ASTM C1341-13(2023)

Standard Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites

SIGNIFICANCE AND USE
5.1 This test method is used for material development, quality control, and material flexural specifications. Although flexural test methods are commonly used to determine design strengths of monolithic advanced ceramics, the use of flexure test data for determining tensile or compressive properties of CFCC materials is strongly discouraged. The nonuniform stress distributions in the flexure test specimen, the dissimilar mechanical behavior in tension and compression for CFCCs, low shear strengths of CFCCs, and anisotropy in fiber architecture all lead to ambiguity in using flexure results for CFCC material design data (1-4).3 Rather, uniaxial-forced tensile and compressive tests are recommended for developing CFCC material design data based on a uniformly stressed test condition.  
5.2 In this test method, the flexure stress is computed from elastic beam theory with the simplifying assumptions that the material is homogeneous and linearly elastic. This is valid for composites where the principal fiber direction is coincident/transverse with the axis of the beam. These assumptions are necessary to calculate a flexural strength value, but limit the application to comparative type testing such as used for material development, quality control, and flexure specifications. Such comparative testing requires consistent and standardized test conditions, that is, test specimen geometry/thickness, strain rates, and atmospheric/test conditions.  
5.3 Unlike monolithic advanced ceramics which fracture catastrophically from a single dominant flaw, CFCCs generally experience “graceful” fracture from a cumulative damage process. Therefore, the volume of material subjected to a uniform flexural stress may not be as significant a factor in determining the flexural strength of CFCCs. However, the need to test a statistically significant number of flexure test specimens is not eliminated. Because of the probabilistic nature of the strength of the brittle matrices and of the ceramic...
SCOPE
1.1 This test method covers the determination of flexural properties of continuous fiber-reinforced ceramic composites in the form of rectangular bars formed directly or cut from sheets, plates, or molded shapes. Three test geometries are described as follows:  
1.1.1 Test Geometry I—A three-point loading system utilizing center point force application on a simply supported beam.  
1.1.2 Test Geometry IIA—A four-point loading system utilizing two force application points equally spaced from their adjacent support points, with a distance between force application points of one-half of the support span.  
1.1.3 Test Geometry IIB—A four-point loading system utilizing two force application points equally spaced from their adjacent support points, with a distance between force application points of one-third of the support span.  
1.2 This test method applies primarily to all advanced ceramic matrix composites with continuous fiber reinforcement: unidirectional (1D), bidirectional (2D), tridirectional (3D), and other continuous fiber architectures. In addition, this test method may also be used with glass (amorphous) matrix composites with continuous fiber reinforcement. However, flexural strength cannot be determined for those materials that do not break or fail by tension or compression in the outer fibers. This test method does not directly address discontinuous fiber-reinforced, whisker-reinforced, or particulate-reinforced ceramics. Those types of ceramic matrix composites are better tested in flexure using Test Methods C1161 and C1211.  
1.3 Tests can be performed at ambient temperatures or at elevated temperatures. At elevated temperatures, a suitable furnace is necessary for heating and holding the test specimens at the desired testing temperatures.  
1.4 This test method includes the following:    
Section    
Scope  
1  
Referenced Documents  
2  
Terminology  
3  
Summary of Test Method  
...

General Information

• Status: Published
• Publication Date: 30-Apr-2023
• ICS: 81.060.30 - Advanced ceramics
• Technical Committee: C28 - Advanced Ceramics
• Drafting Committee: C28.07 - Ceramic Matrix Composites

Relations

• Refers: ASTM D6856/D6856M-23 - Standard Guide for Testing Fabric-Reinforced “Textile” Composite Materials
• Effective Date: 01-Nov-2023
• Refers: ASTM D3878-19a - Standard Terminology for Composite Materials
• Effective Date: 15-Oct-2019
• Refers: ASTM C1145-19 - Standard Terminology of Advanced Ceramics
• Effective Date: 01-Jul-2019
• Refers: ASTM D3878-19 - Standard Terminology for Composite Materials
• Effective Date: 15-Apr-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 D3878-18 - Standard Terminology for Composite Materials
• Effective Date: 01-Apr-2018
• Refers: ASTM D790-17 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Jul-2017
• Refers: ASTM D6856/D6856M-03(2016) - Standard Guide for Testing Fabric-Reinforced “Textile” Composite Materials
• Effective Date: 01-Sep-2016
• Refers: ASTM D3878-16 - Standard Terminology for Composite Materials
• Effective Date: 01-Aug-2016
• Refers: ASTM D790-15e1 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM D790-15 - Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• Effective Date: 01-Dec-2015
• Refers: ASTM D3878-15 - Standard Terminology for Composite Materials
• Effective Date: 01-Jul-2015
• Refers: ASTM E4-14 - Standard Practices for Force Verification of Testing Machines
• Effective Date: 01-Jun-2014
• Refers: ASTM E177-14 - Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
• Effective Date: 01-May-2014
• Refers: ASTM E220-13 - Standard Test Method for Calibration of Thermocouples By Comparison Techniques
• Effective Date: 01-Nov-2013

Overview

ASTM C1341-13(2023): Standard Test Method for Flexural Properties of Continuous Fiber-Reinforced Advanced Ceramic Composites is a globally recognized ASTM standard that details procedures for determining the flexural properties of continuous fiber-reinforced ceramic composites (CFCCs). This test method is specifically designed for materials in the form of rectangular bars formed directly, or cut from sheets, plates, or molded shapes.

CFCCs are essential in applications requiring high strength, toughness, and thermal stability. The standard primarily supports material development, quality control, and establishing comparative specifications for flexural properties. It outlines three specific test geometries: three-point bending, and two variations of four-point bending, allowing for comprehensive assessment of flexural behavior under varied loading scenarios.

Key Topics

• Scope of Application:
  This standard focuses on continuous fiber-reinforced ceramic composites, including unidirectional (1D), bidirectional (2D), tridirectional (3D), and similar architectures. It is also applicable to glass (amorphous) matrix composites with continuous fiber reinforcement. It does not directly address discontinuous fiber, whisker-reinforced, or particulate-reinforced ceramics.

