ASTM C1424-99
(Test Method)Standard Test Method for Monotonic Compressive Strength of Advanced Ceramics at Ambient Temperatures
Standard Test Method for Monotonic Compressive Strength of Advanced Ceramics at Ambient Temperatures
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 specfic 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 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.
1.3 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.
1.4 Values expressed in this test method are in accordance with the International System of Units (SI) and Practice E 380.
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Designation: C 1424 – 99
Standard Test Method for
Monotonic Compressive Strength of Advanced Ceramics at
Ambient Temperature
This standard is issued under the fixed designation C 1424; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 1145 Terminology on Advanced Ceramics
D 695 Test Method for Compressive Properties of Rigid
1.1 This test method covers the determination of compres-
Plastics
sive strength including stress-strain behavior, under monotonic
E 4 Practices for Force Verification of Testing Machines
uniaxial loading of advanced ceramics at ambient temperature.
E 6 Terminology Relating to Methods of Mechanical Test-
This test method is restricted to specific test specimen geom-
ing
etries. In addition, test specimen fabrication methods, testing
E 83 Practice for Verification and Classification of Exten-
modes (load or displacement), testing rates (load rate, stress
someters
rate, displacement rate, or strain rate), allowable bending, and
E 337 Test Method for Measured Humidity with Psychrom-
data collection and reporting procedures are addressed. Com-
eter (the Measurement of Wet-and Dry-Bulb Tempera-
pressive strength as used in this test method refers to the
tures)
compressive strength obtained under monotonic uniaxial load-
E 380 Practice for Use of International System of Units (SI)
ing. Monotonic loading refers to a test conducted at a constant
(the Modernized Metric System)
rate in a continuous fashion, with no reversals from test
E 1012 Practice for Verification of Specimen Alignment
initiation to final fracture.
Under Tensile Loading
1.2 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-
3.1 Definitions—The definitions of terms relating to com-
priate safety and health practices and determine the applica-
pressive testing appearing in Terminology E 6, Test Method
bility of regulatory limitations prior to use.
D 695, and Terminology C 1145 may apply to the terms used in
1.3 This test method is intended primarily for use with
this test method. Pertinent definitions as listed in Practice
advanced ceramics that macroscopically exhibit isotropic,
E 1012, Terminology C 1145, and Terminology E 6 are shown
homogeneous, continuous behavior. While this test method is
in the following with the appropriate source given in paren-
intended for use on monolithic advanced ceramics, certain
theses. Additional terms used in conjunction with this test
whisker- or particle-reinforced composite ceramics as well as
method are defined in the following.
certain discontinuous fiber-reinforced composite ceramics may
3.1.1 advanced ceramic, n—a highly engineered, high-
also meet these macroscopic behavior assumptions. Generally,
performance predominately nonmetallic, inorganic, ceramic
continuous fiber ceramic composites (CFCCs) do not macro-
material having specific functional attributes. (C 1145)
scopically exhibit isotropic, homogeneous, continuous behav-
3.1.2 axial strain, n [L/L]—the average longitudinal strains
ior and, application of this test method to these materials is not
measured at the surface on opposite sides of the longitudinal
recommended.
axis of symmetry of the specimen by two strain-sensing
1.4 Values expressed in this test method are in accordance
devices located at the mid length of the reduced section.
with the International System of Units (SI) and Practice E 380.
(E 1012)
2. Referenced Documents 3.1.3 bending strain, n [L/L]—the difference between the
strain at the surface and the axial strain. In general, the bending
2.1 ASTM Standards:
strain varies from point to point around and along the reduced
C 773 Test Method for Compressive (Crushing) Strength of
section of the test specimen. (E 1012)
Fired Whiteware Materials
1 3
This test method is under the jurisdiction of ASTM Committee C-28 on Annual Book of ASTM Standards, Vol 15.01.
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on Annual Book of ASTM Standards, Vol 08.01.
Properties and Performance. Annual Book of ASTM Standards, Vol 03.01.
Current edition approved May 10, 1999. Published September 1999. Annual Book of ASTM Standards, Vol 11.03.
2 7
Annual Book of ASTM Standards, Vol 15.02. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1424
3.1.4 breaking load, n [F]—the load at which fracture ity) may have an influence on the measured compressive
occurs. (E 6) strength. Testing to evaluate the maximum strength potential of
3.1.5 compressive strength, n [F/L ]—the maximum com- a material can be conducted in inert environments or at
pressive stress which a material is capable of sustaining. sufficiently rapid testing rates, or both, so as to minimize any
Compressive strength is calculated from the maximum load environmental effects. Conversely, testing can be conducted in
during a compression test carried to rupture and the original environments, test modes, and test rates representative of
cross-sectional area of the specimen. (E 6) service conditions to evaluate material performance under use
3.1.6 gage length, n [L]—the original length of that portion conditions. When testing is conducted in uncontrolled ambient
of the specimen over which strain or change of length is air with the intent of evaluating maximum strength potential,
determined. (E 6) relative humidity and temperature must be monitored and
3.1.7 modulus of elasticity, n [F/L ]—the ratio of stress to reported.
