ASTM C1557-03(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C1557 − 03(Reapproved 2008)
Standard Test Method for
Tensile Strength and Young’s Modulus of Fibers
This standard is issued under the fixed designation C1557; 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.
1. Scope designed to be self-aligning if possible, and as thin as practi-
cable to minimize fiber misalignment.
1.1 This test method covers the preparation, mounting, and
3.1.3 system compliance—the contribution by the load train
testing of single fibers (obtained either from a fiber bundle or
system and specimen-gripping system to the indicated cross-
a spool) for the determination of tensile strength and Young’s
head displacement, by unit of force exerted in the load train.
modulus at ambient temperature. Advanced ceramic, glass,
carbon and other fibers are covered by this test standard.
3.2 For definitions of other terms used in this test method,
refer to Terminologies D3878 and E6.
1.2 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this
4. Summary of Test Method
standard.
1.3 This standard may involve hazardous materials, 4.1 A fiber is extracted randomly from a bundle or from a
operations, and equipment. This standard does not purport to spool.
address all of the safety concerns, if any, associated with its
4.2 The fiber is mounted in the testing machine, and then
use. It is the responsibility of the user of this standard to
stressed to failure at a constant cross-head displacement rate.
establish appropriate safety and health practices and deter-
4.3 Avalid test result is considered to be one in which fiber
mine the applicability of regulatory limitations prior to use.
failure doesn’t occur in the gripping region.
2. Referenced Documents
4.4 Tensile strength is calculated from the ratio of the peak
force and the cross-sectional area of a plane perpendicular to
2.1 ASTM Standards:
the fiber axis, at the fracture location or in the vicinity of the
C1239Practice for Reporting Uniaxial Strength Data and
fracture location, while Young’s modulus is determined from
EstimatingWeibull Distribution Parameters forAdvanced
thelinearregionofthetensilestressversustensilestraincurve.
Ceramics
D3878Terminology for Composite Materials
5. Significance and Use
E4Practices for Force Verification of Testing Machines
E6Terminology Relating to Methods of MechanicalTesting
5.1 Properties determined by this test method are useful in
E1382Test Methods for Determining Average Grain Size
the evaluation of new fibers at the research and development
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Using Semiautomatic and Automatic Image Analysis
levels.Fiberswithdiametersupto250×10 marecoveredby
this test method.Very short fibers (including whiskers) call for
3. Terminology 3
specializedtesttechniques (1) andarenotcoveredbythistest
3.1 Definitions: method. This test method may also be useful in the initial
3.1.1 bundle—a collection of parallel fibers. Synonym, tow. screeningofcandidatefibersforapplicationsinpolymer,metal
or ceramic matrix composites, and quality control purposes.
3.1.2 mounting tab—a thin paper, cardboard, compliant
Because of their nature, ceramic fibers do not have a unique
metal, or plastic strip with a center hole or longitudinal slot of
strength, but rather, a distribution of strengths. In most cases
fixed gage length. The mounting tab should be appropriately
when the strength of the fibers is controlled by one population
of flaws, the distribution of fiber strengths can be described
This test method is under the jurisdiction of ASTM Committee C28 on
using a two-parameter Weibull distribution, although other
Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on
distributions have also been suggested (2,3). This test method
Ceramic Matrix Composites.
constitutes a methodology to obtain the strength of a single
Current edition approved Aug. 1, 2008. Published September 2008. Originally
´1
fiber. For the purpose of determining the parameters of the
approved in 2003. Last previous edition approved in 2004 as C1557–03 . DOI:
10.1520/C1557-03R08.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standardsvolumeinformation,refertothestandard’sDocumentSummarypageon Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1557 − 03 (2008)
distribution of fiber strengths it is recommended to follow this range of the testing machine as defined in Practice E4.To
test method in conjunction with Practice C1239. determine the appropriate capacity of the load cell, the follow-
ing table lists the range of strength and diameter values of
6. Interferences
representative glass, graphite, organic and ceramic fibers.
