Designation: C1674 − 16Standard Test Method forFlexural Strength of Advanced Ceramics with EngineeredPorosity (Honeycomb Cellular Channels) at AmbientTemperatures1This standard is issued under the fixed designation C1674; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (´) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of the flexuralstrength (modulus of rupture in bending) at ambient conditionsof advanced ceramic structures with 2-dimensional honeycombchannel architectures.1.2 The test method is focused on engineered ceramiccomponents with longitudinal hollow channels, commonlycalled “honeycomb” channels. (See Fig. 1.) The componentsgenerally have 30 % or more porosity and the cross-sectionaldimensions of the honeycomb channels are on the order of1 mm or greater. Ceramics with these honeycomb structuresare used in a wide range of applications (catalytic conversionsupports (1),2high temperature filters (2, 3), combustionburner plates (4), energy absorption and damping (5), etc.).Thehoneycomb ceramics can be made in a range of ceramiccompositions—alumina, cordierite, zirconia, spinel, mullite,silicon carbide, silicon nitride, graphite, and carbon. Thecomponents are produced in a variety of geometries (blocks,plates, cylinders, rods, rings).1.3 The test method describes two test specimen geometriesfor determining the flexural strength (modulus of rupture) for aporous honeycomb ceramic test specimen (see Fig. 2):1.3.1 Test Method A—A4-point or 3-point bending test withuser-defined specimen geometries, and1.3.2 Test Method B—A4-point-1⁄4 point bending test with adefined rectangular specimen geometry (13 mm × 25 mm × 116 mm) and a 90 mm outer support span geometry suitable forcordierite and silicon carbide honeycombs with small cellsizes.1.4 The test specimens are stressed to failure and thebreaking force value, specimen and cell dimensions, andloading geometry data are used to calculate a nominal beamstrength, a wall fracture strength, and a honeycomb structurestrength.1.5 Test results are used for material and structuraldevelopment, product characterization, design data, qualitycontrol, and engineering/production specifications.1.6 The test method is meant for ceramic materials that arelinear-elastic to failure in tension. The test method is notapplicable to polymer or metallic porous structures that fail inan elastomeric or an elastic-ductile manner.1.7 The test method is defined for ambient testing tempera-tures. No directions are provided for testing at elevated orcryogenic temperatures.1.8 The values stated in SI units are to be regarded asstandard (IEEE/ASTM SI 10). English units are sparsely usedin this standard for product definitions and tool descriptions,per the cited references and common practice in the USautomotive industry.1.9 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3C373 Test Methods for Determination of Water Absorptionand Associated Properties by Vacuum Method for PressedCeramic Tiles and Glass Tiles and Boil Method forExtruded Ceramic Tiles and Non-tile Fired CeramicWhiteware ProductsC1145 Terminology of Advanced CeramicsC1161 Test Method for Flexural Strength of AdvancedCeramics at Ambient Temperature1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and is the direct responsibility of Subcommittee C28.04 onApplications.Current edition approved Dec. 15, 2016. Published January 2017. Originallyapproved in 2008. Last previous edition approved in 2011 as C1674 – 11. DOI:10.1520/C1674-16.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at

[email protected] For Annual Book of ASTMStandards volume information, refer to the standard’s Document Summary page onthe ASTM website.*A Summary of Changes section appears at the end of this standardCopyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1C1198 Test Method for Dynamic Young’s Modulus, ShearModulus, and Poisson’s Ratio for Advanced Ceramics bySonic ResonanceC1239 Practice for Reporting Uniaxial Strength Data andEstimating Weibull Distribution Parameters for AdvancedCeramicsC1259 Test Method for Dynamic Young’s Modulus, ShearModulus, and Poisson’s Ratio for Advanced Ceramics byImpulse Excitation of VibrationC1292 Test Method for Shear Strength of Continuous Fiber-Reinforced Advanced Ceramics at Ambient TemperaturesC1341 Test Method for Flexural Properties of ContinuousFiber-Reinforced Advanced Ceramic CompositesC1368 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress-Rate Strength Testing at Ambient TemperatureC1525 Test Method for