ASTM C1819-21

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.
Designation: C1819 − 21
Standard Test Method for
Hoop Tensile Strength of Continuous Fiber-Reinforced
Advanced Ceramic Composite Tubular Test Specimens at
Ambient Temperature Using Elastomeric Inserts
This standard is issued under the fixed designation C1819; 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 (3D, braid and weave). These types of ceramic matrix com-
posites can be composed of a wide range of ceramic fibers
1.1 This test method covers the determination of the hoop
(oxide, graphite, carbide, nitride, and other compositions) in a
tensile strength including stress-strain response of continuous
wide range of crystalline and amorphous ceramic matrix
fiber-reinforced advanced ceramic tubes subjected to an inter-
compositions (oxide, carbide, nitride, carbon, graphite, and
nalpressureproducedbytheexpansionofanelastomericinsert
other compositions).
undergoing monotonic uniaxial loading at ambient tempera-
ture.This type of test configuration is sometimes referred to as
1.4 Thistestmethoddoesnotdirectlyaddressdiscontinuous
an overhung tube. This test method is specific to tube geom-
fiber-reinforced, whisker-reinforced, or particulate-reinforced
etries because flaw populations, fiber architecture, and speci-
ceramics, although the test methods detailed here may be
men geometry factors are often distinctly different in compos-
equally applicable to these composites.
ite tubes, as compared to flat plates.
1.5 Thetestmethodisapplicabletoarangeoftestspecimen
1.2 In the test method a composite tube/cylinder with a
tube geometries based on a non-dimensional parameter that
defined gage section and a known wall thickness is loaded via
includes composite material property and tube radius. Lengths
internal pressurization from the radial expansion of an elasto-
of the composite tube, pushrods, and elastomeric insert are
meric insert (located midway inside the tube) that is longitu-
determined from this non-dimensional parameter so as to
dinally compressed from either end by pushrods. The elasto-
provide a gage length with uniform internal radial pressure.A
mericinsertexpandsundertheuniaxialcompressiveloadingof
wide range of combinations of material properties, tube radii,
the pushrods and exerts a uniform radial pressure on the inside
wall thicknesses, tube lengths, and insert lengths are possible.
of the tube. The resulting hoop stress-strain response of the
1.5.1 This test method is specific to ambient temperature
composite tube is recorded until failure of the tube. The hoop
testing.Elevatedtemperaturetestingrequireshigh-temperature
tensile strength and the hoop fracture strength are determined
furnaces and heating devices with temperature control and
from the resulting maximum pressure and the pressure at
measurement systems and temperature-capable grips and load-
fracture, respectively. The hoop tensile strains, the hoop
ing fixtures, which are not addressed in this test standard.
proportional limit stress, and the modulus of elasticity in the
hoop direction are determined from the stress-strain data. Note 1.6 This test method addresses tubular test specimen
geometries, test specimen methods, testing rates (force rate,
that hoop tensile strength as used in this test method refers to
the tensile strength in the hoop direction from the induced induced pressure rate, displacement rate, or strain rate), and
data collection and reporting procedures in the following
pressure of a monotonic, uniaxially loaded elastomeric insert,
where “monotonic” refers to a continuous, nonstop test rate sections.
without reversals from test initiation to final fracture.
Section
Scope 1
1.3 This test method applies primarily to advanced ceramic
Referenced Documents 2
matrix composite tubes with continuous fiber reinforcement: Terminology 3
Summary of Test Method 4
unidirectional (1D, filament wound and tape lay-up), bidirec-
Significance and Use 5
tional (2D, fabric/tape lay-up and weave), and tridirectional
Interferences 6
Apparatus 7
Hazards 8
Test Specimens 9
This test method is under the jurisdiction of ASTM Committee C28 on
Test Procedure 10
Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on
Calculation of Results 11
Ceramic Matrix Composites.
Report 12
Current edition approved July 1, 2021. Published August 2021. Originally
Precision and Bias 13
approved in 2015. Last previous edition approved in 2015 as C1819–15. DOI:
Keywords 14
10.1520/C1819-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1819 − 21
PertinentdefinitionsaslistedinPracticeE1012andTerminolo-
Section
Appendixes
giesC1145,D3878,andE6areshowninthefollowingwiththe
Verification of Load Train Alignment Appendix X1
appropriate source given in parentheses.Additional terms used
Stress Factors for Calculation of Maximum Hoop Stress Appendix X2
in conjunction with this test method are defined in the
Axial Force to Internal Pressure Appendix X3
following:
1.7 Values expressed in this test method are in accordance
3.1.2 advanced ceramic, n—a highly engineered, high-
with the International System of Units (SI) (IEEE/ASTM SI
performance, predominantly nonmetallic, inorganic, ceramic
10).
material having specific functional attributes. (See Terminol-
1.8 This standard does not purport to address all of the
ogy C1145.)
safety concerns, if any, associated with its use. It is the
3.1.3 breaking force, n—the force at which fracture occurs.
responsibility of the user of this standard to establish appro-
(See Terminology E6.)
