1、Designation: C 393/C 393M 06Standard Test Method forCore Shear Properties of Sandwich Constructions by BeamFlexure1This standard is issued under the fixed designation C 393/C 393M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, th
2、e year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the 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. Within the text theinch-pound units are shown in brackets. The values stated ineach system are not exact equivalents; therefore, each sy
5、stemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.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 establish
6、appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 273 Test Method for Shear Properties of Sandwich CoreMaterialsC 274 Terminology of Structural Sandwich ConstructionsD 883 Terminology Relating
7、 to PlasticsD 3878 Terminology for Composite MaterialsD 5229/D 5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsD 7249/D 7249M Test Method for Facing Properties ofSandwich Constructions by Long Beam FlexureD 7250/D 7250M Practice
8、for Determining SandwichBeam Flexural and Shear StiffnessE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 122 Practice for Calculating Sample Size to Estimate,With a Specified Tolerable Error, the Average for aCharacteristic of a Lot o
9、r ProcessE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE 1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced
10、 Composite Materials in Databases3. Terminology3.1 DefinitionsTerminology D 3878 defines terms relatingto high-modulus fibers and their composites. TerminologyC 274 defines terms relating to structural sandwich construc-tions. Terminology D 883 defines terms relating to plastics.Terminology E6define
11、s terms relating to mechanical testing.Terminology E 456 and Practice E 177 define terms relating tostatistics. In the event of a conflict between terms, TerminologyD 3878 shall have precedence over the other terminologies.3.2 Symbols:b = specimen widthc = core thicknessCV = coefficient of variation
12、 statistic of a sample populationfor a given property (in percent)d = sandwich total thicknessDF,nom= effective sandwich flexural stiffnessEf= effective facing chord moduluse = measuring strain in facingFu= facing ultimate strength (tensile or compressive)Fc= core compression allowable strengthFs= c
13、ore shear allowable strengthFsult= core shear ultimate strengthFsyield= core shear yield strengthk = core shear strength factor to ensure core failureL = length of loading span1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of
14、Subcommittee D30.09 onSandwich Construction.Current edition approved Sept. 1, 2006. Published October 2006. Originallyapproved in 1957. Last previous edition approved in 2000 as C 393 00.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at servicea
15、stm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.S = length of support spanlpad= length of loading padn = nu
16、mber of specimensP = applied forcePmax= 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 propertys = facing stress or strengtht =
17、 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 ofsandwich construction to a bendin
18、g 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 acceptablefailure mode. Use Test Meth
19、od D 7249 to determine facingstrength.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. Tests to evaluate core shear strength
20、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 beam flexural and shear stiffness usingPra
21、ctice D 7250.NOTE 1Core shear strength and shear modulus are best determined inaccordance with Test Method C 273 provided bare core material isavailable.5.3 Facing strength is best determined in accordance withTest Method D 7249.5.4 Practice D 7250 covers the determination of sandwichflexural and sh
22、ear stiffness and core shear modulus usingcalculations involving measured deflections of sandwich flex-ure specimens.5.5 This test method can be used to produce core shearstrength and core-to-facing shear strength data for structuraldesign allowables, material specifications, and research anddevelop
23、ment 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, methods of material fabrica-tion, core geometry (cell size)
24、, core density, adhesive thick-ness, 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 different betweenprecured/bonded and co-cured facings
25、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 pads may assist indistributing the loads.6. Interfe
26、rences6.1 Material and Specimen PreparationPoor materialfabrication practices and damage induced by improper speci-men machining are known causes of high data scatter incomposites and sandwich structures in general. A specificmaterial factor that affects sandwich cores is variability in coredensity.
27、 Important aspects of sandwich core specimen prepa-ration that contribute to data scatter include the existence ofjoints, voids or other core discontinuities, out-of-plane curva-ture, and surface roughness.6.2 GeometrySpecific geometric factors that affect coreshear strength include core orthotropy
28、(that is, ribbon versustransverse direction for honeycomb core materials) and corecell geometry.6.3 EnvironmentResults are affected by the environmen-tal conditions under which specimens are conditioned, as wellas the conditions under which the tests are conducted. Speci-mens tested in various envir
29、onments can exhibit significantdifferences 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) that is tested.6.4 Core MaterialIf the core mat
30、erial 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 there is both facing andcore failure in the vi
31、cinity 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 the direction that the core is orientedrelative
32、 to the length of the specimen.7. Apparatus7.1 Micrometers and CalipersA micrometer having a flatanvil interface, or a caliper of suitable size, shall be used. Theinstrument(s) shall have an accuracy of 625 mm 60.001 in.for thickness measurement, and an accuracy of 6250 mm60.010 in. for length and w
33、idth measurement.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 the specimen w
34、idth located below thespecimen, and one or two loading bars that span the specimenwidth located on the top of the specimen (Fig. 1), The forceC 393/C 393M 062shall be applied vertically through the loading bar(s), with thesupport bars fixed in place in the test machine.7.2.1 Standard ConfigurationTh
35、e 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 do
36、cumented 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 C 393, (b) because some sandwich paneldesigns require the
37、use of non-standard loading configurationsto achieve core or bond failure modes, and (c) load-deflectiondata from non-standard configurations may be used withPractice D 7250 to obtain sandwich beam flexural and shearstiffnesses.7.2.3 Support and Loading BarsThe bars shall be de-signed to allow free
38、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 significantdeflectio
39、n. 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 loading
40、 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 the(a) 3-Point Loading (Standard Configuration)(b) 4-Point Loading (Non-Standard Configuration)Configuration Support Span (S) Load Span (L)S
41、tandard 3-Point (Mid-Span) 150 mm 6.0 in. 0.0Non-Standard 4-Point (Quarter-Span) SS/24-Point (Third-Span) /3FIG. 1 Loading ConfigurationsFIG. 2 Sandwich Panel Thickness DimensionsFIG. 3 Short Beam4-Point (Third-Span) Short BeamLoading ConfigurationC 393/C 393M 063groove shall be such that the sides
42、of the loading bars do notcontact the sides of the V-groove during the test. Loading barsconsisting 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 s
43、pecimen deflects when cylindricalloading bars without V-grooved loading pads are used (forexample, 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 widt
44、h of the specimen shall be used between theloading bars and specimen to prevent local damage to thefacings.7.3 Testing MachineThe testing machine shall be inaccordance with Practices E4and shall satisfy the followingrequirements:7.3.1 Testing Machine ConfigurationThe testing machineshall have both a
45、n essentially stationary head and a movablehead.7.3.2 Drive MechanismThe 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
46、11.4.7.3.3 Force IndicatorThe testing machine force-sensingdevice 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
47、(s) ofinterest of within 61 % of the indicated value.7.4 Deflectometer (LVDT)The deflection of the specimenshall be measured in the center of the support span by aproperly calibrated device having an accuracy of 61% orbetter.NOTE 4The use of crosshead or actuator displacement for the beammid-span de
48、flection 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-level
49、controlled environmental conditioning chamber is required thatshall be capable of maintaining the required temperature towithin 63C 65F and the required relative humidity levelto within 63 %. Chamber conditions shall be monitored eitheron an automated continuous basis or on a manual basis atregular intervals.7.6 Environmental Test ChamberAn environmental testchamber is required for test environments other than ambienttesting laboratory conditions. This chamber shall be capable ofmaintaining the gage section of the test specimen at ther