Determination of Thermal ShockResistance for Advanced Ceramics by Water QuenchingC1576 Test Method for Determination of Slow CrackGrowth Parameters of Advanced Ceramics by ConstantStress Flexural Testing (Stress Rupture) at Ambient Tem-peratureD2344/D2344M Test Method for Short-Beam Strength ofPolymer Matrix Composite Materials andTheir LaminatesE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsIEEE/ASTM SI 10 Standard for Use of the InternationalSystem of Units (SI) (The Modern Metric System)3. Terminology3.1 The definitions of terms relating to flexure testingappearing in Terminology E6 apply to the terms used in thistest method. The definitions of terms relating to advancedceramics appearing in Terminology C1145 apply to the termsused in this test method. Pertinent definitions, as listed inTerminology C1145, Test Method C1161, and Terminology E6are shown in the following section with the appropriate sourcegiven in brackets. Additional terms used in conjunction withthis test method are also defined.3.2 Definitions:3.2.1 advanced ceramic, n—a highly engineered, high-performance, predominately nonmetallic, inorganic, ceramicmaterial having specific functional attributes. C11453.2.2 breaking force, [F],n—the force at which fractureoccurs in a test specimen. E63.2.2.1 Discussion—In this test method, fracture consists ofbreakage of the test bar into two or more pieces or a loss of atleast 50 % of the maximum force carrying capacity.3.2.3 cell pitch, (p), [L],n—the unit dimension/s for thecross-section of a cell in the honeycomb component. The cellpitch p is calculated by measuring the specimen dimension ofinterest, the cell count in that dimension, and a cell wallthickness, where p =(d–t)/n. (See Fig. 3.)3.2.3.1 Discussion—The cell pitch can be measured for bothFIG. 1 General Schematics of Typical Honeycomb Ceramic StructuresL = Outer Span Length (for Test Method A, L = User defined; for Test Method B, L =90mm)NOTE 1—4-Point-1⁄4 Loading for Test Methods A1 and B.NOTE 2—3-Point Loading for Test Method A2.FIG. 2 Flexure Loading ConfigurationsC1674 − 162the height and width of the cell; those two measurements willbe equal for a square cell geometry and uniform cell wallthickness and will be unequal for a rectangular cell geometry.3.2.4 cell wall thickness, (t), [L],n—the nominal thicknessof the walls that form the cell channels of the honeycombstructure. (See Fig. 3.)3.2.5 channel porosity, n—porosity in the porous ceramiccomponent that is defined by the large, open longitudinalhoneycomb channels. Channel porosity generally has cross-sectional dimensions on the order of 1 mm or greater.3.2.6 complete gage section, n—the portion of the specimenbetween the two outer bearings in four-point flexure andthree-point flexure fixtures.3.2.6.1 Discussion—In this standard, the complete 4-pointflexure gage section is twice the size of the inner gage section.Weibull statistical analysis only includes portions of thespecimen volume or surface which experience tensile stresses.3.2.7 engineered porosity, n—porosity in a component thatis deliberately produced and controlled for a specific functionand engineered performance. The porosity can be microporous(micron and submicron pores in the body of the ceramic) ormacroporous (millimeter and larger) cells and channels in theceramic. The porosity commonly has physical properties (vol-ume fraction, size, shape, structure, architecture, dimensions,etc.) that are produced by a controlled manufacturing process.The porosity in the component has a direct effect on theengineering properties and performance and often has to bemeasured for quality control and performance verification.3.2.8 four-point-1⁄4 point flexure, n—a configuration of flex-ural strength testing where a specimen is symmetrically loadedat two inner span locations that are situated one quarter of theoverall span inside the span of the outer two support bearings.(See Fig. 2.) C11613.2.9 fractional open frontal area, (OFA), [ND],n—a frac-tional ratio of the open frontal area of the honeycombarchitecture, calculated by dividing the total frontal area of theopen channels by the full frontal area of the full size specimen,as a whole.3.2.9.1 Discussion—The fractional open frontal area of thefull size specimen can be calculated from the shape anddimensions of the cells and the wall thickness between cells.