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
3.1.4 ceramic matrix composite (CMC), n—a material con-
Specific hazard statements are given in Section 8 and Note 1.
sisting of two or more materials (insoluble in one another), in
1.9 This international standard was developed in accor-
whichthemajor,continuouscomponent(matrixcomponent)is
dance with internationally recognized principles on standard-
a ceramic, while the secondary component/s (reinforcing
ization established in the Decision on Principles for the
component) may be ceramic, glass-ceramic, glass, metal, or
Development of International Standards, Guides and Recom-
organic in nature. These components are combined on a
mendations issued by the World Trade Organization Technical
macroscale to form a useful engineering material possessing
Barriers to Trade (TBT) Committee.
certain properties or behavior not possessed by the individual
constituents.
2. Referenced Documents
3.1.5 continuous fiber-reinforced ceramic matrix composite
2.1 ASTM Standards:
(CFCC), n—aceramicmatrixcompositeinwhichthereinforc-
C1145Terminology of Advanced Ceramics
ing phase consists of a continuous fiber, continuous yarn, or a
C1239Practice for Reporting Uniaxial Strength Data and
woven fabric.
Estimating Weibull Distribution Parameters forAdvanced
3.1.6 gage length, n—the original length of that portion of
Ceramics
the specimen over which strain or change of length is deter-
D3878Terminology for Composite Materials
mined. (See Terminology E6.)
E4Practices for Force Verification of Testing Machines
3.1.7 hoop tensile strength, n—the maximum tensile com-
E6Terminology Relating to Methods of MechanicalTesting
ponentofhoopstresswhichamaterialiscapableofsustaining.
E83Practice for Verification and Classification of Exten-
Hoop tensile strength is calculated from the maximum internal
someter Systems
pressure induced in a tubular test specimen.
E177Practice for Use of the Terms Precision and Bias in
ASTM Test Methods
3.1.8 matrix cracking stress, n—the applied tensile stress at
E337Test Method for Measuring Humidity with a Psy-
whichthematrixcracksintoaseriesofroughlyparallelblocks
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
normal to the tensile stress.
peratures)
3.1.8.1 Discussion—In some cases, the matrix cracking
E691Practice for Conducting an Interlaboratory Study to
stress may be indicated on the stress-strain curve by deviation
Determine the Precision of a Test Method
from linearity (proportional limit) or incremental drops in the
E1012Practice for Verification of Testing Frame and Speci-
stress with increasing strain. In other cases, especially with
men Alignment Under Tensile and Compressive Axial
materials which do not possess a linear region of the stress-
Force Application
strain curve, the matrix cracking stress may be indicated as the
IEEE/ASTM SI 10American National Standard for Metric
first stress at which a permanent offset strain is detected in the
Practice
during unloading (elastic limit).
3.1.9 modulus of elasticity, n—the ratio of stress to corre-
3. Terminology
spondingstrainbelowtheproportionallimit.(SeeTerminology
3.1 Definitions:
E6.)
3.1.1 The definitions of terms relating to hoop tensile
3.1.10 modulus of resilience, n—strain energy per unit
strength testing appearing in Terminology E6 apply to the
volume required to elastically stress the material from zero to
termsusedinthistestmethod.Thedefinitionsoftermsrelating
the proportional limit indicating the ability of the material to
to advanced ceramics appearing in Terminology C1145 apply
absorb energy when deformed elastically and return it when
to the terms used in this test method. The definitions of terms
unloaded.
relating to fiber-reinforced composites appearing in Terminol-
ogy D3878 apply to the terms used in this test method. 3.1.11 modulus of toughness, n—strain energy per unit
volume required to stress the material from zero to final
fracture indicating the ability of the material to absorb energy
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
beyond the elastic range (that is, damage tolerance of the
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
material).
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. 3.1.11.1 Discussion—Themodulusoftoughnesscanalsobe
C1819 − 21
referred to as the cumulative damage energy and as such is characterization, design data generation, material model
regardedasanindicationoftheabilityofthematerialtosustain verification/validation, or combinations thereof.
damage rather than as a material property. Fracture mechanics
5.2 Continuous fiber-reinforced ceramic composites
methods for the characterization of CMCs have not been
(CFCCs)arecomposedofcontinuousceramic-fiberdirectional
developed. The determination of the modulus of toughness as
(1D, 2D, and 3D) reinforcements in a fine-grain-sized
provided in this test method for the characterization of the
(<50µm) ceramic matrix with controlled porosity. Often these
cumulative damage process in CMCs may become obsolete
composites have an engineered thin (0.1 to 10 µm) interface
whenfracturemechanicsmethodsforCMCsbecomeavailable.
coating on the fibers to produce crack deflection and fiber
pull-out.
