ASTM C1557-03
(Test Method)Standard Test Method for Tensile Strength and Young's Modulus of Fibers
Standard Test Method for Tensile Strength and Young's Modulus of Fibers
SCOPE
1.1 This test method covers the preparation, mounting, and testing of single fibers (obtained either from a fiber bundle or a spool) for the determination of tensile strength and Young's modulus at ambient temperature. Advanced ceramic, glass, carbon and other fibers are covered by this test standard.
1.2 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.
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Designation: C 1557 – 03
Standard Test Method for
Tensile Strength and Young’s Modulus of Fibers
This standard is issued under the fixed designation C 1557; 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 4. Summary of Test Method
1.1 This test method covers the preparation, mounting, and 4.1 A fiber is extracted randomly from a bundle or from a
testing of single fibers (obtained either from a fiber bundle or spool.
a spool) for the determination of tensile strength and Young’s 4.2 The fiber is mounted in the testing machine, and then
modulus at ambient temperature. Advanced ceramic, glass, stressed to failure at a constant cross-head displacement rate.
carbon and other fibers are covered by this test standard. 4.3 A valid test result is considered to be one in which fiber
1.2 This standard may involve hazardous materials, opera- failure doesn’t occur in the gripping region.
tions, and equipment. This standard does not purport to 4.4 Tensile strength is calculated from the ratio of the peak
address all of the safety concerns, if any, associated with its force and the cross-sectional area of a plane perpendicular to
use. It is the responsibility of the user of this standard to the fiber axis, at the fracture location or in the vicinity of the
establish appropriate safety and health practices and deter- fracture location, while Young’s modulus is determined from
mine the applicability of regulatory limitations prior to use. the linear region of the tensile stress versus tensile strain curve.
2. Referenced Documents 5. Significance and Use
2.1 ASTM Standards: 5.1 Properties determined by this test method are useful in
C 1239 Practice for Reporting Uniaxial Strength Data and the evaluation of new fibers at the research and development
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Estimating Weibull Distribution Parameters for Advanced levels. Fibers with diameters up to 250 3 10 m are covered
Ceramics by this test method. Very short fibers (including whiskers) call
D 3878 Terminology of High-Modulus Reinforcing Fibers for specialized test techniques (1) and are not covered by this
and their Composites test method. This test method may also be useful in the initial
E 4 Practices for Load Verification of Testing Machines screening of candidate fibers for applications in polymer, metal
E 6 Terminology Relating to Methods of Mechanical Test- or ceramic matrix composites, and quality control purposes.
ing Because of their nature, ceramic fibers do not have a unique
E 1382 Test Methods for Determining Average Grain Size strength, but rather, a distribution of strengths. In most cases
Using Semiautomatic and Automatic Image Analysis when the strength of the fibers is controlled by one population
of flaws, the distribution of fiber strengths can be described
3. Terminology
using a two-parameter Weibull distribution, although other
3.1 Definitions: distributions have also been suggested (2,3). This test method
3.1.1 bundle—a collection of parallel fibers. Synonym, tow.
constitutes a methodology to obtain the strength of a single
3.1.2 mounting tab—a thin paper, cardboard, compliant fiber. For the purpose of determining the parameters of the
metal, or plastic strip with a center hole or longitudinal slot of
distribution of fiber strengths it is recommended to follow this
fixed gage length. The mounting tab should be appropriately test method in conjunction with Practice C 1239.
designed to be self-aligning if possible, and as thin as practi-
6. Interferences
cable to minimize fiber misalignment.
3.1.3 system compliance—the contribution by the load train 6.1 The test environment may have an influence on the
system and specimen-gripping system to the indicated cross- measured tensile strength of fibers. In particular, the behavior
head displacement, by unit of force exerted in the load train. of fibers susceptible to slow crack growth fracture will be
3.2 For definitions of other terms used in this test method, strongly influenced by test environment and testing rate (4).
refer to Terminologies D 3878 and E 6. Testing to evaluate the maximum strength potential of a fiber
should be conducted in inert environments or at sufficiently
rapid testing rates, or both, so as to minimize slow crack
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on
Ceramic Matrix Composites .
