1、Designation: C393/C393M 16Standard Test Method forCore Shear Properties of Sandwich Constructions by BeamFlexure1This standard is issued under the fixed designation C393/C393M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the ye
2、ar 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method covers de
3、termination of the core shearproperties of flat sandwich constructions subjected to flexure insuch a manner that the applied moments produce curvature ofthe sandwich facing planes. Permissible core material formsinclude those with continuous bonding surfaces (such as balsawood and foams) as well as
4、those with discontinuous bondingsurfaces (such as honeycomb).1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningv
5、alues from the two systems may result in non-conformancewith the standard.1.2.1 Within the text the inch-pound units are shown inbrackets.1.3 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
6、establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C273 Test Method for Shear Properties of Sandwich CoreMaterialsD883 Terminology Relating to PlasticsD3878 Terminology for Composite Ma
7、terialsD5229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsD7249/D7249M Test Method for Facing Properties of Sand-wich Constructions by Long Beam FlexureD7250/D7250M Practice for Determining Sandwich BeamFlexural and Shear Stif
8、fnessE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or ProcessE177 Practice for Use of the Terms Precision and Bias
9、 inASTM Test MethodsE456 Terminology Relating to Quality and Statistics3. Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites, as well as termsrelating to sandwich constructions. Terminology D883 definesterms relating to plastics. Terminology
10、 E6 defines termsrelating to mechanical testing. Terminology E456 and PracticeE177 define terms relating to statistics. In the event of aconflict between terms, Terminology D3878 shall have prece-dence over the other terminologies.3.2 Symbols: b = specimen widthc = core thicknessCV = coefficient of
11、variation statistic of a sample populationfor a given property (in percent)d = sandwich total thicknessDF,nom= effective sandwich flexural stiffnessEf= effective facing chord modulus = measuring strain in facingFu= facing ultimate strength (tensile or compressive)Fc= core compression allowable stren
12、gthFs= core shear allowable strengthFsult= core shear ultimate strengthFsyield= core shear yield strengthk = core shear strength factor to ensure core failureL = length of loading spanS = length of support spanlpad= length of loading padn = number of specimensP = applied force1This test method is un
13、der the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved April 1, 2016. Published April 2016. Originallyapproved in 1957. Last previous edition approved in 2011 as C393 111. DOI:10.1520/C
14、0393_C0393M-16.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor
15、Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1Pmax= maximum force carried by test specimen beforefailureFZftu= ultimate flatwise tensile strengthPmax= maximum force carried by test specimen beforefailureSn-1= standard deviation statistic of a sample population fora given proper
16、ty = facing stress or strengtht = facing thicknessx1= test result for an individual specimen from the samplepopulation for a given propertyx = mean or average (estimate of mean) of a sample popu-lation for a given property4. Summary of Test Method4.1 This test method consists of subjecting a beam of
17、sandwich construction to a bending moment normal to theplane of the sandwich. Force versus deflection measurementsare recorded.4.2 The only acceptable failure modes are core shear orcore-to-facing bond. Failure of the sandwich facing precedingfailure of the core or core-to-facing bond is not an acce
18、ptablefailure mode. Use Test Method D7249/D7249M to determinefacing strength.5. Significance and Use5.1 Flexure tests on flat sandwich construction may beconducted to determine the sandwich flexural stiffness, the coreshear strength and shear modulus, or the facings compressiveand tensile strengths.
