from 0.5 to 5.0 mm/min (0.02 to 0.20 in./min). The testing machine shall conform to the
requirements of Practices E 4. The testing machine shall be equipped with grips to hold the loading hinges, or pins to hold the
loading blocks, that are bonded to the specimen.
7.2 Load Indicator—The testing machine load-sensing device shall be capable of indicating the total load carried by the test
specimen. This device shall be essentially free from inertia lag a
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