ASTM C1273-18

Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Ambient Temperatures

SIGNIFICANCE AND USE
4.1 This test method may be used for material development, material comparison, quality assurance, characterization, and design data generation.  
4.2 High-strength, monolithic advanced ceramic materials generally characterized by small grain sizes (  
4.3 Although the volume or surface area of material subjected to a uniform tensile stress for a single uniaxially loaded tensile test may be several times that of a single flexure test specimen, the need to test a statistically significant number of tensile test specimens is not obviated. Therefore, 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. Note that size-scaling effects as discussed in Practice C1239 will affect the strength values. Therefore, strengths obtained using different recommended tensile test specimens with different volumes or surface areas of material in the gage sections will be different due to these size differences. Resulting strength values can be scaled to an effective volume or surface area of unity as discussed in Practice C1239.  
4.4 Tensile tests provide information on the strength and deformation of materials under uniaxial tensile stresses. Uniform stress states are required to effectively evaluate any nonlinear stress-strain behavior which may develop as the result of testing mode, testing rate, processing or alloying effects, or environmental influences. These effects may be consequences of stress corrosion or subcritical (slow) crack growth, which can be minimized by testing at appropriately rapid rates as outlined in this test method.  
4.5 The results of tensile tests of test specimens fabricated to standardized dimensions from a particular material or selected portions, or both, of a part may not totally represent the strength and deforma...
SCOPE
1.1 This test method covers the determination of tensile strength under uniaxial loading of monolithic advanced ceramics at ambient temperatures. This test method addresses, but is not restricted to, various suggested test specimen geometries as listed in the appendixes. 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. Note that 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 that 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 practice to these materials is not recommended.  
1.3 Values expressed in this test method are in accordance with the International System of Units (SI) and IEEE/ASTM SI 10.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 7.  
1.5 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, Guid...

General Information

• Status: Published
• Publication Date: 30-Jun-2018
• ICS: 81.060.30 - Advanced ceramics
• ICS: 81.060.99 - Other standards related to ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.01 - Mechanical Properties and Performance

Relations

• Replaces: ASTM C1273-15 - Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Ambient Temperatures
• Effective Date: 01-Jul-2018
• Refers: ASTM C1322-15(2019) - Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM C1145-19 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM C1239-13(2018) - Standard Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• Effective Date: 01-Jul-2018
• Refers: ASTM C1322-15 - Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• Effective Date: 01-Jul-2015
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM C1239-13 - Standard Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• Effective Date: 01-Aug-2013
• Refers: ASTM C1161-13 - Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
• Effective Date: 01-Aug-2013
• Refers: ASTM C1145-06(2013)e1 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Feb-2013
• Refers: ASTM C1145-06(2013) - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Feb-2013
• Refers: ASTM E1012-12 - Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• Effective Date: 01-Jun-2012
• Refers: ASTM E1012-12e1 - Standard Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force Application
• Effective Date: 01-Jun-2012
• Refers: ASTM C1322-05b(2010) - Standard Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• Effective Date: 15-Jul-2010
• Refers: ASTM E4-10 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2010
• Refers: ASTM E83-10a - Standard Practice for Verification and Classification of Extensometer Systems
• Effective Date: 01-Jun-2010

Overview

ASTM C1273-18: Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Ambient Temperatures, published by ASTM International, specifies a procedure for determining the tensile strength of monolithic advanced ceramics under uniaxial loading at ambient temperatures. This method accommodates a range of specimen geometries, preparation techniques, and testing modes to characterize the mechanical behavior of advanced ceramics, supporting research, development, quality assurance, and material comparison. The standard is fundamental in generating reliable design data for ceramics with critical load-bearing requirements.

Key Topics

• Scope and Applicability

  • Applies primarily to monolithic advanced ceramics exhibiting isotropic, homogeneous, and continuous behavior.
  • Also suitable for some whisker- or particle-reinforced ceramic composites and discontinuous fiber-reinforced ceramics, provided they meet macroscopic behavior requirements.
  • Not recommended for materials like continuous fiber ceramic composites (CFCCs) lacking uniform mechanical response.

• Test Procedures

  • Describes multiple specimen geometries (cylindrical, flat, etc.).
  • Details test modes (force, displacement, or strain control) and corresponding rates.
  • Presents guidelines for minimizing non-uniform stresses and preventing specimen bending during testing.

• Data and Analysis

  • Emphasizes the need for a statistically significant number of tests due to the probabilistic nature of ceramic failure.
  • Recommends analysis methods for deriving Weibull distribution parameters following Practice C1239.
  • Supports scaling of measured strength values based on the effective stressed volume or surface area.

• Surface Preparation and Environmental Control

  • Highlights the impact of surface quality, machining damage, and environmental factors (humidity, temperature) on measured tensile strength.
  • Suggests rigorous reporting and control of preparation and testing environments to ensure reproducibility.

• Safety Considerations

  • Addresses risks associated with brittle fracture and the potential for flying fragments.
  • Advises on containment procedures and post-test fractographic analysis.

Applications

This tensile strength testing standard is vital for:

• Material Development and Comparison: Enables R&D teams to benchmark material performance and compare advanced ceramics produced via different manufacturing or processing routes.
• Quality Assurance: Offers a reproducible method for batch testing and monitoring the consistency of ceramic products.
• Design Data Generation: Supplies engineers with reliable tensile strength data needed for structural design, particularly for applications requiring high strength, wear, and corrosion resistance at ambient temperatures.
• Failure Analysis and Material Characterization: Facilitates the understanding of fracture behavior through controlled testing and post-failure analysis.
• Statistical Analysis: Supports robust evaluation of strength distributions, critical for predicting service life and reliability of brittle ceramics in demanding applications.

Related Standards

To ensure proper implementation and interpretation, ASTM C1273-18 references several related standards:

• ASTM C1145 – Terminology of Advanced Ceramics
• ASTM C1161 – Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
• ASTM C1239 – Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• ASTM C1322 – Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
• ASTM E4 – Practices for Force Verification of Testing Machines
• ASTM E83 – Practice for Verification and Classification of Extensometer Systems
• ASTM E1012 – Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force
• IEEE/ASTM SI 10 – American National Standard for Use of the International System of Units (SI)

Conclusion

ASTM C1273-18 provides a comprehensive, internationally recognized framework for measuring the tensile strength of advanced ceramics at ambient temperatures. Using this standard ensures consistency, comparability, and the generation of reliable mechanical property data essential for research, design, and quality assurance across the advanced ceramics industry. By adhering to its protocols and recommendations, organizations can optimize ceramic selection, improve manufacturing processes, and enhance the safety and performance of ceramic components in critical applications.

Standards Content (Sample)