19、 Tests to evaluate core shear strength mayalso be used to evaluate core-to-facing bonds.5.2 This test method is limited to obtaining the core shearstrength or core-to-facing shear strength and the stiffness of thesandwich beam, and to obtaining load-deflection data for use incalculating sandwich bea
20、m flexural and shear stiffness usingPractice D7250/D7250M.NOTE 1Core shear strength and shear modulus are best determined inaccordance with Test Method C273 provided bare core material isavailable.5.3 Facing strength is best determined in accordance withTest Method D7249/D7249M.5.4 Practice D7250/D7
21、250M covers the determination ofsandwich flexural and shear stiffness and core shear modulususing calculations involving measured deflections of sandwichflexure specimens.5.5 This test method can be used to produce core shearstrength and core-to-facing shear strength data for structuraldesign allowa
22、bles, material specifications, and research anddevelopment applications; it may also be used as a qualitycontrol test for bonded sandwich panels.5.6 Factors that influence the shear strength and shalltherefore be reported include the following: facing material,core material, adhesive material, metho
23、ds of materialfabrication, core geometry (cell size), core density, adhesivethickness, specimen geometry, specimen preparation, specimenconditioning, environment of testing, specimen alignment,loading procedure, speed of testing, and adhesive void content.Further, core-to-facing strength may be diff
24、erent betweenprecured/bonded and co-cured facings in sandwich panels withthe same core and facing material.NOTE 2Concentrated loads on beams with thin facings and lowdensity cores can produce results that are difficult to interpret, especiallyclose to the failure point. Wider load pads with rubber p
25、ads may assist indistributing the loads.6. Interferences6.1 Material and Specimen PreparationPoor material fab-rication practices and damage induced by improper specimenmachining are known causes of high data scatter in compositesand sandwich structures in general. A specific material factorthat aff
26、ects sandwich cores is variability in core density.Important aspects of sandwich core specimen preparation thatcontribute to data scatter include the existence of joints, voidsor other core discontinuities, out-of-plane curvature, and sur-face roughness.6.2 GeometrySpecific geometric factors that af
27、fect coreshear strength include core orthotropy (that is, ribbon versustransverse direction for honeycomb core materials) and corecell geometry.6.3 EnvironmentResults are affected by the environmentalconditions under which specimens are conditioned, as well asthe conditions under which the tests are
28、 conducted. Specimenstested in various environments can exhibit significant differ-ences in both strength behavior and failure mode. Criticalenvironments must be assessed independently for each specificcombination of core material, facing material, and core-to-facing interfacial adhesive (if used) t
29、hat is tested.6.4 Core MaterialIf the core material has insufficientshear or compressive strength, it is possible that the core maylocally crush at or near the loading points, thereby resulting infacing failure due to local stresses. In other cases, facing failurecan cause local core crushing. When
30、there is both facing andcore failure in the vicinity of one of the loading points it can bedifficult to determine the failure sequence in a post-morteminspection of the specimen as the failed specimens look verysimilar for both sequences. For some core materials, the shearstrength is a function of t
31、he direction that the core is orientedrelative to the length of the specimen.7. Apparatus7.1 Micrometers and CalipersA micrometer with a 4 to 7mm 0.16 to 0.28 in. nominal diameter ball-interface or a flatanvil interface shall be used to measure the specimen thick-ness. A ball interface is recommende
32、d for thickness measure-ments when facings are bonded to the core and at least onesurface is irregular (e.g., the bag-side of a thin facing laminatethat is neither smooth nor flat). A micrometer or caliper with aflat anvil interface is recommended for thickness measure-ments when facings are bonded
33、to the core and both surfacesare smooth (e.g., tooled surfaces).Amicrometer or caliper witha flat anvil interface shall be used for measuring length andwidth, as well as the specimen thickness when no facings arepresent. The use of alternative measurement devices is permit-ted if specified (or agree
34、d to) by the test requestor and reportedby the testing laboratory. The accuracy of the instruments shallC393/C393M 162be suitable for reading to within 1 %of the sample dimensions.For typical specimen geometries, an instrument with an accu-racy of 6 0.025 mm 60.001 in. is adequate for the length,wid
