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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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