7.1.2 Grips—The gripping system shall be of such design
6.1 The test environment may have an influence on the
that axial alignment of the fiber along the line of action of the
measured tensile strength of fibers. In particular, the behavior
machine shall be easily accomplished without damaging the
of fibers susceptible to slow crack growth fracture will be
test specimen.Although studies of the effect of fiber misalign-
strongly influenced by test environment and testing rate (4).
ment on the tensile strength of fibers have not been reported,
Testing to evaluate the maximum strength potential of a fiber
the axis of the fiber shall be coaxial with the line of action of
should be conducted in inert environments or at sufficiently
the testing machine within δ, to prevent spurious bending
rapid testing rates, or both, so as to minimize slow crack
strains and/or stress concentrations:
growth effects. Conversely, testing can be conducted in envi-
ronments and testing modes and rates representative of service
l
o
δ# (1)
conditions to evaluate the strength of fibers under those
conditions.
where:
6.2 Fractures that initiate outside the gage section of a fiber
δ = the tolerance, m, and
maybeduetofactorssuchasstressconcentrations,extraneous
l = the fiber gage length, m.
o
stressesintroducedbygripping,orstrength-limitingfeaturesin
7.2 Mounting Tabs—Typical mounting tabs for test speci-
the microstructure of the specimen. Such non-gage section
mens are shown in Fig. 3. Alternative methods of specimen
fractures constitute invalid tests. When using active gripping
mounting may be used, or none at all (that is, the fiber may be
systems, insufficient pressure can lead to slippage, while too
directly mounted into the grips). A simple but effective
much pressure can cause local fracture in the gripping area.
approach for making mounting tabs with repeatable dimen-
6.3 Torsional strains may reduce the magnitude of the
sions consists in printing the mounting tab pattern onto
tensilestrength (5).Cautionmustbeexercisedwhenmounting
cardboardfilefoldersusingalaserprinter.AsillustratedinFig.
the fibers to avoid twisting the fibers.
3,holescanbeobtainedusingathree-holepunch.Fig.3shows
6.4 Many fibers are very sensitive to surface damage.
a typical specimen mounting method. The mounting tabs are
Therefore, any contact with the fiber in the gage length should
grippedorconnectedtotheloadtrain(forexample,bypinand
be avoided (4,6).
clevis)sothatthetestspecimenisalignedaxiallyalongtheline
of action of the test machine.
7. Apparatus
7.2.1 When gripping large diameter fibers using an active
7.1 The apparatus described herein consists of a tensile set of grips without tabs, the grip facing material in contact
testing machine with one actuator (cross-head) that operates in with the test specimen must be of appropriate compliance to
a controllable manner, a gripping system and a load cell. Fig. allow for a firm, non-slipping grip on the fiber. At the same
1 and Fig. 2 show a picture and schematic of such a system. time,thegripfacingmaterialmustpreventcrushing,scoringor
7.1.1 Testing Machine—The testing machine shall be in otherdamagetothetestspecimenthatwouldleadtoinaccurate
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conformance with Practice E4. The failure forces shall be results.Largediameterfibers(diameter>50×10 m)canalso
accurate within 61% at any force within the selected force be mounted inside hypodermic needles filled with an adhesive
FIG. 1 Typical Fiber Tester
C1557 − 03 (2008)
FIG. 2
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TABLE 1 Room Temperature Tensile Strength of Fibers (25 × 10
an immediate record of the test as a supplement to the digital
m Gage Length)
record. Recording devices must be accurate to 6 1% of full
Fiber Diameter, m Strength, Pa
scale and shall have a minimum data acquisition rate of 10 Hz
-6 9
CVD-SiC 50-150 × 10 2-3.5 × 10
with a response of 50 Hz deemed more than sufficient.
-6 9
polymer-derived SiC 10-18 × 10 2-3.5 × 10
-6 9
sol-gel derived oxide 1-20 × 10 1-3×10
-6 9
8. Precautionary Statement
single-crystal oxide 70-250 × 10 1.5-3.5 × 10
-6 9
graphite 1-15 × 10 1-6×10
-6 9 8.1 Duringtheconductofthistestmethod,thepossibilityof
glass 1-250 x× 10 1-4×10
-6 9
aramid 12-20 × 10 2-4×10
flying fragments of broken fibers may be high. Means for
containing these fragments for later fractographic reconstruc-
tion and analysis is highly recommended. For example,
(7). This is a good alternative to avoid crushing the fiber if vacuum grease has been used successfully to dampen the fiber
pneumatic/hydraulic/mechanical grips were to be used. The during failure and capture the fragments. In this case, vacuum
adhesive must be sufficiently strong to withstand the gripping grease is applied in the gage section of the fiber so that the
process, and prevent fiber “pull-out” during testing. former does not bear any force.An appropriate solvent can be
used afterwards to remove the vacuum grease.
