ASTM D7775-21

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7775 − 16 D7775 − 21
Standard Guide for
Measurements on Small Graphite Specimens
This standard is issued under the fixed designation D7775; 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*
1.1 This guide covers best practice for properties measurements on small (nonstandard) graphite specimens and requirements for
representing properties of the bulk material. This guide is aimed specifically at measurements required on nuclear graphites, where
there may be constraints on the geometry or volume of the test specimen, or both. The objective of this guide is to provide advice
on how the application of selected standards under noncompliant conditions can be tested for suitability.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
C559 Test Method for Bulk Density by Physical Measurements of Manufactured Carbon and Graphite Articles
C565 Test Methods for Tension Testing of Carbon and Graphite Mechanical Materials
C611 Test Method for Electrical Resistivity of Manufactured Carbon and Graphite Articles at Room Temperature
C651 Test Method for Flexural Strength of Manufactured Carbon and Graphite Articles Using Four-Point Loading at Room
Temperature
C695 Test Method for Compressive Strength of Carbon and Graphite
C714 Test Method for Thermal Diffusivity of Carbon and Graphite by Thermal Pulse Method
C747 Test Method for Moduli of Elasticity and Fundamental Frequencies of Carbon and Graphite Materials by Sonic Resonance
C748 Test Method for Rockwell Hardness of Graphite Materials
C749 Test Method for Tensile Stress-Strain of Carbon and Graphite
C769 Test Method for Sonic Velocity in Manufactured Carbon and Graphite Materials for Use in Obtaining an Approximate
Value of Young’s Modulus
C781 Practice for Testing Graphite Materials for Gas-Cooled Nuclear Reactor Components
C886 Test Method for Scleroscope Hardness Testing of Carbon and Graphite Materials
C1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
This guide is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.F0 on Manufactured Carbon and Graphite Products.
Current edition approved Dec. 15, 2016Nov. 1, 2021. Published February 2017November 2021. Originally approved in 2011. Last previous edition approved in 20152016
as D7775 – 11 (2015).D7775 – 16. DOI: 10.1520/D7775-16.10.1520/D7775-21.
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 Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7775 − 21
C1259 Test Method for Dynamic Young’s Modulus, Shear Modulus, and Poisson’s Ratio for Advanced Ceramics by Impulse
Excitation of Vibration
D7779 Test Method for Determination of Fracture Toughness of Graphite at Ambient Temperature
D7972 Test Method for Flexural Strength of Manufactured Carbon and Graphite Articles Using Three-Point Loading at Room
Temperature
D8289 Test Method for Tensile Strength Estimate by Disc Compression of Manufactured Graphite
D8356 Test Method for Sonic Velocity in Manufactured Carbons and Graphite Materials for use in Obtaining Approximate
Elastic Constants: Young’s Modulus, Shear Modulus, and Poisson’s Ratio
E228 Test Method for Linear Thermal Expansion of Solid Materials With a Push-Rod Dilatometer
E1461 Test Method for Thermal Diffusivity by the Flash Method
3. Summary of Guide
3.1 There is currently a suite of ASTM standards (see 2.1) that can be applied to graphite covering a range of physical, mechanical,
electrical and thermal property measurements. Each of these standards has been developed with the objective of optimizing the
method of measurement in the absence of any constraints on test specimen production. Without exception, these standards specify
limits on the ratio between test specimen dimensions and coke and filler grain sizes or prescribe test specimen geometries or size
ranges, or both. The default position for any user should be to follow these standards exactly as described. However, in some
applications, available test material or experiment design constraints on test specimen sizes may result in noncompliance. The
objective of this guide is to provide advice on how the application of selected standards under noncompliant conditions can be
tested for suitability. The ultimate objective is to provide guidance on the use of each of the ASTM standards listed. The 20162021
issue of this guide addresses nine standards: Test Method C559 for Bulk Density by Physical Measurement of Manufactured
Carbon and Graphite Articles, Test Method C611 for Electrical Resistivity of Manufactured Carbon and Graphite Articles at Room
Temperature, Test Method C747 for Moduli of Elasticity and Fundamental Frequencies of Carbon and Graphite Materials by Sonic
Resonance, Test Method C769 for Sonic Velocity in Manufactured Carbon and Graphite Materials for Use in Obtaining Young’s
Modulus, Test Method C749 for Tensile Stress-Strain of Carbon and Graphite and Graphite, Test Method D7972 for Flexural
Strength of Manufactured Carbon and Graphite Articles Using Three-Point Loading at Room Temperature, Test Method E228 for
Linear Thermal Expansion of Solid Materials with a Push-Rod Dilatometer, and Test Method E1461 for Thermal Diffusivity by
the Flash Method.