3.1.12 proportional limit stress, n—the greatest stress that a
material is capable of sustaining without any deviation from
5.3 CFCC components have a distinctive and synergistic
proportionality of stress to strain (Hooke’s law).
combinationofmaterialproperties,interfacecoatings,porosity
3.1.12.1 Discussion—Many experiments have shown that
control,compositearchitecture(1D,2D,and3D),andgeomet-
valuesobservedfortheproportionallimitvarygreatlywiththe
ric shape that are generally inseparable. Prediction of the
sensitivity and accuracy of the testing equipment, eccentricity
mechanical performance of CFCC tubes (particularly with
of loading, the scale to which the stress-strain diagram is
braidand3Dweavearchitectures)cannotbemadebyapplying
plotted, and other factors. When determination of proportional
measured properties from flat CFCC plates to the design of
limit is required, the procedure and sensitivity of the test
tubes. In particular, tubular components comprised of CMCs
equipment should be specified. (See Terminology E6.)
materialformauniquesynergisticcombinationofmaterialand
geometric shape that are generally inseparable. In other words,
3.1.13 slow crack growth, n—subcritical crack growth (ex-
predictionofmechanicalperformanceofCMCtubesgenerally
tension) which may result from, but is not restricted to, such
cannot be made by using properties measured from flat plates.
mechanisms as environmentally assisted stress corrosion or
Strength tests of internally pressurized CMC tubes provide
diffusive crack growth.
information on mechanical behavior and strength for a multi-
axially stressed material.
4. Summary of Test Method
5.4 Unlike monolithic advanced ceramics which fracture
4.1 In the test method a composite tube/cylinder with a
catastrophically from a single dominant flaw, CMCs generally
defined gage section and a known wall thickness is loaded by
experience “graceful” fracture from a cumulative damage
the radial expansion an elastomeric insert (located midway
process.Therefore,whilethevolumeofmaterialsubjectedtoa
inside the tube) that is compressed longitudinally between
uniform hoop tensile stress for a single uniformly pressurized
pushrods. The elastomeric insert expands under the uniaxial
tube test may be a significant factor for determining matrix
compressive loading of the pushrods and exerts a uniform
cracking stress, this same volume may not be as significant a
radial pressure on the inside of the tube. The resulting hoop
factor in determining the ultimate strength of a CMC.
stress-strain response of the composite tube is recorded until
However, the probabilistic nature of the strength distributions
failure of the tube. The hoop tensile strength and the hoop
of the brittle matrices of CMCs requires a statistically signifi-
fracture strength are determined from the resulting maximum
cant number of test specimens for statistical analysis and
pressure and the pressure at fracture. The hoop tensile strains,
design. Studies to determine the exact influence of test speci-
theproportionallimithoopstress,andthemodulusofelasticity
men volume on strength distributions for CMCs have not been
inthehoopdirectionaredeterminedfromthestress-straindata.
completed. It should be noted that hoop tensile strengths
4.2 Hoop tensile strength as used in this test method refers
obtained using different recommended test specimens with
to the tensile strength in the hoop direction from the induced
different volumes of material in the gage sections may be
pressure of a monotonic, uniaxially loaded elastomeric insert,
different due to these volume effects.
where “monotonic” refers to a continuous test rate with no
5.5 Hoop tensile strength tests provide information on the
reversals.
strength and deformation of materials under biaxial stresses
4.3 Thetestmethodisapplicabletoarangeoftestspecimen
induced from internal pressurization of tubes. Nonuniform
tube geometries based on a non-dimensional parameter that
stress states are inherent in these types of tests and subsequent
includes composite material property and tube radius. Lengths
evaluation of any nonlinear stress-strain behavior must take
of the composite tube, pushrods, and elastomeric insert are
into account the unsymmetric behavior of the CMC under
determined from this non-dimensional parameter so as to
biaxial stressing. This nonlinear behavior may develop as the
provide a gage length with uniform internal radial pressure.A
result of cumulative damage processes (for example, matrix
wide range of combinations of material properties, tube radii,
cracking, matrix/fiber debonding, fiber fracture, delamination,
wall thicknesses, tube lengths, and insert lengths are possible.
etc.) which may be influenced by testing mode, testing rate,
processing or alloying effects, or environmental influences.
5. Significance and Use
Some of these effects may be consequences of stress corrosion
or subcritical (slow) crack growth that can be minimized by
5.1 Thistestmethod(alsoknownasoverhungtubemethod)
testingatsufficientlyrapidratesasoutlinedinthistestmethod.
may be used for material development, material comparison,
material screening, material down selection, and quality assur- 5.6 The results of hoop tensile strength tests of test speci-
ance. This test method is not recommended for material mens fabricated to standardized dimensions from a particular
C1819 − 21
material or selected portions of a part, or both, may not totally minimum stresses occurring at the test specimen surface,
represent the strength and deformation properties of the entire, leading to fractures originating at surfaces or near geometrical
full-size end product or its in-service behavior in different transitions.Inaddition,ifdeformationsorstrainsaremeasured
environments. at surfaces where maximum or minimum stresses occur,
bending may introduce over or under measurement of strains
5.7 For quality control purposes, results derived from stan-
dependingonthelocationofthestrain-measuringdeviceonthe
dardized tubular hoop tensile strength test specimens may be
specimen. Similarly, fracture from surface flaws may be
considered indicative of the response of the material from
accentuated or suppressed by the presence of the nonuniform
which they were taken for, given primary processing condi-
stresses caused by bending.
tions and post-processing heat treatments.
