ASTM C1366-97
(Test Method)Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Elevated Temperatures
Standard Test Method for Tensile Strength of Monolithic Advanced Ceramics at Elevated Temperatures
SCOPE
1.1 This test method covers the determination of tensile strength under uniaxial loading of monolithic advanced ceramics at elevated temperatures. This test method addresses, but is not restricted to, various suggested test specimen geometries as listed in the appendix. In addition, specimen fabrication methods, testing modes (load displacement, or strain control), testing rates (load rate, stress rate, displacement rate, or strain rate), allowable bending, and data collection and reporting procedures are addressed. Tensile strength as used in this test method refers to the tensile strength obtained under uniaxial loading.
General Information
Relations
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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: C 1366 – 97
Standard Test Method for
Tensile Strength of Monolithic Advanced Ceramics at
Elevated Temperatures
This standard is issued under the fixed designation C 1366; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 1239 Practice for Reporting Uniaxial Strength Data and
Estimating Weibull Distribution Parameters for Advanced
1.1 This test method covers the determination of tensile
Ceramics
strength under uniaxial loading of monolithic advanced ceram-
C 1322 Practice for Fractography and Characterization of
ics at elevated temperatures. This test method addresses, but is
Fracture Origins in Advanced Ceramics
not restricted to, various suggested test specimen geometries as
D 3379 Test Method for Tensile Strength and Young’s
listed in the appendix. In addition, specimen fabrication
Modulus for High-Modulus Single-Filament Materials
methods, testing modes (load, displacement, or strain control),
E 4 Practices for Force Verification of Testing Machines
testing rates (load rate, stress rate, displacement rate, or strain
E 6 Terminology Relating to Methods of Mechanical Test-
rate), allowable bending, and data collection and reporting
ing
procedures are addressed. Tensile strength as used in this test
E 21 Practice for Elevated Temperature Tension Tests of
method refers to the tensile strength obtained under uniaxial
Metallic Materials
loading.
E 83 Practice for Verification and Classification of Exten-
1.2 This test method applies primarily to advanced ceramics
someters
which macroscopically exhibit isotropic, homogeneous, con-
E 220 Method for Calibration of Thermocouples by Com-
tinuous behavior. While this test method applies primarily to
parison Techniques
monolithic advanced ceramics, certain whisker, or particle-
E 337 Test Method for Measure Humidity with a Psychrom-
reinforced composite ceramics as well as certain discontinuous
eter (The Measurement of Wet- and Dry-Bulb Tempera-
fiber-reinforced composite ceramics may also meet these
tures)
macroscopic behavior assumptions. Generally, continuous fiber
E 380 Practice for Use of the International System of Units
ceramic composites (CFCCs) do not macroscopically exhibit
(SI) (The Modernized Metric System)
isotropic, homogeneous, continuous behavior and application
E 1012 Practice for Verification of Specimen Alignment
of this test method to these materials is not recommended.
Under Tensile Loading
1.3 The values stated in SI units are to be regarded as the
2.2 Military Handbook:
standard and are in accordance with Practice E 380.
MIL-HDBK-790 Fractography and Characterization of
1.4 This standard does not purport to address all of the
Fracture Origins in Advanced Structural Ceramics
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
3. Terminology
priate safety and health practices and determine the applica-
3.1 Definitions:
bility of regulatory limitations prior to use. Refer to Section 7
3.1.1 Definitions of terms relating to tensile testing and
for specific precautions.
advanced ceramics as they appear in Terminology E 6 and
2. Referenced Documents Terminology C 1145, respectively, apply to the terms used in
this test method. Pertinent definitions are shown in the follow-
2.1 ASTM Standards:
ing with the appropriate source given in parenthesis. Additional
C 1145 Terminology of Advanced Ceramics
terms used in conjunction with this test method are defined in
C 1161 Test Method for Flexural Strength of Advanced
the following.
Ceramics at Ambient Temperature
Annual Book of ASTM Standards, Vol 03.01.
1 4
This test method is under the jurisdiction of ASTM Committee C–28 on Annual Book of ASTM Standards, Vol 14.03.
Advanced Ceramics and is the direct responsibility of Subcommittee C28.01 on Annual Book of ASTM Standards, Vol 11.03.
Properties and Performance. Annual Book of ASTM Standards, Vol 14.02.