Current edition approved April 10, 2003. Published August 2003. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards,Vol this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1557–03
l
growth effects. Conversely, testing can be conducted in envi-
o
d # (1)
ronments and testing modes and rates representative of service
conditions to evaluate the strength of fibers under those
where:
conditions.
d = the tolerance, m, and
6.2 Fractures that initiate outside the gage section of a fiber
l = the fiber gage length, m.
o
may be due to factors such as stress concentrations, extraneous
7.2 Mounting Tabs—Typical mounting tabs for test speci-
stresses introduced by gripping, or strength-limiting features in
mens are shown in Fig. 3. Alternative methods of specimen
the microstructure of the specimen. Such non-gage section
mounting may be used, or none at all (that is, the fiber may be
fractures constitute invalid tests. When using active gripping
directly mounted into the grips). A simple but effective
systems, insufficient pressure can lead to slippage, while too
approach for making mounting tabs with repeatable dimen-
much pressure can cause local fracture in the gripping area.
sions consists in printing the mounting tab pattern onto
6.3 Torsional strains may reduce the magnitude of the
cardboard file folders using a laser printer. As illustrated in Fig.
tensile strength (5). Caution must be exercised when mounting
3, holes can be obtained using a three-hole punch. Fig. 3 shows
the fibers to avoid twisting the fibers.
a typical specimen mounting method. The mounting tabs are
6.4 Many fibers are very sensitive to surface damage.
gripped or connected to the load train (for example, by pin and
Therefore, any contact with the fiber in the gage length should
clevis) so that the test specimen is aligned axially along the line
be avoided (4,6).
of action of the test machine.
7.2.1 When gripping large diameter fibers using an active
7. Apparatus
set of grips without tabs, the grip facing material in contact
7.1 The apparatus described herein consists of a tensile
with the test specimen must be of appropriate compliance to
testing machine with one actuator (cross-head) that operates in
allow for a firm, non-slipping grip on the fiber. At the same
a controllable manner, a gripping system and a load cell. Fig.
time, the grip facing material must prevent crushing, scoring or
1 and Fig. 2 show a picture and schematic of such a system.
other damage to the test specimen that would lead to inaccurate
7.1.1 Testing Machine—The testing machine shall be in
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results. Large diameter fibers (diameter > 50 3 10 m) can
conformance with Practice E 4. The failure forces shall be
also be mounted inside hypodermic needles filled with an
accurate within 61 % at any force within the selected force
adhesive (7). This is a good alternative to avoid crushing the
range of the testing machine as defined in Practice E 4. To
fiber if pneumatic/hydraulic/mechanical grips were to be used.
determine the appropriate capacity of the load cell, the follow-
The adhesive must be sufficiently strong to withstand the
ing table lists the range of strength and diameter values of
gripping process, and prevent fiber “pull-out” during testing.
representative glass, graphite, organic and ceramic fibers.
7.1.2 Grips—The gripping system shall be of such design 7.3 Data Acquisition—At a minimum, autographic records
that axial alignment of the fiber along the line of action of the of applied force and cross-head displacement versus time shall
machine shall be easily accomplished without damaging the be obtained. Either analog chart recorders or digital data
test specimen. Although studies of the effect of fiber misalign- acquisition systems may be used for this purpose although a
ment on the tensile strength of fibers have not been reported, digital record is recommended for ease of later data analysis.
the axis of the fiber shall be coaxial with the line of action of Ideally, an analog chart recorder or plotter shall be used in
the testing machine within d, to prevent spurious bending conjunction with the digital data acquisition system to provide
an immediate record of the test as a supplement to the digital
strains and/or stress concentrations:
FIG. 1 Typical Fiber Tester
C1557–03
FIG. 2
TABLE 1 Room Temperature Tensile Strength of Fibers (25 3
grease is applied in the gage section of the fiber so that the
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10 m Gage Length)
former does not bear any force. An appropriate solvent can be
Fiber Diameter, m Strength, Pa
used afterwards to remove the vacuum grease.
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CVD-SiC 50-150 3 10 2-3.5 3 10
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polymer-derived SiC 10-18 3 10 2-3.5 3 10
9. Procedure
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sol-gel derived oxide 1-20 3 10 1-3 3 10
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single-crystal oxide 70-250 3 10 1.5-3.5 3 10
9.1 Test Specimen Mounting:
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graphite 1-15 3 10 1-6 3 10
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glass 1-250 x3 10 1-4 3 10
9.1.1 Randomly choose, and carefully separate, a suitable
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aramid 12-20 3 10 2-4 3 10
single-fiber specimen from the bundle or fiber spool. The total
length of the specimen should be sufficiently long (at least 1.5
times longer than the gage length) to allow for convenient
record. Recording devices must be accurate to 6 1 % of full
handling and gripping. Handle the test specimen at its ends and
scale and shall have a minimum data acquisition rate of 10 Hz
avoid touching it in the test gage length.
with a response of 50 Hz deemed more than sufficient.