6.4 Friction between the insert and the rough and/or unlu-
5.8 The hoop tensile stress behavior and strength of a CMC
bricated inner surface of tubular test specimen can produce
are dependent on its inherent resistance to fracture, the pres-
compressive stresses on the inner bore of the tube that will
ence of flaws, or damage accumulation processes, or both.
reducethathoopstressinthetube.Inaddition,thisfrictionwill
Analysis of fracture surfaces and fractography, though beyond
accentuate axial bending stress.
the scope of this test method, is highly recommended.
6.5 Fractures that initiate outside the gage section of a test
6. Interferences
specimenmaybeduetofactorssuchasstressconcentrationsor
6.1 Test environment (vacuum, inert gas, ambient air, etc.),
geometrical transitions, extraneous stresses introduced by
including moisture content (for example, relative humidity),
fixtures/load apparatuses, or strength-limiting features in the
may have an influence on the measured hoop tensile strength.
microstructure of the specimen. Such non-gage section frac-
In particular, the behavior of materials susceptible to slow
tures will usually constitute invalid tests.
crack growth fracture will be strongly influenced by test
environmentandtestingrate.Testingtoevaluatethemaximum
7. Apparatus
strength potential of a material should be conducted in inert
7.1 Testing Machines—Machinesusedforapplyinguniaxial
environmentsoratsufficientlyrapidtestingrates,orboth,soas
forces to elastomeric inserts for hoop tensile strength testing
to minimize slow crack growth effects. Conversely, testing can
shall conform to the requirements of Practices E4. The axial
be conducted in environments and testing modes and rates
force used in inducing the internal pressure shall be accurate
representative of service conditions to evaluate material per-
within 61%atanyforcewithintheselectedforcerangeofthe
formance under use conditions. When testing is conducted in
testing machine as defined in Practices E4. A schematic
uncontrolled ambient air with the intent of evaluating maxi-
showing pertinent features of the hoop tensile strength testing
mum strength potential, relative humidity and temperature
apparatus is shown in Fig. 1.
must be monitored and reported. Testing at humidity levels
7.2 Fixtures:
>65% relative humidity (RH) is not recommended and any
7.2.1 General—Compression loading fixtures are generally
deviations from this recommendation must be reported.
composed of two parts: (1) basic steel test machine grips (for
6.2 Surface preparation of test specimens, although nor-
example, hydraulically loaded V-grips) attached to the test
mally not considered a major concern in CMCs, can introduce
machine, and (2) pushrods that are held rigidly in the test
fabrication flaws that may have pronounced effects on hoop
machine grips and act as the interface between the grips and
tensilestressmechanicalpropertiesandbehavior(forexample,
elastomeric insert.Aschematic drawing of such a fixture and a
shapeandleveloftheresultingstress-straincurve,hooptensile
test specimen is shown in Fig. 2. A figure showing an actual
strength and strain, proportional limit hoop stress and strain,
test setup is shown in Fig. 3. Another variation of the
etc.). Machining damage introduced during test specimen
compression loading fixture can use (1) compression platens
preparation can be either a random interfering factor in the
attached to the test machine, and (2) pushrods that are held
determination of ultimate strength of pristine material (that is,
against the platens in the test machine and act as the interface
increased frequency of surface-initiated fractures compared to
between the platens and elastomeric insert.
volume-initiated fractures), or an inherent part of the strength
7.2.2 With insert testing, the only ‘connection’between the
characteristics to be measured. Surface preparation can also
pressurizing ‘machinery’ and the tube under test is a trapped
lead to the introduction of residual stresses. Universal or
film of high-pressure lubricant (Fig. 2). Tests have shown that
standardizedtestmethodsofsurfacepreparationdonotexist.It
this lubricant film retains a constant thickness during testing to
should be understood that final machining steps may or may
the maximum pressure (1). The objective is to transmit the
not negate machining damage introduced during the initial
appliedforcefromthepushrodthroughthelubricantfilmtothe
machining.Thus,testspecimenfabricationhistorymayplayan
inner wall of the tube under test. However, evidence indicates
important role in the measured strength distributions and
that the insert behaves as a hydraulic fluid also up to longitu-
should be reported. In addition, the nature of fabrication used
dinal compressions of at least 5 % strain.
forcertaincomposites(forexample,chemicalvaporinfiltration
7.2.3 Inserts—Typically, commercial insert materials are
orhotpressing)mayrequirethetestingoftestspecimensinthe
used because of the wide range of hardnesses available. The
as-processed condition (that is, it may not be possible to
machine the test specimen faces).
6.3 Internally pressurized tests of CMC tubes can produce
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
biaxial and triaxial stress distributions with maximum and this standard.
