ASTM C1424-10(2015)

Standard Test Method for Monotonic Compressive Strength of Advanced Ceramics at Ambient Temperature

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 Generally, resistance to compression is the measure of the greatest strength of a monolithic advanced ceramic. Ideally, ceramics should be compressively stressed in use, although engineering applications may frequently introduce tensile stresses in the component. Nonetheless, compressive behavior is an important aspect of mechanical properties and performance. Although tensile strength distributions of ceramics are probabilistic and can be described by a weakest link failure theory, such descriptions have been shown to be inapplicable to compressive strength distributions in at least one study (1).3 However, the need to test a statistically significant number of compressive test specimens is not obviated. Therefore, a sufficient number of test specimens at each testing condition is required for statistical analysis and design.  
4.3 Compression tests provide information on the strength and deformation of materials under uniaxial compressive stresses. Uniform stress states are required to effectively evaluate any nonlinear stress-strain behavior which may develop as the result of cumulative damage processes (for example, microcracking) which may be influenced by testing mode, testing rate, processing or compositional effects, microstructure, or environmental influences.  
4.4 The results of compression tests of test specimens fabricated to standardized dimensions from a particular material or selected portions of a part, or both, may not totally represent the strength and deformation properties in the entire, full-size product or its in-service behavior in different environments.  
4.5 For quality control purposes, results derived from standardized compressive test specimens may be considered indicative of the response of the material from which they were taken for given primary processing conditions and post-proce...
SCOPE
1.1 This test method covers the determination of compressive strength including stress-strain behavior, under monotonic uniaxial loading of advanced ceramics at ambient temperature. This test method is restricted to specific test specimen geometries. In addition, test specimen fabrication methods, testing modes (load or displacement), testing rates (load rate, stress rate, displacement rate, or strain rate), allowable bending, and data collection and reporting procedures are addressed. Compressive strength as used in this test method refers to the compressive strength obtained under monotonic uniaxial loading. Monotonic loading refers to a test conducted at a constant rate in a continuous fashion, with no reversals from test initiation to final fracture.  
1.2 This test method is intended primarily for use with advanced ceramics that macroscopically exhibit isotropic, homogeneous, continuous behavior. While this test method is intended for use on monolithic advanced ceramics, certain whisker- or particle-reinforced composite ceramics as well as certain discontinuous fiber-reinforced composite ceramics may also meet these macroscopic behavior assumptions. Generally, continuous fiber ceramic composites (CFCCs) do not macroscopically exhibit isotropic, homogeneous, continuous behavior and, application of this test method to these materials is not recommended.  
1.3 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 and health practices and determine the applicability of regulatory limitations prior to use.

General Information

• Status: Historical
• Publication Date: 31-Dec-2014
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.01 - Mechanical Properties and Performance

Relations

• Replaces: ASTM C1424-10 - Standard Test Method for Monotonic Compressive Strength of Advanced Ceramics at Ambient Temperature
• Effective Date: 01-Jan-2015
• Replaced By: ASTM C1424-15 - Standard Test Method for Monotonic Compressive Strength of Advanced Ceramics at Ambient Temperature
• Effective Date: 01-Jul-2015

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: C1424 − 10(Reapproved 2015)
Standard Test Method for
Monotonic Compressive Strength of Advanced Ceramics at
Ambient Temperature
This standard is issued under the fixed designation C1424; 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 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of compres-
C773Test Method for Compressive (Crushing) Strength of
sivestrengthincludingstress-strainbehavior,undermonotonic
Fired Whiteware Materials
uniaxial loading of advanced ceramics at ambient temperature.
C1145Terminology of Advanced Ceramics
This test method is restricted to specific test specimen geom-
D695Test Method for Compressive Properties of Rigid
etries. In addition, test specimen fabrication methods, testing
Plastics
modes (load or displacement), testing rates (load rate, stress
E4Practices for Force Verification of Testing Machines
rate, displacement rate, or strain rate), allowable bending, and
E6Terminology Relating to Methods of MechanicalTesting
data collection and reporting procedures are addressed. Com-
E83Practice for Verification and Classification of Exten-
pressive strength as used in this test method refers to the
someter Systems
compressive strength obtained under monotonic uniaxial load-
E337Test Method for Measuring Humidity with a Psy-
ing. Monotonic loading refers to a test conducted at a constant
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
rate in a continuous fashion, with no reversals from test
peratures)
initiation to final fracture.