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: C1273 − 18
Standard Test Method for
Tensile Strength of Monolithic Advanced Ceramics at
Ambient Temperatures
This standard is issued under the fixed designation C1273; 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 mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This test method covers the determination of tensile
strengthunderuniaxialloadingofmonolithicadvancedceram-
2. Referenced Documents
ics at ambient temperatures. This test method addresses, but is
2.1 ASTM Standards:
notrestrictedto,varioussuggestedtestspecimengeometriesas
C1145Terminology of Advanced Ceramics
listed in the appendixes. In addition, test specimen fabrication
C1161Test Method for Flexural Strength of Advanced
methods,testingmodes(force,displacement,orstraincontrol),
Ceramics at Ambient Temperature
testing rates (force rate, stress rate, displacement rate, or strain
C1239Practice for Reporting Uniaxial Strength Data and
rate), allowable bending, and data collection and reporting
Estimating Weibull Distribution Parameters forAdvanced
procedures are addressed. Note that tensile strength as used in
Ceramics
this test method refers to the tensile strength obtained under
C1322Practice for Fractography and Characterization of
uniaxial loading.
Fracture Origins in Advanced Ceramics
1.2 Thistestmethodappliesprimarilytoadvancedceramics
D3379TestMethodforTensileStrengthandYoung’sModu-
that macroscopically exhibit isotropic, homogeneous, continu-
lus for High-Modulus Single-Filament Materials
ous behavior. While this test method applies primarily to
E4Practices for Force Verification of Testing Machines
monolithic advanced ceramics, certain whisker- or particle-
E6Terminology Relating to Methods of MechanicalTesting
reinforcedcompositeceramicsaswellascertaindiscontinuous
E83Practice for Verification and Classification of Exten-
fiber-reinforced composite ceramics may also meet these
someter Systems
macroscopicbehaviorassumptions.Generally,continuousfiber
E337Test Method for Measuring Humidity with a Psy-
ceramic composites (CFCCs) do not macroscopically exhibit
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
isotropic, homogeneous, continuous behavior and application
peratures)
of this practice to these materials is not recommended.
E1012Practice for Verification of Testing Frame and Speci-
1.3 Values expressed in this test method are in accordance
men Alignment Under Tensile and Compressive Axial
withtheInternationalSystemofUnits(SI)andIEEE/ASTMSI
Force Application
10.
IEEE/ASTM SI 10American National Standard for Metric
Practice
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
3. Terminology
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
3.1 Definitions:
mine the applicability of regulatory limitations prior to use.
3.1.1 The definitions of terms relating to tensile testing
Specific precautionary statements are given in Section 7.
appearing in Terminology E6 apply to the terms used in this
1.5 This international standard was developed in accor-
test method on tensile testing.The definitions of terms relating
dance with internationally recognized principles on standard-
to advanced ceramics testing appearing inTerminology C1145
ization established in the Decision on Principles for the
applytothetermsusedinthistestmethod.Pertinentdefinitions
Development of International Standards, Guides and Recom-
as listed in Practice C1239, Practice E1012, Terminology
C1145, and Terminology E6 are shown in the following with
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on
Mechanical Properties and Performance. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedJuly1,2018.PublishedJuly2018.Originallyapproved contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
in 1994. Last previous edition approved in 2015 as C1273–15. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
C1273-18. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1273 − 18
the appropriate source given in parentheses. Additional terms each testing condition is required for statistical analysis and
used in conjunction with this test method are defined in the eventual design, with guidelines for sufficient numbers pro-
following: vided in this test method. Note that size-scaling effects as
3.1.2 advanced ceramic—a highly engineered, high- discussed in Practice C1239 will affect the strength values.
performance, predominately nonmetallic, inorganic, ceramic Therefore, strengths obtained using different recommended
material having specific functional attributes. C1145 tensile test specimens with different volumes or surface areas
–1
of material in the gage sections will be different due to these
3.1.3 axial strain [LL ], n—the average of longitudinal
size differences. Resulting strength values can be scaled to an
strains measured at the surface on opposite sides of the
effective volume or surface area of unity as discussed in
longitudinal axis of symmetry of the specimen by two strain
Practice C1239.
sensing devices located at the mid length of the reduced
section. E1012
4.4 Tensile tests provide information on the strength and
–1
deformation of materials under uniaxial tensile stresses. Uni-
3.1.4 bending strain [LL ], n—the difference between the
form stress states are required to effectively evaluate any
strainatthesurfaceandtheaxialstrain.Ingeneral,thebending
nonlinear stress-strain behavior which may develop as the
strain varies from point to point around and along the reduced
result of testing mode, testing rate, processing or alloying
section of the specimen. E1012
effects, or environmental influences. These effects may be
3.1.5 breaking force [F], n—the force at which fracture
consequences of stress corrosion or subcritical (slow) crack
occurs. E6
growth, which can be minimized by testing at appropriately
3.1.6 fractography—means and methods for characterizing
rapid rates as outlined in this test method.
a fractured specimen or component. C1145
4.5 The results of tensile tests of test specimens fabricated
3.1.7 fracture origin—thesourcefromwhichbrittlefracture
to standardized dimensions from a particular material or
commences. C1145
selected portions, or both, of a part may not totally represent
3.1.8 percent bending—thebendingstraintimes100divided
the strength and deformation properties of the entire, full-size
by the axial strain. E1012
end product or its in-service behavior in different environ-
ments.
3.1.9 slow crack growth (SCG)—subcritical crack growth
(extension)whichmayresultfrom,butisnotrestrictedto,such
4.6 For quality control purposes, results derived from stan-
mechanisms as environmentally assisted stress corrosion or
dardized tensile test specimens can be considered to be
diffusive crack growth. C1145
indicativeoftheresponseofthematerialfromwhichtheywere
–2
3.1.10 tensile strength, S [FL ], n—the maximum tensile taken for given primary processing conditions and post-
u
processing heat treatments.
stress which a material is capable of sustaining. Tensile
strengthiscalculatedfromthemaximumforceduringatension
4.7 The tensile strength of a ceramic material is dependent
test carried to rupture and the original cross-sectional area of
on both its inherent resistance to fracture and the presence of
the specimen. E6
flaws. Analysis of fracture surfaces and fractography, though
beyond the scope of this test method, is highly recommended
4. Significance and Use
for all purposes, especially for design data.
4.1 Thistestmethodmaybeusedformaterialdevelopment,
material comparison, quality assurance, characterization, and 5. Interferences
design data generation.
5.1 Test environment (vacuum, inert gas, ambient air, etc.),
4.2 High-strength, monolithic advanced ceramic materials including moisture content (for example, relative humidity),
generallycharacterizedbysmallgrainsizes(<50µm)andbulk may have an influence on the measured tensile strength. In
densities near the theoretical density are candidates for load- particular, the behavior of materials susceptible to slow crack
bearing structural applications requiring high degrees of wear growthfracturewillbestronglyinfluencedbytestenvironment
and corrosion resistance and high temperature strength. Al- and testing rate. Testing to evaluate the maximum strength
though flexural test methods are commonly used to evaluate potential of a material should be conducted in inert environ-
strength of advanced ceramics, the nonuniform stress distribu- ments or at sufficiently rapid testing rates, or both, so as to
tion of the flexure test specimen limits the volume of material minimizeslowcrackgrowtheffects.Conversely,testingcanbe
subjectedtothemaximumappliedstressatfracture.Uniaxially conducted in environments and testing modes and rates repre-
loaded tensile strength tests provide information on strength- sentative of service conditions to evaluate material perfor-
limiting flaws from a greater volume of uniformly stressed mance under use conditions. When testing is conducted in
material. uncontrolled ambient air with the intent of evaluating maxi-
mum strength potential, relative humidity and temperature
4.3 Although the volume or surface area of material sub-
must be monitored and reported. Testing at humidity levels
jected to a uniform tensile stress for a single uniaxially loaded
>65% relative humidity (RH) is not recommended, and any
tensile test may be several times that of a single flexure test
deviations from this recommendation must be reported.
specimen, the need to test a statistically significant number of
tensiletestspecimensisnotobviated.Therefore,becauseofthe 5.2 Surface preparation of test specimens can introduce
probabilistic strength distributions of brittle materials such as fabrication flaws that may have pronounced effects on tensile
advanced ceramics, a sufficient number of test specimens at strength. Machining damage introduced during test specimen
C1273 − 18
preparation can be either a random interfering factor in the
determination of ultimate strength of pristine material (that is,
increased frequency of surface initiated fractures compared to
volume initiated fractures), or an inherent part of the strength
characteristics to be measured. Surface preparation can also
lead to the introduction of residual stresses. Universal or
standardizedtestmethodsofsurfacepreparationdonotexist.It
should be understood that final machining steps may or may
not negate machining damage introduced during the early
coarse or intermediate machining. Thus, test specimen fabri-
cation history may play an important role in the measured
strength distributions and should be reported.
5.3 Bending in uniaxial tensile tests can cause or promote
nonuniform stress distributions with maximum stresses occur-
ring at the test specimen surface leading to non-representative
fracturesoriginatingatsurfacesorneargeometricaltransitions.
