1、Designation: C393/C393M 11Standard 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 Department of Defense.1. Scope1.1 This test method covers determi
3、nation 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 those
4、 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. Combiningvalues
5、 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 estab
6、lish 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 CoreMaterialsC274 Terminology of Structural Sandwich ConstructionsD883 Terminology Relati
7、ng to PlasticsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsD7249/D7249M Test Method for Facing Properties ofSandwich Constructions by Long Beam FlexureD7250/D7250M Practice for D
8、etermining Sandwich BeamFlexural and Shear StiffnessE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate,With Specified Precision, the Average for a Characteristicof a Lot or ProcessE177 P
9、ractice for Use of the Terms Precision and Bias inASTM Test MethodsE456 Terminology Relating to Quality and StatisticsE1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Material
10、s in Databases3. Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites. TerminologyC274 defines terms relating to structural sandwich construc-tions. Terminology D883 defines terms relating to plastics.Terminology E6 defines terms relating to m
11、echanical testing.Terminology E456 and Practice E177 define terms relating tostatistics. In the event of a conflict between terms, TerminologyD3878 shall have precedence over the other terminologies.3.2 Symbols:b = specimen widthc = core thicknessCV = coefficient of variation statistic of a sample p
12、opulationfor 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)1This test method is under the jurisdiction of ASTM Committee D30 onC
13、omposite Materials and is the direct responsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved Oct. 1, 2011. Published November 2011. Originallyapproved in 1957. Last previous edition approved in 2006 as C393 06. DOI:10.1520/C0393_C0393M-11.2For referenced ASTM standards
14、, 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19
15、428-2959, United States.Fc= core compression allowable strengthFs= 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 =
16、 number 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 strength
17、t = 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 ben
18、ding 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 M
19、ethod 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. Tests to evaluate core shear
20、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 beam flexural and shear stiffness
21、 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/D7250M covers the determination
22、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 allowables, material specifications,
23、 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, methods of material fabrica-tion, c
24、ore geometry (cell size), 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/bond
25、ed 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 pads may assist indistribut
26、ing the loads.6. Interferences6.1 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 var
27、iability in coredensity. 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
28、include core orthotropy (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
29、 tested in various environments 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
30、 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 there is both facing a
31、ndcore 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 the direction that the
32、core is orientedrelative 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.
33、010 in. for length and width measurement.NOTE 3The accuracies given above are based on achieving measure-ments that are within 1 % of the sample length, width and thickness.C393/C393M 1127.2 Loading FixturesThe loading fixture shall consist ofeither a 3-point or 4-point loading configuration with tw
34、osupport bars that span 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 St
35、andard ConfigurationThe 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 fixtur
36、e geometry shall be documented 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 pane
37、ldesigns require the use 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
38、be de-signed to allow free 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 cons
39、idered significantdeflection. 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 a(a) 3-Point Loading (Standard Configuration)(b) 4-Point Loading (Non-Standard Configuration)Configuration Suppo
40、rt 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 ConfigurationsFIG. 2 Sandwich Panel Thickness DimensionsFIG. 3 Short Beam4-Point (Third-Span) Short BeamLoading ConfigurationC393/C393M 113cylindrical
41、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 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 shal
42、l be such that the sides 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 lengths
43、tend to increase as the specimen 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.
44、and spanningthe full width 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 E4 and shall satisfy the followingrequirements:7.3.1 Testing Machine ConfigurationThe testin
45、g machineshall have both an 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 beingreg
46、ulated in accordance with 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 acc
47、uracy over the force range(s) ofinterest of within 61 % of the indicated value.7.4 DeflectometerThe 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 fo
48、r 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 te
49、mperature/vapor-levelcontrolled 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 th
