ASTM D5528-01(2007)e1
(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.
General Information
Relations
Buy Standard
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
e1
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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Added research report reference to Section 14 editorially in March 2008.
1. Scope
1.1 This test method describes the determination of the
opening Mode I interlaminar fracture toughness, G , of con-
Ic
tinuous 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
(a) with piano hinges (b) with loading blocks
laminates with brittle and tough single-phase polymer matri-
FIG. 1 Double Cantilever Beam Specimen
ces. This limited scope reflects the experience gained in
round-robin testing. This test method may prove useful for
D 3878 Terminology for Composite Materials
other types and classes of composite materials; however,
D 5229/D 5229M Test Method for Moisture Absorption
certain interferences have been noted (see 6.5).
Properties and Equilibrium Conditioning of Polymer Ma-
1.3 The values stated in SI units are to be regarded as the
trix Composite Materials
standard. The values given in parentheses are for information
E4 Practices for Force Verification of Testing Machines
only.
E6 Terminology Relating to Methods of Mechanical Test-
1.4 This standard may involve hazardous materials, opera-
ing
tions, and equipment.
E 122 Practice for Calculating Sample Size to Estimate,
1.5 This standard does not purport to address all of the
With Specified Precision, the Average for a Characteristic
safety concerns, if any, associated with its use. It is the
of a Lot or Process
responsibility of the user of this standard to establish appro-
E 177 Practice for Use of the Terms Precision and Bias in
priate safety and health practices and determine the applica-
ASTM Test Methods
bility of regulatory limitations prior to use.
E 456 Terminology Relating to Quality and Statistics
E 691 Practice for Conducting an Interlaboratory Study to
2. Referenced Documents
2 Determine the Precision of a Test Method
2.1 ASTM Standards:
D 883 Terminology Relating to Plastics
3. Terminology
D 2651 Guide for Preparation of Metal Surfaces for Adhe-
3.1 Terminology D 3878 defines terms relating to high-
sive Bonding
modulus fibers and their composites. Terminology D 883
D 2734 Test Methods for Void Content of Reinforced Plas-
defines terms relating to plastics. Terminology E6 defines
tics
terms relating to mechanical testing. Terminology E 456 and
D 3171 Test Methods for Constituent Content of Composite
PracticeE 177definetermsrelatingtostatistics.Intheeventof
Materials
conflict between terms, Terminology D 3878 shall have prece-
dence over the other terminology standards.
3.2 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee D30 on
3.2.1 crack opening mode (Mode I)—fracture mode in
Composite Materials and is the direct responsibility of Subcommittee D30.06 on
which the delamination faces open away from each other.
Interlaminar Properties.
3.2.2 Mode I interlaminar fracture toughness, G —the
Current edition approved May 1, 2007. Published June 2007. Originally
Ic
approved in 1994. Last previous edition approved in 2001 as D 5528 – 01.
critical value of G for delamination growth as a result of an
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
opening load or displacement.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
3.2.3 energy release rate, G—the loss of energy, dU, in the
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. test specimen per unit of specimen width for an infinitesimal
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
e1
D 5528 – 01 (2007)
increaseindelaminationlength,da,foradelaminationgrowing 4.2 A record of the applied load versus opening displace-
under a constant displacement. In mathematical form, ment is recorded on an X-Y recorder, or equivalent real-time
plotting device or stored digitally and postprocessed. Instanta-
1 dU
G52 (1)
neous delamination front locations are marked on the chart at
b da
intervals of delamination growth. The Mode I interlaminar
where:
fracture toughness is calculated using a modified beam theory
U = total elastic energy in the test specimen,
or compliance calibration method.
b = specimen width, and
a = delamination length.
5. Significance and Use
3.3 Symbols:
5.1 Susceptibility to delamination is one of the major
1/3
3.3.1 A —slope of plot of a/b versus C .
weaknesses of many advanced laminated composite structures.
3.3.2 a—delamination length.
Knowledge of a laminated composite material’s resistance to
3.3.3 a —initial delamination length.
interlaminar fracture is useful for product development and
3.3.4 b—width of DCB specimen.
material selection. Furthermore, a measurement of the Mode I
3.3.5 C—compliance, d/P, of DCB specimen.
interlaminar fracture toughness, independent of specimen ge-
3.3.6 CV—coefficient of variation, %.
ometry or method of load introduction, is useful for establish-
3.3.7 da—differential increase in delamination length.
ing design allowables used in damage tolerance analyses of
3.3.8 dU—differential increase in strain energy.
composite structures made from these materials.