In addition, if strains or deformations are measured at surfaces
where maximum or minimum stresses occur, bending may
FIG. 2 Example of a Smooth, Split-Collet Active Gripping System
introduce over or under measurement of strains. Similarly,
for Cylindrical Test Specimens
fracturefromsurfaceflawsmaybeaccentuatedormutedbythe
presence of the nonuniform stresses caused by bending.
6.2 Gripping Devices:
6. Apparatus
6.2.1 General—Various types of gripping devices may be
used to transmit the measured force applied by the testing
6.1 Testing Machines—Machines used for tensile testing
machine to the test specimens. The brittle nature of advanced
shall conform to the requirements of Practices E4. The forces
ceramics requires a uniform interface between the grip com-
used in determining tensile strength shall be accurate to within
ponents and the gripped section of the test specimen. Line or
61%atanyforcewithintheselectedforcerangeofthetesting
point contacts and nonuniform pressure can produce Hertizan-
machine as defined in Practices E4. A schematic showing
type stresses, leading to crack initiation and fracture of the test
pertinent features of the tensile testing apparatus is shown in
specimen in the gripped section. Gripping devices can be
Fig. 1.
classed generally as those employing active and those employ-
ing passive grip interfaces as discussed in the following
sections.
6.2.2 Active Grip Interfaces—Active grip interfaces require
a continuous application of a mechanical, hydraulic, or pneu-
matic force to transmit the force applied by the test machine to
the test specimen. Generally, these types of grip interfaces
causeaforcetobeappliednormaltothesurfaceofthegripped
sectionofthetestspecimen.Transmissionoftheuniaxialforce
applied by the test machine is then accomplished by friction
between the test specimen and the grip faces. Thus, important
aspects of active grip interfaces are uniform contact between
the gripped section of the test specimen and the grip faces and
constant coefficient of friction over the grip/specimen inter-
face.
6.2.2.1 For cylindrical test specimens, a one-piece split-
collet arrangement acts as the grip interface (1, 2) as illus-
trated in Fig. 2. Generally, close tolerances are required for
concentricity of both the grip and test specimen diameters. In
addition, the diameter of the gripped section of the test
specimen and the unclamped, open diameter of the grip faces
must be within similarly close tolerances to promote uniform
contactatthetestspecimen/gripinterface.Toleranceswillvary
depending on the exact configuration as shown in the appro-
priate test specimen drawings.
FIG. 1 Schematic Diagram of One Possible Apparatus for Con- The boldface numbers given in parentheses refer to a list of references at the
ducting a Uniaxially Loaded Tensile Test end of the text.
C1273 − 18
6.2.2.2 For flat test specimens, flat-faced, wedge-grip faces 6.3 Load Train Couplers:
actasthegripinterfaceasillustratedinFig.3.Generally,close
6.3.1 General—Various types of devices (load train cou-
tolerances are required for the flatness and parallelism as well
plers)maybeusedtoattachtheactiveorpassivegripinterface
as wedge angle of the grip faces. In addition, the thickness,
assemblies to the testing machine. The load train couplers, in
flatness, and parallelism of the gripped section of the test
conjunction with the type of gripping device, play major roles
specimen must be within similarly close tolerances to promote
in the alignment of the load train and thus subsequent bending
uniform contact at the test specimen/grip interface. Tolerances
imposed in the test specimen. Load train couplers can be
willvarydependingontheexactconfigurationasshowninthe
classified as fixed and nonfixed as discussed in the following
appropriate test specimen drawings.
sections. Note that use of well-aligned fixed or self-aligning
6.2.3 Passive Grip Interfaces—Passivegripinterfacestrans-
nonfixed couplers does not automatically guarantee low bend-
mit the force applied by the test machine to the test specimen
ing in the gage section of the tensile test specimen. Well-
through a direct mechanical link. Generally, these mechanical
aligned fixed or self-aligning nonfixed couplers provide for
links transmit the test forces to the test specimen via geometri-
well aligned load trains, but the type and operation of grip
cal features of the test specimens such as button-head fillets,
interfaces,aswellastheas-fabricateddimensionsofthetensile
shank shoulders, or holes in the gripped head. Thus, the
test specimen, can add significantly to the final bending
important aspect of passive grip interfaces is uniform contact
imposed in the gage section of the test specimen.
between the gripped section of the test specimen and the grip
faces.
6.3.1.1 Regardless of which type of coupler is used, align-
6.2.3.1 For cylindrical test specimens, a multi-piece, split-
mentofthetestingsystemmustbeverifiedataminimumatthe
collet arrangement acts as the grip interface at button-head
beginningandendofatestseries.Anadditionalverificationof
fillets of the test specimen (3) as illustrated in Fig. 4. Because
alignment is recommended, although not required, at the
of the limited contact area at the test specimen/grip interface,
middle of the test series. Either a dummy or actual test
soft,deformablecolletmaterialsmaybeusedtoconformtothe
specimen and the alignment verification procedures detailed in
exact geometry of the test specimen. In some cases, tapered
the appendixes must be used.Allowable bending requirements
colletsmaybeusedtotransfertheaxialforceintotheshankof
are discussed in 6.4.Tensile test specimens used for alignment
the test specimen rather than into the button-head radius (3).
verification should be equipped with a recommended eight
Moderately close tolerances are required for concentricity of
separate longitudinal strain gages to determine bending contri-
both the grip and test specimen diameters. In addition, toler-
butions from both eccentric and angular misalignment of the
ances on the collet height must be maintained to promote
grip heads. (Although it is possible to use a minimum of six
uniform axial loading at the test specimen/grip interface.
separate longitudinal strain gages for test specimens with
Tolerances will vary depending on the exact configuration as
circular cross sections, eight strain gages are recommended
shown in the appropriate test specimen drawings.
here for simplicity and consistency in describing the technique
6.2.3.2 For flat test specimens, pins or pivots act as grip
forbothcircularandrectangularcrosssections).Ifdummytest
interfaces at either the shoulders of the test specimen shank or
specimens are used for alignment verification, they should
at holes in the gripped test specimen head (4-6). Close
have the same geometry and dimensions of the actual test
tolerances are required of shoulder radii and grip interfaces to
specimens as well as the same mechanical properties (that is,
promote uniform contact along the entire test specimen/grip
elastic modulus, hardness, etc.) as the test material to ensure
interface, as well as to provide for non-eccentric loading as
similar axial and bending stiffness characteristics as the actual
shown in Fig. 5. Moderately close tolerances are required for
test specimen and material.
longitudinal coincidence of the pin and hole centerlines as
illustrated in Fig. 6.
6.3.2 Fixed Load Train Couplers—Fixed couplers may
incorporate devices that require either a one-time, pre-test
alignment adjustment of the load train which remains constant
for all subsequent tests or an in-situ, pre-test alignment of the
load train that is conducted separately for each test specimen
and each test. Such devices (8, 9) usually employ angularity
andconcentricityadjusterstoaccommodateinherentloadtrain
misalignments.Regardlessofwhichmethodisused,alignment
verification must be performed as discussed in 6.3.1.1.
6.3.3 Nonfixed Load Train Couplers—Nonfixed couplers
may incorporate devices that promote self-alignment of the
load train during the movement of the crosshead or actuator.
Generally, such devices rely upon freely moving linkages to
eliminate applied moments as the load train components are
loaded.Knifeedges,universaljoints,hydrauliccouplers,orair
bearings are examples (4, 8, 10-12) of such devices. Examples
of two such devices are shown in Fig. 7. Although nonfixed
FIG. 3 Example of a Smooth, Wedge Active Gripping System for
Flat Test Specimens load train couplers are intended to be self-aligning and thus
C1273 − 18
FIG. 4 Examples of Straight- and Tapered-Collet Passive Gripping Systems for Cylindrical Test Specimens (3)
FIG. 5 Examples of Shoulder-Loaded, Passive Gripping Systems for Flat Test Specimens (4, 5)
of the strength distribution parameters (for example, Weibull
modulus, mˆ, and characteristic strength, σˆ ), allowable percent
θ
bending as defined in Practice E1012 should not exceed five.
Theseconclusions (3)assumethattensilestrengthfracturesare
due to fracture origins in the volume of the material, all tensile
testspecimensexperiencedthesamelevelofbending,andthat
Weibull modulus, mˆ, was constant.Thus, the maximum allow-
ablepercentbendingatfracturefortestspecimenstestedunder
this test method shall not exceed five. However, it should be
noted that unless all test specimens are properly strain gaged
and percent bending monitored until fracture, there will be no
record of percent bending at fracture for each test specimen.
Therefore, the testing system shall be verified using the
proceduredetailedintheappendixessuchthatpercentbending
does not exceed five at a mean strain equal to one-half the
anticipated strain at fracture. This verification shall be con-
FIG. 6 Example of a Pin-Loaded, Passive Gripping System for
ducted at a minimum at the beginning and end of each test
Flat Test Specimens (7)
series as recommended in previous sections. An additional
verification of alignment is recommended, although not
eliminate the need to evaluate the bending in the test specimen
required, at the middle of the test series.
for each test, the operation of the couplers must be verified as
6.5 Data Acquisition—At minimum, an autographic record
discussed in 6.3.1.1.
of applied force versus time should be obtained. Either analog
6.4 Allowable Bending—Analytical and empirical studies chart recorders or digital data acquisition systems can be used
(3) have concluded that for negligible effects on the estimates for this purpose, although a digital record is recommended for
C1273 − 18
FIG. 7 Examples of Hydraulic, Self-Aligning, Nonfixed Load Train Couplers (10, 11)
ease of later data analysis. Ideally, an analog chart recorder or 8.1.1 General—The geometry of tensile test specimens is
plotter should be used in conjunction with the digital data dependent on the ultimate use of the tensile strength data. For