E1012Practice for Verification of Testing Frame and Speci-
1.2 This test method is intended primarily for use with men Alignment Under Tensile and Compressive Axial
advanced ceramics that macroscopically exhibit isotropic, Force Application
IEEE/ASTM SI 10Standard for Use of the International
homogeneous, continuous behavior. While this test method is
intended for use on monolithic advanced ceramics, certain System of Units (SI) (The Modern Metric System
whisker- or particle-reinforced composite ceramics as well as
3. Terminology
certaindiscontinuousfiber-reinforcedcompositeceramicsmay
3.1 Definitions:
also meet these macroscopic behavior assumptions. Generally,
3.1.1 The definitions of terms relating to compressive test-
continuous fiber ceramic composites (CFCCs) do not macro-
ing appearing in Terminology E6, Test Method D695, and
scopically exhibit isotropic, homogeneous, continuous behav-
Terminology C1145 may apply to the terms used in this test
iorand,applicationofthistestmethodtothesematerialsisnot
method. Pertinent definitions as listed in Practice E1012,
recommended.
Terminology C1145, and Terminology E6 are shown in the
1.3 Values expressed in this test method are in accordance
following with the appropriate source given in parentheses.
withtheInternationalSystemofUnits(SI)andIEEE/ASTMSI
Additional terms used in conjunction with this test method are
10.
defined in the following.
3.1.2 advanced ceramic, n—a highly engineered, high-
1.4 This standard does not purport to address all of the
performance predominately nonmetallic, inorganic, ceramic
safety concerns, if any, associated with its use. It is the
material having specific functional attributes. (C1145)
responsibility of the user of this standard to establish appro-
3.1.3 axial strain, n [L/L]—the average longitudinal strains
priate safety and health practices and determine the applica-
measured at the surface on opposite sides of the longitudinal
bility of regulatory limitations prior to use.
axis of symmetry of the specimen by two strain-sensing
devices located at the mid length of the reduced section.
(E1012)
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
Current edition approved Jan. 1, 2015. Published April 2015. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
published in 1999. Last previous edition approved in 2010 as C1424–10. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/C1424-10R15. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1424 − 10 (2015)
3.1.4 bending strain, n [L/L]—the difference between the dicative of the response of the material from which they were
strainatthesurfaceandtheaxialstrain.Ingeneral,thebending taken for given primary processing conditions and post-
strain varies from point to point around and along the reduced processing heat treatments.
section of the test specimen. (E1012)
5. Interferences
3.1.5 breaking load, n [F]—the load at which fracture
5.1 Testenvironment(vacuum,inertgas,ambientair,andso
occurs. (E6)
forth)includingmoisturecontent(forexample,relativehumid-
3.1.6 compressive strength, n [F/L ]—the maximum com-
ity) may have an influence on the measured compressive
pressive stress which a material is capable of sustaining.
strength.Testingtoevaluatethemaximumstrengthpotentialof
Compressive strength is calculated from the maximum load
a material can be conducted in inert environments or at
during a compression test carried to rupture and the original
sufficiently rapid testing rates, or both, so as to minimize any
cross-sectional area of the specimen. (E6)
environmental effects. Conversely, testing can be conducted in
3.1.7 gage length, n [L]—the original length of that portion
environments, test modes, and test rates representative of
of the specimen over which strain or change of length is
service conditions to evaluate material performance under use
determined. (E6)
conditions.When testing is conducted in uncontrolled ambient
3.1.8 modulus of elasticity, n [F/L ]—the ratio of stress to air with the intent of evaluating maximum strength potential,
corresponding strain below the proportional limit. (E6)
relative humidity and temperature must be monitored and
reported.