4. Significance and Use
4.1 The purpose of this guide is to report considerations, which should be included in testing nonstandard specimens that lie
outside the constraints imposed on size/volume in existing ASTM standards for graphite (noting that there are some generic ASTM
standards with no such constraints). These constraints may be real or may be an artifact of the round-robin test program that
supported the standard. It is the responsibility of the user to demonstrate that the application of a standard outside any specified
constraints is valid and reasonably provides properties of the bulk material from which the nonstandard specimen was extracted.
5. Test Specimen Volume/Size Constraints in Current Standards
5.1 Test Method C559—Applies to test specimens with rectangular parallelepiped or right circular cylinder geometry. The
minimum test volume is specified as 500 mm . The minimum test specimen dimension should be 10 times the length of the largest
visible grain.
5.2 Test Methods C565—Applies to reduced diameter uniaxial tensile specimens. Grain size must be smaller than 0.79 mm; while
not specified, it is assumed that this refers to average grain size. The acceptable fracture zone shall be 19 mm long with the centre
of the zone at the point of minimum diameter. The ratio of specimen diameter to grain size or flaw size must be greater than 5.
5.3 Test Method C611—Applies to strip, rod, bar or tube geometries. Specimen length to maximum cross-sectional dimension
should be 6:1. No dimension should be smaller than 5 times the length of the largest visible grain.
5.4 Test Method C651—Applies to rectangular parallelepiped geometries. The minimum dimension should be greater than 5 times
the largest grain dimension. Test specimen length to thickness should be greater than 8. The ratio of test specimen width to
thickness should be less than or equal to 2.
5.5 Test Method C695—Applies to right cylinder geometry. The test specimen diameter should be greater than 10 times the
D7775 − 21
maximum grain size. The test specimen height to diameter ratio should be in the range 1.9 to 2.1. The minimum test size is
specified as 9.5 mm diameter and 19.1 mm height.
5.6 Test Method C714—Applies to circular disks, 22 mm to 4 mm 4 mm thick and 66 mm to 12 mm 12 mm in diameter. The
diameter must not be too large relative to the flash source as the front surface needs to be heated uniformly. The specimen thickness
must be selected such that τ/t is smaller than 0.02, where τ is the pulse time and t is the time for the rear surface temperature
1/2 1/2
to rise to one half of its maximum value.
5.7 Test Method C747—Applies to slender rod or bar geometries. The test specimen length to thickness ratio should lie in the range
5 to 20:1.
5.8 Test Method C748—Applies to flat specimens of minimum thickness 6.35 mm. The grain size of the test material should be
less than 0.8 mm, with a hardness range 0 to 120 Rockwell L.
5.9 Test Method C749—Applies to reduced-diameter uniaxial tensile test geometries as defined in Fig. 9 of that standard. Gauge
diameter must be greater than 3 to 5 times the maximum grain size.
5.10 Test Method C769—Applies to right cylinder geometry. The user should minimize attenuation of the sonic pulse by selecting
a wavelength appropriate to the grain size of the test material. If the test specimen is a few grains thick, acceptability of application
should be tested over a range of lengths. Specimen should have a diameter of at least a factor of two and ideally a factor of five
greater than the wavelength of sound within the material.
5.11 Test Method C886—Can be applied to any convenient test specimen size, but test surfaces smaller than 5 mm by 5 mm are
not recommended. The material must have a grain size less than 0.8 mm. The minimum specimen thickness is 5 mm.
5.12 Test Method C1161—Applies to rectangular parallelepiped geometries and can be adapted for graphite. The average grain size
should be less than 2 % of the beam thickness. For beam lengths of 25 mm, 45 mm, and 90 mm, specified widths are 2 mm, 4 mm,
and 8 mm, respectively, and specified depths are 1.5 mm, 3 mm, and 6 mm, respectively.