acquisitionsystemtoprovideanimmediaterecordofthetestas example, if the tensile strength of an as-fabricated component
a supplement to the digital record. Recording devices shall be
is required, the dimensions of the resulting tensile test speci-
accurate to within 1% for total testing system, including menmayreflectthethickness,width,andlengthrestrictionsof
readout unit, as specified in Practices E4 and should have a
thecomponent.Ifitisdesiredtoevaluatetheeffectsofinherent
minimum data acquisition rate of 10 Hz, with a response of flaw distributions for a particular material manufactured from
50Hz deemed more than sufficient.
a particular processing route, then the size of the test specimen
6.5.1 Wherestrainorelongationofthegagesectionarealso and resulting gage section will reflect the desired volume to be
measured, these values should be recorded either similarly to
sampled. In addition, grip interfaces and load train couplers as
the force or as independent variables of force. Crosshead
discussedinSection6willinfluencethefinaldesignofthetest
displacement of the test machine may also be recorded but
specimen geometry.
should not be used to define displacement or strain in the gage
8.1.1.1 Fig. 8 illustrates a range of tensile test specimen
section, especially when self-aligning couplers are used in the
geometries that have been applied to testing advanced ceram-
load train.
ics. Note that Fig. 8 provides only a sampling of possible
tensile test specimens for ceramics and by no means purports
6.6 Dimension Measuring Devices—Micrometers and other
devices used for measuring linear dimensions should be to represent all possible configurations past or present. The
accurate and precise to at least one-half the smallest unit to following subsections discuss the more common, and thus
whichtheindividualdimensionisrequiredtobemeasured.For proven, of these test specimen geometries, although any
the purposes of this test method, cross-sectional dimensions geometry is acceptable if it meets the gripping and bending
should be measured to within 0.02 mm, requiring dimension requirements of this test method. If deviations from the
measuring devices with accuracies of 0.01 mm. recommendedgeometriesaremade,astressanalysisofthetest
specimen should be conducted to ensure that stress concentra-
7. Precaution
tions that could lead to undesired fractures outside the gage
section do not exist.
7.1 Duringtheconductofthistestmethod,thepossibilityof
flying fragments of broken test material is quite high. The
8.1.2 Cylindrical Tensile Test Specimens—Cylindrical test
brittle nature of advanced ceramics and the release of strain
specimens are generally fabricated from rods of material and
energy contribute to the potential release of uncontrolled
offer the potential of testing the largest volume of the various
fragments upon fracture. Means for containment and retention
tensiletestspecimens.Inaddition,thesizeofthetestspecimen
of these fragments for later fractographic reconstruction and
lendsitselftomorereadilyevaluatingthemechanicalbehavior
analysis is highly recommended.
of a material for engineering purposes. Disadvantages include
the relatively large amount of material required for the starting
8. Test Specimens
billet, the large amount of material which must be removed
8.1 Test Specimen Geometry: during test specimen fabrication, and the need to fabricate the
C1273 − 18
NOTE 1—All dimensions are in mm.
NOTE2—Acronyms:NPL,U.K.=NationalPhysicalLaboratory,UnitedKingdom;ORNL=OakRidgeNationalLaboratory;NGK=NGKInsulators;
SoRI = Southern Research Institute; ASEA = ASEA-Ceram; NIST = National Institute of Standards and Technology; GIRI = Government Industrial
Research Institute.
FIG. 8 Examples of Variety of Tensile Test Specimens Used for Advanced Ceramics
test specimen cylindrically usually requiring numerically con- flexuretests(seeTestMethodC1161).Importanttolerancesfor
trolled grinding machines, all of which may add substantially the flat tensile test specimens include cylindricity of the gage
to the total cost per test specimen. Gripped ends include section, parallelism of faces, and longitudinal alignment of
various types of button-heads (3, 8-13) as shown in Figs. load lines (pinhole centers or shoulder loading points), all of
X2.1-X2.3. In addition, straight-shank geometries have been whichwillvarydependingontheexactconfigurationasshown
successfully used (1, 2) as shown in Figs. X2.4 and X2.5. in the appropriate test specimen drawings.
Important tolerances for the cylindrical tensile test specimens
8.2 Test Specimen Preparation:
include concentricity and cylindricity that will vary depending
8.2.1 Dependingupontheintendedapplicationofthetensile
on the exact configuration as shown in the appropriate test
strength data, use one of the following test specimen prepara-
specimen drawings.
tion procedures. Regardless of the preparation procedure used,
8.1.3 Flat Tensile Test Specimens—Flat test specimens are
sufficient details regarding the procedure must be reported to
generallyfabricatedfromplatesorblocksofmaterialandoffer
allow replication.
the potential for ease of material procurement, ease of
8.2.2 As-Fabricated—The tensile test specimen should
fabrication, and subsequent lower cost per test specimen.
simulatethesurface/edgeconditionsandprocessingrouteofan
Disadvantages include the relatively small volume of material
application where no machining is used; for example, as-cast,
testedandsensitivityofthetestspecimentosmalldimensional
sintered, or injection-molded part. No additional machining
tolerances or disturbances in the load train. Gripped ends
specifications are relevant.As-processed test specimens might
include various types of shoulder-loaded shanks (4, 5) as
possess rough surface textures and non-parallel edges, and as
shown in Figs. X2.6 and X2.7. In addition, pin-loaded gripped
such may cause excessive misalignment or be prone to
ends (6) have also been used successfully as shown in Fig.
non-gage section fractures, or both.
X2.8. It should be noted that gage sections of flat tensile test
8.2.3 Application-Matched Machining—The tensile test
specimens for strength measurements are sometimes cylindri-
specimen should have the same surface/edge preparation as
cal. While this type of gage section adds to the difficulty of
that given to the component. Unless the process is proprietary,
fabrication and therefore cost of the flat tensile test specimen,
the report should be specific about the stages of material
it does avoid the problem of fractures initiating at corners of
removal, wheel grits, wheel bonding, amount of material
non-cylindrical gage sections. Corner fractures may be initi-
removed per pass, and type of coolant used.
atedbystressconcentrationsduetotheelasticconstraintofthe
corners but are more generally initiated by damage (chipping, 8.2.4 Customary Practices—Ininstanceswhereacustomary
etc.) that can be treated by chamfering the corners similar to machining procedure has been developed that is completely
that recommended for rectangular cross section bars used for satisfactory for a class of materials (that is, it induces no
C1273 − 18
unwanted surface/subsurface damage or residual stresses), this periodic dressing and shaping (truing), that can be done
procedure should be used. dynamicallywithinthetestmachinetomaintainthecuttingand
dimensional integrity.
8.2.5 Standard Procedure—In instances where 8.2.2 – 8.2.4
8.2.6.3 The most serious concern is not necessarily the
are not appropriate, 8.2.5 should apply. The procedure in 8.2.5
surface finish (on the order of R = 0.2–0.4 µm) that is a result
(or as discussed in Test Method C1161) should serve as
a
of the final machining steps. Instead, the subsurface damage is
minimum requirements, and a more stringent procedure may
critically important although this damage is not readily ob-
be necessary.
served or measured and, therefore, must be inferred as the
8.2.5.1 Do all grinding or cutting with an ample supply of
result of the grinding history. More details of this aspect have
appropriatefilteredcoolanttokeeptheworkpieceandgrinding
been discussed elsewhere (3). In all cases, the final grinding
wheel constantly flooded and particles flushed. Do grinding in
operation (“spark out”) performed in the gage section is to be
at least two stages, ranging from coarse to fine rate of material
along the longitudinal axis of the test specimen to ensure that
removal. All cutting can be done in one stage appropriate for
any residual grinding marks are parallel to the applied stress.
the depth of cut.
(Warning—Handling Precaution—Extreme care should be
8.2.5.2 Stock removal rate should not exceed 0.03 mm per
exercised in storage and handling of finished test specimens to
pass to the last 0.06 mm. Final finishing should be performed
avoid the introduction of random and severe flaws (for
withdiamondtoolsthathavebetween320and600grit.Noless
example, test specimens impact or scratch against each other).
than 0.06 mm per face should be removed during the final
It is therefore highly recommended that each test specimen be
finishingphase,andataratenotmorethan0.002mmperpass.
stored in separate nonmetallic containers or in a nonmetallic
Remove equal stock from each face where applicable.
container restricted from contact with other test specimens by
8.2.5.3 Edgefinishingmustbecomparabletothatappliedto
dividers. In addition, attention should be given to pre-test
testspecimensurfaces.Inparticular,thedirectionofmachining
storage of test specimens in controlled environments or desic-
should be parallel to the longitudinal axis of the test specimen.
cators to avoid unquantifiable environmental degradation of
8.2.5.4 Materials with low fracture toughness and a greater
test specimens prior to testing.)
susceptibility to grinding damage may require finer grinding
wheels at very low removal rates. 8.3 Number of Test Specimens—AsnotedinPracticeC1239,
thetotalnumberoftestspecimensplaysasignificantroleinthe
8.2.5.5 Generally, surface finishes on the order of average
estimates of strength distribution parameters (for example,
roughnesses, R , of 0.2 to 0.4 µm are recommended to
a
Weibull modulus, mˆ, and characteristic strength, σˆ ). Initially,
minimize surface fractures related to surface roughness. θ
the uncertainty associated with parameter estimates decreases
However, in some cases the final surface finish may not be as
significantly as the number of test specimens increases.
important as the route of fabrication due to the generation of
However, a point of diminishing returns is reached when the
subsurface damage during the fabrication process.
cost of performing additional tensile strength tests may not be
8.2.5.6 Geometric features such as holes, button-head
justified. This suggests that a practical number of tensile
radiuses, or transition radiuses require just as stringent atten-