3.1.9 percent bending, n—the bending strain times 100
divided by the axial strain. (E1012)
5.2 Fabricationoftestspecimenscanintroducedimensional
variations which may have pronounced effects on compressive
4. Significance and Use
mechanical properties and behavior (for example, shape and
4.1 Thistestmethodmaybeusedformaterialdevelopment,
level of the resulting stress-strain curve, compressive strength,
material comparison, quality assurance, characterization, and
induced bending, and so forth). Machining effects introduced
design data generation.
duringtestspecimenpreparationcanbeaninterferingfactorin
the determination of ultimate strength of pristine material (that
4.2 Generally, resistance to compression is the measure of
is, increased frequency of loading block related fractures (see
thegreateststrengthofamonolithicadvancedceramic.Ideally,
Fig.1)comparedtovolume-initiatedfractures).Surfaceprepa-
ceramics should be compressively stressed in use, although
ration can also lead to the introduction of residual stresses.
engineering applications may frequently introduce tensile
Universal or standardized test methods of surface preparation
stresses in the component. Nonetheless, compressive behavior
do not exist. It should be understood that final machining steps
is an important aspect of mechanical properties and perfor-
may or may not negate machining damage introduced during
mance.Although tensile strength distributions of ceramics are
the initial machining. Note that final compressive fracture of
probabilistic and can be described by a weakest link failure
advanced ceramics can be attributed to the interaction of large
theory,suchdescriptionshavebeenshowntobeinapplicableto
numbersofmicrocracksthataregeneratedinthevolumeofthe
compressive strength distributions in at least one study (1).
materialandultimatelyleadtolossofstructuralintegrity. (1,2).
However, the need to test a statistically significant number of
Therefore, although surface roughness in the gage section of
compressive test specimens is not obviated. Therefore, a
the test specimen is not as critical for determining maximum
sufficient number of test specimens at each testing condition is
strength potential as it is for flexure or tension tests of
required for statistical analysis and design.
4.3 Compression tests provide information on the strength
and deformation of materials under uniaxial compressive
stresses. Uniform stress states are required to effectively
evaluate any nonlinear stress-strain behavior which may de-
velop as the result of cumulative damage processes (for
example, microcracking) which may be influenced by testing
mode, testing rate, processing or compositional effects,
microstructure, or environmental influences.
4.4 The results of compression tests of test specimens
fabricated to standardized dimensions from a particular mate-
rial or selected portions of a part, or both, may not totally
represent the strength and deformation properties in the entire,
full-size product or its in-service behavior in different environ-
ments.
4.5 For quality control purposes, results derived from stan-
dardized compressive test specimens may be considered in-
The boldface numbers in parenthesis refer to the list of references at the end of FIG. 1 Schematic Diagram of One Possible Apparatus for Con-
this test method ducting a Uniaxially Loaded Compression Test
C1424 − 10 (2015)
advanced ceramics, test specimen fabrication history may play
an important role in the measured compressive strength distri-
butions and should be reported. In addition, the nature of
fabrication used for certain advanced ceramics (for example,
pressureless sintering, hot pressing) may require the testing of
testspecimenswithgagesectionsintheas-processedcondition
(that is, it may not be possible or desired/required to machine
some test specimen surfaces not directly in contact with test
fixture components). For very rough or wavy as-processed
surfaces eccentricities in the stress state due to nonsymmetric
cross sections as well as variation in the cross-sectional
dimensions may also interfere with the compressive strength
measurement. Finally, close geometric tolerances, particularly
in regard to flatness, concentricity, and cylindricity of test
specimen surfaces or geometric entities in contact with the test
fixture components) are critical requirements for successful
compression tests.
5.3 Bending in uniaxial compression tests can introduce
eccentricity leading to geometric instability of the test speci-
men and buckling failure before valid compressive strength is
attained.Inaddition,ifdeformationsorstrainsaremeasuredat
surfaces where maximum or minimum stresses occur, bending
mayintroduceoverorundermeasurementofstrainsdepending
on the location of the strain-measuring device on the test
specimen.