• Test Geometries:

  • Geometry I: Three-point loading system (center point force application).
  • Geometry IIA: Four-point loading system with force application points one-half of the support span apart.
  • Geometry IIB: Four-point loading system with force application points one-third of the support span apart.

• Significance and Limitations:

  • Material Comparison: The test enables standardized, comparative flexural testing for material development and quality control.
  • Not for Tensile/Compressive Design Properties: Due to the nonuniform stress distributions and the unique failure mechanisms in CFCCs, flexural data should not substitute for uniaxial tensile or compressive property determination.
  • Behavioral Insights: Unlike monolithic ceramics which fracture catastrophically, CFCCs often fail via a gradual, cumulative damage process, making test interpretation distinct.
  • Statistical Considerations: A sufficient number of specimens must be tested for reliable statistical analysis due to the probabilistic strength of brittle matrix and fiber components.

• Testing Conditions:

  • Tests can be performed at ambient and elevated temperatures, with the need for temperature control and uniformity if high-temperature testing is involved.
  • Consistent test specimen geometry, strain rates, and environmental conditions are required to ensure meaningful comparative results.

Applications

ASTM C1341 is highly relevant for:

• Material Development: Assists researchers and manufacturers in evaluating and comparing new CFCC materials during formulation and processing.
• Quality Control: Enables manufacturers to assure that batches of advanced ceramic composites meet flexural property specifications before deployment in high-performance applications.
• Specification Compliance: Provides an objective basis for flexural strength requirements in industries such as aerospace, energy, and high-temperature structural engineering.
• Research and Development: Facilitates scientific studies of damage mechanisms, fiber architecture effects, and environmental influences on flexural behavior.

This standard is not suitable for discontinuous fiber composites or for defining absolute design properties where uniform stress conditions are critical.

Related Standards

To ensure comprehensive testing and reporting, ASTM C1341 references several related ASTM standards:

• ASTM C1161: Test Method for Flexural Strength of Advanced Ceramics at Ambient Temperature
• ASTM C1211: Test Method for Flexural Strength of Advanced Ceramics at Elevated Temperatures
• ASTM C1239: Practice for Reporting Uniaxial Strength Data and Estimating Weibull Distribution Parameters for Advanced Ceramics
• ASTM D790: Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
• ASTM C1292: Test Method for Shear Strength of Continuous Fiber-Reinforced Advanced Ceramics at Ambient Temperatures

These standards provide complementary methods for the mechanical characterization of ceramics and composites, supporting robust and accurate material assessment.

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Keywords: ASTM C1341, flexural properties, continuous fiber-reinforced ceramic composites, CFCC, advanced ceramics, flexural strength testing, ceramic matrix composites, quality control, material development, high-temperature composites, three-point bend, four-point bend.

