ASTM C1366-04(2009)
(Test Method)Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Elevated Temperatures
Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Elevated Temperatures
SIGNIFICANCE AND USE
This test method may be used for material development, material comparison, quality assurance, characterization, reliability assessment, and design data generation.
High strength, monolithic advanced ceramic materials are generally characterized by small grain sizes ( 50 μm) and bulk densities near the theoretical density. These materials are candidates for load-bearing structural applications requiring high degrees of wear and corrosion resistance and elevated-temperature strength. Although flexural test methods are commonly used to evaluate strength of advanced ceramics, the non uniform stress distribution of the flexure specimen limits the volume of material subjected to the maximum applied stress at fracture. Uniaxially-loaded tensile strength tests provide information on strength-limiting flaws from a greater volume of uniformly stressed material.
Because of the probabilistic strength distributions of brittle materials such as advanced ceramics, a sufficient number of test specimens at each testing condition is required for statistical analysis and eventual design with guidelines for sufficient numbers provided in this test method. Size-scaling effects as discussed in practice C 1239 will affect the strength values. Therefore, strengths obtained using different recommended tensile test specimen geometries with different volumes or surface areas of material in the gage sections will be different due to these size differences. Resulting strength values can, in principle, be scaled to an effective volume or effective surface area of unity as discussed in Practice C 1239.
Tensile tests provide information on the strength and deformation of materials under uniaxial stresses. Uniform stress states are required to effectively evaluate any non-linear stress-strain behavior which may develop as the result of testing mode, testing rate, processing or alloying effects, environmental influences, or elevated temperatures. These effects may be consequences of stress co...
SCOPE
1.1 This test method covers the determination of tensile strength under uniaxial loading of monolithic advanced ceramics at elevated temperatures. This test method addresses, but is not restricted to, various suggested test specimen geometries as listed in the appendix. In addition, test specimen fabrication methods, testing modes (force, displacement, or strain control), testing rates (force rate, stress rate, displacement rate, or strain rate), allowable bending, and data collection and reporting procedures are addressed. Tensile strength as used in this test method refers to the tensile strength obtained under uniaxial loading.
1.2 This test method applies primarily to advanced ceramics which macroscopically exhibit isotropic, homogeneous, continuous behavior. While this test method applies primarily to monolithic advanced ceramics, certain whisker, or particle-reinforced composite ceramics as well as certain discontinuous fiber-reinforced composite ceramics may also meet these macroscopic behavior assumptions. Generally, continuous fiber ceramic composites (CFCCs) do not macroscopically exhibit isotropic, homogeneous, continuous behavior and application of this test method to these materials is not recommended.
1.3 The values stated in SI units are to be regarded as the standard and are in accordance with Practice E 380.
1.4 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. Refer to Section 7 for specific precautions.
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Designation: C1366 − 04(Reapproved 2009)
Standard Test Method for
Tensile Strength of Monolithic Advanced Ceramics at
Elevated Temperatures
This standard is issued under the fixed designation C1366; 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 2. Referenced Documents
1.1 This test method covers the determination of tensile 2.1 ASTM Standards:
strength under uniaxial loading of monolithic advanced ceram- C1145 Terminology of Advanced Ceramics
ics at elevated temperatures. This test method addresses, but is C1161 Test Method for Flexural Strength of Advanced
not restricted to, various suggested test specimen geometries as Ceramics at Ambient Temperature
listed in the appendix. In addition, test specimen fabrication C1239 Practice for Reporting Uniaxial Strength Data and
methods,testingmodes(force,displacement,orstraincontrol), Estimating Weibull Distribution Parameters forAdvanced
testing rates (force rate, stress rate, displacement rate, or strain Ceramics
rate), allowable bending, and data collection and reporting C1322 Practice for Fractography and Characterization of
procedures are addressed. Tensile strength as used in this test Fracture Origins in Advanced Ceramics
method refers to the tensile strength obtained under uniaxial D3379 Test Method forTensile Strength andYoung’s Modu-
loading. lus for High-Modulus Single-Filament Materials
E4 Practices for Force Verification of Testing Machines
1.2 This test method applies primarily to advanced ceramics
E6 Terminology Relating to Methods of Mechanical Testing
which macroscopically exhibit isotropic, homogeneous, con-
E21 TestMethodsforElevatedTemperatureTensionTestsof
tinuous behavior. While this test method applies primarily to
Metallic Materials
monolithic advanced ceramics, certain whisker, or particle-
E83 Practice for Verification and Classification of Exten-
reinforced composite ceramics as well as certain discontinuous
someter Systems
fiber-reinforced composite ceramics may also meet these
E220 Test Method for Calibration of Thermocouples By
macroscopicbehaviorassumptions.Generally,continuousfiber
Comparison Techniques
ceramic composites (CFCCs) do not macroscopically exhibit
E337 Test Method for Measuring Humidity with a Psy-
isotropic, homogeneous, continuous behavior and application
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
of this test method to these materials is not recommended.