5.13 Test Method C1259—Can be applied to graphite test specimens with both round and rectangular cross sections. The ratio of
test specimen length to minimal cross-sectional dimension should be greater than 10, and preferably greater than 20. For shear
modulus measurements, the test specimen width to thickness ratio should be greater than 5.
5.14 Test Method D7779—The recommended test specimen configuration has a 15 mm by 20 mm rectangular cross section with
a machined notch in the center of the specimen long dimension, with the depth of the machined notch as 40 % of the specimen
depth. Other specimen sizes with the same scaling may be used in order to sample an adequate quantity of pores and grains of
various graphite grades. Specimen size/volume should reflect graphite structure. As a minimum recommendation, dimensions in
the notch plane should be 5 to 10 times the maximum particle size of the graphite. The user of this test method must be satisfied
with appropriate technical basis that the ratio of the notch size to graphite grain size does not affect the test results.
5.15 Test Method D7972—Applies only to those specimen sizes and geometries selected for the interlaboratory study that
underwrites the standard. Reference should be made to the table of specimen sizes and testing configurations included in the
standard. It is recommended that the size of the test specimen is selected such that the minimum dimension of the specimen is
greater than 5 times the largest particle dimension. It is recommended that the test specimen has a length to thickness/diameter ratio
of at least 6, and a width to thickness ratio not greater than 2.
5.16 Test Method D8289—Applies to cylinders with a minimum specimen diameter of 6 mm. Specimen geometries used in the
intra-laboratory study (Ø6 × 3 mm, Ø8 × 4 mm, Ø10 × 5 mm, and Ø12.7 × 6.35 mm) define the maximum allowed thickness for
the corresponding diameter.
5.17 Test Method D8356—Applies to specimens with a diameter (circular section specimens) or lateral dimensions (width,
thickness) for rectangular section specimens that is at least a factor of five, greater than the wavelength of sound in the material
under test. If the grain size of the carbon or graphite is greater than or about equal to the wavelength of the sonic pulse, the method
may not provide a value of the Young’s modulus representative of the bulk material. Therefore it would be desirable to test a lower
D7775 − 21
frequency (longer wavelength) to demonstrate that the range of obtained velocity values are within acceptable levels of accuracy.
Significant signal attenuation should be expected when grain size of the material is greater than or about equal to the wavelength
of the transmitted sonic pulse or the material is more porous than would be expected for as-manufactured graphite. If the sample
is only a few grains thick, the acceptability of the method’s application should be demonstrated by initially performing
measurements on a series of dummy specimens covering a range of lengths between the proposed test specimen’s length and a
specimen length incorporating sufficient grains to adequately represent the bulk material.
5.18 Test Method E228—Applies to right cylinder (preferable) or slab geometries. Ideally, test specimens should be 25 mm to
60 mm long and 5 mm to 10 mm in diameter or equivalent (although there is no fundamental limitation provided the instrument
controls the maximum thermal gradient to better than 62 °C ⁄50 mm). The specimen length should be such that the accuracy of
determining the expansion ΔL/L is at least 620 mm ⁄m.
5.19 Test Method E1461—Applies to thin circular disk specimens with the front surface area less than that of the energy beam.
Typically, test specimens should be 10 mm to 12.5 mm in diameter and 1 mm to 6 mm in thickness.
6. General Principle for Measurements Outside Specified Specimen Volume/Size Constraints in Current Standards
6.1 The default position for any user should be to follow these standards exactly as described.
6.2 Specimen size and volume constraints may be set by a particular measurement technique and hence apply to any test material,
but some may depend upon the microstructure and composition of the material. In such cases, it is preferable to provide technical
data and basis to support the choice of the adapted measurement technique and test specimen dimensions used.
6.3 A simple, general principle should be applied to any proposed measurements that are noncompliant with respect to
volume/size.
6.3.1 The user must first specify the level of accuracy required for the measurements together with tolerable repeatability,
tolerance, and bias uncertainties associated with the measured properties. This may need to take into account the number of
specimens used for the measurements.
6.3.2 These qualifying measurement criteria must be demonstrated using representative material in a manner compliant with the
ASTM standard. The user should take account of in-service changes to test material (for example, irradiation, oxidation) when
selecting representative material for such a demonstration; as-manufactured material may not be sufficiently representative for such
purposes.