5.4 Fractures that initiate outside the uniformly stressed
gage section or splitting of the test specimen along its
longitudinal centerline may be due to factors such as stress
FIG. 2 Example of Basic Fixturing and Test Specimen for Com-
pression Testing
concentrations or geometrical transitions, extraneous stresses
introduced by the load fixtures, misalignment of the test
specimen/loading blocks, nonflat loading blocks or nonflat test
specimen ends, or both, or strength-limiting features in the interface between the loading fixtures and the test specimen.
microstructure of the test specimen. Such non-gage section Line or point contact stresses lead to crack initiation and
fractures will normally constitute invalid tests. fracture of the test specimen at stresses less than the actual
compressive strength (that is, where actual strength is the
6. Apparatus intrinsic strength of the material not influenced by the test or
test conditions). In addition, large mismatches of Poisson’s
6.1 Testing Machines—Machinesusedforcompressiontest-
ratios or elastic moduli between the loading fixture and test
ing shall conform to the requirements of Practices E4. The
specimen, or both, can introduce lateral tensile forces leading
forces used in determining compressive strength shall be
to splitting of the compression test specimen. Similarly, plastic
accurate within 61% at any force within the selected force
deformationoftheloadfixturecaninducelateraltensileforces
range of the testing machine as defined in Practices E4.A
with the same effect.
schematicshowingpertinentfeaturesofonepossiblecompres-
6.2.1.1 Hardened (>48 HR ) steel compression platens shall
c
sive testing apparatus is shown in Fig. 1. Check that the
be greater in diameter (≥25.4 mm) than the loading blocks and
expectedbreakingforceforthedesiredtestspecimengeometry
shall be at least 25.4 mm in thickness. The loading surfaces of
and test material is within the capacity of the test machine and
the compression platens shall be flat to 0.005 mm. In addition,
force transducer. Advanced ceramic compression test speci-
the two loading surfaces (loading face used to contact the
mensrequiremuchgreaterforcestofracturethanthoseusually
loading blocks and bolted face used to attach the platen to the
encountered in tension or flexure test specimens of the same
test machine) shall be parallel to 0.005 mm. When installed in
material.
the test machine, the loading surfaces of the upper and lower
6.2 Loading Fixtures:
compression platens shall be parallel to each other within 0.01
6.2.1 General—Compression loading fixtures are generally mm and perpendicular to the load line of the test machine to
composedoftwoparts:(1)basicsteelcompressionfixtures(for within 0.01 mm (2).The upper and lower compression platens
example, platens) attached to the test machine and (2) loading shallbeconcentricwithin0.005mmofeachotherandtheload
blockswhicharenon-fixedandactastheinterfacebetweenthe line of the test machine.Angular and concentricity alignments
compression platens and the test specimen. An assembly have been achieved with commercial alignment devices or by
drawing of such a fixture and a test specimen is shown in Fig. using available hole tolerances in commercial compression
2. The brittle nature of advanced ceramics requires a uniform platens in conjunction with shims (2).
C1424 − 10 (2015)
6.2.1.2 Loading blocks as shown in Fig. 3 shall have the ¯ ¯
S .S (3)
UC2LB UC2S
same diameter as the test specimen ends at their interface.
6.3 Alignment
...

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: C1424 − 10 C1424 − 10 (Reapproved 2015)
Standard Test Method for
Monotonic Compressive Strength of Advanced Ceramics at
Ambient Temperature
This standard is issued under the fixed designation C1424; 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 compressive strength including stress-strain behavior, under monotonic
uniaxial loading of advanced ceramics at ambient temperature. This test method is restricted to specific test specimen geometries.
In addition, test specimen fabrication methods, testing modes (load or displacement), testing rates (load rate, stress rate,
displacement rate, or strain rate), allowable bending, and data collection and reporting procedures are addressed. Compressive
strength as used in this test method refers to the compressive strength obtained under monotonic uniaxial loading. Monotonic
loading refers to a test conducted at a constant rate in a continuous fashion, with no reversals from test initiation to final fracture.
1.2 This test method is intended primarily for use with advanced ceramics that macroscopically exhibit isotropic, homogeneous,
continuous behavior. While this test method is intended for use on monolithic advanced ceramics, certain whisker- or
particle-reinforced composite ceramics as well as certain discontinuous fiber-reinforced composite ceramics may also meet these
macroscopic behavior assumptions. Generally, continuous fiber ceramic composites (CFCCs) do not macroscopically exhibit
isotropic, homogeneous, continuous behavior and, application of this test method to these materials is not recommended.
