ASTM C1674-08
(Test Method)Standard Test Method for Flexural Strength of Advanced Ceramics with Engineered Porosity (Honeycomb Cellular Channels) at Ambient Temperatures
Standard Test Method for Flexural Strength of Advanced Ceramics with Engineered Porosity (Honeycomb Cellular Channels) at Ambient Temperatures
SIGNIFICANCE AND USE
This test method is used to determine the mechanical properties in flexure of engineered ceramic components with multiple longitudinal hollow channels, commonly described as “honeycomb” channel architectures. The components generally have 30 % or more porosity and the cross-sectional dimensions of the honeycomb channels are on the order of 1 millimeter or greater.
The experimental data and calculated strength values from this test method are used for material and structural development, product characterization, design data, quality control, and engineering/ production specifications.
Note 1—Flexure testing is the preferred method for determining the nominal “tensile fracture” strength of these components, as compared to a compression (crushing) test. A nominal tensile strength is required, because these materials commonly fail in tension under thermal gradient stresses. A true tensile test is difficult to perform on these honeycomb specimens because of gripping and alignment challenges.
The mechanical properties determined by this test method are both material and architecture dependent, because the mechanical response and strength of the porous test specimens are determined by a combination of inherent material properties and microstructure and the architecture of the channel porosity [porosity fraction/relative density, channel geometry (shape, dimensions, cell wall thickness, etc.), anisotropy and uniformity, etc.] in the specimen. Comparison of test data must consider both differences in material/composition properties as well as differences in channel porosity architecture between individual specimens and differences between and within specimen lots.
Test Method A is a user-defined specimen geometry with a choice of four-point or three-point flexure testing geometries. It is not possible to define a single fixed specimen geometry for flexure testing of honeycombs, because of the wide range of honeycomb architectures and cell sizes and considerations o...
SCOPE
1.1 This test method covers the determination of the flexural strength (modulus of rupture in bending) at ambient conditions of advanced ceramic structures with 2-dimensional honeycomb channel architectures.
1.2 The test method is focused on engineered ceramic components with longitudinal hollow channels, commonly called “honeycomb” channels. (See Fig. 1.) The components generally have 30 % or more porosity and the cross-sectional dimensions of the honeycomb channels are on the order of 1 millimeter or greater. Ceramics with these honeycomb structures are used in a wide range of applications (catalytic conversion supports (1), high temperature filters (2, 3), combustion burner plates (4), energy absorption and damping (5), etc.). The honeycomb ceramics can be made in a range of ceramic compositions—alumina, cordierite, zirconia, spinel, mullite, silicon carbide, silicon nitride, graphite, and carbon. The components are produced in a variety of geometries (blocks, plates, cylinders, rods, rings).
1.3 The test method describes two test specimen geometries for determining the flexural strength (modulus of rupture) for a porous honeycomb ceramic test specimen (see Fig. 2):
1.3.1 Test Method A—A 4-point or 3-point bending test with user-defined specimen geometries, and
1.3.2 Test Method B—A 4-point- ¼ point bending test with a defined rectangular specimen geometry (13 mm × 25 mm × > 116 mm) and a 90 mm outer support span geometry suitable for cordierite and silicon carbide honeycombs with small cell sizes.
1.4 The test specimens are stressed to failure and the breaking force value, specimen and cell dimensions, and loading geometry data are used to calculate a nominal beam strength, a wall fracture strength, and a honeycomb structure strength.
1.5 Test results are used for material and structural development, product characterization, design data, quality control, and engineering/production specifications.
1.6 T...
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: C1674 – 08
Standard Test Method for
Flexural Strength of Advanced Ceramics with Engineered
Porosity (Honeycomb Cellular Channels) at Ambient
Temperatures
This standard is issued under the fixed designation C1674; 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 1.5 Test results are used for material and structural devel-
opment, product characterization, design data, quality control,
1.1 Thistestmethodcoversthedeterminationoftheflexural
and engineering/production specifications.
strength (modulus of rupture in bending) at ambient conditions
1.6 The test method is meant for ceramic materials that are
ofadvancedceramicstructureswith2-dimensionalhoneycomb
linear-elastic to failure in tension. The test method is not
channel architectures.