peratures)
1.3 The values stated in SI units are to be regarded as the
E380 Practice for Use of the International System of Units
standard and are in accordance with Practice E380.
(SI) (The Modernized Metric System)
1.4 This standard does not purport to address all of the
E1012 Practice for Verification of Testing Frame and Speci-
safety concerns, if any, associated with its use. It is the men Alignment Under Tensile and Compressive Axial
responsibility of the user of this standard to establish appro-
Force Application
priate safety and health practices and determine the applica- IEEE/ASTM SI 10 Standard for Use of the International
bility of regulatory limitations prior to use. Refer to Section 7
System of Units (SI) (The Modern Metric System)
for specific precautions.
1 2
This test method is under the jurisdiction of ASTM Committee C28 on For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Mechanical Properties and Performance. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved July 1, 2009. Published September 2009. Originally the ASTM website.
approved in 1997. Last previous edition approved in 2004 as C1366 – 04. DOI: Withdrawn. The last approved version of this historical standard is referenced
10.1520/C1366-04R09. on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1366 − 04 (2009)
3. Terminology mation on strength-limiting flaws from a greater volume of
uniformly stressed material.
3.1 Definitions:
4.3 Because of the probabilistic strength distributions of
3.1.1 Definitions of terms relating to tensile testing and
advanced ceramics as they appear in Terminology E6 and brittle materials such as advanced ceramics, a sufficient num-
ber of test specimens at each testing condition is required for
Terminology C1145, respectively, apply to the terms used in
this test method. Pertinent definitions are shown in the follow- statistical analysis and eventual design with guidelines for
sufficient numbers provided in this test method. Size-scaling
ingwiththeappropriatesourcegiveninparenthesis.Additional
terms used in conjunction with this test method are defined in effects as discussed in practice C1239 will affect the strength
values. Therefore, strengths obtained using different recom-
the following.
mended tensile test specimen geometries with different vol-
3.1.2 advanced ceramic, n—a highly engineered, high per-
umes or surface areas of material in the gage sections will be
formance predominately non-metallic, inorganic, ceramic ma-
different due to these size differences. Resulting strength
terial having specific functional attributes. (See Terminology
values can, in principle, be scaled to an effective volume or
C1145.)
–1 effective surface area of unity as discussed in Practice C1239.
3.1.3 axial strain [LL ], n—theaveragelongitudinalstrains
4.4 Tensile tests provide information on the strength and
measured at the surface on opposite sides of the longitudinal
deformation of materials under uniaxial stresses. Uniform
axis of symmetry of the specimen by two strain-sensing
stress states are required to effectively evaluate any non-linear
devices located at the mid length of the reduced section. (See
stress-strain behavior which may develop as the result of
Practice E1012.)
–1 testing mode, testing rate, processing or alloying effects,
3.1.4 bending strain [LL ], n—the difference between the
environmental influences, or elevated temperatures. These
strainatthesurfaceandtheaxialstrain.Ingeneral,thebending
effects may be consequences of stress corrosion or sub critical
strain varies from point to point around and along the reduced
(slow) crack growth which can be minimized by testing at
section of the specimen. (See Practice E1012.)
appropriately rapid rates as outlined in this test method.
3.1.5 breaking load [F], n—the load at which fracture
4.5 The results of tensile tests of specimens fabricated to
occurs. (See Terminology E6.)
standardized dimensions from a particular material or selected
3.1.6 fractography, n—the means and methods for charac-
portions of a part, or both, may not totally represent the
terizing a fractured specimen or component. (See Terminology
strength and deformation properties of the entire, full-size end
C1145.)
product or its in-service behavior in different environments.
3.1.7 fracture origin, n—the source from which brittle
4.6 For quality control purposes, results derived from stan-
fracture commences. (See Terminology C1145).
dardized tensile test specimens can be considered to be
3.1.8 percent binding, n—the bending strain times 100
indicativeoftheresponseofthematerialfromwhichtheywere
divided by the axial strain. (See Practice E1012.)
taken for particular primary processing conditions and post-
processing heat treatments.