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: C1341 − 13 (Reapproved 2023)
Standard Test Method for
Flexural Properties of Continuous Fiber-Reinforced
Advanced Ceramic Composites
This standard is issued under the fixed designation C1341; 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
Referenced Documents 2
Terminology 3
1.1 This test method covers the determination of flexural
Summary of Test Method 4
properties of continuous fiber-reinforced ceramic composites Significance and Use 5
Interferences 6
in the form of rectangular bars formed directly or cut from
Apparatus 7
sheets, plates, or molded shapes. Three test geometries are
Precautionary Statement 8
described as follows: Test Specimens 9
Procedures 10
1.1.1 Test Geometry I—A three-point loading system utiliz-
Calculation of Results 11
ing center point force application on a simply supported beam.
Report 12
Precision and Bias 13
1.1.2 Test Geometry IIA—A four-point loading system uti-
Keywords 14
lizing two force application points equally spaced from their
References
adjacent support points, with a distance between force appli-
CFCC Surface Condition and Finishing Annex A1
Conditions and Issues in Hot Loading of Test Annex A2
cation points of one-half of the support span.
Specimens into Furnaces
1.1.3 Test Geometry IIB—A four-point loading system uti-
Toe Compensation on Stress-Strain Curves Annex A3
lizing two force application points equally spaced from their
Corrections for Thermal Expansion in Flexural Annex A4
Equations
adjacent support points, with a distance between force appli-
Example of Test Report Appendix X1
cation points of one-third of the support span.
1.5 The values stated in SI units are to be regarded as the
1.2 This test method applies primarily to all advanced
standard in accordance with IEEE/ASTM SI 10.
ceramic matrix composites with continuous fiber reinforce-
1.6 This standard does not purport to address all of the
ment: unidirectional (1D), bidirectional (2D), tridirectional
safety concerns, if any, associated with its use. It is the
(3D), and other continuous fiber architectures. In addition, this
responsibility of the user of this standard to establish appro-
test method may also be used with glass (amorphous) matrix
priate safety, health, and environmental practices and deter-
composites with continuous fiber reinforcement. However,
mine the applicability of regulatory limitations prior to use.
flexural strength cannot be determined for those materials that
1.7 This international standard was developed in accor-
do not break or fail by tension or compression in the outer
dance with internationally recognized principles on standard-
fibers. This test method does not directly address discontinuous
ization established in the Decision on Principles for the
fiber-reinforced, whisker-reinforced, or particulate-reinforced
Development of International Standards, Guides and Recom-
ceramics. Those types of ceramic matrix composites are better
mendations issued by the World Trade Organization Technical
tested in flexure using Test Methods C1161 and C1211.
Barriers to Trade (TBT) Committee.
1.3 Tests can be performed at ambient temperatures or at
elevated temperatures. At elevated temperatures, a suitable
2. Referenced Documents
furnace is necessary for heating and holding the test specimens
2.1 ASTM Standards:
at the desired testing temperatures.
C1145 Terminology of Advanced Ceramics
1.4 This test method includes the following:
C1161 Test Method for Flexural Strength of Advanced
Section
Ceramics at Ambient Temperature
Scope 1
C1211 Test Method for Flexural Strength of Advanced
Ceramics at Elevated Temperatures
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.07 on
Ceramic Matrix Composites. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2023. Published June 2023. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1996. Last previous edition approved in 2018 as C1341 – 13 (2018). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/C1341-13R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
C1341 − 13 (2023)
C1239 Practice for Reporting Uniaxial Strength Data and nature. These components are combined on a macroscale to
Estimating Weibull Distribution Parameters for Advanced form a useful engineering material possessing certain proper-
Ceramics ties or behavior not possessed by the individual constituents.
C1292 Test Method for Shear Strength of Continuous Fiber-
3.1.5 continuous fiber-reinforced ceramic composite
Reinforced Advanced Ceramics at Ambient Temperatures
(CFCC), n—ceramic matrix composite in which the reinforc-
D790 Test Methods for Flexural Properties of Unreinforced
ing phase consists of a continuous fiber, continuous yarn, or a
and Reinforced Plastics and Electrical Insulating Materi-
woven fabric.
als
−2
3.1.6 flexural strength [FL ], n—measure of the ultimate
D2344/D2344M Test Method for Short-Beam Strength of
strength of a specified beam in bending. C1161
Polymer Matrix Composite Materials and Their Laminates
D3878 Terminology for Composite Materials 3.1.7 four-point- ⁄3-point flexure, n—a configuration of flex-
ural strength testing where a test specimen is symmetrically
D6856/D6856M Guide for Testing Fabric-Reinforced “Tex-
tile” Composite Materials loaded at two locations that are situated one-third of the overall
span away from the outer two support bearings.
E4 Practices for Force Calibration and Verification of Test-
ing Machines
3.1.8 four-point- ⁄4-point flexure, n—a configuration of flex-
E6 Terminology Relating to Methods of Mechanical Testing
ural strength testing where a test specimen is symmetrically
E122 Practice for Calculating Sample Size to Estimate, With
loaded at two locations that are situated one-quarter of the
Specified Precision, the Average for a Characteristic of a
overall span away from the outer two support bearings. C1161
Lot or Process
−2
3.1.9 fracture strength [FL ], n—the calculated flexural
E177 Practice for Use of the Terms Precision and Bias in
stress at the breaking force.
ASTM Test Methods
−2
3.1.10 modulus of elasticity [FL ], n—the ratio of stress to
E220 Test Method for Calibration of Thermocouples By
corresponding strain below the proportional limit. E6
Comparison Techniques
−2
E337 Test Method for Measuring Humidity with a Psy-
3.1.11 proportional limit stress [FL ], n—greatest stress
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
that a material is capable of sustaining without any deviation
peratures)
from proportionality of stress to strain (Hooke’s law).
E691 Practice for Conducting an Interlaboratory Study to
3.1.11.1 Discussion—Many experiments have shown that
Determine the Precision of a Test Method
values observed for the proportional limit vary greatly with the
IEEE/ASTM SI 10 American National Standard for Use of
sensitivity and accuracy of the testing equipment, eccentricity
the International System of Units (SI): The Modern Metric
of force application, the scale to which the stress-strain
System
diagram is plotted, and other factors. When determination of
proportional limit is required, the procedure and sensitivity of
3. Terminology
the test equipment shall be specified. E6
3.1 Definitions:
3.1.12 slow crack growth, n—subcritical crack growth (ex-
3.1.1 The definitions of terms relating to flexure testing