6.3.3 The measurements should then be repeated on the same material, progressively reducing the volume/size of the specimen
and repeating the measurements. Ideally, this procedure would involve the successive re-sizing of the starting specimen. This
would ensure that no specimen to specimen variability affected the results. Consideration should be given to within specimen
variability and any potential effects of specimen preparation that might affect the property measurement. This process should be
continued until there are sufficient compliant data to benchmark the measurement technique against the material; there should be
sufficient data at and below the desired test specimen geometry to characterize the dependence of the measured property upon
volume/size. It may be necessary to study more than one parameter and these should be varied singly in order not to confound the
results.
6.3.4 The results should be analyzed to establish either the standard can be applied directly to an extended specimen volume/size
range or it can be applied with volume/size corrections. In both cases, the accuracy and uncertainty of the measurement at the
desired specimen volume/size should be evaluated and assessed for acceptability against the original specification.
6.3.5 It is good practice to retain the test specimens as checks or secondary standards in the subsequent measurement campaigns.
7. Bulk Density by Physical Measurement (Test Method C559)
7.1 Test Method C559 requires a mass measurement and a volume determination by mensuration on a test specimen with either
a rectangular parallelepiped or right cylinder geometry. The standard specifies that the specimen volume should not be less than
500 mm and the minimum dimension must be at least ten times the length of the largest visible grain. The minimum dimension
should also be more than 2000 times the resolution of the measuring device. The volume determination involves four length
measurements (longest dimension) either at the center of each long face in the case of the rectangular parallelepiped or 90° apart
D7775 − 21
on the periphery of the circular end faces in the case of the right cylinder. For the rectangular parallelepiped, width and thickness
at each end and at two intermediate points along the length are required. For the right cylinder, two sets of diameter measurements
are required, each set consisting of four measurements, one at each end and two at two intermediate points along an axial line.
7.2 The accuracy of contact measuring devices must be assessed in the context of point and flat contact options.
7.3 Principal sources of mensuration error will arise from geometry irregularity and from surface condition.
7.4 For specimens of regular geometry, mensuration could be carried out with automated multi-measurement contact devices that
record and analyze results for prescribed measurement patterns.
7.5 Non-contact scanning devices can also be used to determine volumes of both regular and non-regular geometry specimens.
Such devices need careful qualification before use to ensure the detectors respond consistently for graphite surfaces. The
calibration and accuracy of the device must be tested on volume standards made from materials that respond to the scanning beam
in a simple manner to graphite.
7.6 Bulk density can also be determined using Archimedes’ Principle, as an alternative to mensuration techniques. The specimen
immersed in a fluid is subject to an upwards buoyancy force equal to the weight of the fluid displaced by the specimen. By
measuring the weight of the immersed specimen, the buoyancy force can be deduced, and by using the measured mass of the dry
specimen the density can be calculated. This “immersion” method has the advantage of being applicable to non-regular specimen
geometries. For a porous material, the method depends upon a constant level of penetration of the open pores by the fluid. The
level of penetration is not important provided it is reproducible between repeat immersions.
7.7 An application of the immersion method is described as follows:
7.7.1 The dry test specimen is first weighed then immersed in water and reweighed while immersed; the specimen is removed from
the water and the excess water removed by blotting on a damp chamois leather. The “blotted” specimen is reweighed and then
immersed and weighed again while immersed. The difference between these two measurements is calculated and the cycle of
measurements is repeated until three consecutive pairs of measurements are achieved with prescribed limits. Assuming a density
-3
of water of ρ = 1000 kg m , the density of the test specimen is:
W
ρ5 ρ (1)
W
W
ρ5 ρ (1)
W
where:
-3
ρ = test specimen density, kg m ,
-3
ρ = density of water, kg m ,
W = dry mass of test specimen, kg,
W = mass difference from (W – W ), kg,
4 3 2
W = dried mass, kg, and
W = immersed mass, kg.
7.7.2 Corrections can be made to account for variations in the density of water due to temperature, dissolved air and purity. In
-3
practice, these effects are negligible compared to uncertainties in the overall method (and a water density of 1.0 g cm is normally
assumed). Surface tension forces associated with the pan suspension wire and the water may need to be accounted for in the
claimed level of accuracy.