NOTE 1—Because the strength of fibers is statistical in nature, the
8. Precautionary Statement
magnitude of the strength will depend on the dimensions of the fiber being
evaluated. In composite material applications, the gage length of the fiber
8.1 During the conduct of this test method, the possibility of
is usually of the order of several fiber diameters, but it has been customary
flying fragments of broken fibers may be high. Means for
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to test fibers with a gage length of 25.4 3 10 m. However, other gage
containing these fragments for later fractographic reconstruc-
lengths can be used as long as they are practical, and in either case, the
tion and analysis is highly recommended. For example,
value of the gage length must be reported.
vacuum grease has been used successfully to dampen the fiber
during failure and capture the fragments. In this case, vacuum 9.1.2 When Using Tabs:
C1557–03
FIG. 3
9.1.2.1 A mounting tab (Fig. 3) may be used for specimen 9.8 If using tabs, with the mounting tab un-strained, cut both
mounting. Center the test specimen over the tab using the sides of the tab very carefully at mid-gage as shown in Fig. 4.
printed pattern with one end taped to the tab. Alternatively, the sides of the tab can be burned using a
9.1.2.2 Tape the opposite end of the test specimen to the tab soldering iron, for example. If the fiber is damaged, then it
must be discarded.
exercising care to prevent fiber twisting. It has been found that
the tensile strength of fibers decreases significantly with 9.9 Initiate the data recording followed by the operation of
the test machine until fiber failure. Record both the cross-head
increasing torsional strain (5).
displacement and force, and strain if applicable.
9.1.2.3 Carefully place a small amount of suitable adhesive
9.10 Recover the fracture surfaces and measure the cross-
(for example, epoxy, red sealing wax) at the marks on the
sectional area of a plane normal to the axis of the fiber at the
mounting tab that define the gage length, and bond the fiber to
fracture location or in the vicinity of the fracture location.
the mounting tab.
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Determine the fiber cross-sectional area using with a linear
9.1.2.4 Determine the gage length to the nearest 6 5 3 10
spatial resolution of 1.0 % of the fiber diameter or better, using
mor 61 % of the gage length, whichever is smaller.
laser diffraction techniques (8-11), or an image analysis system
9.2 Optical Strain Flags—If optical flags are to be used for
in combination with a reflected light microscope or a scanning
strain measurement, they may be attached directly to the fibers
electron microscope (12) (see Test Methods E 1382). Note that
at this time, using a suitable adhesive or other attachment
in practice, a reflected white light microscope can provide a
method. Note that this may not be possible with small-diameter
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maximum resolution of 0.5 3 10 m and therefore its use may
fibers (d <5 3 10 m).
be impractical when measuring the cross-sectional area of
9.3 Test Modes and Rates—The test shall be conducted
small diameter fibers. Because stiff fibers tend to shatter upon
under a constant cross-head displacement rate. Rates of testing
failure, it is recommended to capture the fiber fragments using
must be sufficiently rapid to obtain the maximum possible
vacuum grease, because vacuum grease is an effective medium
strength at fracture within 30 s. The user may try as an initial
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to dampen the energy released by the fiber upon fracture. The
value a test rate of 8 3 10 m/s. However, rates other than
user of this standard should be aware that the need to recover
those recommended here may be used to evaluate rate effects.
the fracture surfaces of the fiber to determine the fiber
In all cases the test mode and rate must be reported.
cross-sectional area is consistent with the need to do fractog-
9.4 Ensure that the machine is calibrated and in equilibrium
raphy to identify the strength-limiting flaws for the proper
(no drift).
estimation of the parameters of the distribution of fiber
9.5 Set the cross-head and data recorder speeds to provide a
strengths.
test time to specimen fracture within 30 s.
NOTE 2—The user of this standard test method must be aware that the
9.6 Grasp a mounted test specimen in one of the two tab
diameter of many ceramic fibers varies not only among fibers in a bundle,
grip areas (or pin load one end of the mounting tab). Zero the
but also along the length of each fiber (13-16). It has been customary t
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