applicable to polymer or metallic porous structures that fail in
1.2 The test method is focused on engineered ceramic
an elastomeric or an elastic-ductile manner.
components with longitudinal hollow channels, commonly
1.7 The test method is defined for ambient testing tempera-
called “honeycomb” channels. (See Fig. 1.) The components
tures. No directions are provided for testing at elevated or
generally have 30 % or more porosity and the cross-sectional
cryogenic temperatures.
dimensions of the honeycomb channels are on the order of 1
1.8 The values stated in SI units are to be regarded as
millimeter or greater. Ceramics with these honeycomb struc-
standard (IEEE/ASTM SI 10). English units are sparsely used
tures are used in a wide range of applications (catalytic
in this standard for product definitions and tool descriptions,
conversion supports (1), high temperature filters (2, 3),
per the cited references and common practice in the US
combustion burner plates (4), energy absorption and damping
automotive industry.
(5), etc.). The honeycomb ceramics can be made in a range of
1.9 This standard does not purport to address all of the
ceramic compositions—alumina, cordierite, zirconia, spinel,
safety concerns, if any, associated with its use. It is the
mullite, silicon carbide, silicon nitride, graphite, and carbon.
responsibility of the user of this standard to establish appro-
The components are produced in a variety of geometries
priate safety and health practices and determine the applica-
(blocks, plates, cylinders, rods, rings).
bility of regulatory limitations prior to use.
1.3 The test method describes two test specimen geometries
for determining the flexural strength (modulus of rupture) for a
2. Referenced Documents
porous honeycomb ceramic test specimen (see Fig. 2):
2.1 ASTM Standards:
1.3.1 Test Method A—A4-pointor3-pointbendingtestwith
C373 Test Method for Water Absorption, Bulk Density,
user-defined specimen geometries, and
Apparent Porosity, andApparent Specific Gravity of Fired
1.3.2 Test Method B—A 4-point- ⁄4 point bending test with
Whiteware Products
a defined rectangular specimen geometry (13 mm 3 25 mm 3
C1145 Terminology of Advanced Ceramics
> 116 mm) and a 90 mm outer support span geometry suitable
C1161 Test Method for Flexural Strength of Advanced
for cordierite and silicon carbide honeycombs with small cell
Ceramics at Ambient Temperature
sizes.
C1198 Test Method for Dynamic Young’s Modulus, Shear
1.4 The test specimens are stressed to failure and the
Modulus, and Poisson’s Ratio for Advanced Ceramics by
breaking force value, specimen and cell dimensions, and
Sonic Resonance
loading geometry data are used to calculate a nominal beam
C1239 Practice for Reporting Uniaxial Strength Data and
strength, a wall fracture strength, and a honeycomb structure
Estimating Weibull Distribution Parameters for Advanced
strength.
Ceramics
C1259 Test Method for Dynamic Young’s Modulus, Shear
Modulus, and Poisson’s Ratio for Advanced Ceramics by
This test method is under the jurisdiction of ASTM Committee C28 on
Advanced Ceramics and is the direct responsibility of Subcommittee C28.04 on
Applications.
Current edition approved June 1, 2008. Published July 2008. DOI: 10.1520/ For referenced ASTM standards, visit the ASTM website, www.astm.org, or
C1674-08. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
The boldface numbers in parentheses refer to the list of references at the end of Standards volume information, refer to the standard’s Document Summary page on
this standard. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C1674 – 08
FIG. 1 General Schematics of Typical Honeycomb Ceramic Structures
L = Outer Span Length (for Test Method A, L = User defined; for Test Method B, L=90mm)
NOTE 1—4-Point- ⁄4 Loading for Test Methods A1 and B.
NOTE 2—3-Point Loading for Test Method A2.
FIG. 2 Flexure Loading Configurations
Impulse Excitation of Vibration are shown in the following section with the appropriate source
C1292 TestMethodforShearStrengthofContinuousFiber- given in brackets. Additional terms used in conjunction with
Reinforced Advanced Ceramics at Ambient Temperatures this test method are also defined.