strength tests should be performed to obtain a desired level of
tiontofabricationdetailasthatpaidtogagesection.Therefore,
confidence associated with a parameter estimate. The number
the minimum requirements outlined here should be applied to
of test specimens needed depends on the precision required in
these geometric features as well as to the gage section.
the resulting parameter estimate.Additional details concerning
8.2.6 Cylindrical Tensile Test Specimen Procedure—
the determination of the strength distribution parameters are
Because of the axial symmetry of the button-head tensile test
provided in Practice C1239.
specimen, fabrication of the test specimens is generally con-
8.3.1 It is therefore impossible to state the actual number of
ductedonalathe-typeapparatus.Inmanyinstances,thebulkof
test specimens required under this test method, since the
thematerialisremovedinacircumferentialgrindingoperation
number of test specimens needed depends on the precision
with a final longitudinal grinding operation performed in the
required in the resulting parameter estimate and thus depends
gage section to ensure that any residual grinding marks are
ontheuniquerequirementsofeachapplication.PracticeC1239
parallel to the applied stress. Beyond those guidelines given
requires the reporting of 90% confidence bounds for Weibull
here, Ref. (3) provides more specific details of recommended
modulus, mˆ, and characteristic strength, σˆ , when a single flaw
θ
fabrication methods for cylindrical tensile test specimens.
population is responsible for strength distributions. As an
8.2.6.1 Generally, computer numerical control (CNC) fab-
illustrative example, Table 1 shows the upper and lower 90%
rication methods are necessary to obtain consistent test speci-
mens with the proper dimensions within the required toler-
TABLE 1 Example of Upper and Lower 90 % Confidence Bounds
ances. A necessary condition for this consistency is the
for Weibull Parameter Estimates Assuming a Single Flaw
complete fabrication of the test specimen without removing it A
Population
from the grinding apparatus, thereby avoiding the introduction
Number of test
mˆ mˆ (σˆ ) (σˆ )
upper lower θ upper θ lower
of unacceptable tolerances into the finished test specimen. specimens, n
5 14.6 3.6 566 448
8.2.6.2 Formed, resinoid-bonded, diamond-impregnated
10 13.5 5.5 534 469
wheels (minimum 320 grit in a resinoid bond) are necessary to
30 12.2 7.5 517 483
bothfabricatecriticalshapes(forexample,button-headradius)
A
For a biased Weibull modulus, mˆ, of 10 and a characteristic strength, σˆ ,of500
θ
and to minimize grinding vibrations and subsurface damage in
MPa.
the test material. The formed, resin-bonded wheels require
C1273 − 18
confidence bounds for mˆ and σˆ for five, ten, and 30 tests 9.2.1 When contacting extensometers are employed, exer-
θ
assumingabiasedmˆ of10and σˆ of500MPaforasingleflaw cise extreme care so as not to damage the surface of the gage
θ
population.As a rule of thumb, a minimum of five tests can be
section. Similarly, preparation of the surface for application of
conducted to determine an indication of material properties if resistance strain gages should avoid the use of abrasive
material cost or test specimen availability limit the number of
techniques that can locally increase surface roughness, possi-
tests to be conducted. A minimum of ten tests is required for
bly promoting surface-related fractures.
the purposes of estimating a mean.
9.3 Test Modes and Rates:
9.3.1 General—Test modes and rates can have distinct and
9. Procedure
strong influences on the fracture behavior of advanced
9.1 Test Specimen Dimensions—Determine the diameter or
ceramics, even at ambient temperatures, depending on test
thickness and width of the gage section of each test specimen
environmentorconditionofthetestspecimen.Testmodesmay
to within 0.02 mm. Make measurements on at least three
involve force, displacement, or strain control. Recommended
different cross-sectional planes in the gage section. In the case
ratesoftestingareintendedtobesufficientlyrapidtoobtainthe
of cylindrical test specimens, two measurements (90° apart)
maximum possible tensile strength at fracture of the material.
should be made on each plane.To avoid damage in the critical
However, rates other than those recommended here may be
gage section area, it is recommended that these measurements
usedtoevaluaterateeffects.Inallcases,thetestmodeandrate
be made either optically (for example, an optical comparator)
must be reported.
or mechanically using a flat, anvil-type micrometer. In either
9.3.2 Force Rate—For most advanced ceramics exhibiting
case, the resolution of the instrument must be as specified in
linear elastic behavior, fracture is attributed to a weakest-link
6.6. Exercise extreme caution to prevent damage to the test
fracture mechanism generally attributed to stress-controlled
specimen gage section. Ball-tipped or sharp anvil micrometers
fracture from Griffith-like flaws. Therefore, a force-controlled
are not recommended because localized cracking may be
test, with force generally related directly to tensile stress in
induced. Record the measured dimensions and locations of the
brittle linear elastic advanced ceramics, is the preferred test
measurements and report for use in the calculation of the
mode. Force rate can be directly related to stress rate, thus
tensile stress at fracture. Use the average of the multiple
simplifying data analysis. Stress rates >35 to 50 MPa/s are
measurements in the stress calculations.
recommended to reduce the influence of environmental effects
9.1.1 Alternatively, to avoid damage to the gage section,
and thus obtain the greatest value of ultimate tensile strength.
post-fracturemeasurementsofthegagesectiondimensionscan
Alternatively,selectstressratestoproducefinalfracturein5to
be made using procedures described in 9.1. Note that in some
10stominimizeenvironmentaleffectswhentestinginambient
cases, the fracture process can severely fragment the gage
air. Some materials may not be as sensitive to stress rate and
section in the immediate vicinity of the fracture, thus making
less rapid stress rates may be employed in these situations.
post-fracture measurements of dimensions difficult. In these
Force rate is calculated as:
cases, it is advisable to follow the procedures outlined in 9.1
for pretest measurements to ensure reliable measurements.
dP
˙
P 5 5 σ˙A (1)
9.1.2 It is advisable to conduct periodic, if not 100%,
dt
inspection/measurements of all test specimens and test speci-
where:
men dimensions to ensure compliance with the drawing
˙
P = the required force rate in units of N/s,
specifications. Generally, high-resolution optical methods (for
P = the applied force in units of N,
example, an optical comparator) or high-resolution digital
t = time in units of s,
point contact methods (for example, coordinate measurement
σ˙ = the recommended (or desired stress rate) in units of
machine) are satisfactory as long as the equipment meets the
MPa/s, and
specification in 6.6. Note that the frequency of gage section
A = the cross-sectional area of the test specimen gage
fractures and bending in the gage section are dependent on
section in units of mm .
maintainingproperoveralltestspecimendimensionswithinthe
required tolerances. The cross-sectional area A is calculated as:
9.1.3 Measure surface finish to quantify the surface condi-
A 5 wbforrectangularcrosssections (2)
tion. Such methods as contacting profilometry can be used to
or
determine surface roughness parallel to the tensile axis. When
quantified, report surface roughness. 2
πd
A 5 for circularcrosssections (3)
9.2 Strain Measurements—Although strain measurement
techniques are not required in this test method, their use is
where:
highly recommended. In particular, multiple axial strain gages
w = the width of the gage section in units of mm,
ordualaxialextensometersconformingtoClassB1ofPractice
b = the thickness of the gage section in units of mm, and
E83 can be used to monitor bending for each test. In addition,
d = the diameter of the gage section in units of mm.
appropriate strain measurements can be used to determine
elastic constants in the linear region of the stress-strain curves 9.3.3 Displacement Rate—The size differences of each test
specimen geometry require a different loading rate for any
and can serve to indicate underlying fracture mechanisms
manifested as nonlinear stress-strain behavior. given stress rate. Displacement mode is defined as the control
C1273 − 18
of, or free-running displacement of, the test machine cross- require a unique procedure for mounting the test specimen in
head.Thus, the displacement rate can be calculated as follows. the load train. If special components (for example, annealed,
˙
Calculate P using the required (desired) stress rate as detailed copper collets) are required for each test, these should be
in 9.3.2. Calculate the displacement rate as: identified and noted in the test report. Mark the test specimen
withanindeliblemarkerastothetopandfront(sidefacingthe
d δ 1 1
˙ ˙
δ 5 5 1 P (4)
S D operator) in relation to the test machine. In the case of
dt k k
m s
strain-gaged test specimens, orient the test specimen such that
where:
the “front” of the test specimen and a unique strain gage (for
˙
δ = the required (desired) displacement rate of the cross example, Strain Gage 1 designated SG1) coincide.
head in units of mm/s,
9.4.2 Preparations for Testing—Set the test mode and test
δ = the crosshead displacement in units of mm,
rate on the test machine. Preload the test specimen to remove
k = the stiffness of the test machine and load train (includ-
m
the “slack” from the load train. The amount of preload force
ing the test specimen ends and the grip interfaces) in
willdependonthematerialandtensiletestspecimengeometry
units of N/mm, and
and, therefore, must be determined and reported for each
k = the stiffness of the uniform gage section of the test
s
situation. If necessary, mount the extensometer on the test
specimen in units of N/mm.
specimen gage section and zero the output, or, attach the lead
Note that k can be calculated as k = AE/L, where A is the
wires of the strain gages to the signal conditioner and zero the
s s
cross-sectional area of the gage section, E is the elastic outputs. (Note that if strain gages are used to monitor bending,
modulus of the test material, and L is the gripped length of the the strain gages should be zeroed with the test specimen
test specimen. The stiffness, k , can be determined in accor- attached at only one end of the fixtures, that is, hanging free.
m
dance with Test Method D3379 by measuring the force- Thiswillensurethatbendingduetothegripclosureisfactored
displacementcurvesforvarioustestspecimenlengths.Theplot into the measured bending.) Ready the autograph data acqui-
of k (slope of force-displacement curve
...

