ASTM C749-92(1996)
(Test Method)Standard Test Method for Tensile Stress-Strain of Carbon and Graphite
Standard Test Method for Tensile Stress-Strain of Carbon and Graphite
SCOPE
1.1 This test method covers the testing of carbon and graphite in tension to obtain the tensile stress-strain behavior, to failure, from which the ultimate strength, the strain to failure, and the elastic moduli may be calculated as may be required for engineering applications. lists suggested sizes of specimens that can be used in the tests.
Note 1—The results of about 400 tests, on file at ASTM as RR:C05-1000, show the ranges of materials that have been tested, the ranges of specimen configurations, and the agreement between the testers.
Note 2—For safety considerations, it is recommended that the chains be surrounded by suitable members so that at failure all parts of the load train behave predictably and do not constitute a hazard for the operator.
1.2 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.
1.3 The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are for information only.
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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NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn.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: C 749 – 92 (Reapproved 1996)
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
Tensile Stress-Strain of Carbon and Graphite
This standard is issued under the fixed designation C 749; 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
4.1 A tensile specimen (Fig. 1) is placed within a load train
1.1 This test method covers the testing of carbon and
assembly made up of precision chains and other machined
graphite in tension to obtain the tensile stress-strain behavior,
parts (Fig. 2). A load is applied to the specimen provided with
to failure, from which the ultimate strength, the strain to
means of measuring strain until it is caused to fracture. This
failure, and the elastic moduli may be calculated as may be
required for engineering applications. Table 1 lists suggested test yields the tensile strength, elastic constants, and strain to
failure of carbons and graphites.
sizes of specimens that can be used in the tests.
NOTE 1—The results of about 400 tests, on file at ASTM as RR:C05- 5. Significance and Use
1000, show the ranges of materials that have been tested, the ranges of
5.1 This test method is intended to be used for both carbons
specimen configurations, and the agreement between the testers.
and graphites whose particle sizes are of the order of 1 mil to
NOTE 2—For safety considerations, it is recommended that the chains
⁄4 in. (0.0254 to 6.4 mm) and larger. This wide range of
be surrounded by suitable members so that at failure all parts of the load
carbons and graphites can be tested with uniform gage diam-
train behave predictably and do not constitute a hazard for the operator.
eters with minimum parasitic stresses to provide quality data
1.2 This standard does not purport to address all of the
for use in engineering applications rather than simply for
safety concerns, if any, associated with its use. It is the
quality control. This test method can be easily adapted to
responsibility of the user of this standard to establish appro-
elevated temperature testing of carbons and graphites without
priate safety and health practices and determine the applica-
changing the specimen size or configuration by simply utilizing
bility of regulatory limitations prior to use.
elevated temperature materials for the load train. This test
1.3 The values stated in inch-pound units are to be regarded
method has been utilized for temperatures as high as 4352°F
as the standard. The values given in parentheses are for
(2400°C). The design of the fixtures (Figs. 2-9 and Table 2) and
information only.
description of the procedures are intended to bring about, on
the average, parasitic stresses of less than 5 %. The specimens
2. Referenced Documents
for the different graphites have been designed to ensure
fracture within the gage section commensurate with experi-
2.1 ASTM Standards:
enced variability in machining and testing care at different
E 4 Practices for Force Verification of Testing Machines
facilities. The constant gage diameter permits rigorous analyti-
E 6 Terminology Relating to Methods of Mechanical Test-
cal treatment.
ing
E 177 Practice for Use of the Terms Precision and Bias in
6. Apparatus
ASTM Test Methods
6.1 Testing Machine—The machine used for tensile testing
E 691 Practice for Conducting an Interlaboratory Study to
shall conform to the requirements of Practices E 4. The testing
Determine the Precision of a Test Method
machine shall have a load measurement capacity such that the
breaking load of the test specimen falls between 10 and 90 %
3. Terminology
of the scale capacity. This range must be linear to within 1 %
3.1 Definitions—The terms as related to tension testing as
over 1 % increments either by design or by calibration.
given in Terminology E 6 shall be considered as applying to the
6.2 Strain Measurements:
terms used in this test method.