3.1.9 slow crack growth, n—sub critical crack growth (ex-
tension) that may result from, but is not restricted to, such
4.7 The tensile strength of a ceramic material is dependent
mechanisms as environmentally-assisted stress corrosion or on both its inherent resistance to fracture and the presence of
diffusive crack growth.
flaws. Analysis of fracture surfaces and fractography as de-
scribed in Practice C1322 and MIL-HDBK-790, though be-
3.1.10 tensile strength, S [FL ], n—the maximum tensile
u
yond the scope of this test method, are recommended for all
stress which a material is capable of sustaining. Tensile
purposes, especially for design data.
strength is calculated from the maximum load during a tension
test carried to rupture and the original cross-sectional area of
5. Interferences
the specimen. (See Terminology E6.)
5.1 Test environment (vacuum, inert gas, ambient air, etc.)
including moisture content for example relative humidity) may
4. Significance and Use
have an influence on the measured tensile strength. In particu-
4.1 This test method may be used for material development,
lar, the behavior of materials susceptible to slow crack growth
material comparison, quality assurance, characterization, reli-
fracturewillbestronglyinfluencedbytestenvironment,testing
ability assessment, and design data generation.
rate, and elevated temperatures. Testing to evaluate the maxi-
4.2 High strength, monolithic advanced ceramic materials mum strength potential of a material should be conducted in
are generally characterized by small grain sizes (< 50 µm) and inert environments or at sufficiently rapid testing rates, or both,
bulk densities near the theoretical density. These materials are to minimize slow crack growth effects. Conversely, testing can
candidates for load-bearing structural applications requiring be conducted in environments and testing modes and rates
high degrees of wear and corrosion resistance and elevated- representative of service conditions to evaluate material per-
temperature strength. Although flexural test methods are com- formance under use conditions. When testing is conducted in
monly used to evaluate strength of advanced ceramics, the non uncontrolled ambient air with the intent of evaluating maxi-
uniform stress distribution of the flexure specimen limits the mum strength potential, monitor and report relative humidity
volume of material subjected to the maximum applied stress at and ambient temperature. Testing at humidity levels > 65 %
fracture. Uniaxially-loaded tensile strength tests provide infor- relative humidity (RH) is not recommended.
C1366 − 04 (2009)
5.2 Surface preparation of test specimens can introduce
fabrication flaws that may have pronounced effects on tensile
strength. Machining damage introduced during test specimen
preparation can be either a random interfering factor in the
determination of ultimate strength of pristine material (that is
increase frequency of surface initiated fractures compared to
volume initiated fractures), or an inherent part of the strength
characteristics. Surface preparation can also lead to the intro-
duction of residual stresses. Universal or standardized test
methods of surface preparation do not exist. Final machining
steps may, or may not negate machining damage introduced
duringtheearlycoarseorintermediatemachining.Thus,report
testspecimenfabricationhistorysinceitmayplayanimportant
role in the measured strength distributions.
5.3 Bending in uniaxial tensile tests can cause or promote
non uniform stress distributions with maximum stresses occur-
ring at the test specimen surface leading to non representative
fracturesoriginatingatsurfacesorneargeometricaltransitions.
Bending may be introduced from several sources including
misaligned load trains, eccentric or mis-shaped test specimens,
and non-uniformly heated test specimens or grips. In addition,
if strains or deformations are measured at surfaces where
maximum or minimum stresses occur, bending may introduce
over or under measurement of strains. Similarly, fracture from
FIG. 1 Schematic Diagram of One Possible Apparatus for Con-
surface flaws may be accentuated or muted by the presence of
ducting a Uniaxially-Loaded Tensile Test
the non uniform stresses caused by bending.