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: C1273 − 15 C1273 − 18
Standard Test Method for
Tensile Strength of Monolithic Advanced Ceramics at
Ambient Temperatures
This standard is issued under the fixed designation C1273; 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
ambient temperatures. This test method addresses, but is not restricted to, various suggested test specimen geometries as listed in
the appendix.appendixes. 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. Note that 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 that 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 practice to these materials is not recommended.
1.3 Values expressed in this test method are in accordance with the International System of Units (SI) and SI10-02 IEEE/ASTM
SI 10.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Specific precautionary statements are given in Section 7.
1.5 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:
C1145 Terminology of Advanced Ceramics
C1161 Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
C1239 Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
C1322 Practice for Fractography and Characterization of Fracture Origins in Advanced Ceramics
D3379 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
E83 Practice for Verification and Classification of Extensometer Systems
E337 Test Method for Measuring Humidity with a Psychrometer (the Measurement of Wet- and Dry-Bulb Temperatures)
E1012 Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial Force
Application
SI10-02 IEEE/ASTM SI 10 American National Standard for Use of the International System of Units (SI): The Modern Metric
SystemMetric Practice
This test method is under the jurisdiction of ASTM Committee C28 on Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on Mechanical
Properties and Performance.
Current edition approved July 1, 2015July 1, 2018. Published September 2015July 2018. Originally approved in 1994. Last previous edition approved in 20102015 as
C1273 – 05 (2010).C1273 – 15. DOI: 10.1520/C1273-15.10.1520/C1273-18.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1273 − 18
3. Terminology
3.1 Definitions:
3.1.1 The definitions of terms relating to tensile testing appearing in Terminology E6 apply to the terms used in this test method
on tensile testing. The definitions of terms relating to advanced ceramics testing appearing in Terminology C1145 apply to the
terms used in this test method. Pertinent definitions as listed in Practice C1239, Practice E1012, Terminology C1145, and
Terminology E6 are shown in the following with the appropriate source given in parentheses. Additional terms used in conjunction
with this test method are defined in the following:
3.1.2 advanced ceramic—a highly engineered, high performance high-performance, predominately nonmetallic, inorganic,
ceramic material having specific functional attributes. C1145
–1
3.1.3 axial strain—strain [LL ], n—the average of longitudinal strains measured at the surface on opposite sides of the
longitudinal axis of symmetry of the specimen by two strain-sensing strain sensing devices located at the mid length of the reduced
section. E1012
–1
3.1.4 bending strain—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. E1012
3.1.5 breaking force—force [F], n—the force at which fracture occurs. E6
3.1.6 fractography—means and methods for characterizing a fractured specimen or component. C1145
3.1.7 fracture origin—the source from which brittle fracture commences. C1145
3.1.8 percent bending—the bending strain times 100 divided by the axial strain. E1012
3.1.9 slow crack growth (SCG)—subcritical crack growth (extension) which may result from, but is not restricted to, such
mechanisms as environmentally-assisted environmentally assisted stress corrosion or diffusive crack growth. C1145
–2
3.1.10 tensile strength,—strength, S [FL ], n—Sthe —the maximum tensile stress which a material is capable of sustaining.
u u
Tensile strength is calculated from the maximum force during a tension test carried to rupture and the original cross-sectional area
of the specimen. E6
4. Significance and Use
4.1 This test method may be used for material development, material comparison, quality assurance, characterization, and
design data generation.
4.2 High strength, High-strength, monolithic advanced ceramic materials generally characterized by small grain sizes (<50 μm)
and bulk densities near the theoretical density are candidates for load-bearing structural applications requiring high degrees of wear
and corrosion resistance,resistance and high temperature strength. Although flexural test methods are commonly used to evaluate
strength of advanced ceramics, the non-uniformnonuniform stress distribution of the flexure test specimen limits the volume of
material subjected to the maximum applied stress at fracture. Uniaxially-loaded Uniaxially loaded tensile strength tests provide
information on strength-limiting flaws from a greater volume of uniformly stressed material.
4.3 Although the volume or surface area of material subjected to a uniform tensile stress for a single uniaxially-loaded uniaxially
loaded tensile test may be several times that of a single flexure test specimen, the need to test a statistically significant number of
tensile test specimens is not obviated. Therefore, 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. Note that size-scaling effects as discussed in Practice
C1239 will affect the strength values. Therefore, strengths obtained using different recommended tensile test specimens with
different volumes or surface areas of material in the gage sections will be different due to these size differences. Resulting strength
values can be scaled to an effective volume or surface area of unity as discussed in Practice C1239.
4.4 Tensile tests provide information on the strength and deformation of materials under uniaxial tensile stresses. Uniform stress
states are required to effectively evaluate any non-linearnonlinear stress-strain behavior which may develop as the result of testing
mode, testing rate, processing or alloying effects, or environmental influences. These effects may be consequences of stress
corrosion or subcritical (slow) crack growth, which can be minimized by testing at appropriately rapid rates as outlined in this test
method.
4.5 The results of tensile tests of test specimens fabricated to standardized dimensions from a particular material or selected
portions, or both, of a part 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 given 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, though beyond the scope of this test method, is highly recommended for all
purposes, especially for design data.
C1273 − 18
5. Interferences
5.1 Test environment (vacuum, inert gas, ambient air, etc.)etc.), including moisture content (for example, relative
humidity)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 and testing rate. Testing to evaluate the maximum
strength potential of a material should be conducted in inert environments or at sufficiently rapid testing rates, or both, so as to
minimize slow crack growth effects. Conversely, testing can be conducted in environments and testing modes and rates
representative of service conditions to evaluate material performance under use conditions. When testing is conducted in
uncontrolled ambient air with the intent of evaluating maximum strength potential, relative humidity and temperature must be
monitored and reported. Testing at humidity levels >65 % relative humidity (RH) is not recommended, and any deviations from
this recommendation must be reported.
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, increaseincreased frequency of surface initiated fractures compared to volume
initiated fractures), or an inherent part of the strength characteristics to be measured. Surface preparation can also lead to the
introduction of residual stresses. Universal or standardized test methods of surface preparation do not exist. It should be understood
that final machining steps may or may not negate machining damage introduced during the early coarse or intermediate machining.
Thus, test specimen fabrication history may play an important role in the measured strength distributions and should be reported.
5.3 Bending in uniaxial tensile tests can cause or promote non-uniformnonuniform stress distributions with maximum stresses
occurring at the test specimen surface leading to non-representative fractures originating at surfaces or near geometrical transitions.
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-uniformnonuniform stresses caused by bending.
6. Apparatus
6.1 Testing Machines—Machines used for tensile testing shall conform to the requirements of Practices E4. The forces used in
determining tensile strength shall be accurate to within 61 % at any force within the selected force range of the testing machine
as defined in Practices E4. A schematic showing pertinent features of the 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 force applied by the testing machine
to the test specimens. The brittle nature of advanced ceramics requires a uniform interface between the grip components and the
FIG. 1 Schematic Diagram of One Possible Apparatus for Conducting a Uniaxially-Loaded Uniaxially Loaded Tensile Test
C1273 − 18
FIG. 2 Example of a Smooth, Split Collet Split-Collet Active Gripping System for Cylindrical Test Specimens
gripped section of the test specimen. Line or point contacts and non-uniformnonuniform pressure can produce Hertizan-type
stresses, leading to crack initiation and fracture of the test specimen in the gripped section. Gripping devices can be classed
generally as those employing active and those employing passive grip interfaces as discussed in the following sections.
6.2.2 Active Grip Interfaces—Active grip interfaces require a continuous application of a mechanical, hydraulic, or pneumatic
force to transmit the force applied by the test machine to the test specimen. Generally, these types of grip interfaces cause a force
to be applied normal to the surface of the gripped section of the test specimen. Transmission of the uniaxial force applied by the
test machine is then accomplished by friction between the test specimen and the grip faces. Thus, important aspects of active grip
interfaces are uniform contact between the gripped section of the test specimen and the grip faces and constant coefficient of
friction over the grip/specimen interface.
6.2.2.1 For cylindrical test specimens, a one-piece split-collet arrangement acts as the grip interface (1, 2) as illustrated in Fig.
2. Generally, close tolerances are required for concentricity of both the grip and test specimen diameters. In addition, the diameter
of the gripped section of the test specimen and the unclamped, open diameter of the grip faces must be within similarly close
tolerances to promote uniform contact at the test specimen/grip interface. Tolerances will vary depending on the exact
configuration as shown in the appropriate test specimen drawings.
6.2.2.2 For flat test specimens, flat-face,flat-faced, wedge-grip faces act as the grip interface as illustrated in Fig. 3. Generally,
close tolerances are required for the flatness and parallelism as well as wedge angle of the grip faces. In addition, the thickness,
flatness, and parallelism of the gripped section of the test specimen must be within similarly close tolerances to promote uniform
contact at the test specimen/grip interface. Tolerances will vary depending on the exact configuration as shown in the appropriate
test specimen drawings.
FIG. 3 Example of a Smooth, Wedge Active Gripping System for Flat Test Specimens
The boldface numbers given in parentheses refer to a list of references at the end of the text.
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6.2.3 Passive Grip Interfaces—Passive grip interfaces transmit the force applied by the test machine to the test specimen
through a direct mechanical link. Generally, these mechanical links transmit the test forces to the test specimen via geometrical
features of the test specimens such as button-head fillets, shank shoulders, or holes in the gripped head. Thus, the important aspect
of passive grip interfaces is uniform contact between the gripped section of the test specimen and the grip faces.
6.2.3.1 For cylindrical test specimens, a multi-piece split collet multi-piece, split-collet arrangement acts as the grip interface
at button-head fillets of the test specimen (3) as illustrated in Fig. 4. Because of the limited contact area at the test specimen/grip
interface, soft, deformable collet materials may be used to conform to the exact geometry of the test specimen. In some cases,
tapered collets may be used to transfer the axial force into the shank of the test specimen rather than into the button-head radius
(3). Moderately close tolerances are required for concentricity of both the grip and test specimen diameters. In addition, tolerances
on the collet height must be maintained to promote uniform axial-loading axial loading at the test specimen/grip interface.
Tolerances will vary depending on the exact configuration as shown in the appropriate test specimen drawings.
6.2.3.2 For flat test specimens, pins or pivots act as grip interfaces at either the shoulders of the test specimen shank or at holes