C1819 − 21
FIG. 1 Schematic Diagram of One Possible Apparatus for Applying a Uniaxial Force to an Elastomeric Insert for Conducting
an Internally Pressurized Hoop Strength Test of a CMC Tube
“correct” hardness is chosen by determining the insert force However, a final grinding to finished size on diameter and
and related pressure at failure of the CMC tubular test
length is essential so that end surfaces are perpendicular to
specimen. diameter.
7.2.3.2 Insert length is chosen based on tubular test speci-
NOTE 1—Common insert materials include urethane (such as Du Pont
Adiprene)orneoprene (1)mainlybecauseofthewiderangeofhardnesses
men dimensions and test material properties. The insert takes
commercially available. Other inert materials successfully employed
uponlythecentralportionofthetubefortworeasons: (1)tube
included silicon rubber such as Dow Corning Silastic.
ends act a guide for the pushrods and (2) when correctly
7.2.3.1 Inserts can be machined from a pre-cast block or
dimensioned per the requirement of this test method, the
cast “in place” (that is, inside the tubular test specimen).
C1819 − 21
FIG. 3 Example of Test Setup for Uniaxially Loaded Tube (1)
TABLE 1 Maximum Recommended Insert Pressure
Maximum Recommended
Shore Hardness (A) Pressure
(MPa = N/mm )
70 12
90 50
95 ~130
FIG. 2 Schematic of Uniaxially Loaded Insert (1)
where:
unpressurized tube ends can be made such that the stresses in
ν = Poisson’s ratio of test material,
tube
the end surfaces during testing are negligible.
r = inner radius of tubular test specimen in units of mm,
i
7.2.3.3 Previous studies (1) have shown that pressurized
and
length of the tube, L, and hence initial length of the insert
t = wall thickness of tubular test specimen in units of
should be:
mm.
NOTE 2—Example of a commercial CMC (ν = 0.15) tube with outer
L$9⁄β
diameterof100mmandwallandtubewallthicknessof2mm.Inthiscase
and
2 2
4 4
3 1 2 ν 3 1 2 0.15
~ ! ~ !
(1)
5 =0.1331/mmsuchthat
4 β5
3 1 2 ν Œ Œ
~ ! tube 2 2 2 2
r t 100 2 2 2 ⁄2 2
~ ! ~@ ~ !# !
i
β 5
Œ
tube 2 2
r t L=9/β = 9/0.133 = 67.38 mm.
~ !
i
C1819 − 21
7.2.4 Pushrods—Pushrods are made from any material with calibrated periodically in accordance with Practice E83. For
sufficient compressive strength to prevent yielding of the extensometers mechanically attached to the test specimen, the
pushrod and sufficient stiffness to prevent buckling. Final
attachment should be such as to cause no damage to the
grindingofthepushroddiametersandpushrodendsisrequired specimen surface.
to meet the requirements for wall clearance, face flatness, and
7.3.2 Alternatively, strain can also be determined directly
perpendicularity/straightness as shown in Fig. 4.
from strain gages. Ideally, to eliminate the effect of misaligned
7.2.4.1 Clearance between the pushrod and tube wall of the
uniaxial strain gages, three-element rosette strain gages should
test specimen shall fall within the following limits:
be mounted to determine maximum principal strain which
0.04 mm should be in the hoop direction. Unless it can be shown that
tube pushrod
0.04 mm# c 5 ~r 2 r !#max % (2)
H
i o pushrod
strain gage readings are not unduly influenced by localized
0.05* 2r
~ !
strain events such as fiber crossovers, strain gages should not
7.2.4.2 Concentricity of the pushrod over the entire length
be less than 9 to 12 mm in length for the longitudinal direction
shall be 0.005mm. Flatness of the pushrod end shall be
and not less than 6 mm in length for the transverse direction.
0.005mm. Perpendicularity of the pushrod end shall be
Notethatlargerstraingagesthanthoserecommendedheremay
0.005mm with a run-out of 0.024 mm per 24 mm.
be required for fabric reinforcements to average the localized
7.2.4.3 Length of each pushrod should include the unpres-
strain effects of the fiber crossovers. The strain gages, surface
surized length of the tube, plus the length of the pushrod
preparation, and bonding agents should be chosen to provide
inserted into the grip, plus the length of the tube required to
adequate performance on the subject materials and suitable
take up the compression of the insert during testing. Too long
strain recording equipment should be employed. Note that
of a pushrod could contribute to buckling during testing. Too
many CMCs may exhibit high degrees of porosity and surface
short of a pushrod could lead to interference of the test
roughness and therefore require surface preparation, including
specimen with the test machine/grip during testing. A recom-
surface filling, before the strain gages can be applied.
mended (1) pushrod length is half minimum unpressurized
length of the tubular test specimen plus the grip length of the
7.4 Data Acquisition—At the minimum, autographic record
pushrod, such that:
of applied load and gage section elongation or strain versus
L $ 5 3.5 ⁄ β 1grip length time should be obtained. Either analog chart recorders or
~ !