C1341 Test Method for Flexural Properties of Continuous
3.1.1 advanced ceramic, n—a highly engineered, high-
Fiber-Reinforced Advanced Ceramic Composites
performance, predominately nonmetallic, inorganic, ceramic
C1368 Test Method for Determination of Slow Crack
material having specific functional attributes. C1145
Growth Parameters of Advanced Ceramics by Constant
3.1.2 breaking force, [F], n—the force at which fracture
Stress-Rate Flexural Testing at Ambient Temperature
occurs in a test specimen. E6
C1525 Test Method for Determination of Thermal Shock
3.1.2.1 Discussion—In this test method, fracture consists of
Resistance for Advanced Ceramics by Water Quenching
breakage of the test bar into two or more pieces or a loss of at
C1576 Test Method for Determination of Slow Crack
least 50 % of the maximum force carrying capacity.
Growth Parameters of Advanced Ceramics by Constant
3.1.3 cell pitch, (p), [L], n—the unit dimension/s for the
Stress Flexural Testing (Stress Rupture) at Ambient Tem-
cross-section of a cell in the honeycomb component. The cell
perature
pitch p is calculated by measuring the specimen dimension of
D2344/D2344M Test Method for Short-Beam Strength of
interest, the cell count in that dimension, and a cell wall
Polymer Matrix Composite Materials andTheir Laminates
thickness, where p=(d–t )/n. (See Fig. 3.)
E4 Practices for Force Verification of Testing Machines
3.1.3.1 Discussion—The cell pitch can be measured for
E6 TerminologyRelatingtoMethodsofMechanicalTesting
both the height and width of the cell; those two measurements
E337 Test Method for Measuring Humidity with a Psy-
will be equal for a square cell geometry and uniform cell wall
chrometer (the Measurement of Wet- and Dry-Bulb Tem-
thickness and will be unequal for a rectangular cell geometry.
peratures)
3.1.4 cell wall thickness, (t), [L], n—the nominal thickness
IEEE/ASTM SI 10 Standard for Use of the International
of the walls that form the cell channels of the honeycomb
System of Units (SI) (The Modern Metric System)
structure. (See Fig. 3.)
3. Terminology
3.1.5 channel porosity, n—porosity in the porous ceramic
component that is defined by the large, open longitudinal
3.1 The definitions of terms relating to flexure testing
honeycomb channels. Channel porosity generally has cross-
appearing in Terminology E6 apply to the terms used in this
sectional dimensions on the order of 1 millimeter or greater.
test method. The definitions of terms relating to advanced
ceramics appearing in Terminology C1145 apply to the terms 3.1.6 complete gage section, n—theportionofthespecimen
used in this test method. Pertinent definitions, as listed in between the two outer bearings in four-point flexure and
Terminology C1145, Test Method C1161, and Terminology E6 three-point flexure fixtures.
C1674 – 08
b = specimen width
d = specimen thickness
t = cell wall thickness
p = cell pitch
n = linear cell count (height)
m = linear cell count (width)
FIG. 3 Schematic of Honeycomb Structure with Square Cells Showing Geometric Terms
3.1.6.1 Discussion—In this standard, the complete 4-point either side. (See Annex A1 for schematics and discussion.)
flexure gage section is twice the size of the inner gage section. C1161
Weibull statistical analysis only includes portions of the
3.1.11 honeycomb cell density, n—a characterization of the
specimen volume or surface which experience tensile stresses.
honeycomb cell structure that lists the number of cells per unit
3.1.7 engineered porosity, n—porosity in a component that
area and the nominal cell wall thickness. It is common practice
is deliberately produced and controlled for a specific function
in the automotive catalyst industry to use English units for this
and engineered performance. The porosity can be microporous
term, for example:
(micron and submicron pores in the body of the ceramic) or 2
100/17 density = 100 cells/in. with a cell wall thickness of 0.017 in.
macroporous (millimeter and larger) cells and channels in the 200/12 density = 200 cells/in. with a cell wall thickness of 0.012 in.
ceramic. The porosity commonly has physical properties (vol-
3.1.12 honeycomb cellular architecture, n—an engineered
ume fraction, size, shape, structure, architecture, dimensions,
component architecture in which long cylindrical cells of
etc.) that are produced by a controlled manufacturing process.
defined geometric cross-section form a porous structure with
The porosity in the component has a direct effect on the
open channels in one dimension and a nominal closed-cell
engineering properties and performance and often has to be
architecture in the remaining two dimensions. The cross
measured for quality control and performance verification.
sectional geometry of the honeycomb cells can have a variety
3.1.8 four-point- ⁄4 point flexure, n—a configuration of flex-
of shapes—square, hexagonal, triangular, circular, etc. (See
ural strength testing where a specimen is symmetrically loaded
Fig. 1.)
at two inner span locations that are situated one quarter of the
3.1.12.1 Discussion—The cell walls in a honeycomb struc-
overall span inside the span of the outer two support bearings.
ture may have controlled wall porosity levels, engineered for
(See Fig. 2.) C1161
filtering, separation effects, and mechanical strength.