tension) that may result from, but is not restricted to, such
appearing in Terminology E6 apply to the terms used in this
mechanisms as environmentally assisted stress corrosion or
test method. The definitions of terms relating to advanced
diffusive crack growth.
ceramics appearing in Terminology C1145 apply to the terms
3.1.13 span-to-depth ratio [nd], n—for a particular test
used in this test method. The definitions of terms relating to
specimen geometry and flexure test configuration, the ratio
fiber-reinforced composites appearing in Terminology D3878
(L/d) of the outer support span length (L) of the flexure test
apply to the terms used in this test method. Pertinent definitions
specimen to the thickness/depth (d) of test specimen (as used
as listed in Test Method C1161, Test Methods D790, Termi-
and described in Test Methods D790).
nology C1145, Terminology D3878, and Terminology E6 are
shown in the following, with the appropriate source given in 3.1.14 three-point flexure, n—a configuration of flexural
strength testing where a test specimen is loaded at a location
brackets. Additional terms used in conjunction with this test
method are also defined in the following. midway between two support bearings. C1161
3.1.2 advanced ceramic, n—highly engineered, high-
performance, predominately nonmetallic, inorganic, ceramic 4. Summary of Test Method
material having specific functional attributes. C1145
4.1 A bar of rectangular cross section is tested in flexure as
3.1.3 breaking force [F], n—the force at which fracture
a beam as in one of the following three geometries:
occurs. (In this test method, fracture consists of breakage of the
4.1.1 Test Geometry I—The bar rests on two supports and
test bar into two or more pieces or a loss of at least 20 % of the
force is applied by means of a loading roller midway between
maximum force carrying capacity.) E6
the supports (see Fig. 1).
3.1.4 ceramic matrix composite, n—material consisting of 4.1.2 Test Geometry IIA—The bar rests on two supports and
two or more materials (insoluble in one another) in which the force is applied at two points (by means of two inner rollers),
major, continuous component (matrix component) is a ceramic, each an equal distance from the adjacent outer support point.
while the secondary component(s) (reinforcing component) The inner support points are situated one-quarter of the overall
may be ceramic, glass-ceramic, glass, metal, or organic in span away from the outer two support bearings. The distance
C1341 − 13 (2023)
FIG. 1 Flexure Test Geometries and Force Diagram
between the inner rollers (that is, the load span) is one-half of material design data (1-4). Rather, uniaxial-forced tensile and
the support span (see Fig. 1). compressive tests are recommended for developing CFCC
4.1.3 Test Geometry IIB—The bar rests on two supports and material design data based on a uniformly stressed test condi-
force is applied at two points (by means of two loading rollers), tion.
situated one-third of the overall span away from the outer two
5.2 In this test method, the flexure stress is computed from
support bearings. The distance between the inner rollers (that
elastic beam theory with the simplifying assumptions that the
is, the inner support span) is one-third of the outer support span
material is homogeneous and linearly elastic. This is valid for
(see Fig. 1).
composites where the principal fiber direction is coincident/
4.2 The test specimen is deflected until rupture occurs in the transverse with the axis of the beam. These assumptions are
outer fibers or until there is a 20 % decrease from the peak necessary to calculate a flexural strength value, but limit the
force. application to comparative type testing such as used for
material development, quality control, and flexure specifica-
4.3 The flexural properties of the test specimen (flexural
tions. Such comparative testing requires consistent and stan-
strength and strain, fracture strength and strain, modulus of
dardized test conditions, that is, test specimen geometry/
elasticity, and stress-strain curves) are calculated from the
thickness, strain rates, and atmospheric/test conditions.
force and deflection using elastic beam equations.
5.3 Unlike monolithic advanced ceramics which fracture
5. Significance and Use
catastrophically from a single dominant flaw, CFCCs generally
experience “graceful” fracture from a cumulative damage
5.1 This test method is used for material development,
process. Therefore, the volume of material subjected to a
quality control, and material flexural specifications. Although
uniform flexural stress may not be as significant a factor in
flexural test methods are commonly used to determine design
determining the flexural strength of CFCCs. However, the need
strengths of monolithic advanced ceramics, the use of flexure
to test a statistically significant number of flexure test speci-
test data for determining tensile or compressive properties of
mens is not eliminated. Because of the probabilistic nature of
CFCC materials is strongly discouraged. The nonuniform
the strength of the brittle matrices and of the ceramic fiber in
stress distributions in the flexure test specimen, the dissimilar
mechanical behavior in tension and compression for CFCCs,
low shear strengths of CFCCs, and anisotropy in fiber archi-
The boldface numbers in parentheses refer to a list of references at the end of
tecture all lead to ambiguity in using flexure results for CFCC this standard.
C1341 − 13 (2023)
CFCCs, a sufficient number of test specimens at each testing geometry of the test specimen must be chosen so that shear
condition is required for statistical analysis, with guidelines for stresses are kept low relative to the tension and compression
sufficient numbers provided in 9.7. Studies to determine the stresses. This is done by maintaining a high ratio between the
exact influence of test specimen volume on strength distribu- support span (L) and the thickness/depth (d) of the test
tions for CFCCs are not currently available. specimen. This L/d ratio is generally kept at values of ≥16 for
three-point testing and ≥30 for four-point testing. If the
5.4 The four-point loading geometries (Geometries IIA and
span-to-depth ratio is too low, the test specimen may fail in
IIB) are preferred over the three-point loading geometry
shear, invalidating the test. If the desired mode of failure is
(Geometry I). In the four-point loading geometry, a larger
shear, then an appropriate shear test method should be used,
portion of the test specimen is subjected to the maximum
such as Test Method C1292 or D2344/D2344M.
tensile and compressive stresses, as compared to the three-
6.2 Time-dependent phenomena, such as stress corrosion
point loading geometry. If there is a statistical/Weibull charac-
and slow crack growth, can interfere with the determination of
ter failure in the particular composite system being tested, the
the flexural strength at room and elevated temperatures. Creep
size of the maximum stress region will play a role in deter-
phenomena also become significant at elevated temperatures.
mining the mechanical properties. The four-point geometry
Both mechanisms can cause stress relaxation in flexure test