pushrod
digital data acquisition systems can be used for this purpose,
and
although a digital record is recommended for ease of later data
X 53.5⁄β
(3)
analysis. Ideally, an analog chart recorder or plotter should be
5minimum unpressurized half length
used in conjunction with the digital data acquisition system to
of tubular test specimen
provide an immediate record of the test as a supplement to the
NOTE 3—Example of a commercial CMC (ν = 0.15) tube with outer
diameterof100mmandwallandtubewallthicknessof2mm.Inthiscase
digital record. Recording devices shall be accurate to within
2 2
4 4
3~1 2 ν ! 3~1 2 0.15 ! 60.1 % for the entire testing system including readout unit as
5 =0.1331/mmsuchthat
β5
Œ Œ
tube 2 2 2 2
r t 100 2 2 2 ⁄2 2
~ ! ~@ ~ !# ! specified in Practices E4 and shall have a minimum data
i
X = 3.5/β = 3.5/0.133 = 26.2 in L = 26.2 + L mm.
pushrod grip
acquisition rate of 10 Hz, with a response of 50 Hz deemed
7.3 Strain Measurement—Strain should be determined by
more than sufficient.
means of either a suitable diametral or circumferential
7.4.1 Strain or elongation of the gage section, or both,
extensometers, strain gages, or appropriate optical methods. If
should be recorded either similarly to the force or as indepen-
Poisson’s ratio is to be determined, the tubular test specimen
dent variables of force. Crosshead displacement of the test
must be instrumented to measure strain in both longitudinal
machinemayalsoberecordedbutshouldnotbeusedtodefine
and lateral directions.
displacement or strain in the gage section.
7.3.1 Diametral or circumferential extensometers used for
7.5 Dimension-Measuring Devices—Micrometers and other
testing of CMC tubular test specimens shall satisfy Practice
devices used for measuring linear dimensions should be
E83, Class B-1 requirements and are recommended to be used
in place of strain gages for test specimens with gage lengths of accurate and precise to at least one half the smallest unit to
whichtheindividualdimensionisrequiredtobemeasured.For
≥25 mm and shall be used for high-performance tests beyond
the range of strain gage applications. Extensometers shall be the purposes of this test method, cross-sectional dimensions
FIG. 4 Details of Interface Between Pushrod and Insert
C1819 − 21
NOTE 4—Example of a commercial CMC (ν = 0.15) tube with outer
should be measured to within 0.02 mm, thereby requiring
diameterof100mmandwallandtubewallthicknessof2mm.Inthiscase
dimension-measuring devices with accuracies of 0.01 mm.
2 2
4 4
3 1 2 ν 3 1 2 0.15
~ ! ~ !
5 =0.1331/mmsuchthat
β5Œ Œ
tube 2 2 2 2
8. Hazards
~r ! t ~@100 2 2 ~2!#⁄2! 2
i
L ≥ 16/β = 119.8 mm.
t
8.1 Duringtheconductofthistestmethod,thepossibilityof
9.2 Test Specimen Preparation:
flying fragments of broken test material is high. The brittle
9.2.1 Depending upon the intended application of the hoop
nature of advanced ceramics and the release of strain energy
tensile strength data, use one of the following test specimen
contribute to the potential release of uncontrolled fragments
preparation procedures. Regardless of the preparation proce-
upon fracture. Means for containment and retention of these
dure used, sufficient details regarding the procedure must be
fragments for later fractographic reconstruction and analysis is
reported to allow replication.
highly recommended.
9.2.2 As-Fabricated—The tubular test specimen should
8.2 Exposed fibers at the edges of CMC test specimens
simulatethesurface/edgeconditionsandprocessingrouteofan
present a hazard due to the sharpness and brittleness of the
application where no machining is used; for example, as-cast,
ceramic fiber. All those required to handle these materials
sintered, or injection molded part. No additional machining
should be well informed of such conditions and the proper
specifications are relevant.As-processed test specimens might
handling techniques.
possess rough surface textures and nonparallel edges and as
such may cause excessive misalignment or be prone to
9. Test Specimens
non-gage section fractures, or both.
9.1 Test Specimen Geometry:
9.2.3 Application-Matched Machining—The tubular test
9.1.1 General—The geometry of tubular test specimens is
specimen should have the same surface/edge preparation as
dependentontheultimateuseofthehooptensilestrengthdata.
that given to the component. Unless the process is proprietary,
For example, if the hoop tensile strength of an as-fabricated
the report should be specific about the stages of material
component is required, the dimensions of the resulting test
removal, wheel grits, wheel bonding, amount of material
specimen may reflect the wall thickness, tube diameter, and
removed per pass, and type of coolant used.
length restrictions of the component. If it is desired to evaluate
9.2.4 Customary Practices—In instances where customary
the effects of interactions of various constituent materials for a
machining procedure has been developed that is completely
particularCMCmanufacturedviaaparticularprocessingroute,
satisfactory for a class of materials (that is, it induces no
then the size of the test specimen and resulting gage section
unwanted surface/subsurface damage or residual stresses), this
(that is, insert length or pressurized length) will reflect the
procedure should be used.