corresponding strain below the proportional limit. (E 6) 5.2 Fabrication of test specimens can introduce dimensional
3.1.8 percent bending, n—the bending strain times 100 variations which may have pronounced effects on compressive
divided by the axial strain. (E 1012) mechanical properties and behavior (for example, shape and
level of the resulting stress-strain curve, compressive strength,
4. Significance and Use
induced bending, and so forth). Machining effects introduced
4.1 This test method may be used for material development,
during test specimen preparation can be an interfering factor in
material comparison, quality assurance, characterization, and
the determination of ultimate strength of pristine material (that
design data generation.
is, increased frequency of loading block related fractures (see
4.2 Generally, resistance to compression is the measure of
Fig. 1) compared to volume-initiated fractures). Surface prepa-
the greatest strength of a monolithic advanced ceramic. Ideally,
ration can also lead to the introduction of residual stresses.
ceramics should be compressively stressed in use, although
Universal or standardized test methods of surface preparation
engineering applications may frequently introduce tensile
do not exist. It should be understood that final machining steps
stresses in the component. Nonetheless, compressive behavior
may or may not negate machining damage introduced during
is an important aspect of mechanical properties and perfor-
the initial machining. Note that final compressive fracture of
mance. Although tensile strength distributions of ceramics are
advanced ceramics can be attributed to the interaction of large
probabilistic and can be described by a weakest link failure
numbers of microcracks that are generated in the volume of the
theory, such descriptions have been shown to be inapplicable to
material and ultimately lead to loss of structural integrity. (1,2).
compressive strength distributions in at least one study (1).
Therefore, although surface roughness in the gage section of
However, the need to test a statistically significant number of
the test specimen is not as critical for determining maximum
compressive test specimens is not obviated. Therefore, a
strength potential as it is for flexure or tension tests of
sufficient number of test specimens at each testing condition is
advanced ceramics, test specimen fabrication history may play
required for statistical analysis and design.
an important role in the measured compressive strength distri-
4.3 Compression tests provide information on the strength
butions and should be reported. In addition, the nature of
and deformation of materials under uniaxial compressive
fabrication used for certain advanced ceramics (for example,
stresses. Uniform stress states are required to effectively
pressureless sintering, hot pressing) may require the testing of
evaluate any nonlinear stress-strain behavior which may de-
test specimens with gage sections in the as-processed condition
velop as the result of cumulative damage processes (for
(that is, it may not be possible or desired/required to machine
example, microcracking) which may be influenced by testing
some test specimen surfaces not directly in contact with test
mode, testing rate, processing or compositional effects, micro-
structure, 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-
dicative 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 humid-
The boldface numbers in parenthesis refer to the list of references at the end of FIG. 1 Schematic Diagram of One Possible Apparatus for
this test method Conducting a Uniaxially Loaded Compression Test
C 1424
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. 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
FIG. 2 Example of Basic Fixturing and Test Specimen for
6.1 Testing Machines—Machines used for compression test-
Compression Testing
ing shall conform to the requirements of Practices E 4. The
loads used in determining compressive strength shall be
accurate within 61 % at any load within the selected load
6.2.1.1 Hardened (>48 HR ) steel compression platens shall
c
range of the testing machine as defined in Practices E 4. A
be greater in diameter ($25.4 mm) than the loading blocks and
schematic showing pertinent features of one possible compres-
shall be at least 25.4 mm in thickness. The loading surfaces of
sive testing apparatus is shown in Fig. 1. Check that the
the compression platens shall be flat to 0.005 mm. In addition,
expected breaking load for the desired test specimen geometry
the two loading surfaces (loading face used to contact the
and test material is within the capacity of the test machine and
loading blocks and bolted face used to attach the platen to the
load cell. Advanced ceramic compression test specimens re-
test machine) shall be parallel to 0.005 mm. When installed in
quire much greater loads to fracture than those usually encoun-
the test machine, the loading surfaces of the upper and lower
tered in tension or flexure test specimens of the same material.
compression platens shall be parallel to each other within 0.01
6.2 Loading Fixtures:
mm and perpendicular to the load line of the test machine to
6.2.1 General—Compression loading fixtures are generally
within 0.01 mm (2). The upper and lower compression platens
composed of two parts: (1) basic steel compression fixtures (for
shall be concentric within 0.005 mm of each other and the load
example, platens) attached to the test machine and (2) loading
line of the test machine. Angular and concentricity alignments
blocks which are non-fixed and act as the interface between the
have been achieved with commercial alignment devices or by
compression platens and the test specimen. An assembly
using available hole tolerances in commercial compression
drawing of such a fixture and a test specimen is shown in Fig.
platens in conjunction with shims (2).
2. The brittle nature of advanced ceramics requires a uniform
interface between the loading fixtures and the test specimen. 6.2.1.2 Loading blocks as shown in Fig. 3 shall have the
Line or point contact stresses lead to crack initiation and same diameter as the test specimen ends at their interface.
fracture of the test specimen at stresses less than the actual Parallelism and flatness of faces as well as concentricity of the
compressive strength (that is, where actual strength is the loading blocks shall be as given in Fig. 3. The material for the
intrinsic strength of the material not influenced by the test or loading blocks shall be chosen to meet the following require-
test conditions). In addition, large mismatches of Poisson’s ments. Generally, cobalt-sintered tungsten carbide (Co-WC)
ratios or elastic moduli between the loading fixture and test has worked satisfact
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