ASTM D7291/D7291M-07

Standard Test Method for Through-Thickness "Flatwise" Tensile Strength and Elastic Modulus of a Fiber-Reinforced Polymer Matrix Composite Material

SIGNIFICANCE AND USE
This test method is designed to produce through-thickness failure data for structural design and analysis, quality assurance, and research and development. Factors that influence the through-thickness tensile strength, and should therefore be reported, include the following: material and fabric reinforcement, methods of material and fabric preparation, methods of processing and specimen fabrication, specimen stacking sequence, specimen conditioning, environment of testing, specimen alignment, speed of testing, time at temperature, void content, and volume reinforcement content.
SCOPE
1.1 This test method determines the through-thickness "flatwise" tension strength and elastic modulus of fiber reinforced polymer matrix composite materials. A tensile force is applied normal to the plane of the composite laminate using adhesively bonded thick metal end-tabs. The composite material forms are limited to continuous-fiber or discontinuous fiber (tape or 2-dimensional fabric, or both) reinforced composites.
1.2 The through-thickness strength results using this test method will in general not be comparable to Test Method D 6415 since this method subjects a relatively large volume of material to an almost uniform stress field while Test Method D 6415 subjects a small volume of material to a non-uniform stress field.
1.3 This standard does not purport to address all of the safety problems, 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.
1.4 The values stated in either SI units or inch-pound units are to be regarded separately as standard. Within the text, the inch-pound units are shown in brackets. The values stated in each system are not exact equivalents; therefore, each system must be used independently of the other. Combining values from the two systems may result in nonconformance with the standard.

General Information

• Status: Historical
• Publication Date: 31-Mar-2007
• ICS: 83.120 - Reinforced plastics
• Technical Committee: D30 - Composite Materials
• Drafting Committee: D30.06 - Interlaminar Properties

Relations

• Referred By: ASTM D4762-18 - Standard Guide for Testing Polymer Matrix Composite Materials
• Effective Date: 01-Apr-2007