desiredvolumetobesampled.Inaddition,calculatedlengthof
9.2.5 Standard Procedure—In instances where 9.2.2 – 9.2.4
the insert (that is, pressurized length) plus the length of the
are not appropriate, 9.2.5 should apply. Studies to evaluate the
pushrods (that is, unpressurized length) will influence the final
machinability of CMCs have not been completed. Therefore,
design of the test specimen geometry. Tubular test specimen
the standard procedure of 9.2.5 can be viewed as starting point
geometries to maximize or minimize stresses through the wall
guidelines and a more stringent procedure may be necessary.
thickness have been studied experimentally and analytically
9.2.5.1 All grinding or cutting should be done with ample
(1-3).
supply of appropriate filtered coolant to keep the workpiece
9.1.1.1 The following sections discuss the required hoop
and grinding wheel constantly flooded and particles flushed.
tensilestrengthtubulartestspecimengeometries,althoughany
Grinding can be done in at least two stages, ranging from
geometryisacceptableifitmeetstherequirementsforpushrod
coarse to fine rate of material removal.All cutting can be done
and test specimen dimensions as well as those for fracture
in one stage appropriate for the depth of cut.
locationofthistestmethod.Deviationsfromtherecommended
9.2.5.2 Stock removal rate should be on the order of
geometries may be necessary depending upon the particular
0.03mm per pass using diamond tools that have between 320
CMC being evaluated. Stress analyses of untried test speci-
and 600 grit. Remove equal stock where applicable.
mens should be conducted to ensure that stress concentrations
NOTE 5—Care should be exercised in storage and handling of finished
thatcanleadtoundesiredfracturesoutsidethegagesectionsdo
test specimens to avoid the introduction of random and severe flaws. In
not exist. It should be noted that contoured specimens by their
addition, attention should be given to pre-test storage of test specimens in
nature contain inherent stress concentrations due to geometric
controlled environments or desiccators to avoid unquantifiable environ-
mental degradation of specimens prior to testing.
transitions that are in addition to stress due to finite length
elastomeric inserts. Stress analyses can indicate the magnitude
9.3 Number of Test Specimens—A minimum of five test
of such stress concentrations while revealing the success of specimens tested validly is required for the purposes of
producing a near uniform hoop tensile stress state in the gage
estimating a mean. A greater number of test specimens tested
section of the test specimen. validlymaybenecessaryifestimatesregardingtheformofthe
9.1.2 Test Specimen Dimensions—Although the diameters
strength distribution are required. If material cost or test
and wall thickness of CMC tubes can vary widely depending
specimenavailabilitylimitsthenumberofpossibletests,fewer
on the application, analytical and experimental studies have
tests can be conducted to determine an indication of material
shown (1-3) that successful tests can be maximized by using
properties.
consistent ranges of overall tube length as follows:
9.4 ValidTest—Avalidindividualtestisonewhichmeetsall
L $16 ⁄β (4) the following requirements of this test method with final
t
C1819 − 21
fracture in the uniformly stressed gage section (that is, pres- testing are intended to be sufficiently rapid to obtain the
surized insert length) unless those tests fracturing outside the maximum possible hoop tensile strength at fracture of the
gage section are interpreted as interrupted tests for the purpose
material. However, rates other than those recommended here
of censored test analyses.
may be used to evaluate rate effects. In all cases, the test mode
and rate must be reported.
10. Test Procedure
10.2.1.1 Formonolithicadvancedceramicsexhibitinglinear
elasticbehavior,fractureisattributedtoaweakest-linkfracture
10.1 Test Specimen Dimensions—Determine the wall thick-
ness and outer diameter of the gage section of each test mechanism generally attributed to stress-controlled fracture
fromGriffith-likeflaws.Therefore,aforce-controlledtest,with
specimen to within 0.02 mm. Make measurements on at least
three different cross-sectional planes in the gage section. To force generally related directly to hoop tensile stress, is the
avoid damage in the critical gage section area, it is recom- preferred test mode. However, in CMCs the nonlinear stress-
mended that these measurements be made either optically (for strainbehaviorcharacteristicofthe“graceful”fractureprocess
example, an optical comparator) or mechanically using a of these materials indicates a cumulative damage process that
self-limiting (friction or ratchet mechanism) flat, anvil-type
is strain dependent. Generally, displacement or strain con-
micrometer. When measuring dimensions between the woven trolled tests are employed in such cumulative damage or
faces of woven materials, in general, use a self-limiting
yielding deformation processes to prevent a “runaway” condi-
(friction or ratchet mechanism) flat, anvil-type micrometer
tion (that is, rapid uncontrolled deformation and fracture)
havinganvilcross-sectionaldimensionsofatleast5mm.Inall
characteristic of force- or stress-controlled tests. Thus, to
cases the resolution of the instrument shall be as specified in
elucidate the potential “toughening” mechanisms under con-
7.5. Exercise caution to prevent damage to the test specimen
trolled fracture of the CMC, displacement or strain control is
gage section. Ball-tipped or sharp-anvil micrometers may be
preferred. However, for sufficiently rapid test rates, differences
preferred when measuring small-diameter test specimens or
in the fracture process may not be noticeable and any of these
materials with rough or uneven nonwoven surfaces. Record
test modes may be appropriate.
and report the measured dimensions and locations of the
10.2.2 Strain Rate—Strain is the independent variable in
measurements for use in the calculation of the hoop tensile
nonlinear analyses such as yielding. As such, strain rate is a
stress. Use the average of the multiple measurements in the
method of controlling tests of deformation processes to avoid
stress calculations.