3.3.9 E —modulus of elasticity in the fiber direction.
11 5.2 This test method can serve the following purposes:
3.3.10 E —modulus of elasticity in the fiber direction
5.2.1 To establish quantitatively the effect of fiber surface
1f
measured in flexure.
treatment, local variations in fiber volume fraction, and pro-
3.3.11 F—large displacement correction factor.
cessing and environmental variables on G of a particular
Ic
3.3.12 G—strain energy release rate.
composite material.
3.3.13 G —opening Mode I interlaminar fracture tough- 5.2.2 To compare quantitatively the relative values of G
Ic Ic
ness.
for composite materials with different constituents.
3.3.14 h—thickness of DCB specimen. 5.2.3 To develop delamination failure criteria for composite
3.3.15 L—length of DCB specimen. damage tolerance and durability analyses.
3.3.16 L8—half width of loading block.
6. Interferences
3.3.17 m—number of plies in DCB specimen.
3.3.18 N—loading block correction factor. 6.1 Linear elastic behavior is assumed in the calculation of
G used in this test method. This assumption is valid when the
3.3.19 NL—point at which the load versus opening dis-
placement curve becomes nonlinear. zone of damage or nonlinear deformation at the delamination
front, or both, is small relative to the smallest specimen
3.3.20 n—slope of plot of Log C versus Log a.
dimension, which is typically the specimen thickness for the
3.3.21 P—applied load.
DCB test.
3.3.22 P —maximum applied load during DCB test.
max
6.2 In the DCB test, as the delamination grows from the
3.3.23 SD—standard deviation.
insert, a resistance-type fracture behavior typically develops
3.3.24 t—distance from loading block pin to center line of
wherethecalculated G firstincreasesmonotonically,andthen
top specimen arm. Ic
stabilizeswithfurtherdelaminationgrowth.Inthistestmethod,
3.3.25 U—strain energy.
a resistance curve (R curve) depicting G as a function of
3.3.26 VIS—point at which delamination is observed visu- Ic
delamination length will be generated to characterize the
ally on specimen edge.
initiation and propagation of a delamination in a unidirectional
3.3.27 V—fiber volume fraction, %.
f
specimen (Fig. 2). The principal reason for the observed
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 speci-
men containing a nonadhesive insert on the midplane that
servesasadelaminationinitiator.Openingforcesareappliedto
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. FIG. 2 Delamination Resistance Curve (R Curve) from DCB Test
e1
D 5528 – 01 (2007)
resistance to delamination is the development of fiber bridging 6.5.1 Toughnessvaluesmeasuredonunidirectionalcompos-
(1-3). Thisfiberbridgingmechanismresultsfromgrowingthe iteswithmultiple-phasematricesmayvarydependinguponthe
delamination between two 0° unidirectional plies. Because tendency for the delamination to wander between various
most delaminations that form in multiply laminated composite matrix phases. Brittle matrix composites with tough adhesive
structures occur between plies of dissimilar orientation, fiber interleaves between plies may be particularly sensitive to this
bridging does not occur. Hence, fiber bridging is considered to phenomenon resulting in two apparent interlaminar fracture
be an artifact of the DCB test on unidirectional materials. toughness values: one associated with a cohesive-type failure
Therefore, the generic significance of G propagation values within the interleaf and one associated with an adhesive-type
Ic
calculated beyond the end of the implanted insert is question- failure between the tough polymer film and the more brittle
able, and an initiation value of G measured from the composite matrix.
Ic
implanted insert is preferred. Because of the significance of the 6.5.2 Nonunidirectional DCB configurations may experi-
initiation point, the insert must be properly implanted and ence branching of the delamination away from the midplane
inspected (8.2). through matrix cracks in off-axis plies. If the delamination
6.3 Threedefinitionsforaninitiationvalueof G havebeen branches away from the midplane, a pure Mode I fracture may
Ic
evaluated during round-robin testing (4). These include G not be achieved as a result of the structural coupling that may
Ic
values determined using the load and deflection measured (1) exist in the asymmetric sublaminates formed as the delamina-
atthepointofdeviationfromlinearityintheload-displacement tion grows. In addition, nonunidirectional specimens may
curve (NL), (2) at the point at which delamination is visually experience significant anticlastic bending effects that result in
observed on the edge (VIS) measured with a microscope as nonuniform delamination growth along the specimen width,
specified in 7.5, and (3) at the point at which the compliance particularly affecting the observed initiation values.
hasincreasedby5 %ortheloadhasreachedamaximumvalue 6.5.3 Woven composites may yield significantly greater
(5 %/max) (see Section 11). The NL G value, which is scatter and unique R curves associated with varying toughness
Ic
typically the lowest of the three G initiation values, is within and away from interlaminar resin pockets as the
Ic
recommended for generating delamination failure criteria in delamination grows. Composites with significant strength or
durability and damage tolerance analyses of laminated com- toughness through the laminate thickness, such as composites
posite structures (5.2.3). Recommendations for obtaining the with metal matrices or 3D fiber reinforcement, may experience
NLpoint are given inAnnexA2.All three initiation values can failures of the beam arms rather than the intended interlaminar
be used for the other purposes cited in the scope (5.2.1 and failures.