7.7.3 In principle, there are no constraints on test specimen geometry. In practice, irregular geometries may trap air bubbles and
are more difficult to dry between immersions.
7.7.4 In principle, there is no limit on test specimen size although the practical limit is set by the size of the pan on the balance.
Also, as the test specimen volume decreases, uncertainties in density determinations increase due to the increasing significance of
surface effects.
D7775 − 21
7.7.5 The test method as described requires the density of the test specimen to be greater than that of water. For low density
material, a fixed weight kept immersed in the water reservoir is placed on the immersed specimen and its mass subtracted in the
density evaluation.
7.7.6 Uncertainties in measurement may arise if the graphite specimen is friable. This can be quantified by ensuring that the
oven-dried weight of the test specimen is known before and after measurement.
7.7.7 For highly porous materials, varying penetration of the water between immersions may lead to uncertainties in bulk density
determinations. Water may “drain” out of the test specimen during surface drying and repenetrate the porosity to a varying degree
during immersion. This can be addressed by waxing the test specimen, where the open porosity is partly filled with wax and the
surface tension on the surface of the specimen is changed to prevent water penetration. This treatment is invasive and only
applicable if no further measurements on the specimen are required. Care needs to be taken in the evaluation of the bulk density.
The dry mass of the test specimen must be the mass measured before waxing, the difference in apparent weight between the test
specimen immersed and the test specimen removed from the water being equal to the weight of the water being displaced by the
removed specimen.
8. Electrical Resistivity (Test Method C611)
8.1 Test Method C611 applies to specimens in the form of a strip, rod, bar, or tube with a uniform cross-section. No dimension
shall be smaller than five times the length of the largest visible grain.
8.2 The resistance of the material is measured by passing an electric current between two contact points on the specimen and
measuring the potential drop. Numerous measurements are advised (16 is the recommended number) in order to minimize
specimen or contact point artifacts which might lead to erroneous resistance values. The resistivity of the specimen is defined as
ρ in the following relationship:
R·A
ρ5 (2)
L
where:
ρ = resistivity in mΩ meters,
R = resistance of the material,
A = uniform cross section, mm , and
L = distance between potential contacts, mm.
8.3 The specimen geometry requirement of a specimen length to maximum cross-sectional dimension of at least 6:1 may pose a
challenge to test specimens with specific size constraints when coupled with the 5:1 ratio of smallest dimension to grain or visible
particle size.
8.4 For specimens with length to cross-section dimensions of less than 6:1, the number of measurements taken and resulting
spread of data will indicate whether the measured resistivity values are reliable. Care should be taken to ensure that the length
measurement between contact points can still be measured to within 60.5 %, as errors due to contact length variation will be
magnified commensurate with the total length available for attachment of electrical contacts. Small specimen errors can again be
“averaged” by multiple measurements, as required by the specification even for ideally sized test specimens.
8.5 Small specimens that will not meet the minimum required grain or particle size restriction should, where possible, be evaluated
through a systematic set of resistivity measurements with progressively larger specimens. A measurable shift in resistivity as more
grains are included in scoping specimen sets will provide the operator with an indication of the expected contribution of grain
boundary effects in the electrical resistance of the cross-section of the material.
8.6 Reported results for resistivity measurements on specimens that do not meet the dimensional restrictions of Test Method C611,
in addition to the resistivity value calculated from the average resistance measured, should also record each individual
measurement so that an evaluation can be made with respect to the spread of values collected and precision of the measurement
technique.
D7775 − 21
9. Compressive Strength (Test Method C695)
9.1 Test Method C695 applies to specimens with a right cylinder geometry. The test specimen diameter should be greater than ten
times the maximum grain size. The test specimen height to diameter ratio should be in the range 1.9 to 2.1. The minimum test size
is specified as 9.5 mm diameter and 19.1 mm height.
9.2 A specimen size effect study was published (1) in which the effects of specimen size on the compressive strength and Weibull
modulus were investigated for nuclear graphite of different coke particle sizes. Two types of cylindrical specimens, i.e., where the
diameter to length ratio was 1:2 or 1:1 were prepared for six diameters (3 mm, 4 mm, 5 mm, 10 mm, 15 mm, and 20 mm) and
-4 -1
tested at room temperature (compressive strain rate: 2.08 × 10 s ). The results showed that the effects of specimen size appeared
negligible for the compressive strength, but grade dependent for the Weibull modulus. In view of specimen miniaturization,
deviations from the standard specimen size requirements require an investigation into the effects of size for the grade of graphite
of interest, and the specimen size effects should be considered for Weibull modulus determination.