6.2.1 The axial strain can be measured at room temperature
by the use of strain gages, mechanical extensometers, Tucker-
man gages, optical systems, or other devices applied diametri-
This test method is under the jurisdiction of ASTM Committee C-5 on
cally opposite in the gage length portion of the specimen. Two
Manufactured Carbon and Graphite Productsand is the direct responsibility of
Subcommittee C05.03 on Property Measurements (Chemical, Physical, and Sam- opposing gages provide some compensation for bending and
pling).
some assurance that it was not severe. Different graphites
Current edition approved Aug. 15, 1992. Published October 1992. Originally
require different attachment procedures and extreme care is
published as C 749 – 73. Last previous edition C 749 – 87.
necessary. A proven device for mounting the specimen with
Annual Book of ASTM Standards, Vol 03.01.
Annual Book of ASTM Standards, Vol 14.02. minimum damage and for enabling the specimen to receive
C 749
A A
TABLE 1 Sample Sizes Used in Round-Robin Tests (Suggested Specimen Size )
B
Material Max Grain Sample, in. Specimen Recommended
Size, in. Size, in. Shank and
Maximum Gage,
in.
1 C 1 3
AXM-50 0.001 5 by 5 by 5, molded ⁄2 by 0.200 ⁄2 by ⁄16
3 1
⁄4 by ⁄4
1 1
9326 0.001 20 by 10 by 2, molded ⁄2 by ⁄4
⁄4 by 0.3
C
1 3
⁄2 by ⁄16
1 3
⁄2 by ⁄16
3 1
⁄4 by ⁄4
1 1 1 3
9326A 0.001 20 by 10 by 2, molded ⁄2 by ⁄4 ⁄2 by ⁄16
3 3
⁄4 by ⁄8
3 3
⁄4 by 0.3 ⁄4 by 0.3
3 3
⁄4 by ⁄8
1 1 1 1
ATJ 0.006 13, rounds, molded ⁄2 by ⁄4 ⁄2 by ⁄4
3 3 3 1
⁄4 by ⁄8 ⁄4 by ⁄4
3 3 3 1
⁄4 by ⁄8 ⁄4 by ⁄4
3 3
⁄4 by ⁄8
1 1 3 3
HLM 0.033 molded, 10 by 18 by 25 ⁄2 by ⁄4 ⁄4 by ⁄8
3 3
⁄4 by ⁄8
3 3
⁄4 by ⁄8
3 3
⁄4 by ⁄8
CS 0.030 10, rounds, extruded 2 by 1
3 3 3 3
⁄4 by ⁄8 ⁄4 by ⁄8
1 1
⁄2 by ⁄4
1 1
⁄2 by ⁄4
AGR 0.250 25, rounds, extruded 2 by 1 2 by 1
1 5
2by1 1 ⁄4 by ⁄8
2by1
1 5
1 ⁄4 by ⁄8
CGE 0.265 14, rounds, extruded 2 by 1 ⁄4
3 1
⁄4 by ⁄2 2by1
3 1 3 1
Graphitar . . . carbon-graphite, resin impregnated ⁄4 by ⁄4 ⁄4 by ⁄4
C
1 1 1
Grade 86 ⁄2 by ⁄4 ⁄2 by 0.2
1 1
⁄2 by ⁄4
3 1 3 1
Purebon P-59 . . . carbon-graphite, copper treated ⁄4 by ⁄4 ⁄4 by ⁄4
C
1 1 1 3
⁄2 by ⁄4 ⁄2 by ⁄16
1 1
⁄2 by ⁄4
A
Based on RR:C5-1000 (see Note 1).
B
Identity of suppliers available from ASTM Headquarters.
C
Gas-bearings.