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
Designation: D7291/D7291M − 07
StandardTest Method for
Through-Thickness “Flatwise” Tensile Strength and Elastic
Modulus of a Fiber-Reinforced Polymer Matrix Composite
Material
This standard is issued under the fixed designation D7291/D7291M; 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.
1. Scope D883 Terminology Relating to Plastics
D3171 Test Methods for Constituent Content of Composite
1.1 This test method determines the through-thickness “flat-
Materials
wise” tension strength and elastic modulus of fiber reinforced
D3878 Terminology for Composite Materials
polymer matrix composite materials.Atensile force is applied
D5229/D5229M TestMethodforMoistureAbsorptionProp-
normaltotheplaneofthecompositelaminateusingadhesively
erties and Equilibrium Conditioning of Polymer Matrix
bondedthickmetalend-tabs.Thecompositematerialformsare
Composite Materials
limited to continuous-fiber or discontinuous fiber (tape or
D5687/D5687M Guide for Preparation of Flat Composite
2-dimensional fabric, or both) reinforced composites.
Panels with Processing Guidelines for Specimen Prepara-
1.2 The through-thickness strength results using this test
tion
method will in general not be comparable to Test Method
D6415 Test Method for Measuring the Curved Beam
D6415 since this method subjects a relatively large volume of
Strength of a Fiber-Reinforced Polymer-Matrix Compos-
material to an almost uniform stress field while Test Method
ite
D6415 subjects a small volume of material to a non-uniform
E4 Practices for Force Verification of Testing Machines
stress field.
E6 Terminology Relating to Methods of Mechanical Testing
1.3 This standard does not purport to address all of the E122 Practice for Calculating Sample Size to Estimate,With
safety problems, if any, associated with its use. It is the
Specified Precision, the Average for a Characteristic of a
responsibility of the user of this standard to establish appro- Lot or Process
priate safety and health practices and determine the applica-
E177 Practice for Use of the Terms Precision and Bias in
bility of regulatory limitations prior to use.
ASTM Test Methods
1.4 The values stated in either SI units or inch-pound units E251 Test Methods for Performance Characteristics of Me-
are to be regarded separately as standard. Within the text, the
tallic Bonded Resistance Strain Gages
inch-pound units are shown in brackets. The values stated in E456 Terminology Relating to Quality and Statistics
each system are not exact equivalents; therefore, each system
E1012 Practice for Verification of Testing Frame and Speci-
must be used independently of the other. Combining values men Alignment Under Tensile and Compressive Axial
from the two systems may result in nonconformance with the
Force Application
standard. E1309 Guide for Identification of Fiber-Reinforced
Polymer-Matrix Composite Materials in Databases
2. Referenced Documents
E1434 Guide for Recording Mechanical Test Data of Fiber-
Reinforced Composite Materials in Databases
2.1 ASTM Standards:
E1471 Guide for Identification of Fibers, Fillers, and Core
D792 Test Methods for Density and Specific Gravity (Rela-
Materials in Computerized Material Property Databases
tive Density) of Plastics by Displacement
3. Terminology
This test method is under the jurisdiction of ASTM Committee D30 on
3.1 Definitions—Terminology D3878 defines terms relating
Composite Materials and is the direct responsibility of Subcommittee D30.06 on
to high-modulus fibers and their composites. Terminology
Interlaminar Properties.
D883definestermsrelatingtoplastics.TerminologyE6defines
Current edition approved April 1, 2007. Published May 2007. DOI: 10.1520/
D7291_D7291M-07.
terms relating to mechanical testing. Terminology E456 and
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Practice E177 define terms relating to statistics. In the event of
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
a conflict between terms, Terminology D3878 shall have
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. precedence over the other terminologies.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7291/D7291M − 07
NOTE 1—If the term represents a physical quantity, its analytical
“spool”isadhesivelybondedtocylindricalmetalendtabs.The
dimensionsarestatedimmediatelyfollowingtheterm(orlettersymbol)in
bonded assembly is loaded under “flatwise” tension loading by
fundamental dimension form, using the following ASTM standard sym-
a force applied normal to the plane of the composite laminate
bology for fundamental dimensions, shown within square brackets: [M]
until failure of the laminate occurs (Fig. 1). The test is
for mass, [L] for length, [T] for time, [Θ] for thermodynamic temperature,
considered valid only when failure occurs entirely within the
and[nd]fornon-dimensionalquantities.Useofthesesymbolsisrestricted
to analytical dimensions when used with square brackets, as the symbols
composite laminate. The test is considered invalid if failure of
may have other definitions when used without the brackets.
the bond-line or partial failure of the bond-line and the surface
3.2 Definitions of Terms Specific to This Standard:
layer of the composite occurs. The failure mode of this test is
tu −1 −2
3.2.1 flatwise tensile ultimate strength, F [M L T ], not controlled; therefore, the actual failure may be intralaminar
n—the ultimate strength of the composite material in the
or interlaminar in nature.
out-of-plane (through-thickness) direction.
4.2 If force-strain data are required, the specimen may be
chord −1 −2
3.2.2 through-thickness tensile modulus, E [M L T
instrumented with strain gages provided certain specimen
],n—thechordmodulusofelasticityofthecompositematerial
thickness requirements are satisfied (see 8.2).
in the out-of-plane (through-thickness) direction.
5. Significance and Use
3.3 Symbols:
5.1 This test method is designed to produce through-
3.3.1 A—cross-sectional area of specimen in the through-
thickness failure data for structural design and analysis, quality
thickness direction,
assurance, and research and development. Factors that influ-
3.3.2 CV—coefficient of variation statistic of a sample
ence the through-thickness tensile strength, and should there-
population for a given property (in percent),
fore be reported, include the following: material and fabric
chord
3.3.3 E — through-thickness tensile modulus.
reinforcement, methods of material and fabric preparation,
tu
methods of processing and specimen fabrication, specimen
3.3.4 F — flatwise tensile ultimate strength.
stacking sequence, specimen conditioning, environment of
3.3.5 n—number of specimens.
testing, specimen alignment, speed of testing, time at
3.3.6 P — maximum force carried by test specimen
max
temperature, void content, and volume reinforcement content.
before failure.
6. Interferences
3.3.7 s —sample standard deviation.
n−1
6.1 MaterialandSpecimenPreparation—Poormaterialfab-
3.3.8 x— measured or derived property for an individual
i
rication practices, lack of control of fiber alignment, voids, and
specimen from the sample population.