10. Moduli of Elasticity and Fundamental Frequencies by Sonic Resonance (Test Method C747)
10.1 Test Method C747 applies to specimen geometries that are straight and have uniform cross section. Accurate results will
depend upon appropriate shape factors that rely on careful dimensional measurements, which are more prone to error or variation
in smaller geometries.
10.2 Specimens having relatively small or large ratios of length to thickness may be difficult to excite in the fundamental
frequency modes, and therefore a length to width ratio between 5 and 20 is required by this test method.
10.3 The elastic modulus or modulus of rigidity, as appropriate, is calculated in the transverse (or flexural) mode, the longitudinal
mode, or the torsional mode based upon the use of the specimen‘s fundamental mode of vibration, appropriate to the calculated
modulus.
10.4 Deviations from the recommended test specimen ratio range introduce an elevated level of difficulty in obtaining a
measurable fundamental frequency. The modulus of the test material is first established from the measured frequency of a large
test specimen and this modulus is used to estimate a frequency for the small test specimens. It is recommended that two additional
guidelines be employed in order to increase the confidence in the recorded frequency:
10.4.1 Determine the fundamental frequency using specimens that are within the recommended length to width ratio of between
5 and 20, or use progressively larger specimens as necessary, in order to establish baseline frequency characteristics of the material
being evaluated. The expected value for fundamental frequency of a nonstandard specimen can be calculated based upon the
measured geometry and the known fundamental frequency of a standard specimen, and any deviation or shift can be appropriately
noted.
10.4.2 In all cases, use the required procedural practices employed in Test Method C1259 for the number of readings taken. For
small test specimens, there is a risk that the excited mode is not the intended mode and consequently the formula applied to
calculate modulus from the frequency will be wrong. Spurious vibration modes are more easily discounted with the fundamental
frequency of the required mode having been measured if the test is repeated on the same specimen until ten readings are within
610 % of the mean. It is acknowledged that for less ideal specimen geometries, the frequency mean that is eventually used for
the modulus calculation may require an extended number of measurements until an appropriate group of ten readings is obtained.
In this case, the total number of measurements required to obtain the group of ten readings should be reported. It is good practice
to confirm independently that the excited mode is the intended one by using an alternative experimental, numerical or analytical
method.
10.5 The report shall contain additional information pertaining to the testing that may have been carried out per item 9.4.110.4.1,
and the individual numerical values recorded and the mean value obtained per item 9.4.210.4.2.
11. Tensile Stress-Strain (Test Method C749)
11.1 Test Method C749 applies to reduced-diameter uniaxial tensile test geometries as defined in Fig. 9 of that standard. Gauge
diameter must be greater than 3 to 5 times the maximum grain size.
The boldface numbers in parentheses refer to a list of references at the end of this standard.
D7775 − 21
11.2 PracticeThe C781 includes an annex describing modifications to test specimen configurations referred to in Test Method
C749 to extend its application to small test specimens. This annex does not address gauge diameter to grain size constraints but
it does describe how bonding connectors to specimens can extend applicability of the method described in Test Methodincorporate
integral grooved heads for mounting the specimens in the gripping devices and reduced gage sections to control fracture location.
However, test parameters for some studies (irradiation and oxidation studies and quality assurance tests for many manufactured
carbon and graphite articles) may impose such stringent requirements on volume, diameter, and geometry that the C749 from the
standard reduced-diameter uniaxial test geometry to a simple right cylindrical geometry. In order for this guide to contain a
complete compilation of methods for small graphite specimens, the procedure in Annex A4 of Practice resultant test specimen may
be simply a right circular cylinder. Alternatively, bonding connectors to cylindrical specimens can be performed to conduct tensile
tests.C781 has been reproduced here.
11.2.1 Test Specimen—The test specimen shall be cylindrical with ends machined perpendicular to the longitudinal axis.
11.2.1.1 The recommended test specimen size is 6.5 mm diameter.
11.2.1.2 The recommended height to diameter ra
...