6. Apparatus
elevated-temperature oxidizing environment. Cooled grips lo-
cated outside the heated zone are termed“ cold grips” and
6.1 Testing Machines—Machines used for tensile testing
generally induce a steep thermal gradient in the test specimen
shall conform to the requirements of Practice E4. The forces
at a greater relative expense because of grip cooling equipment
used in determining tensile strength shall be accurate within 6
and allowances, although with the advantage of consistent
1 % at any force within the selected force range of the testing
alignment and little degradation from exposure to elevated
machine as defined in Practice E4. A schematic showing
temperatures.
pertinent features of a possible tensile testing apparatus is
shown in Fig. 1
NOTE 1—The expense of the cooling system for cold grips is balanced
against maintaining alignment which remains consistent from test to test
6.2 Gripping Devices:
(stable grip temperature) and decreased degradation of the grips due to
6.2.1 General—Various types of gripping devices may be
exposure to the elevated-temperature oxidizing environment. When grip
used to transmit the measured load applied by the testing
cooling is employed, means should be provided to control the cooling
machine to the test specimen. The brittle nature of advanced medium to maximum fluctuations of 5 K (less than 1 K preferred) about
a setpoint temperature (1) over the course of the test to minimize
ceramics requires a uniform interface between the grip com-
thermally-induced strain changes in the test specimen. In addition,
ponents and the gripped section of the test specimen. Line or
opposing grip temperatures should be maintained at uniform and consis-
point contacts and non uniform pressure can produce Hertzian-
tent temperatures within6 5 K (less than 6 1 K preferred) (1) so as to
type stress leading to crack initiation and fracture of the test
avoid introducing unequal thermal gradients and subsequent non uniaxial
specimen in the gripped section. Gripping devices can be stresses in the test specimen. Generally, the need for control of grip
temperature fluctuations or differences may be indicated if test specimen
classed generally as those employing active and those employ-
gage-section temperatures cannot be maintained within the limits required
ing passive grip interfaces as discussed in the following
in 9.3.2
sections. Uncooled grips located inside the heated zone are
6.2.1.1 Active Grip Interfaces—Active grip interfaces re-
termed “hot grips” and generally produce almost no thermal
quire a continuous application of a mechanical, hydraulic, or
gradient in the test specimen but at the relative expense of grip
pneumatic force to transmit the load applied b
...
This document is not anASTM standard and is intended only to provide the user of anASTM 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:C 1366–97 Designation: C 1366 – 04 (Reapproved 2009)
Standard Test Method for
Tensile Strength of Monolithic Advanced Ceramics at
Elevated Temperatures
This standard is issued under the fixed designation C 1366; 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 test method covers the determination of tensile strength under uniaxial loading of monolithic advanced ceramics at
elevated temperatures. This test method addresses, but is not restricted to, various suggested test specimen geometries as listed in
the appendix. In addition, test specimen fabrication methods, testing modes (load,(force, displacement, or strain control), testing
rates (load(force rate,stressrate,displacementrate,orstrainrate),allowablebending,anddatacollectionandreportingprocedures
are addressed. Tensile strength as used in this test method refers to the tensile strength obtained under uniaxial loading.
1.2 Thistestmethodappliesprimarilytoadvancedceramicswhichmacroscopicallyexhibitisotropic,homogeneous,continuous
behavior. While this test method applies primarily to monolithic advanced ceramics, certain whisker, or particle-reinforced
composite ceramics as well as certain discontinuous fiber-reinforced composite ceramics may also meet these macroscopic
behavior assumptions. Generally, continuous fiber ceramic composites (CFCCs) do not macroscopically exhibit isotropic,
homogeneous, continuous behavior and application of this test method to these materials is not recommended.
1.3 The values stated in SI units are to be regarded as the standard and are in accordance with Practice E380.E 380.
1.4 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. Refer to Section 7 for specific precautions.
2. Referenced Documents
2.1 ASTM Standards:
C 1145 Terminology of Advanced Ceramics
C 1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
C 1239 Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters forAdvanced Ceramics
C 1322 Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
D 3379 Test Method for Tensile Strength and Young’s Modulus for High-Modulus Single-Filament Materials
E4 Practices for Force Verification of Testing Machines
E6 Terminology Relating to Methods of Mechanical Testing
E21 Practice Test Methods for Elevated Temperature Tension Tests of Metallic Materials
E83 Practice for Verification and Classification of Extensometer Systems
E 220 Test Method for Calibration of Thermocouples byBy Comparison Techniques
E 337 Test Method for MeasureMeasuring Humidity with a Psychrometer (The(the Measurement of Wet- and Dry-Bulb
Temperatures)
E 380 Practice for Use of the International System of Units (SI) (The Modernized Metric System)
E 1012 Practice for Verification of Specimen Alignment Under Tensile Loading
2.2 Military Handbook:
MIL-HDBK-790Fractography and Characterization of Fracture Origins in Advanced Structural Ceramics Practice for
Verification of Test Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) (The Modern Metric System)
This test method is under the jurisdiction ofASTM Committee C–28 C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.01 on Properties
and Performance.