1.3 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 and health practices and determine the applicability of regulatory
limitations prior to use.
2. Referenced Documents
2.1 ASTM Standards:
C773 Test Method for Compressive (Crushing) Strength of Fired Whiteware Materials
C1145 Terminology of Advanced Ceramics
D695 Test Method for Compressive Properties of Rigid Plastics
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
IEEE/ASTM SI 10 Standard for Use of the International System of Units (SI) (The Modern Metric System
3. Terminology
3.1 Definitions:
3.1.1 The definitions of terms relating to compressive testing appearing in Terminology E6, Test Method D695, and
Terminology C1145 may apply to the terms used in this test method. Pertinent definitions as listed in 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.
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 Dec. 1, 2010Jan. 1, 2015. Published January 2011April 2015. Originally published in 1999. Last previous edition approved in 20042010 as
C1424 – 04.C1424 – 10. DOI: 10.1520/C1424-10.10.1520/C1424-10R15.
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
C1424 − 10 (2015)
3.1.2 advanced ceramic, n—a highly engineered, high-performance predominately nonmetallic, inorganic, ceramic material
having specific functional attributes. (C1145)
3.1.3 axial strain, n [L/L]—the average longitudinal strains measured at the surface on opposite sides of the longitudinal axis
of symmetry of the specimen by two strain-sensing devices located at the mid length of the reduced section. (E1012)
3.1.4 bending strain, n [L/L]—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 test specimen. (E1012)
3.1.5 breaking load, n [F]—the load at which fracture occurs. (E6)
3.1.6 compressive strength, n [F/L ]—the maximum compressive stress which a material is capable of sustaining. Compressive
strength is calculated from the maximum load during a compression test carried to rupture and the original cross-sectional area of
the specimen. (E6)
3.1.7 gage length, n [L]—the original length of that portion of the specimen over which strain or change of length is determined.
(E6)
3.1.8 modulus of elasticity, n [F/L ]—the ratio of stress to corresponding strain below the proportional limit. (E6)
3.1.9 percent bending, n—the bending strain times 100 divided by the axial strain. (E1012)
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 Generally, resistance to compression is the measure of the greatest strength of a monolithic advanced ceramic. Ideally,
ceramics should be compressively stressed in use, although engineering applications may frequently introduce tensile stresses in
the component. Nonetheless, compressive behavior is an important aspect of mechanical properties and performance. Although
tensile strength distributions of ceramics are probabilistic and can be described by a weakest link failure theory, such descriptions
have been shown to be inapplicable to compressive strength distributions in at least one study (1). However, the need to test a
statistically significant number of compressive test specimens is not obviated. Therefore, a sufficient number of test specimens at
each testing condition is required for statistical analysis and design.
4.3 Compression tests provide information on the strength and deformation of materials under uniaxial compressive stresses.
Uniform stress states are required to effectively evaluate any nonlinear stress-strain behavior which may develop as the result of
cumulative damage processes (for example, microcracking) which may be influenced by testing mode, testing rate, processing or
compositional effects, microstructure, or environmental influences.
4.4 The results of compression tests of test specimens fabricated to standardized dimensions from a particular material or
selected portions of a part, or both, may not totally represent the strength and deformation properties in the entire, full-size product
or its in-service behavior in different environments.
4.5 For quality control purposes, results derived from standardized compressive test specimens may be considered indicative
of the response of the material from which they were taken for given primary processing conditions and post-processing heat
treatments.
5. Interferences
5.1 Test environment (vacuum, inert gas, ambient air, and so forth) including moisture content (for example, relative humidity)
may have an influence on the measured compressive strength. Testing to evaluate the maximum strength potential of a material
can be conducted in inert environments or at sufficiently rapid testing rates, or both, so as to minimize any environmental effects.
Conversely, testing can be conducted in environments, test modes, and test 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.