in the gripped test specimen head (44-6, 5, 6). Close tolerances are required of shoulder radii and grip interfaces to promote
uniform contact along the entire test specimen/grip interface, as well as to provide for non-eccentric loading as shown in Fig. 5.
Moderately close tolerances are required for longitudinal coincidence of the pin and hole centerlines as illustrated in Fig. 6.
6.3 Load Train Couplers:
6.3.1 General—Various types of devices (load train couplers) may be used to attach the active or passive grip interface
assemblies to the testing machine. The load train couplers, in conjunction with the type of gripping device, play major roles in the
alignment of the load train and thus subsequent bending imposed in the test specimen. Load train couplers can be classified as fixed
and nonfixed as discussed in the following sections. Note that use of well-aligned fixed or self-aligning non fixed nonfixed couplers
does not automatically guarantee low bending in the gage section of the tensile test specimen. Well-aligned fixed or self-aligning
non fixed nonfixed couplers provide for well aligned load trains, but the type and operation of grip interfaces, as well as the
as-fabricated dimensions of the tensile test specimen, can add significantly to the final bending imposed in the gage section of the
test specimen.
6.3.1.1 Regardless of which type of coupler is used, alignment of the testing system must be verified asat a minimum at the
beginning and end of a test series. An additional verification of alignment is recommended, although not required, at the middle
of the test series. Either a dummy or actual test specimen and the alignment verification procedures detailed in the
appendixappendixes must be used. Allowable bending requirements are discussed in 6.4. Tensile test specimens used for alignment
verification should be equipped with a recommended eight separate longitudinal strain gages to determine bending contributions
from both eccentric and angular misalignment of the grip heads. (Although it is possible to use a minimum of six separate
longitudinal strain gages for test specimens with circular cross sections, eight strain gages are recommended here for simplicity
and consistency in describing the technique for both circular and rectangular cross sections). If dummy test specimens are used
for alignment verification, they should have the same geometry and dimensions of the actual test specimens as well as the same
mechanical properties (that is, elastic modulus, hardness, etc.) as the test material to ensure similar axial and bending stiffness
characteristics as the actual test specimen and material.
6.3.2 Fixed Load Train Couplers—Fixed couplers may incorporate devices that require either a one-time, pre-test alignment
adjustment of the load train which remains constant for all subsequent tests or an in-situ, pre-test alignment of the load train that
FIG. 4 Examples of Straight- and Tapered-Collet Passive Gripping Systems for Cylindrical Test Specimens (3)
C1273 − 18
FIG. 5 Examples of Shoulder-Loaded, Passive Gripping Systems for Flat Test Specimens (4, 5)
FIG. 6 Example of a Pin-Loaded, Passive Gripping System for Flat Test Specimens (7)
is conducted separately for each test specimen and each test. Such devices (8, 9) usually employ angularity and concentricity
adjusters to accommodate inherent load train misalignments. Regardless of which method is used, alignment verification must be
performed as discussed in 6.3.1.1.
6.3.3 Non Fixed Nonfixed Load Train Couplers—Non fixed Nonfixed couplers may incorporate devices that promote
self-alignment of the load train during the movement of the crosshead or actuator. Generally, such devices rely upon freely moving
linkages to eliminate applied moments as the load train components are loaded. Knife edges, universal joints, hydraulic couplers,
or air bearings are examples (4, 8, 1010-12, 11, 12) of such devices. Examples of two such devices are shown in Fig. 7. Although
non fixed nonfixed load train couplers are intended to be self-aligning and thus eliminate the need to evaluate the bending in the
test specimen for each test, the operation of the couplers must be verified as discussed in 6.3.1.1.
6.4 Allowable Bending—Analytical and empirical studies (3) have concluded that for negligible effects on the estimates of the
strength distribution parameters (for example, Weibull modulus, mˆ, and characteristic strength, σˆ )), allowable percent bending
θ
as defined in Practice E1012 should not exceed five. These conclusions (3) assume that tensile strength fractures are due to fracture
origins in the volume of the material, all tensile test specimens experienced the same level of bending, and that Weibull modulus,
mˆ, was constant. Thus, the maximum allowable percent bending at fracture for test specimens tested under this test method shall
not exceed five. However, it should be noted that unless all test specimens are properly strain gaged and percent bending monitored
until fracture, there will be no record of percent bending at fracture for each test specimen. Therefore, the testing system shall be
verified using the procedure detailed in the appendixappendixes such that percent bending does not exceed five at a mean strain
equal to one half one-half the anticipated strain at fracture. This verification shall be conducted at a minimum at the beginning and
eachend of each test series as recommended in previous sections. An additional verification of alignment is recommended, although
not required, at the middle of the test series.
6.5 Data Acquisition—At the minimum, an autographic record of applied force versus time should be obtained. Either analog
chart recorders or digital data acquisition systems can be used for this purpose, although a digital record is recommended for ease
of later data analysis. Ideally, an analog chart recorder or plotter should be used in conjunction with the digital data acquisition
system to provide an immediate record of the test as a supplement to the digital record. Recording devices shall be accurate to
within 1 % for total testing system, including readout unit, as specified in Practices E4 and should have a minimum data acquisition
rate of 10 Hz, with a response of 50 Hz 50 Hz deemed more than sufficient.
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FIG. 7 Examples of Hydraulic, Self-Aligning, Non Fixed Nonfixed Load Train Couplers (10, 11)
6.5.1 Where strain or elongation of the gage section are also measured, these values should be recorded either similarly to the
force or as independent variables of force. Cross-headCrosshead displacement of the test machine may also be recorded but should
not be used to define displacement or strain in the gage section, especially when self-aligning couplers are used in the load train.
6.6 Dimension-Measuring Dimension Measuring Devices—Micrometers and other devices used for measuring linear dimen-
sions should be accurate and precise to at least one half one-half the smallest unit to which the individual dimension is required
to be measured. For the purposes of this test method, cross sectional cross-sectional dimensions should be measured to within 0.02
mm, requiring dimension measuring devices with accuracies of 0.01 mm.
7. Precaution
7.1 During the conduct of this test method, the possibility of flying fragments of broken test material is quite high. The brittle
nature of advanced ceramics and the release of strain energy contribute to the potential release of uncontrolled fragments upon
fracture. Means for containment and retention of these fragments for later fractographic reconstruction and analysis is highly
recommended.
8. Test Specimens
8.1 Test Specimen Geometry:
8.1.1 General—The geometry of tensile test specimenspecimens is dependent on the ultimate use of the tensile strength data.
For example, if the tensile strength of an as-fabricated component is required, the dimensions of the resulting tensile test specimen
may reflect the thickness, width, and length restrictions of the component. If it is desired to evaluate the effects of inherent flaw
distributions for a particular material manufactured from a particular processing route, then the size of the test specimen and
resulting gage section will reflect the desired volume to be sampled. In addition, grip interfaces and load train couplers as discussed
in Section 66 will influence the final design of the test specimen geometry.
8.1.1.1 Fig. 8 illustrates a range of tensile test specimen geometries that have been applied to testing advanced ceramics. Note
that Fig. 8 provides only a sampling of possible tensile test specimens for ceramics and by no means purports to represent all
possible configurations past or present. The following subsections discuss the more common, and thus proven, of these test
specimen geometries, although any geometry is acceptable if it meets the gripping and bending requirements of this test method.
If deviations from the recommended geometries are made, a stress analysis of the test specimen should be conducted to ensure that
stress concentrations that could lead to undesired fractures outside the gage section do not exist.
8.1.2 Cylindrical Tensile Test Specimens—Cylindrical test specimens are generally fabricated from rods of material and offer
the potential of testing the largest volume of the various tensile test specimens. In addition, the size of the test specimen lends itself
to more readily evaluating the mechanical behavior of a material for engineering purposes. Disadvantages include the relatively
large amount of material required for the starting billet, the large amount of material which must be removed during test specimen
fabrication, and the need to fabricate the test specimen cylindrically usually requiring numerically controlled grinding machines,
all of which may add substantially to the total cost per test specimen. Gripped ends include various types of button-heads (3, 8-13)
C1273 − 18
NOTE 1—All dimensions are in mm.
NOTE 2—Acronyms: NPL, U.K. = National Physical Laboratory, United Kingdom; ORNL = Oak Ridge National Laboratory; NGK = NGK Insulators;
SoRI = Southern Research Institute; ASEA = ASEA-Ceram; NIST = National Institute of Standards and Technology; GIRI = Government Industrial
Research Institute.
FIG. 8 Examples of Variety of Tensile Test Specimens Used for Advanced Ceramics
as shown in Fig. X2.1Figs. X2.1-X2.3, Fig. X2.2, and Fig. X2.3. In addition, straight shank straight-shank geometries have been
successfully used (1, 2) as shown in Fig. X2.4Figs. X2.4 and X2.5 and Fig. X2.5. Important tolerances for the cylindrical tensile
test specimens include concentricity and cylindricity that will vary depending on the exact configuration as shown in the
appropriate test specimen drawings.
8.1.3 Flat Tensile Test Specimens—Flat test specimens are generally fabricated from plates or blocks of material and offer the
potential for ease of material procurement, ease of fabrication, and subsequent lower cost per test specimen. Disadvantages include
the relatively small volume of material tested and sensitivity of the test specimen to small dimensional tolerances or disturbances
in the load train. Gripped ends include various types of shoulder-loaded shanks (4, 5) as shown in Fig. X2.6Figs. X2.6 and X2.7
and Fig. X2.7. In addition, pin-loaded gripped ends (6) have also been used successfully as shown in Fig. X2.8. It should be noted
that gage sections of flat tensile test specimens for strength measurements are sometimes cylindrical. While this type of gage
section adds to the difficulty of fabrication and therefore cost of the flat tensile test specimen, it does avoid the problem of fractures
initiating at corners of non cylindrical non-cylindrical gage sections. Corner fractures may be initiated by stress concentrations due
to the elastic constraint of the corners but are more generally initiated by damage (chipping, etc.) that can be treated by chamfering
the corners similar to that recommended for rectangular cross section bars used for flexure tests (see Test Method C1161).
Important tolerances for the flat tensile test specimens include cylindricity of the gage section, parallelism of faces, and
longitudinal alignment of load lines (pin hole (pinhole centers or shouldshoulder loading points)points), all of which will vary
depending on the exact configuration as shown in the appropriate test specimen drawings.
8.2 Test Specimen Preparation:
8.2.1 Depending upon the intended application of the tensile strength data, use one of the following test specimen preparation
procedures. Regardless of the preparation procedure used, sufficient details regarding the procedure must be reported to allow
replication.
8.2.2 As-Fabricated—The tensile test specimen should simulate the surface/edge conditions and processing route of an
application where no machining is used; for example, as-cast, sintered, or injection molded injection-molded part. No additional
machining specifications are relevant. As-processed test specimens might possess rough surface textures and non-parallel edges,
and as such may cause excessive misalignment and/oror be prone to non-gage section fractures.fractures, or both.
8.2.3 Application-Matched Machining—The tensile test specimen should have the same surface/edge preparation as that given
to the component. Unless the process is proprietary, the report should be specific about the stages of material removal, wheel grits,