35、th, and thickness measurements.NOTE 3The accuracies given above are based on achieving measure-ments that are within 1 % of the sample length, width and thickness.7.2 Loading FixturesThe loading fixture shall consist ofeither a 3-point or 4-point loading configuration with twosupport bars that span
36、the specimen width located below thespecimen, and one or two loading bars that span the specimenwidth located on the top of the specimen (Fig. 1), The forceshall be applied vertically through the loading bar(s), with thesupport bars fixed in place in the test machine.7.2.1 Standard ConfigurationThe
37、standard loading fixtureshall be a 3-point configuration and shall have the centerlinesof the support bars separated by a distance of 150 mm 6.0 in.7.2.2 Non-Standard ConfigurationsAll other loading fix-ture configurations are considered non-standard, and details ofthe fixture geometry shall be docu
38、mented in the test report. Fig.3 shows a typical 4-point short beam test fixture. Non-standard3- and 4-point loading configurations have been retained withinthis standard (a) for historical continuity with previous ver-sions of Test Method C393, (b) because some sandwich paneldesigns require the use
39、 of non-standard loading configurationsto achieve core or bond failure modes, and (c) load-deflectiondata from non-standard configurations may be used withPractice D7250/D7250M to obtain sandwich beam flexural andshear stiffnesses.7.2.3 Support and Loading BarsThe bars shall be de-signed to allow fr
40、ee rotation of the specimen at the loading andsupport points. The bars shall have sufficient stiffness to avoidsignificant deflection of the bars under load; any obviousbowing of the bars or any gaps occurring between the bars andthe test specimen during loading shall be considered significantdeflec
41、tion. The recommended configuration has a 25 mm 1.0in. wide flat steel loading block to contact the specimen(through rubber pressure pads) and is loaded via either acylindrical pivot or a V-shaped bar riding in a V-groove in thetop of the flat-bottomed steel loading pad. The tips of theV-shaped load
42、ing bars shall have a minimum radius of 3 mm0.12 in. The V-groove in the loading pad shall have a radiuslarger than the loading bar tip and the angular opening of thegroove shall be such that the sides of the loading bars do notcontact the sides of the V-groove during the test. Loading barsconsistin
43、g of 25 mm 1.0 in. diameter steel cylinders may alsobe used, but there is a greater risk of local specimen crushingwith cylindrical bars. Also, the load and support span lengthstend to increase as the specimen deflects when cylindricalloading bars without V-grooved loading pads are used (forexample,
44、 rolling supports).7.2.4 Pressure PadsRubber pressure pads having a ShoreA durometer of approximately 60, a nominal width of 25 mm1.0 in., a nominal thickness of 3 mm 0.125 in. and spanningthe full width of the specimen shall be used between theloading bars and specimen to prevent local damage to th
45、efacings.(a) 3-Point Loading (Standard Configuration)(b) 4-Point Loading (Non-Standard Configuration)Configuration Support Span (S) Load Span (L)Standard 3-Point (Mid-Span) 150 mm 6.0 in. 0.0Non-Standard 4-Point (Quarter-Span) SS/24-Point (Third-Span) /3FIG. 1 Loading Configurations FIG. 2 Sandwich
46、Panel Thickness DimensionsC393/C393M 1637.3 Testing MachineThe testing machine shall be in ac-cordance with Practices E4 and shall satisfy the followingrequirements:7.3.1 Testing Machine ConfigurationThe testing machineshall have both an essentially stationary head and a movablehead.7.3.2 Drive Mech
47、anismThe testing machine drive mecha-nism shall be capable of imparting to the movable head acontrolled velocity with respect to the stationary head. Thevelocity of the movable head shall be capable of beingregulated in accordance with 11.4.7.3.3 Force IndicatorThe testing machine force-sensingdevic
48、e shall be capable of indicating the total force beingcarried by the test specimen. This device shall be essentiallyfree from inertia lag at the specified rate of testing and shallindicate the force with an accuracy over the force range(s) ofinterest of within 61 % of the indicated value.7.4 Deflect
49、ometerThe deflection of the specimen shall bemeasured in the center of the support span by a properlycalibrated device having an accuracy of 61 % or better.NOTE 4The use of crosshead or actuator displacement for the beammid-span deflection produces inaccurate results, particularly for 4-pointloading configurations; the direct measurement of the deflection of themid-span of the beam must be made by a suitable instrument.7.5 Conditioning ChamberWhen conditioning materialsat non-laboratory environments, a temperature/vapor-levelcontrolled e