may then produce more reliable statistical data.
specimens during a strength test, thereby causing the elastic
5.5 Flexure tests provide information on the strength and
formula calculations to be in error. Test environment (vacuum,
deformation of materials under complex flexural stress condi-
inert gas, ambient air, etc.), including moisture content (for
tions. In CFCCs nonlinear stress-strain behavior may develop
example, relative humidity), may have an accelerating effect on
as the result of cumulative damage processes (for example,
stress corrosion and slow crack growth. Testing to evaluate the
matrix cracking, matrix/fiber debonding, fiber fracture,
maximum strength potential of a material should be conducted
delamination, etc.) which may be influenced by testing mode,
in inert environments or at sufficiently rapid testing rates, or
testing rate, processing effects, or environmental influences.
both, so as to minimize slow crack growth effects. Conversely,
Some of these effects may be consequences of stress corrosion
testing can be conducted in environments and testing modes
or subcritical (slow) crack growth which can be minimized by
and rates representative of service conditions to evaluate
testing at sufficiently rapid rates as outlined in 10.3 of this test
material performance under use conditions. When testing is
method.
conducted in uncontrolled ambient air with the intent of
5.6 Because of geometry effects, the results of flexure tests
evaluating maximum strength potential, monitor and report the
of test specimens fabricated to standardized test dimensions
relative humidity and temperature.
from a particular material or selected portions of a component,
6.3 Surface preparation of test specimens, although nor-
or both, cannot be categorically used to define the strength and
mally not considered a major concern in CFCCs, can introduce
deformation properties of the entire, full-size end product or its
fracture sources on the surface which may have pronounced
in-service behavior in different environments. The effects of
effects on flexural mechanical properties and behavior (for
size and geometry shall be carefully considered in extrapolat-
example, elastic and nonelastic regions of the stress-strain
ing the test results to other configurations and performance
curve, flexural strength and strain, proportional limit stress and
conditions.
strain, etc.). Machining damage introduced during test speci-
5.7 For quality control purposes, results from standardized
men preparation can be either a random interfering factor in the
flexure test specimens may be considered indicative of the
determination of flexure strength of test specimen or an
response of the material lot from which they were taken with
inherent part of the strength characteristics being measured.
the given primary processing conditions and post-processing
Surface preparation can also lead to the introduction of residual
heat treatments.
stresses. Universal or standardized test methods of surface
preparation for CFCCs do not exist. It should be understood
5.8 The flexure behavior and strength of a CFCC are
that final machining steps may or may not negate machining
dependent on its inherent resistance to fracture, the presence of
damage introduced during the initial machining. Thus, test
fracture sources, damage accumulation processes, or combina-
specimen fabrication history may play an important role in the
tions thereof. Analysis of fracture surfaces and fractography,
measured strength distributions and should be reported. In
though beyond the scope of this test method, is highly
addition, the nature of fabrication used for certain composites
recommended.
(for example, chemical vapor infiltration, hot pressing, and
6. Interferences
preceramic polymer lamination) may require the testing of
specimens in the as-processed condition (that is, it may not be
6.1 A CFCC material tested in flexure may fail in a variety
possible or appropriate to machine the test specimen faces).
of distinct fracture modes, depending on the interaction of the
nonuniform stress fields in the flexure test specimen and the 6.4 Fractures that initiate outside the uniformly stressed
local mechanical properties. The test specimen may fail in region of a flexure test specimen (between the inner support
tension, compression, shear, or in a mix of different modes, points in four-point and under the center point in three-point)
depending on which mode reaches the critical stress level for may be due to factors such as stress concentrations or strength
failure to initiate. To obtain a valid flexural strength by this test limiting features in the microstructure of the test specimen.
method, the material must fail in the outer fiber surface in Fractures that do occur outside the uniformly stressed sections
tension or compression, rather than by shear failure. The will normally constitute invalid tests. If the flexure data is used
C1341 − 13 (2023)
TABLE 1 Recommended Dimensions for Test Specimens of 9.1
in the context of estimating Weibull parameters, then appro-
for Various Outer Support Span-to-Depth Ratios – Test Geometry
priate computational methods shall be used for such censored
I
data. These methods are outlined in Practice C1239.
(3-Point)
6.5 Flexural strength at elevated temperatures may be Nominal Test Test
Support
Rate of
Test Specimen Specimen Specimen
A
strongly dependent on force application rate as a consequence
Span
Crosshead
Depth/ Width Length
(mm) Motion (mm/s)
of creep, stress corrosion, or slow crack growth effects. This
Thickness (mm) (mm) (mm)
test method measures the flexural strength at high force
L/d = 16 to 1
application rates in order to minimize these effects. 1 3 26 16 0.04
2 6 45 32 0.09
3 9 60 48 0.13
7. Apparatus
4 12 75 64 0.17
5 15 90 80 0.21
7.1 Testing Machine—Test the flexure test specimens in a
6 18 105 96 0.26
10 30 180 160 0.43
properly calibrated testing machine that can be operated at
15 45 270 240 0.64
constant rates of crosshead motion over the range required. The
20 60 360 320 0.86
error in the force measuring system shall not exceed 61 % of
L/d = 32 to 1
1 3 42 32 0.17
the maximum force being measured. The force-indicating
2 6 75 64 0.34
mechanism shall be essentially free from inertial lag at the
3 9 105 96 0.51
crosshead rate used. Although not recommended, if the cross-
4 12 145 128 0.68
5 15 180 160 0.86
head displacement is used to determine the test specimen
6 18 210 192 1.03
deflection for the three-point loading geometry, determine the
10 30 360 320 1.71
compliance of the load train (see Appendix X1) so that
15 45 530 480 2.57
20 60 710 640 3.42
appropriate corrections can be made to the deflection measure-
L/d = 40 to 1
ment. Equip the system with a means for retaining the readout
1 3 50 40 0.27
of the maximum force, as well as a record of force versus time.
2 6 90 80 0.53
3 9 135 120 0.80
Verify the accuracy of the testing machine in accordance with
4 12 180 160 1.07
Practices E4.
5 15 220 200 1.34
6 18 265 240 1.60
7.2 Loading Fixtures—The outer support span and the
10 30 440 400 2.67
desired test geometry determine the dimensions and geometry
15 45 660 600 4.01
20 60 880 800 5.34
of the loading fixture. Select the fixture geometry from one of
L/d = 60 to 1