(See 11.4 on calculations.)3.2.10 fully-articulating fixture, n—a flexure fixture de-signed to be used both with flat and parallel specimens andwith uneven or nonparallel specimens. The fixture allows fullindependent articulation, or pivoting, of all load and supportrollers about the specimen long axis to match the specimensurface. In addition, the upper or lower roller pairs are free topivot to distribute force evenly to the bearing cylinders oneither side. (See Annex A1 for schematics and discussion.)C11613.2.11 honeycomb cell density, n—a characterization of thehoneycomb cell structure that lists the number of cells per unitarea and the nominal cell wall thickness. It is common practicein the automotive catalyst industry to use English units for thisterm, for example:100/17 density = 100 cells/in.2with a cell wall thickness of 0.017 in.200/12 density = 200 cells/in.2with a cell wall thickness of 0.012 in.3.2.12 honeycomb cellular architecture, n—an engineeredcomponent architecture in which long cylindrical cells ofdefined geometric cross-section form a porous structure withopen channels in one dimension and a nominal closed-cellarchitecture in the remaining two dimensions. The crosssectional geometry of the honeycomb cells can have a varietyof shapes—square, hexagonal, triangular, circular, etc. (SeeFig. 1.)3.2.12.1 Discussion—The cell walls in a honeycomb struc-ture may have controlled wall porosity levels, engineered forfiltering, separation effects, and mechanical strength.3.2.13 honeycomb structure strength, SHS, [FL–2],n—ameasure of the maximum strength in bending of a specifiedb = specimen widthd = specimen thicknesst = cell wall thicknessp = cell pitchn = linear cell count (height)m = linear cell count (width)FIG. 3 Schematic of Honeycomb Structure with Square Cells Showing Geometric TermsC1674 − 163honeycomb test specimen, calculated by considering the com-plex moment of inertia of the test specimen with its channelpore structure and adjusting for the open frontal area of thecellular specimen. (See Section 11 and Appendix X1.)3.2.13.1 Discussion—The honeycomb structure strengthgives a continuum strength that is more representative of thetrue continuum strength as compared to the nominal beamstrength SNB, particularly for specimens where the linear cellcount in the smallest cross sectional dimension is less than 15.3.2.13.2 Discussion—The honeycomb structure strengthmay be used to compare tests for specimens of different cellarchitectures and sizes and specimen dimensions. However, thecalculated honeycomb structure strength is not representativeof the failure stress in the outer fiber surface (the wall fracturestrength) of the test specimen.3.2.14 linear cell count, [ND],n—the integer number ofcells along a given cross-sectional dimension of a test speci-men. For the specimen width, the linear cell count is defined asm. For the specimen thickness dimension, the linear cell countis defined as n. (See Fig. 3.)3.2.15 modulus of elasticity, [FL–2] ,n—the ratio of stress tocorresponding strain below the proportional limit. E63.2.16 nominal beam strength, SNB, [FL–2],n—In honey-comb test specimens, a measure of the maximum strength inbending, calculated with the simple elastic beam equationsusing the overall specimen dimensions, disregarding thecellular/channel architecture, and making the simplifying as-sumption of a solid continuum in the bar. The nominal beamstrength is not necessarily representative of the true failurestress in the outer fiber face, because it does not take the effectof channel porosity on the moment of inertia into account. (SeeSection 11 and Appendix X1.)3.2.16.1 Discussion—The nominal beam strength is calcu-lated without consideration of the dimensions, geometry/shape,cell wall thickness, or linear cell count of the cellular channelarchitecture in the test specimen. The nominal beam strengthcan be used for material comparison and quality control forflexure test specimens of equal size, comparable cell geometry,and equivalent loading configuration.3.2.16.2 Discussion—For specimens where the minimumlinear cell count is less than 15, the nominal beam strengthshould not be used for design purposes or material propertycharacterization, because it is not necessarily an accurateapproximation of the true failure stress (material strength) inthe outer fiber face of the specimen.3.2.17 relative density (percent), n—a relative measurementof the density of a porous material, defined as the ratio(expressed as a percent) of the bulk density of the specimen tothe true/theoretical density of the material composition. Therelative density of the specimen is equal to 1 minu