damage induced by improper specimen machining are known
3.3.9 x¯—sample mean (average).
causesofhighmaterialdatascatterincompositesingeneral.In
3.3.10 ε—indicated through-thickness tensile strain from
addition, surface finish of the cylindrical machined surface and
strain transducer.
lack of control of parallelism of laminate surfaces can lead to
erroneous through-thickness strength results. Laminate stack-
3.3.11 σ—through-thickness tensile stress.
ing sequences that are not balanced and symmetric could lead
4. Summary of Test Method to adhesive bondline failures.
4.1 A composite specimen in the shape of either a straight- 6.2 Material with Coarse Structure—This test method as-
sided cylindrical disk or a reduced gage section cylindrical sumes that the material is relatively homogeneous with respect
FIG. 1 Flatwise Tension Specimen and End Tab Assembly
D7291/D7291M − 07
to the size of the test section. Certain fabric and braided test. The threads on the end tabs provide a means to attach the
composites with large repeating unit cell sizes (>12 mm [0.5 specimen and end tab assembly to the loading fixture. They
in.]) should not be tested with this specimen size. It may be also provide a means to attach constant diameter bushings for
possible to scale-up the specimen size and fixtures to accom- the purpose of aligning the specimen and end tab assembly in
modate such materials, but this is beyond the scope of this test the bonding fixture. The end tab thickness shall be a minimum
method. of 12.7 mm [0.5 in.]. Section 8.3 provides further requirements
for the end tabs.
6.3 Load Eccentricity—Bending of the specimen during
7.2.3 The end tab bonding fixture (Figs. 4-6) is used to
loading can occur, affecting strength results. Bending may
provide support and alignment to the specimen and end tab
occur due to poor specimen preparation, non-parallel laminate
assembly during the entire bonding process.The threads on the
surfaces, improper bonding of the specimen to the end tabs, or
endtabsareusedtoattachbushingstothemduringthebonding
machine/load train misalignment.
process. These bushings provide a fixed diameter reference
6.4 Void content—The through-thickness tension strength
surface for aligning the specimen and end tab assembly during
measuredusingthismethodisextremelysensitivetoreinforce-
bonding, thus allowing the resuse and re-machining of the end
ment volume and void content. Consequently, the test results
tabs.
may reflect manufacturing quality as much as material prop-
erties. 7.3 Testing Machine—The testing machine shall conform
with Practice E4, and shall satisfy these requirements:
7. Apparatus
7.3.1 Testing Machine Heads—The testing machine shall
have two crossheads, with either a stationary head and a
7.1 Micrometers—The micrometer(s) shall usea4to6mm
movable head or two movable heads.
[0.16 to 0.25 in.] diameter ball-interface on irregular surfaces
such as the bag-side of a laminate, and a flat anvil interface on 7.3.2 Platens/Adapter—One of the testing machine heads
machined or very-smooth tooled surfaces. The accuracy of the
shall be capable of being attached to the lower half of the
instrument(s) shall be suitable for reading to within 1 % of the specimen end tab by an adapter or platen interface as required.
sample diameter and thickness. For typical specimen geom-
The other head shall be capable of being attached to the upper
etries an instrument with an accuracy of 625 µm [60.001 in.] half of the specimen end tab.
is desirable for both diameter and thickness measurements.
7.3.3 Drive Mechanism—The testing machine drive mecha-
nism shall be capable of imparting to the movable head a
7.2 Fixtures—The apparatus consists of three different fix-
controlled velocity with respect to the stationary head. The
tures.
velocity of the movable head shall be capable of regulation as
7.2.1 The loading fixtures are used to load the specimen and
specified in 11.3.
end tab assembly.They can be either self-aligning or fixed grip
and shall not apply eccentric loads. 7.3.4 Force Indicator—The testing machine force-sensing
7.2.2 The end tabs are bonded to the specimen (Figs. 2 and device shall be capable of indicating the total force applied to
3). The end tabs are attached to the loading fixture during the the test specimen. This device shall be essentially free from
FIG. 2 Drawing of End Tabs and Cylindrical Specimen Assembly (SI units)
D7291/D7291M − 07
FIG. 3 Drawing of End Tabs and Cylindrical Specimen Assembly (inch-pound units)
FIG. 4 Drawing of Alignment and Bonding Fixture (showing 12 specimens)
response lag at the specified testing rate and shall indicate the 7.5 Strain-Indicating Device—For the measurement of
force with an accuracy over the load range(s) of interest of
through-thickness modulus, bonded resistance strain gages
within 61 % of the indicated value, as specified by Practice shall be used to measure strain. Either two strain gages at
E4.Theloadrange(s)ofinterestmaybefairlylowformodulus
locations that are 180 degrees apart or three strain gages at 120
evaluation, much higher for strength evaluation, or both, as
degrees apart are required around the cylindrical surface of the
required.
specimen at the center of the gage section.
7.5.1 Bonded Resistance Strain Gages—Strain gage selec-
7.4 Force versus Displacement Record—An X-Y plotter, or
similar device, shall be used to make a permanent record of the tion is a compromise based on the type of material. An active
gage length of 1.5 mm [0.062 in.] is recommended for most
force versus displacement during the test. Alternatively, the
data may be stored digitally and post-processed. materials although larger gages may be more suitable for some
D7291/D7291M − 07
FIG. 5 Drawing of Alignment and Bonding Fixture (SI units)
FIG. 6 Drawing of Alignment and Bonding Fixture (inch-pound units)
woven fabrics (with consolidated tow thicknesses larger than at moderate strain levels (>1000 µε). A system showing
1.5 mm [0.062 in.]), provided the specimen gage length can
excessive bending for the given application should be re-
accommodatesuchgages(asspecifiedin8.2).Gagecalibration adjusted or modified.
certification shall comply with Test Method E251. For lami-
7.7 Conditioning Chamber—When conditioning materials
nated composites, the strain gage should cover a minimum of
in other than ambient laboratory environments, a temperature/
three laminate plies.
vapor-level controlled environmental conditioning chamber is
7.6 System Alignment—Poor system alignment can be a
required, that shall be capable of maintaining the required
major contributor to premature failure, to elastic property data
relative temperature to within 63°C [65°F] and the required
scatter, or both. Practice E1012 describes bending evaluation
relative vapor level to within 63 %. Chamber conditions shall
guidelines and describes potential sources of misalignment
be monitored either on an automated continuous basis or on a
during tensile testing. Alignment should be checked using a
manual basis at regular intervals.
cylindrical metal specimen with a minimum of three strain
7.8 Environmental Test Chamber—An environ
...