three configurations: three-point, four-point- ⁄4-point, and four-
1 3 70 60 0.60
point- ⁄3-point. The thickness of the test specimen to be tested
2 6 135 120 1.20
3 9 200 180 1.80
determines the critical outer span dimension (L) of the loading
4 12 265 240 2.40
fixture. The overall dimensions of the test specimen and the
5 15 330 300 3.01
required inner and outer support spans are selected based on
6 18 400 360 3.61
10 30 660 600 6.01
the specimen thickness, the desired test geometry, and the
15 45 1000 900 9.02
required span-to-depth ratio. Tables 1-3 give the recommended
20 60 1350 1200 12.02
support spans for different span/depth ratios, test specimen
A
Rates indicated are for a strain rate of 0.001 mm/mm·s.
thicknesses, and the three test geometries. Loading fixtures
shall be wide enough to support the entire width of the selected
test specimen geometry.
tested in a fully articulating fixture. (A representative design
7.2.1 Ensure that the design and construction of the fixtures
for a four-point fixture is illustrated in Fig. 3.)
produce even and uniform forces along the bearing-to-
7.2.4 The test fixture shall be made of a material that is
specimen surfaces. A rigid loading fixture is permitted, if it is
suitably rigid and resistant to permanent deformation at the
designed and aligned so that forces are evenly applied to the
forces and temperatures of testing. The test fixture material
test specimen, particularly for four-point loading geometries. It
shall be essentially inert at the desired test temperatures.
is preferred, however, that load fixtures with an articulating
geometry be used. An articulated loading fixture reduces or
7.3 Inner/Outer/Center Support Bearings—In both the
eliminates uneven force application caused by geometry varia-
three-point and four-point flexure test fixtures, use cylindrical
tions of the test specimen or misalignment of the test fixtures.
bearings for support of the test specimen and for force
7.2.2 Semi-Articulating Fixtures—Test specimens prepared
application. The cylinders shall be made of a tool steel or a
in accordance with and meeting the parallelism requirement of
ceramic with an elastic modulus between 200 GPa and
9.4 may be tested in a semi-articulating fixture. The bearing
400 GPa and a flexural strength no less than 275 MPa. The
cylinders shall be parallel to each other within 0.1 mm over
inner/outer/center support bearing cylinders shall remain elas-
their length. (A representative design for a four-point fixture is
tic over the force and temperature ranges used.
illustrated in Fig. 2.)
7.3.1 Ensure that the inner/outer/center support bearings
7.2.3 Fully Articulating Fixture—Test specimens with slight have cylindrical surfaces that are smooth and parallel along
warp, twist, or bowing may not meet the parallelism require- their length to an accuracy of 60.05 mm. In order to avoid
ments of 9.4. It is recommended that such test specimens be excessive indentation or crushing failure directly under the
C1341 − 13 (2023)
TABLE 2 Recommended Dimensions for Test Specimens of 9.1 TABLE 3 Recommended Dimensions for Test Specimens of 9.1
for Various Outer Support Span-to-Depth Ratios – Test Geometry for Various Outer Support Span-to-Depth Ratios – Test Geometry
IIA IIB
1 1
(4-Point- ⁄4-Point) (4-Point- ⁄3-Point)
Nominal Nominal
Test Test Test Test Test Test
Rate of Rate of
Support Force Support Force
A A
Specimen Specimen Specimen Specimen Specimen Specimen
Crosshead Crosshead
Span Span Span Span
Depth/ Width Length Motion Depth/ Width Length Motion
(mm) (mm) (mm) (mm)
(mm/s) (mm/s)
Thickness (mm) (mm) Thickness (mm) (mm)
(mm) (mm)
L/d = 16 to 1 L/d = 16 to 1
1 3 26 16 8 0.04 1 3 26 16 5.3 0.05
2 6 45 32 16 0.09 2 6 45 32 10.6 0.09
3 9 60 48 24 0.13 3 9 60 48 16.0 0.14
4 12 75 64 32 0.17 4 12 75 64 21.3 0.19
5 15 90 80 40 0.21 5 15 90 80 26.7 0.24
6 18 105 96 48 0.26 6 18 105 96 32.0 0.28
10 30 180 160 80 0.43 10 30 180 160 53.3 0.47
15 45 270 240 120 0.64 15 45 270 240 80.0 0.71
20 60 360 320 160 0.86 20 60 360 320 106.7 0.95
L/d = 32 to 1 L/d = 32 to 1
1 3 42 32 16 0.17 1 3 42 32 10.7 0.19
2 6 75 64 32 0.34 2 6 75 64 21.3 0.38
3 9 105 96 48 0.51 3 9 105 96 32.0 0.57
4 12 145 128 64 0.68 4 12 145 128 42.7 0.76
5 15 180 160 80 0.86 5 15 180 160 53.3 0.95
6 18 210 192 96 1.03 6 18 210 192 64.0 1.14
10 30 360 320 160 1.71 10 30 360 320 106.7 1.89
15 45 530 480 240 2.57 15 45 530 480 160.0 2.84
20 60 710 640 320 3.42 20 60 710 640 213.3 3.79
L/d = 40 to 1 L/d = 40 to 1
1 3 50 40 20 0.27 1 3 50 40 13.3 0.30
2 6 90 80 40 0.53 2 6 90 80 26.7 0.59
3 9 135 120 60 0.80 3 9 135 120 40.0 0.89
4 12 180 160 80 1.07 4 12 180 160 53.3 1.18
5 15 220 200 100 1.34 5 15 220 200 66.7 1.48
6 18 265 240 120 1.60 6 18 265 240 80.0 1.78
10 30 440 400 200 2.67 10 30 440 400 133.3 2.96
15 45 660 600 300 4.01 15 45 660 600 200.0 4.44
20 60 880 800 400 5.34 20 60 880 800 266.7 5.92
L/d = 60 to 1 L/d = 60 to 1
1 3 70 60 30 0.60 1 3 70 60 20.0 0.67
2 6 135 120 60 1.20 2 6 135 120 40.0 1.33
3 9 200 180 90 1.80 3 9 200 180 60.0 2.00
4 12 265 240 120 2.40 4 12 265 240 80.0 2.66
5 15 330 300 150 3.01 5 15 330 300 100.0 3.33
6 18 400 360 180 3.61 6 18 400 360 120.0 4.00
10 30 660 600 300 6.01 10 30 660 600 200.0 6.66
15 45 1000 900 450 9.02 15 45 1000 900 300.0 9.99
20 60 1350 1200 600 12.02 20 60 1350 1200 400.0 13.32
25 75 1650 1500 500.0 16.65
A
Rates indicated are for a strain rate of 0.001 mm/mm·s.
A
Rates indicated are for a strain rate of 0.001 mm/mm·s.
bearing contact surface, the bearing surface diameter shall be at
configurations shall be properly positioned with respect to the
least 3.0 mm. The bearing surface diameter shall be approxi-
support (outer) bearings to an accuracy of 1 % of the outer span
mately 1.5 times the beam depth of the test specimen size used.
length.
If the test specimen has low through-thickness compressive
7.3.3 For articulating fixtures, the bearing cylinders shall be
strength, the cylinder diameter shall be four times the beam
free to rotate in order to relieve frictional constraints (with the
thickness to prevent crushing at the force application points.
exception of the center bearing cylinder in three-point flexure,
NOTE 1—In such circumstances, however, there is a possible error due
which need not rotate). This can be accomplished as shown in
to contact-point tangency shift due to the change in force application point
Figs. 2 and 3. Note that the outer support bearings roll outward,
as the test specimen deflects during force application. The magnitude of
and the inner support bearings roll inward.
this error can be estimated from Ref (5).
7.3.2 Position the outer support bearing cylinders carefully NOTE 2—In general, fixed-pin fixtures have frictional constraints that
have been shown to cause a systematic error on the order of 5 % to 15 %
such that the outer support span distance is accurate to a
in flexural strength for monolithic ceramics. Since this error is systematic,
tolerance of 1 %. The force application bearing for the three-
it will lead to a bias in estimates of mean strength. Rolling-pin fixtures are
point configuration shall be positioned midway between the
required for articulating fixtures by this test method. It is recognized that
support bearings to an accuracy of 1 % of the outer span length.