Current edition approved Feb. 10, 1997. Published December 1997. Available from Army Research Laboratory—Materials Directorate, Aberdeen
Annual Book of ASTM Standards, Vol 15.01. Proving Ground, MD 21005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1366
3.1.2 advanced ceramic, n—a highly engineered, high per- principle, be scaled to an effective volume or effective surface
formance predominately non-metallic, inorganic, ceramic ma- area of unity as discussed in Practice C 1239.
terial having specific functional attributes. (See Terminology 4.4 Tensile tests provide information on the strength and
C 1145.) deformation of materials under uniaxial stresses. Uniform
–1
stress states are required to effectively evaluate any non-linear
3.1.3 axial strain [LL ], n—the average longitudinal
strains measured at the surface on opposite sides of the stress-strain behavior which may develop as the result of
testing mode, testing rate, processing or alloying effects,
longitudinal axis of symmetry of the specimen by two strain-
sensing devices located at the mid length of the reduced environmental influences, or elevated temperatures. These
effects may be consequences of stress corrosion or sub critical
section. (See Practice E 1012.)
–1
(slow) crack growth which can be minimized by testing at
3.1.4 bending strain [LL ], n—the difference between the
appropriately rapid rates as outlined in this test method.
strain at the surface and the axial strain. In general, the bending
4.5 The results of tensile tests of specimens fabricated to
strain varies from point to point around and along the reduced
standardized dimensions from a particular material or selected
section of the specimen. (See Practice E 1012.)
portions of a part, or both, may not totally represent the
3.1.5 breaking load [F], n—the load at which fracture
strength and deformation properties of the entire, full-size end
occurs. (See Terminology E 6.)
product or its in-service behavior in different environments.
3.1.6 fractography, n—the means and methods for charac-
4.6 For quality control purposes, results derived from stan-
terizing a fractured specimen or component. (See Terminology
dardized tensile test specimens can be considered to be
C 1145.)
indicative of the response of the material from which they were
3.1.7 fracture origin, n—the source from which brittle
taken for particular primary processing conditions and post-
fracture commences. (See Terminology C 1145).
processing heat treatments.
3.1.8 percent binding, n—the bending strain times 100
4.7 The tensile strength of a ceramic material is dependent
divided by the axial strain. (See Practice E 1012.)
on both its inherent resistance to fracture and the presence of
3.1.9 slow crack growth, n—sub critical crack growth
flaws. Analysis of fracture surfaces and fractography as de-
(extension) that may result from, but is not restricted to, such
scribed in Practice C 1322 and MIL-HDBK-790, though be-
mechanisms as environmentally-assisted stress corrosion or
yond the scope of this test method, are recommended for all
diffusive crack growth.
2 purposes, especially for design data.
3.1.10 tensile strength, S [FL ], n—the maximum tensile
u
stress which a material is capable of sustaining. Tensile
5. Interferences
strength is calculated from the maximum load during a tension
5.1 Test environment (vacuum, inert gas, ambient air, etc.)
test carried to rupture and the original cross-sectional area of
including moisture content for example relative humidity) may
the specimen. (See Terminology E 6.)
have an influence on the measured tensile strength. In particu-
lar, the behavior of materials susceptible to slow crack growth
4. Significance and Use
fracture will be strongly influenced by test environment, testing
4.1 This test method may be used for material development,
rate, and elevated temperatures. Testing to evaluate the maxi-
material comparison, quality assurance, characterization, reli-
mum strength potential of a material should be conducted in
ability assessment, and design data generation.
inert environments or at sufficiently rapid testing rates, or both,
4.2 High strength, monolithic advanced ceramic materials to minimize slow crack growth effects. Conversely, testing can
are generally characterized by small grain sizes (< 50 μm) and
be conducted in environments and testing modes and rates
bulk densities near the theoretical density. These materials are representative of service conditions to evaluate material per-
candidates for load-bearing structural applications requiring
formance under use conditions. When testing is conducted in
high degrees of wear and corrosion resistance and elevated-
uncontrolled ambient air with the intent of evaluating maxi-
temperature strength. Although flexural test methods are com-
mum strength potential, monitor and report relative humidity
monly used to evaluate strength of advanced ceramics, the non
and ambient temperature. Testing at humidity levels > 65 %
uniform stress distribution of the flexure specimen limits the
relative humidity (RH) is not recommended.