Current edition approved Feb. 10, 1997. Published December 1997.on Mechanical Properties and Performance.
Current edition approved July 1, 2009. Published September 2009. Originally approved in 1997. Last previous edition approved in 2004 as C 1366 – 04.
Annual Book of ASTM Standards, Vol 15.01.
For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM 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.
Annual Book of ASTM Standards, Vol 03.01.
Withdrawn. The last approved version of this historical standard is referenced on www.astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1366 – 04 (2009)
3. Terminology
3.1 Definitions:
3.1.1 Definitions of terms relating to tensile testing and advanced ceramics as they appear inTerminology E 6 andTerminology
C1145,C 1145, respectively, apply to the terms used in this test method. Pertinent definitions are shown in the following with the
appropriate source given in parenthesis. Additional terms used in conjunction with this test method are defined in the following.
3.1.2 advanced ceramic, n—a highly engineered, high performance predominately non-metallic, inorganic, ceramic material
having specific functional attributes. (See Terminology C1145.)C 1145.)
–1
3.1.3 axial strain [LL ], n—the average longitudinal strains measured at the surface on opposite sides of the longitudinal axis
of symmetry of the specimen by two strain-sensing devices located at the mid length of the reduced section. (See Practice
E1012.)E 1012.)
–1
3.1.4 bending strain [LL ], n—the difference between the strain at the surface and the axial strain. In general, the bending
strain varies from point to point around and along the reduced section of the specimen. (See Practice E1012.)E 1012.)
3.1.5 breaking load [F], n—the load at which fracture occurs. (See Terminology E6.)E 6.)
3.1.6 fractography, n—the means and methods for characterizing a fractured specimen or component. (See Terminology
C1145.)C 1145.)
3.1.7 fracture origin, n—the source from which brittle fracture commences. (See Terminology C1145).C 1145).
3.1.8 percent binding, n—the bending strain times 100 divided by the axial strain. (See Practice E1012.)E 1012.)
3.1.9 slow crack growth, n—subcriticalcrackgrowth(extension)thatmayresultfrom,butisnotrestrictedto,suchmechanisms
as environmentally-assisted stress corrosion or diffusive crack growth.
3.1.10 tensile strength, S [FL ], n—the maximum tensile stress which a material is capable of sustaining. Tensile strength is
u
calculated from the maximum load during a tension test carried to rupture and the original cross-sectional area of the specimen.
(See Terminology E6.)E 6.)
4. Significance and Use
4.1 Thistestmethodmaybeusedformaterialdevelopment,materialcomparison,qualityassurance,characterization,reliability
assessment, and design data generation.
4.2 High strength, monolithic advanced ceramic materials are generally characterized by small grain sizes (< 50 µm) and bulk
densities near the theoretical density.These materials are candidates for load-bearing structural applications requiring high degrees
of wear and corrosion resistance and elevated-temperature strength.Although flexural test methods are commonly used to evaluate
strength of advanced ceramics, the non uniform stress distribution of the flexure specimen limits the volume of material subjected
to the maximum applied stress at fracture. Uniaxially-loaded tensile strength tests provide information on strength-limiting flaws
from a greater volume of uniformly stressed material.
4.3 Because of the probabilistic strength distributions of brittle materials such as advanced ceramics, a sufficient number of test
specimens at each testing condition is required for statistical analysis and eventual design with guidelines for sufficient numbers
providedinthistestmethod.Size-scalingeffectsasdiscussedinpracticeC 1239willaffectthestrengthvalues.Therefore,strengths
obtained using different recommended tensile test specimen geometries with different volumes or surface areas of material in the
gage sections will be different due to these size differences. Resulting strength values can, in principle, be scaled to an effective
volume or effective surface area of unity as discussed in Practice C1239.C 1239.
4.4 Tensile tests provide information on the strength and deformation of materials under uniaxial stresses. Uniform stress states
are required to effectively evaluate any non-linear stress-strain behavior which may develop as the result of testing mode, testing
rate, processing or alloying effects, environmental influences, or elevated temperatures. These effects may be consequences of
stress corrosion or sub critical (slow) crack growth which can be minimized by testing at appropriately rapid rates as outlined in
this test method.
4.5 Theresultsoftensiletestsofspecimensfabricatedtostandardizeddimensionsfromaparticularmaterialorselectedportions
of a part, or both, may not totally represent the strength and deformation properties of the entire, full-size end product or its
in-service behavior in different environments.