they may not be feasible for rigid fixtures, in which case fixed-pin fixtures
The force application (inner) bearings for the four-point may be used. But this shall be stated explicitly in the report.
C1341 − 13 (2023)
FIG. 2 Semi-Articulating Flexure Fixtures
7.4 Deflection Measurement—The test system shall have a specimen across the inner support span section extending from
means of measuring test specimen deflection, appropriate for the center to 5 mm inside the outer support points. The
the geometry and the test temperature. The preferred device temperature uniformity along the inner support span shall be
measures actual deflection at the centerline of the test specimen within 65 °C for test temperatures up to and including 500 °C
support span, using direct contact or optical function. The and 61 % for test temperatures above 500 °C.
calibrated range of the deflectometer shall be such that the
7.6.1.1 In order to determine conformance to the tempera-
linear strain region of the material tested will represent a
ture control and uniformity requirements, determine a tempera-
minimum of 20 % of the calibrated range. The deflectometer
ture profile using thermocouples to measure the test specimen
shall have an accuracy of 1 % of the maximum deflection
temperature at three locations: the test specimen center point
measured.
and two points 5 mm inside the outer support points.
7.5 Strain Measurement—The use of strain gages for ambi-
7.6.1.2 Determine temperature uniformity for all elevated-
ent testing is acceptable, provided that the test material surface
temperature testing and recheck the uniformity if any of the
is smooth with little open porosity and that the applied strain
following parameters are changed: heating method, test speci-
gage is large enough to cover a representative area of the
men material, sample geometry, test temperature, or combina-
composite test specimen. Follow the manufacturer’s recom-
tions thereof.
mendations regarding application and performance. Strain
7.6.2 Temperature Measurement—The use of thermo-
gages shall not interfere with the deflection measuring device.
couples (TC) is recommended and preferred; however, the use
of optical pyrometery is acceptable. For TC measurement,
7.6 Heating Apparatus—For elevated-temperature testing,
any furnace that meets the temperature uniformity and control elevated-temperature tests require the placement of one TC at
requirements described below shall be acceptable. A furnace the test specimen center. The sheathed TC should be within
whose heated cavity is large enough to accept the entire test 1 mm of the test specimen. The use of two additional thermo-
fixture is preferred. couples at locations 5 mm inside the outer support points is
7.6.1 The furnace shall be capable of establishing and recommended to check for temperature uniformity. Thermo-
maintaining a constant temperature (within 65 °C) during each couples shall be calibrated in accordance with Test Method
test period. Measure the temperature uniformity of the test E220, with a verified accuracy of 65 °C.
C1341 − 13 (2023)
NOTE 1—One of the four inner/outer/center support bearings (for example, Roller No. 1) shall not articulate about the x-axis. The other three will
provide the necessary degrees of freedom. The radius R in the bottom fixture shall be sufficiently large such that contact stresses on the roller are
minimized.
FIG. 3 Fully Articulating Flexure Fixture
7.6.3 Atmosphere Control—The furnace may have an air, with the digital data acquisition system to provide an immedi-
inert, or vacuum environment, as required. If an inert or ate record of the test as a supplement to the digital record.
vacuum environment is used, and it is necessary to apply force Ensure that the recording devices have an accuracy of 0.1 % of
through a bellows, fitting, or seal, verify that force losses or full scale and have a minimum data acquisition rate of 10 Hz,
errors do not exceed 1 % of the expected failure forces. with a response of 50 Hz deemed more than sufficient.
7.7 Data Acquisition—At minimum, obtain an autographic 7.8 Dimension Measuring Devices—Micrometers and other
record of the applied force and center-point deflection or devices used for measuring linear dimensions shall be accurate
sample strain versus time for the specified crosshead rate. and precise to at least one-half the smallest unit to which the
Either analog chart recorders or digital data acquisition systems individual dimension is required to be measured. For the
may be used for this purpose, although a digital record is purposes of this test method, measure the cross-sectional
recommended for ease of subsequent data analysis. Ideally, an dimensions to within 0.02 mm with a measuring device with an
analog chart recorder or plotter should be used in conjunction accuracy of 0.01 mm.
C1341 − 13 (2023)
7.9 Calibration—Calibration of equipment shall be pro- minimum, to one weave unit cell width (unit cell count = 1
vided by the supplier, with traceability maintained to the across the width). Two or more weave unit cells are preferred
National Institute of Standards and Technology (NIST). Re- across the width.
calibration shall be performed with a NIST-traceable standard
NOTE 3—The weave unit cell is the smallest section of weave
on all equipment on a six-month interval or whenever accuracy
architecture required to repeat the textile pattern (see Guide D6856/
is in doubt. D6856M). The fiber architecture of a textile composite, which consists of
interlacing yarns, can lead to inhomogeneity of the local displacement
fields within the weave unit cell. The gage dimensions should be large
8. Hazards
enough so that any inhomogenities within the weave unit cell are averaged
8.1 During the conduct of this test method, the possibility of
out across the gage. This is a particular concern for test specimens where
the fabric architecture has large, heavy tows and/or open weaves with
flying fragments of broken test specimens may be high. The
large unit cell dimensions and the gage sections are narrow and/or short.
brittle nature of advanced ceramics and the release of strain
NOTE 4—Deviations from the recommended unit cell counts may be
energy contribute to the potential release of uncontrolled
necessary depending upon the particular geometry of the available
fragments upon fracture. The containment/retention of these
material. Such “small” gage sections should be noted in the test report and
fragments for later fractographic reconstruction and analysis is
used with adequate understanding and assessment of the possible effects
of weave unit cell count on the measured mechanical properties.
highly recommended.
9.1.5 Anisotropy in mechanical properties of composites is
8.2 Exposed fibers at the edges and faces of CFCC test
strongly affected by fiber architecture. Alignment of the long
specimens may present a hazard due to the sharpness and
axis of the flexure test specimen with a principal weave
brittleness of the ceramic fibers. Inform all individuals who
direction must be controlled and monitored. Measure the
handle these materials of potential hazards and the proper
alignment to an angular precision of 65°.
handling techniques.
9.2 Fabrication Method—The test specimens may be cut
9. Test Specimens