5.2.2). However, physical evidence indicates that the initiation
7. Apparatus
value corresponding to the onset of nonlinearity (NL) in the
7.1 Testing Machine—A properly calibrated test machine
load versus opening displacement plot corresponds to the
shall be used that can be operated in a displacement control
physical onset of delamination from the insert in the interior of
mode with a constant displacement rate in the range from 0.5
the specimen width (5). In round-robin testing of AS4/PEEK
to5.0mm/min(0.02to0.20in./min).Thetestingmachineshall
thermoplastic matrix composites, NL G values were 20 %
Ic
conform to the requirements of Practices E4. The testing
lower than VIS and 5 %/max values (4).
machine shall be equipped with grips to hold the loading
6.4 Delamination growth may proceed in one of two ways:
hinges, or pins to hold the loading blocks, that are bonded to
(1) by a slow stable extension or (2) a run-arrest extension in
the specimen.
which the delamination front jumps ahead abruptly. Only the
7.2 Load Indicator—The testing machine load-sensing de-
first type of growth is of interest in this test method. An
vice shall be capable of indicating the total load carried by the
unstable jump from the insert may be an indication of a
test specimen.This device shall be essentially free from inertia
problem with the insert. For example, the insert may not be
lag at the specified rate of testing and shall indicate the load
completely disbonded from the laminate, or may be too thick,
with an accuracy over the load range(s) of interest of within
resulting in a large neat resin pocket, or may contain a tear or
61 % of the indicated value.
fold. Furthermore, rapid delamination growth may introduce
7.3 Opening Displacement Indicator—The opening dis-
dynamic effects in both the test specimen and in the fracture
placement may be estimated as the crosshead separation,
morphology. Treatment and interpretation of these effects is
provided the deformation of the testing machine, with the
beyond the scope of this test method. However, because crack
specimen grips attached, is less than 2 % of the opening
jumpinghasbeenobservedinatleastonematerialinwhichthe
displacement of the test specimen. If not, then the opening
guidelinesforinserts(see8.2)werenotviolated,thespecimens
displacement shall be obtained from a properly calibrated
are unloaded after the first increment of delamination growth
external gage or transducer attached to the specimen. The
and reloaded to continue the test. This procedure induces a
displacement indicator shall indicate the crack opening dis-
natural Mode I precrack in the DCB specimen. The first
placement with an accura
...
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.
e1
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 (e) indicates an editorial change since the last revision or reapproval.
e NOTE—Added research report reference to Section 14 editorially in March 2008.
1. Scope
1.1 This test method describes the determination of the opening Mode I interlaminar fracture toughness, G ,of
Ic
unidirectionalcontinuous 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 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 3171Test Method for Fiber Content of Resin Matrix Composites by Matrix Digestion Test Methods for Constituent Content
of Composite Materials
D 3878Terminology of High-Modulus Reinforced Fibers and Their Composites Terminology for Composite Materials
D 5229/D 5229M TestMethodforMoistureAbsorptionPropertiesandEquilibriumConditioningofPolymerMatrixComposite
Materials
E 4 Practices for Force Verification of Testing Machines
E 6 Terminology Relating to Methods of Mechanical Testing
E 122PracticeforChoiceofSampleSizetoEstimateaMeasureofQualityforaLotorProcess PracticeforCalculatingSample
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
relating to plastics. Terminology E 6 defines terms relating to mechanical testing. Terminology E 456 and Practice E 177 define
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
D30.06 on Interlaminar Properties.
Current edition approved May 15, 1994. Published July 1994. Originally published as D5528–94. Last previous editions D5528–94.
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 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.
e1
D 5528 – 01 (2007)
(a) with piano hinges (b) with loading blocks
FIG. 1 Double Cantilever Beam Specimen
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— opening Mode I interlaminar fracture toughness.
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
3.3.22 P —maximum applied load during DCB test.
max
e1
D 5528 – 01 (2007)
3.3.25— maximum applied load during DCB test.
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.
e1
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 NLG value, which is typically the lowest of the three G initiation values, is recommended for
Ic Ic
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 in Annex A2. 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 .
Ic Ic
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
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.