NOTE 1—Standard Specimen:
r = r ,
1 2
A = A /1.2,
1 2
l = D /2, and
1 2
l = 2 in. (51 mm) or 8 D , whichever is greater.
2 1
FIG. 1 Double Reduction Used to Minimize Radii-Fractures
different extensometers is shown in Fig. 10. When attaching temperature by use of strain gages applied circumferentially.
strain gages, the modification of the surface may result in a Knowledge of the anisotropy in the billet and orientation of the
glue-graphite composite at the skin and thus the resulting strain specimen is necessary in order to properly place the strain-
values may be erroneous and typically low. When using clip-on measuring device. Generally, one can expect three values of
extensometers, the knife edges can initiate fracture. Record, Poisson’s ratio for a nonisotropic material. Hence, the strain
but do not include the fractures at the attachments in the sensing devices must be sized and positioned carefully. Note
averages. If more than 20 % of the failures occur at the the limitations on strain gages mentioned in 6.2.1.
attachment location, change the strain monitoring system or 6.2.3 The diametral strains can be measured by most of the
attachment device. devices with limitations mentioned in 6.2.1 and 6.2.2.
6.2.2 The circumferential strain can be measured at room 6.3 Parasitic Stress Monitor—An optional parasitic stress
C 749
FIG. 2 Tensile Load Train Assembly
monitor can be inserted as an extension of one of the grips. It connections must align to within the tolerances shown through-
shall be a steel rod about 4 in. long with strain gages mounted out the test.
at 90° angles to monitor axial bending moments on the rod and 6.5 General Test Arrangement—The general arrangement
thus on the specimen. The rod shall be sized so that the bending of the specimen, flexible linkages, and crossheads shall be as
moment applied to the specimen being used can be detected to shown in the schematic of Fig. 3.
within a 5 % parasitic stress in the outer fiber of the specimen.
7. Test Specimens
The parasitic stress shall be calculated elastically by translating
the moment and assuming that the specimen is a free-end 7.1 Test specimens shall be produced to the general con-
beam. figurations shown in Fig. 9. The selection of the proper ratio of
6.4 Gripping Devices—Gripping devices that conform to shank to gage diameter is important to prevent excessive
those shown in Fig. 2 shall be used. The centerlines of all head-pops or fracture of the specimen at the groove in the
C 749
Dimensions, Item
in. (mm)
101 115
A 0.250 6 0.001 0.312 6 0.001
(6.35 6 0.03) (7.92 6 0.03)
B 0.500 6 0.001 0.625 6 0.001
(12.70 6 0.03) (15.88 6 0.03)
C 1.000 1.500
(25.40) (38.10)
3 3
D ⁄16 ⁄8
(4.76) (9.52)
NOTE 1—Refer to Fig. 2, Items 101 and 115.
FIG. 4 Crosshead Attachment Yoke
smaller uniform diameter extending from radius tangent to
radius tangent plus 10 %. The additional 10 % is intended to
accommodate the normal statistics of fracture for a material
like graphite. However, at least 50 % of the specimens should
FIG. 3 Schematic of Tensile System for Carbon and Graphite
fracture within the uniform diameter or the specimen should be
redesigned and the system checked. Acceptable fractured are
shanks. The ratios shown in Table 1 have been found satisfac-
shown in Fig. 11.
tory for this use. It is acceptable to double reduce gage 7.4 To determine the cross-sectional area, the diameter of
diameters as necessary (see Fig. 1) to eliminate head pops (or
the specimen at the smaller or constant diameter region shall be
out-of-gage fractures) or reduce them to an acceptable 20 % used. The dimension shall be recorded to the nearest 0.001 in.
maximum of the total fractures. However, the reducing radius
(0.254 mm).