3.1.9 fractional open frontal area, (OFA), [ND], n—a frac-
-2
3.1.13 honeycomb structure strength, S , [FL ], n—a
tional ratio of the open frontal area of the honeycomb archi- HS
measure of the maximum strength in bending of a specified
tecture, calculated by dividing the total frontal area of the open
honeycomb test specimen, calculated by considering the com-
channels by the full frontal area of the full size specimen, as a
plex moment of inertia of the test specimen with its channel
whole.
pore structure and adjusting for the open frontal area of the
3.1.9.1 Discussion—The fractional open frontal area of the
cellular specimen. (See Section 11 and Appendix X1.)
full size specimen can be calculated from the shape and
3.1.13.1 Discussion—The honeycomb structure strength
dimensions of the cells and the wall thickness between cells.
gives a continuum strength that is more representative of the
(See section 11.4 on Calculations.)
true continuum strength as compared to the nominal beam
3.1.10 fully-articulating fixture, n—a flexure fixture de-
strength S , particularly for specimens where the linear cell
signed to be used both with flat and parallel specimens and NB
count in the smallest cross sectional dimension is less than 15.
with uneven or nonparallel specimens. The fixture allows full
independent articulation, or pivoting, of all load and support 3.1.13.2 Discussion—The honeycomb structure strength
rollers about the specimen long axis to match the specimen may be used to compare tests for specimens of different cell
surface. In addition, the upper or lower roller pairs are free to architecturesandsizesandspecimendimensions.However,the
pivot to distribute force evenly to the bearing cylinders on calculated honeycomb structure strength is not representative
C1674 – 08
of the failure stress in the outer fiber surface (the wall fracture 3.1.21 wall porosity, n—porosity found in the cell walls of
strength) of the test specimen. the ceramic component, distinct from the open channel poros-
ity. Wall porosity can exist in the ceramic walls in the form of
3.1.14 linear cell count, [ND], n—the integer number of
closed and open pores, cracks, and interconnected microchan-
cells along a given cross-sectional dimension of a test speci-
nels, and it can have a wide range of dimensions (from 10
men. For the specimen width, the linear cell count is defined as
nanometers to 100 micrometers), depending on the ceramic
m. For the specimen thickness dimension, the linear cell count
microstructure and fabrication method.
is defined as n. (See Fig. 3.)
-2
3.1.15 modulus of elasticity, [FL ], n—the ratio of stress to
4. Summary of Test Method
corresponding strain below the proportional limit. E6
-2
4.1 Atestspecimenwithahoneycombcellularstructureand
3.1.16 nominal beam strength, S , [FL ], n—In honey-
NB
a rectangular cross section is tested as a beam in flexure at
comb test specimens, a measure of the maximum strength in
ambient temperature in one of the following geometries:
bending, calculated with the simple elastic beam equations
4.1.1 Test Method A1 (4-Point Loading)—The test speci-
using the overall specimen dimensions, disregarding the
menwithauser-defined(see9.2)rectangulargeometryrestson
cellular/channel architecture, and making the simplifying as-
two supports and is loaded at two points (by means of two
sumption of a solid continuum in the bar. The nominal beam
loading rollers), each an equal distance from the adjacent
strength is not necessarily representative of the true failure
support point. The inner loading points are positioned one
stress in the outer fiber face, because it does not take the effect
quarter of the overall span away from the outer two support
ofchannelporosityonthemomentofinertiaintoaccount.(See
bearings. The distance between the loading rollers (the inner
Section 11 and Appendix X1.)
gage span) is one half of the complete gage (outer support)
3.1.16.1 Discussion—The nominal beam strength is calcu-
span. (See Fig. 2 and section 5.4.)
latedwithoutconsiderationofthedimensio
...
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