4.6 For quality control purposes, results derived from standardized tensile test specimens can be considered to be indicative of
the response of the material from which they were taken for particular primary processing conditions and post-processing heat
treatments.
4.7 The tensile strength of a ceramic material is dependent on both its inherent resistance to fracture and the presence of flaws.
Analysis of fracture surfaces and fractography as described in Practice C 1322 and MIL-HDBK-790,, though beyond the scope of
this test method, are recommended for all purposes, especially for design data.
5. Interferences
5.1 Test environment (vacuum, inert gas, ambient air, etc.) including moisture content for example relative humidity) may have
an influence on the measured tensile strength. In particular, the behavior of materials susceptible to slow crack growth fracture will
be strongly influenced by test environment, testing rate, and elevated temperatures. Testing to evaluate the maximum strength
potential of a material should be conducted in inert environments or at sufficiently rapid testing rates, or both, to minimize slow
crack growth effects. Conversely, testing can be conducted in environments and testing modes and rates representative of service
C 1366 – 04 (2009)
conditions to evaluate material performance under use conditions. When testing is conducted in uncontrolled ambient air with the
intent of evaluating maximum strength potential, monitor and report relative humidity and ambient temperature. Testing at
humidity levels > 65 % relative humidity (RH) is not recommended.
5.2 Surface preparation of test specimens can introduce fabrication flaws that may have pronounced effects on tensile strength.
Machining damage introduced during test specimen preparation can be either a random interfering factor in the determination of
ultimate strength of pristine material (that is increase frequency of surface initiated fractures compared to volume initiated
fractures), or an inherent part of the strength characteristics. Surface preparation can also lead to the introduction of residual
stresses. Universal or standardized test methods of surface preparation do not exist. Final machining steps may, or may not negate
machining damage introduced during the early coarse or intermediate machining. Thus, report test specimen fabrication history
since it may play an important role in the measured strength distributions.
5.3 Bending in uniaxial tensile tests can cause or promote non uniform stress distributions with maximum stresses occurring
at the test specimen surface leading to non representative fractures originating at surfaces or near geometrical transitions. Bending
may be introduced from several sources including misaligned load trains, eccentric or mis-shaped test specimens, and
non-uniformly heated test specimens or grips. In addition, if strains or deformations are measured at surfaces where maximum or
minimum stresses occur, bending may introduce over or under measurement of strains. Similarly, fracture from surface flaws may
be accentuated or muted by the presence of the non uniform stresses caused by bending.
6. Apparatus
6.1 Testing Machines—Machines used for tensile testing shall conform to the requirements of Practice E4.E 4. The loadsforces
used in determining tensile strength shall be accurate within 6 1 % at any loadforce within the selected loadforce range of the
testing machine as defined in Practice E4.E 4. A schematic showing pertinent features of a possible tensile testing apparatus is
shown in Fig. 1
6.2 Gripping Devices:
6.2.1 General—Various types of gripping devices may be used to transmit the measured load applied by the testing machine
to the test specimen. The brittle nature of advanced ceramics requires a uniform interface between the grip components and the
gripped section of the test specimen. Line or point contacts and non uniform pressure can produce Hertzian-type stress leading to
crack initiation and fracture of the test specimen in the gripped section. Gripping devices can be classed generally as those
employingactiveandthoseemployingpassivegripinterfacesasdiscussedinthefollowingsections.Uncooledgripslocatedinside
the heated zone are termed “hot grips” and generally produce almost no thermal gradient in the test specimen but at the relative
expense of grip materials of at least the same temperature capability as the test material and increased degradation of the grips due
to exposure to the elevated-temperature oxidizing environment. Grips located outside the heated zone surrounding the test
specimen may or may not employ cooling. Uncooled grips located outside the heated zone are termed“ warm grips” and generally
FIG. 1 Schematic Diagram of One Possible Apparatus for
Conducting a Uniaxially-Loaded Tensile Test
C 1366 – 04 (2009)
induce a mild thermal gradient in the test specimen but at the relative expense of elevated-temperature alloys in the grips and
increaseddegradationofthegripsduetoexposuretotheelevated-temperatureoxidizingenvironment.Cooledgripslocatedoutside
the heated zone are termed“ cold grips” and generally induce a steep thermal gradient in the test specimen at a greater relative
expense because of grip c
...
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