must be maintained near the values shown or excessive radii
8. Procedure
breaks will be obtained. Also, the gage diameter should not be
reduced to less than three to five times the maximum particles 8.1 Calibration—Calibrate the micrometres that are to be
size in the material, or the failure mode may be atypical. used for measurement of diameters by measuring the dimen-
7.2 Improperly prepared test specimens often cause unsat- sions of blocks provided by the NBS that are accurate within
isfactory test results. It is important, therefore, that care be 60.0001 in. (0.00254 mm). Calibrate all instrumentation and
exercised in the preparation of specimens both in minimizing
establish shunt calibration for each recorded and each param-
end and side thrusts and in providing a quality surface. Stresses eter. Zero all recorders.
induced during preparation should not exceed 10 % of ultimate 8.2 Specimen—Adapt to the specimen the appropriate strain
fracture stress. Either tool cutting or grinding is acceptable, but instrumentation by bonding strain gages to its surface, adapt-
the latter is preferred. Surface roughness should be no greater ing, or any other strain measuring system so that strain can be
than the maximum particle or void size, whichever is greater. measured during the test. Place the specimen within the load
Usually, they are about equal. train. Make sure all instrumentation is properly calibrated and
7.3 The gage length of the specimen will be measured from zeroed.
the axial center of the specimen. Gage marks can be applied 8.3 Loading—Apply the load at a predetermined constant
with ink or layout dope but no scratching, punching, or stress rate by following the appropriate load time curve either
notching of the specimen is permissible. The gage length is to manually or automatically. Continuously apply the load until
be used in referencing the point of fracture within 0.1 in. (2.5 fracture is induced.
mm). The total gage length is defined as that section with the 8.4 Recording—During the entire load application duration,
C 749
Dimensions Item
in. (mm) 103 117
9 5
E ⁄16 ⁄8
(14.29) (15.88)
5 1
F ⁄16 ⁄2
(7.94) (12.7)
G 0.250 6 0.001 0.3126 0.001
(6.35 6 0.03) (7.92 6 0.03)
H 0.500 0.625
(12.70) (15.88)
3 3
J ⁄16 ⁄8
(4.76) (9.52)
1 3
K ⁄8 ⁄16
(3.18) (4.76)
NOTE 1—Refer to Fig. 2, Items 103 and 117.
FIG. 5 Chain Journal
record the output of the load cell on the vertical axis of an X-Y
where:
recorder and the strain on the horizontal axis, and obtain a
E = modulus of elasticity, psi (Pa),
permanent record of the stress-strain curve for the specimen Ds = incremental stress corresponding to the incremental
being tested during the entire test.
strain, psi (Pa), and
De = incremental strain corresponding to the incremental
8.5 Post Test—Observed the specimen fracture surface. If
the specimen failed outside the gage length as defined in 6.3 stress, in./in. (m/m).
9.3 Calculate the strain-to-failure from the stress-strain
(including head pops), the strength value measured must be
curve as the strain where the maximum stress was obtained and
reported but not included in the average.
the specimen failed.
9. Calculation
10. Report
9.1 Calculate the strength as follows:
P 10.1 Report the following information:
max
s 5 (1)
ult
A
10.1.1 Method of testing, load rate, load calibrations, and
other general testing information,
where: 10.1.2 Material identification: manufacturer, grade number,
s = tensile strength, psi (Pa), lot number, original billet size, grain size, and other data,
ult
P = maximum load, lbf (N), and where available,
max
A = cross-sectional area of the specimen in the constant
10.1.3 Description of the specimen including orientation
2 2
diameter region or gage section, in. (m ).
and position in billet,
9.1.1 The cross-sectional area is given by the equation:
10.1.4 Description of procedures and other environmental
exposures,
pD
A 5 (2)
4 10.1.5 All individual and average ultimate tensile strength
values,
10.1.6 Individual and average strain-to-failure values and
where:
D = average diameter of the constant diameter region (gage details on the method of attachment of the strain sensing
device. If elastic constants are given, the method of
section) of the specimen, in. (m).
9.2 Calculate modulus of elasticity of the specimen from the
determining them should be r
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