5.2 Fabrication of test specimens can introduce dimensional variations which may have pronounced effects on compressive
mechanical properties and behavior (for example, shape and level of the resulting stress-strain curve, compressive strength,
induced bending, and so forth). Machining effects introduced during test specimen preparation can be an interfering factor in the
determination of ultimate strength of pristine material (that is, increased frequency of loading block related fractures (see Fig. 1)
compared to volume-initiated fractures). 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 initial machining. Note that final compressive fracture of advanced ceramics can
be attributed to the interaction of large numbers of microcracks that are generated in the volume of the material and ultimately lead
to loss of structural integrity. (1,2). Therefore, although surface roughness in the gage section of the test specimen is not as critical
The boldface numbers in parenthesis refer to the list of references at the end of this test method
C1424 − 10 (2015)
FIG. 1 Schematic Diagram of One Possible Apparatus for Conducting a Uniaxially Loaded Compression Test
for determining maximum strength potential as it is for flexure or tension tests of advanced ceramics, test specimen fabrication
history may play an important role in the measured compressive strength distributions and should be reported. In addition, the
nature of fabrication used for certain advanced ceramics (for example, pressureless sintering, hot pressing) may require the testing
of test specimens with gage sections in the as-processed condition (that is, it may not be possible or desired/required to machine
some test specimen surfaces not directly in contact with test fixture components). For very rough or wavy as-processed surfaces
eccentricities in the stress state due to nonsymmetric cross sections as well as variation in the cross-sectional dimensions may also
interfere with the compressive strength measurement. Finally, close geometric tolerances, particularly in regard to flatness,
concentricity, and cylindricity of test specimen surfaces or geometric entities in contact with the test fixture components) are
critical requirements for successful compression tests.
5.3 Bending in uniaxial compression tests can introduce eccentricity leading to geometric instability of the test specimen and
buckling failure before valid compressive strength is attained. In addition, if deformations or strains are measured at surfaces where
maximum or minimum stresses occur, bending may introduce over or under measurement of strains depending on the location of
the strain-measuring device on the test specimen.
5.4 Fractures that initiate outside the uniformly stressed gage section or splitting of the test specimen along its longitudinal
centerline may be due to factors such as stress concentrations or geometrical transitions, extraneous stresses introduced by the load
fixtures, misalignment of the test specimen/loading blocks, nonflat loading blocks or nonflat test specimen ends, or both, or
strength-limiting features in the microstructure of the test specimen. Such non-gage section fractures will normally constitute
invalid tests.
6. Apparatus
6.1 Testing Machines—Machines used for compression testing shall conform to the requirements of Practices E4. The forces
used in determining compressive strength shall be accurate 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 one possible compressive testing apparatus is shown
in Fig. 1. Check that the expected breaking force for the desired test specimen geometry and test material is within the capacity
of the test machine and force transducer. Advanced ceramic compression test specimens require much greater forces to fracture
than those usually encountered in tension or flexure test specimens of the same material.
6.2 Loading Fixtures:
6.2.1 General—Compression loading fixtures are generally composed of two parts: (1) basic steel compression fixtures (for
example, platens) attached to the test machine and (2) loading blocks which are non-fixed and act as the interface between the
compression platens and the test specimen. An assembly drawing of such a fixture and a test specimen is shown in Fig. 2. The
brittle nature of advanced ceramics requires a uniform interface between the loading fixtures and the test specimen. Line or point
contact stresses lead to crack initiation and fracture of the test specimen at stresses less than the actual compressive strength (that
is, where actual strength is the intrinsic strength of the material not influenced by the test or test conditions). In addition, large
mismatches of Poisson’s ratios or elastic moduli between the loading fixture and test specimen, or both, can introduce lateral tensile
forces leading to splitting of the compression test specimen. Similarly, plastic deformation of the load fixture can induce lateral
tensile forces with the same effect.
C1424 − 10 (2015)
FIG. 2 Example of Basic Fixturing and Test Specimen for Compression Testing
6.2.1.1 Hardened (>48 HR ) steel compression platens shall be greater in diameter (≥25.4 mm) than the loading blocks and shall
c
be at least 25.4 mm in thickness. The loading surfaces of the compression platens shall be flat to 0.005 mm. In addition, the two
loading surfaces (loading face used to contact the loading blocks and bolted face used to attach the platen to the test machine) shall
be parallel to 0.005 mm. When installed in the test machine, the loading surfaces of the upper and lower compression platens shall
be parallel to each other within 0.01 mm and perpendicular to the
...