volume of material subjected to the maximum applied stress at
5.2 Surface preparation of test specimens can introduce
fracture. Uniaxially-loaded tensile strength tests provide infor- fabrication flaws that may have pronounced effects on tensile
mation on strength-limiting flaws from a greater volume of
strength. Machining damage introduced during specimen
uniformly stressed material. preparation can be either a random interfering factor in the
4.3 Because of the probabilistic strength distributions of determination of ultimate strength of pristine material (that is
brittle materials such as advanced ceramics, a sufficient num- increase frequency of surface initiated fractures compared to
ber of specimens at each testing condition is required for volume initiated fractures), or an inherent part of the strength
statistical analysis and eventual design with guidelines for characteristics. Surface preparation can also lead to the intro-
sufficient numbers provided in this test method. Size-scaling duction of residual stresses. Universal or standardized test
effects as discussed in practice C 1239 will affect the strength methods of surface preparation do not exist. Final machining
values. Therefore, strengths obtained using different recom- steps may, or may not negate machining damage introduced
mended tensile specimen geometries with different volumes or during the early coarse or intermediate machining. Thus, report
surface areas of material in the gage sections will be different specimen fabrication history since it may play an important
due to these size differences. Resulting strength values can, in role in the measured strength distributions.
C 1366
5.3 Bending in uniaxial tensile tests can cause or promote interfaces as discussed in the following sections. Uncooled
non uniform stress distributions with maximum stresses occur- grips located inside the heated zone are termed “hot grips” and
ring at the specimen surface leading to non representative generally produce almost no thermal gradient in the specimen
fractures originating at surfaces or near geometrical transitions. but at the relative expense of grip materials of at least the same
Bending may be introduced from several sources including temperature capability as the test material and increased
misaligned load trains, eccentric or mis-shaped specimens, and degradation of the grips due to exposure to the elevated-
non-uniformly heated specimens or grips. In addition, if strains temperature oxidizing environment. Grips located outside the
or deformations are measured at surfaces where maximum or heated zone surrounding the specimen may or may not employ
minimum stresses occur, bending may introduce over or under cooling. Uncooled grips located outside the heated zone are
measurement of strains. Similarly, fracture from surface flaws termed“ warm grips” and generally induce a mild thermal
may be accentuated or muted by the presence of the non gradient in the specimen but at the relative expense of
uniform stresses caused by bending. elevated-temperature alloys in the grips and increased degra-
dation of the grips due to exposure to the elevated-temperature
6. Apparatus
oxidizing environment. Cooled grips located outside the heated
zone are termed“ cold grips” and generally induce a steep
6.1 Testing Machines—Machines used for tensile testing
thermal gradient in the specimen at a greater relative expense
shall conform to the requirements of Practice E 4. The loads
because of grip cooling equipment and allowances, although
used in determining tensile strength shall be accurate within 6
with the advantage of consistent alignment and little degrada-
1 % at any load within the selected load range of the testing
tion from exposure to elevated temperatures.
machine as defined in Practice E 4. A schematic showing
pertinent features of a possible tensile testing apparatus is
NOTE 1—The expense of the cooling system for cold grips is balanced
shown in Fig. 1
against maintaining alignment which remains consistent from test to test
(stable grip temperature) and decreased degradation of the grips due to
6.2 Gripping Devices:
exposure to the elevated-temperature oxidizing environment. When grip
6.2.1 General—Various types of gripping devices may be
cooling is employed, means should be provided to control the cooling
used to transmit the measured load applied by the testing
medium to maximum fluctuations of 5 K (less than 1 K preferred) about
machine to the test specimen. The brittle nature of advanced
a setpoint temperature (1) over the course of the test to minimize
ceramics requires a uniform interface between the grip com-
thermally-induced strain changes in the specimen. In addition, opposing
ponents and the gripped section of the specimen. Line or point
grip temperatures should be maintained at uniform and consistent tem-
contacts and non uniform pressure can produce Hertzian-type
peratures within6 5 K (less than 6 1 K preferred) (1) so as to avoid
introducing unequal thermal gradients and subsequent non uniaxial
stress leading to crack initiation and fracture of the specimen in
stresses in the specimen. Generally, the need for control of grip tempera-
the gripped section. Gripping devices can be classed generally
ture fluctuations or differences may be indicated if specimen gage-section
as those employing activ
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.