7.3 Data Acquisition—At a minimum, autographic records
of applied force and cross-head displacement versus time shall
9. Procedure
be obtained. Either analog chart recorders or digital data
acquisition systems may be used for this purpose although a 9.1 Test Specimen Mounting:
digital record is recommended for ease of later data analysis. 9.1.1 Randomly choose, and carefully separate, a suitable
Ideally, an analog chart recorder or plotter shall be used in single-fiber specimen from the bundle or fiber spool. The total
conjunction with the digital data acquisition system to provide length of the specimen should be sufficiently long (at least 1.5
C1557 − 03 (2008)
FIG. 3 Mounting Tab
times longer than the gage length) to allow for convenient 9.4 Ensurethatthemachineiscalibratedandinequilibrium
handlingandgripping.Handlethetestspecimenatitsendsand (no drift).
avoid touching it in the test gage length.
9.5 Setthecross-headanddatarecorderspeedstoprovidea
test time to specimen fracture within 30 s.
NOTE 1—Because the strength of fibers is statistical in nature, the
magnitudeofthestrengthwilldependonthedimensionsofthefiberbeing
9.6 Grasp a mounted test specimen in one of the two tab
evaluated. In composite material applications, the gage length of the fiber
grip areas (or pin load one end of the mounting tab). Zero the
isusuallyoftheorderofseveralfiberdiameters,butithasbeencustomary
-3
to test fibers with a gage length of 25.4 × 10 m. However, other gage load cell.
lengths can be used as long as they are practical, and in either case, the
9.7 Position the cross-head so that the other tab grip area
value of the gage length must be reported.
may be grasped as in 9.6. Check the axial specimen alignment
9.1.2 When Using Tabs:
usingwhatevermethodshavebeenestablished,asdescribedin
9.1.2.1 A mounting tab (Fig. 3) may be used for specimen
7.1.2.
mounting. Center the test specimen over the tab using the
9.8 Ifusingtabs,withthemountingtabun-strained,cutboth
printed pattern with one end taped to the tab.
sides of the tab very carefully at mid-gage as shown in Fig. 4.
9.1.2.2 Tapetheoppositeendofthetestspecimentothetab
Alternatively, the sides of the tab can be burned using a
exercising care to prevent fiber twisting. It has been found that
soldering iron, for example. If the fiber is damaged, then it
the tensile strength of fibers decreases significantly with
must be discarded.
increasing torsional strain (5).
9.1.2.3 Carefully place a small amount of suitable adhesive
9.9 Initiate the data recording followed by the operation of
(for example, epoxy, red sealing wax) at the marks on the
the test machine until fiber failure. Record both the cross-head
mounting tab that define the gage length, and bond the fiber to
displacement and force, and strain if applicable.
the mounting tab.
-4 9.10 Recover the fracture surfaces and measure the cross-
9.1.2.4 Determine the gage length to the nearest 65×10
sectional area of a plane normal to the axis of the fiber at the
mor 61% of the gage length, whichever is smaller.
fracture location or in the vicinity of the fracture location.
9.2 Optical Strain Flags—If optical flags are to be used for
Determine the fiber cross-sectional area using with a linear
strainmeasurement,theymaybeattacheddirectlytothefibers
spatialresolutionof1.0%ofthefiberdiameterorbetter,using
at this time, using a suitable adhesive or other attachment
laserdiffractiontechniques (8-11),oranimageanalysissystem
method.Notethatthismaynotbepossiblewithsmall-diameter
in combination with a reflected light microscope or a scanning
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fibers (δ<5×10 m).
electron microscope (12) (see Test Methods E1382). Note that
9.3 Test Modes and Rates—The test shall be conducted in practice, a reflected white light microscope can provide a
-6
underaconstantcross-headdisplacementrate.Ratesoftesting maximum resolution of 0.5 × 10 m and therefore its use may
must be sufficiently rapid to obtain the maximum possible be impractical when measuring the cross-sectional area of
strength at fracture within 30 s. The user may try as an initial small diameter fibers. Because stiff fibers tend to shatter upon
-6
value a test rate of8×10 m/s. However, rates other than failure, it is recommended to capture the fiber fragments using
those recommended here may be used to evaluate rate effects. vacuumgrease,becausevacuumgreaseisaneffectivemedium
In all cases the test mode and rate must be reported. to dampen the energy released by the fiber upon fracture. The
C1557 − 03 (2008)
FIG. 4 Cutting Sides of Tab
user of this standard should be aware that the need to recover
F = force to failure, N, and
the frac
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