“runaway” conditions. For the linear elastic region of CMCs,
10.1.1 Alternatively,toavoiddamagetothegagesection(or
strain rate can be related to strain measurement such that:
in cases where it is not possible to infer or determine gage
dε
section wall thickness), use the procedures described in 9.1 to
ε˙ 5 (5)
L
dT
make post-fracture measurements of the gage section dimen-
sions.Notethatinsomecasesthefractureprocesscanseverely
where:
fragment the gage section in the immediate vicinity of the
ε˙ = strain rate of the insert in units of (mm/mm)/s, and
L
fracture, thus making post-fracture measurements of dimen-
dε/dT = slope of strain-time curve (mm/mm)/s.
sions difficult. In these cases, it is advisable to follow the
Notethatstrain-controlledtestscanbeaccomplishedusinga
procedures outlined in 9.1 for pre-test measurements to ensure
diametral or hoop extensometer contacting the gage section of
reliable measurements.
the specimen as the primary control transducer. Strain rates on
10.1.2 Conduct periodic, if not 100 %, inspection/
–6 –6 –1
the order of5×10 to 50 × 10 s are recommended to
measurements of all test specimens and test specimen dimen-
minimize environmental effects when testing in ambient air.
sions to ensure compliance with the drawing specifications.
Generally, high-resolution optical methods (for example, an Alternately, strain rates shall be selected to produce final
fracture in 5 to 10 s to minimize environmental effects when
optical comparator) or high-resolution digital point contact
methods (for example, coordinate measurement machine) are testing in ambient air.
satisfactory as long as the equipment meets the specifications
10.2.3 Displacement Rate—Thesizedifferencesofeachtest
in 7.5. Note that the frequency of gage section fractures and
specimengeometryrequireadifferenttestingrateforanygiven
bending in the gage section are dependent on proper overall
stressrate.Notethatasthetestspecimenbeginstofracture,the
test specimen dimensions within the required tolerances.
strainrateinthegagesectionofthespecimenwillchangeeven
10.1.3 In some cases it is desirable, but not required, to
though the rate of motion of the crosshead remains constant.
measure surface finish to quantify the surface condition. Such
For this reason, displacement rate-controlled tests can give
methods as contacting profilometry can be used to determine
onlyanapproximatevalueoftheimposedstrainrate.Displace-
surface roughness parallel to the longitudinal axis. When
ment mode is defined as the control of, or free-running
quantified, surface roughness should be reported.
displacement of, the test machine crosshead. Thus, the dis-
10.2 Test Modes and Rates: placement rate can be calculated as follows. Displacement
rates shall be selected to produce final fracture in 5 to 10 s to
10.2.1 General—Test modes and rates can have distinct and
minimize environmental effects when testing in ambient air.
strong influences on fracture behavior of advanced ceramics,
even at ambient temperatures, depending on test environment Using the recommended (or desired) strain rate as detailed in
9.2.2, calculate the displacement rate for the linear elastic
or condition of the test specimen. Test modes may involve
force, displacement, or strain control. Recommended rates of region of CMCs only as:
C1819 − 21
application remains constant. Stress rates >35 to 50 MPa/s
have been used with success to minimize the influence of
environmental effects and thus obtain the greatest value of
ultimate hoop tensile strength.Alternately, stress or force rates
should be selected to produce final fracture in 5 to 10 s to
minimize environmental effects when testing in ambient air.
For the linear elastic region of CMCs, force rate is calculated
as:
dF
˙
F 5 (7)
dT
where:
˙
F = the required force rate in units of N/s,
F = the applied force in units of N, and
T = time in units of s.
10.2.5 Ramp Segments—Normally, tests are conducted in a
single ramp function at a single test rate from zero force to the
maximum force at fracture. However, in some instances
multiple ramp segments might be employed. In these cases, a
slowtestrateisusedtorampfromzeroforcetoanintermediate
force to allow time for removing “slack” from the test system.
The final ramp segment of the test is conducted from the
intermediate force to the maximum force at fracture at the
required (desired) test rate. The type and time duration of the
ramp should be reported.
10.3 Conducting the Hoop Tensile Strength Test:
10.3.1 Mounting the Test Specimen—The pushrods, insert,
andtubulartestspecimenmustbeassembledbeforetestingcan
commence. Components required for each test should be
identified and noted in the test report. Mark the test specimen
with an indelible marker as to the top and bottom and front
(side facing the operator) in relation to the test machine. In the
case of strain-gaged test specimens, orient the test specimen
such that the “front” of the test
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