wheel bonding, amount of material removed per pass, and type of coolant used.
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8.2.4 Customary Practices—In instances where a customary machining procedure has been developed that is completely
satisfactory for a class of materials (that is, it induces no unwanted surface/subsurface damage or residual stresses), this procedure
should be used.
8.2.5 Standard Procedure—In instances where 8.2.28.2.2 – 8.2.4 through 8.2.4are not appropriate, 8.2.5 should apply. The
procedure in 8.2.5 (or as discussed in Test Method C1161) should serve as minimum requirements, and a more stringent procedure
may be necessary.
8.2.5.1 Do all grinding or cutting with an ample supply of appropriate filtered coolant to keep the workpiece and grinding wheel
constantly flooded and particles flushed. Do grinding in at least two stages, ranging from coarse to fine rate of material removal.
All cutting can be done in one stage appropriate for the depth of cut.
8.2.5.2 Stock removal rate should not exceed 0.03 mm per pass to the last 0.06 mm. Final finishing should be performed with
diamond tools that have between 320 and 600 grit. No less than 0.06 mm per face should be removed during the final finishing
phase, and at a rate not more than 0.002 mm per pass. Remove equal stock from each face where applicable.
8.2.5.3 Edge finishing must be comparable to that applied to test specimen surfaces. In particular, the direction of machining
should be parallel to the longitudinal axis of the test specimen.
8.2.5.4 Materials with low fracture toughness and a greater susceptibility to grinding damage may require finer grinding wheels
at very low removal rates.
8.2.5.5 Generally, surface finishes on the order of average roughnesses, R , of 0.2 to 0.4 μm are recommended to minimize
a
surface fractures related to surface roughness. However, in some cases the final surface finish may not be as important as the route
of fabrication due to the generation of subsurface damage during the fabrication process.
8.2.5.6 Geometric features such as holes, button-head radiuses, or transition radiuses require just as stringent attention to
fabrication detail as that paid to gage section. Therefore, the minimum requirements outlined here should be applied to these
geometric features as well as to the gage section.
8.2.6 Cylindrical Tensile Test Specimen Procedure—Because of the axial symmetry of the button-head tensile test specimen,
fabrication of the test specimens is generally conducted on a lathe-type apparatus. In many instances, the bulk of the material is
removed in a circumferential grinding operation with a final,final longitudinal grinding operation performed in the gage section
to assureensure that any residual grinding marks are parallel to the applied stress. Beyond those guidelines given here, Ref. (3)
provides more specific details of recommended fabrication methods for cylindrical tensile test specimens.
8.2.6.1 Generally, computer numerical control (CNC) fabrication methods are necessary to obtain consistent test specimens with
the proper dimensions within the required tolerances. A necessary condition for this consistency is the complete fabrication of the
test specimen without removing it from the grinding apparatus, thereby avoiding the introduction of unacceptable tolerances into
the finished test specimen.
8.2.6.2 Formed, resinoid-bonded, diamond-impregnated wheels (minimum 320 grit in a resinoid bond) are necessary to both
fabricate critical shapes (for example, button-head radius) and to minimize grinding vibrations and subsurface damage in the test
material. The formed, resin-bonded wheels require periodic dressing and shaping (truing), that can be done dynamically within the
test machine,machine to maintain the cutting and dimensional integrity.
8.2.6.3 The most serious concern is not necessarily the surface finish (on the order of R = 0.2–0.4 μm) that is a result of the
a
final machining steps. Instead, the subsurface damage is critically important although this damage is not readily observed or
measured,measured and, therefore, must be inferred as the result of the grinding history. More details of this aspect have been
discussed elsewhere (3). In all cases, the final grinding operation (“spark out”) performed in the gage section is to be along the
longitudinal axis of the test specimen to assureensure that any residual grinding marks are parallel to the applied stress.
(Warning—Handling Precaution—Extreme care should be exercised in storage and handling of finished test specimens to avoid
the introduction of random and severe flaws (for example, test specimens impact or scratch against each other). It is therefore
highly recommended that each test specimen be stored in separate nonmetallic containers or in a nonmetallic container restricted
from contact with other test specimens by dividers. In addition, attention should be given to pre-test storage of test specimens in
controlled environments or desiccators to avoid unquantifiable environmental degradation of test specimens prior to testing.)
8.3 Number of Test Specimens—As noted in Practice C1239, the total number of test specimens plays a significant role in the
estimates of strength distribution parameters (for example, Weibull modulus, mˆ, and characteristic strength, σˆ ). Initially, the
θ
uncertainty associated with parameter estimates decreases significantly as the number of test specimens increases. However, a point
of diminishing returns is reached when the cost of performing additional tensile strength tests may not be justified. This suggests
that a practical number of tensile strength tests should be performed to obtain a desired level of confidence associated with a
parameter estimate. The number of test specimens needed depends on the precision required in the resulting parameter estimate.
Additional details concerning the determination of the strength distribution parameters are provided in Practice C1239.
8.3.1 It is therefore impossible to state the actual number of test specimens required under this test method, since the number
of test specimens needed depends on the precision required in the resulting parameter estimate and thus depends on the unique
requirements of each application. Practice C1239 requires the reporting of 90 % confidence bounds for Weibull modulus, mˆ, and
characteristic strength, σˆ , when a single flaw population is responsible for strength distributions. As an illustrative example, Table
θ
1 shows the upper and lower 90 % confidence bounds for mˆ, and σˆ for 5, 10,five, ten, and 30 tests assuming a biased mˆ of 10
θ
and σˆ of 500 MPa for a single flaw population. As a rule of thumb, a minimum of five tests can be conducted to determine an
θ
C1273 − 18
TABLE 1 Example of Upper and Lower 90 % Confidence Bounds
for Weibull Parameter Estimates Assuming a Single Flaw
A
Population
Number of test
mˆ mˆ (σˆ ) (σˆ )
upper lower θ upper θ lower
specimens, n
5 14.6 3.6 566 448
10 13.5 5.5 534 469
30 12.2 7.5 517 483
A
For a biased Weibull modulus, mˆ, of 10 and a characteristic strength, σˆ , of 500
θ
MPa.
indication of material properties if material cost or test specimen availability limit the number of tests to be conducted. A minimum
of ten tests is required for the purposes of estimating a mean.
9. Procedure
9.1 Test Specimen Dimensions—Determine the diameter or thickness and width of the gage section of each test specimen to
within 0.02 mm. Make measurements on at least three different cross sectional cross-sectional planes in the gage section. In the
case of the cylindrical test specimens, two measurements (90° apart) should be made on each plane. To avoid damage in the critical
gage section area, it is recommended that these measurements be made either optically (for example, an optical comparator) or
mechanically using a flat, anvil-type micrometer. In either case, the resolution of the instrument must be as specified in 6.6.
Exercise extreme caution to prevent damage to the test specimen gage section. Ball-tipped or sharp anvil micrometers are not
recommended because localized cracking may be induced. Record the measured dimensions and locations of the measurements
and report for use in the calculation of the tensile stress at fracture. Use the average of the multiple measurements in the stress
calculations.
9.1.1 Alternatively, to avoid damage to the gage section, post-fracture measurements of the gage section dimensions can be
made using procedures described in 9.1. Note that in some cases, the fracture process can severely fragment the gage section in
the immediate vicinity of the fracture, thus making post-fracture measurements of dimensions difficult. In these cases, it is
advisable to follow the procedures outlined in 9.1 for pretest measurements to ensure reliable measurements.
9.1.2 It is advisable to conduct periodic, if not 100 %, inspection/measurements of all test specimens and test specimen
dimensions to ensure compliance with the drawing specifications. Generally, high resolution high-resolution optical methods (for
example, an optical comparator) or high resolution high-resolution digital point contact methods (for example, coordinate
measurement machine) are satisfactory as long as the equipment meets the specification in 6.6. Note that the frequency of gage
section fractures and bending in the gage section are dependent on maintaining proper overall test specimen dimensions within the
required tolerances.
9.1.3 Measure surface finish to quantify the surface condition. Such methods as contacting profilometry can be used to
determine surface roughness parallel to the tensile axis. When quantified, report surface roughness.
9.2 Strain Measurements—Although strain measurement techniques are not required in this test method, their use is highly
recommended. In particular, multiple axial strain gages or dual axial extensometers conforming to Class B1 of Practice E83 can
be used to monitor bending for each test. In addition, appropriate strain measurements can be used to determine elastic constants
in the linear region of the stress strain stress-strain curves and can serve to indicate underlying fracture mechanisms manifested
as nonlinear stress-strain behavior.
9.2.1 When contacting extensometers are employed, exercise extreme care so as not to damage the surface of the gage section.
Similarly, preparation of the surface for application of resistance strain gages should avoid the use of abrasive techniques that can
locally increase surface roughness, possibly promoting surface-related fractures.
9.3 Test Modes and Rates:
9.3.1 General—Test modes and rates can have distinct and strong influences on the fracture behavior of advanced ceramics,
even at ambient temperatures, depending on test environment or condition of the test specimen. Test modes may involve force,
displacement, or strain control. Recommended rates of testing are intended to be sufficiently rapid to obtain the maximum possible
tensile strength at fracture of the material. However, rates other than those recommended here may be used to evaluate rate effects.
In all cases, the test mode and rate must be reported.
9.3.2 Force Rate—For most advanced ceramics exhibiting linear elastic behavior, fracture is attributed to a weakest-link fracture
mechanism generally attributed to stress-controlled fracture from Griffith-like flaws. Therefore, a force-controlled test, with force
generally related directly to tensile stress in brittle linear elastic advanced ceramics, is the preferred test mode. Force rate can be
directly related to stress rate, thus simplifying data analysis. Stress rates >35 to 50 MPa/s are recommended to reduce the influence
of environmental effects and thus obtain the greatest value of ultimate tensile strength. Alternatively, select stress rates to produce
final fracture in 5 to 10 s to minimize environmental effects when testing in ambient air. Some materials may not be as sensitive
to stress rate and less rapid stress rates may be employed in these situations. Force rate is calculated as:
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dP
˙
P 5 5 σ˙ A (1)
dt
where:
P˙ = the required force rate in units of N/s,
P = the applied force in units of N,
t = time in units of s,
σ˙ = the recommended (or desired stress rate) in units of MPa/s, and
A = the cross sectional area of the test specimen gage section in units of mm .
A = the cross-sectional area of the test specimen gage section in units of mm .
The cross sectional cross-sectional area A is calculated as:
A 5 wb for rectangular cross sections (2)
or
πd
A 5 for circular cross sections (3)
πd
A 5 for circular cross sections (3)
where:
w = the width of the gage section in units of mm,
b = the thickness of the gage section in units of mm, and
d = the diameter of the gage section in units of mm.
9.3.3 Displacement Rate—The size differences of each test specimen geometry require a different loading rate for any given
stress rate. Displacement mode is defined as the control of, or free-running displacement of, the test machine cross head. crosshead.
Thus, the displacement rate can be calculated as follows. Calculate P˙ using the required (desired) stress rate as detailed in 9.3.2.
Calculate the displacement rate as:
d δ 1 1
˙ ˙
δ5 5 1 P (4)
S D
dt k k
m s
where:
˙
δ = the required (desired) displacement rate of the cross head in
...