from sheets, plates, or molded shapes, or may be formed
directly to the required finished dimensions.
9.1 Selection of a specific test specimen geometry depends
on many factors: the geometry of available material, the
9.3 Finishing Method—Depending upon the application of
expected mechanical properties, the geometry of the final
the strength data, use one of the following test specimen
component, geometry limitations in the test equipment, and
finishing procedures: as-fabricated, application-matched,
cost factors.
customary, and standard. These finishing details are described
9.1.1 Test specimens must have a span-to-depth ratio (L/d)
in Annex A2. Regardless of the preparation procedure used,
that produces tensile or compressive failure in the outer fiber
sufficient details regarding the procedure shall be reported to
surfaces of the sample under the bending moment. If the L/d
allow replication.
ratio is too low, the sample may fail due to shear stress,
9.3.1 For a given set of test specimens cut from a sample
producing an invalid test. Three recommended L/d ratios are
panel, prepare and record a cutting diagram showing the
16:1, 32:1, and 40:1. Materials with lower shear strength
location and orientation of individual test specimens with
require higher L/d ratios. A 32:1 ratio is a recommended
respect to the starting panel geometry and the fiber/fabric
starting point for three-point testing (3). A 32:1 ratio is a
orientation.
recommended starting point for four-point testing (3). For
9.4 Dimensional Tolerances—The cross-sectional tolerance
CFCCs with very low interlaminar shear strengths (<3.5 MPa)
for cut/machined dimensions shall be 60.1 mm or 0.5 % of the
based on low matrix density or shear failure at interfaces, L/d
dimension, whichever is greater. Parallelism tolerances on
ratios of 60 may be necessary to prevent shear failures. If shear
cut/machined faces are 0.02 mm or 0.5 %, whichever is greater.
failures are observed during initial testing, a modified test
9.5 General Examination—The mechanical responses of
geometry with a higher L/d ratio (for example, 40:1 or 60:1)
CFCCs are strongly affected by geometry, porosity, and dis-
shall be used for subsequent tests.
continuities. Inspect and characterize each test specimen care-
9.1.2 Prepare the test specimens with dimensions deter-
fully for nonuniformity in major dimensions, warp, twist, and
mined from the appropriate tables (Table 1 for three-point
1 bowing porosity (volume % and size distribution), discontinui-
bending, Table 2 for four-point- ⁄4-point bending, and Table 3
ties such as delaminations, cracks, etc., and surface roughness
for four-point- ⁄3-point bending). Determine the minimum
on as-prepared and finished surfaces. Nondestructive evalua-
dimensions for specimen width and length and the support span
tion (ultrasonics, thermal imaging, computerized tomography,
based on the test specimen thickness and the desired L/d ratio.
etc.) may be used to assess internal morphology
9.1.3 Test specimen width shall not exceed one-fourth of the
(delaminations, porosity concentrations, etc.) in the composite.
support span for specimens greater than 3 mm in depth. The
Record these observations/measurements and the results of any
test specimen shall be long enough to allow for overhang past
nondestructive evaluations and include them in the final report.
the outer supports of at least 5 % of the support span, but in no
case less than 5 mm on each end. Overhang shall be sufficient 9.6 Handling Precaution—Exercise care in the storage and
to minimize shear failures in the test specimen ends and to handling of finished test specimens to avoid the introduction of
prevent the test specimen from slipping through the supports at random and severe fracture sources. In addition, consider
large center-point deflections. pre-test storage of test specimens in controlled environments or
9.1.4 When testing woven fabric laminate composites, it is desiccators to avoid unquantifiable environmental degradation
recommended that the test specimen width (b) is equal, at a of test specimens prior to testing.
C1341 − 13 (2023)
9.7 Number of Test Specimens—A minimum of ten test ening mechanisms under controlled fracture of the CFCC,
specimens is required for the purposes of estimating a mean. A displacement or strain control may be preferred. However, for
greater number of test specimens may be necessary if estimates sufficiently rapid test rates, differences in the fracture process
regarding the form of the strength distribution are required. If may not be apparent and any of these test control modes may
material cost or test specimen availability limits the number of
be appropriate.
tests to be conducted, fewer tests can be conducted to develop
10.3.2 Strain Rate—Strain is the independent variable in
an indication of material properties. The procedures outlined in
nonlinear mechanisms such as yielding. As such, strain rate is
Practice E122 should be used to estimate the number of tests
a method of controlling tests of deformation processes to avoid
needed for determining a mean with a specified precision.
runaway conditions. For the linear elastic region of CFCCs,
strain rate can be related to stress rate such that:
10. Procedure
ε˙ 5 dε/dt 5 σ˙ /E (1)
10.1 Test Specimen Dimensions—Determine the thickness
where:
and width of each test specimen to within 0.02 mm. Measure
−1
the test specimen at least three different cross-sectional planes
ε = the strain rate in the units of s ,
˙
in the stressed section (between the outer force application ε = the maximum strain in the outer fibers,
points). It is recommended that machined surfaces be measured t = time in units of s,
σ˙ = the maximum stress rate in the outer fibers in units of
either optically (for example, by an optical comparator) or
−1
MPa s , and
mechanically, using a flat, anvil-type micrometer. Measure
E = the elastic modulus of the CFCC in units of MPa.
rough or as-processed surfaces with a double-ball interface
micrometer with a ball radius of 4 mm. In all cases, the
Strain-controlled tests can be accomplished using a deflec-
resolution of the instrument shall meet the requirements
tometer contacting the center line of the inner support span of
specified in 7.8. Measure the test specimens with care to
the test specimen to produce the control signal. Strain rates on
prevent surface damage. Record and report the measured −6 −6 −1
the order of 500 × 10 to 5000 × 10 s are recommended
dimensions and locations of the measurements for use in the
to minimize environmental and force application rate effects
calculation of the flexure stress. For the three-point loading
when testing in ambient air. Alternately, strain rates shall be
geometry, use the dimensions at the center force application
selected to produce final fracture in 5 s to 10 s to minimize
point in the stress calculations. For four-point loading
environmental and force application rate effects. Elevated
geometries, use the average of the multiple measurements in
testing temperatures may enhance the environmental or force
the stress calculations.
application rate effects, or both. Minimize those effects by
10.2 In some cases it is desirable, but not required, to increasing the strain rate if the initial material evaluation shows
...