1、Designation: D7249/D7249M 161D7249/D7249M 18Standard Test Method forFacingFacesheet Properties of Sandwich Constructions byLong Beam Flexure1This standard is issued under the fixed designation D7249/D7249M; the number immediately following the designation indicates theyear of original adoption or, i
2、n the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1 NOTEEquation 4 was corrected editorially in April 2017.1. Scope1.1 This test method covers d
3、etermination of facingfacesheet properties of flat sandwich constructions subjected to flexure insuch a manner that the applied moments produce curvature of the sandwich facingfacesheet planes and result in compressive andtensile forces in the facings.facesheets. Permissible core material forms incl
4、ude those with continuous bonding surfaces (such asbalsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb).1.2 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact e
5、quivalents; therefore, each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.2.1 Within the text, the inch-pound units are shown in brackets.1.3 This standard does not purport to address all of the safety concerns
6、, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.NOTE 1Alternate procedures for determining the compressive s
7、trength of unidirectional polymer matrix composites materials in a sandwich beamconfiguration may be found in Test Method D5467/D5467M.1.4 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles fo
8、r the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2C273/C273M Test Method for Shear Properties of Sandwich Core MaterialsC393C393/C393M Test Method for F
9、lexural Core Shear Properties of Sandwich Constructions by Beam FlexureD3410/D3410M Test Method for Compressive Properties of Polymer Matrix Composite Materials with Unsupported GageSection by Shear LoadingD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for Moisture Absorption Prop
10、erties and Equilibrium Conditioning of Polymer Matrix CompositeMaterialsD5467/D5467M Test Method for Compressive Properties of Unidirectional Polymer Matrix Composite Materials Using aSandwich BeamD7250/D7250M Practice for Determining Sandwich Beam Flexural and Shear StiffnessE6 Terminology Relating
11、 to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot orProcessE177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods1 This test method is under the jurisdiction of ASTM Committe
12、e D30 on Composite Materials and is the direct responsibility of Subcommittee D30.09 on SandwichConstruction.Current edition approved July 1, 2016April 1, 2018. Published July 2016April 2018. Originally approved in 2006. Last previous edition approved in 20122016 asD7249/D7249M 12.D7249/D7249M 161.
13、DOI: 10.1520/D7249_D7249M-16E01.10.1520/D7249_D7249M-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This
14、document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions
15、 as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E251 Test Methods for Performance Characteristics of
16、Metallic Bonded Resistance Strain GagesE456 Terminology Relating to Quality and StatisticsE1237 Guide for Installing Bonded Resistance Strain Gages3. Terminology3.1 DefinitionsTerminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology E6defines terms relating t
17、o mechanical testing. Terminology E456 and Practice E177 define terms relating to statistics. In the eventof a conflict between terms, Terminology D3878 shall have precedence over the other terminologies.3.2 Symbols:b = specimen widthc = core thicknessCV = coefficient of variation statistic of a sam
18、ple population for a given property (in percent)d = sandwich total thicknessDF,nom = effective sandwich flexural stiffnessEf = effective facing chord modulusEf = effective facesheet chord modulus = measuring strain in facing = measuring strain in facesheetFu = facing ultimate strength (tensile or co
19、mpressive)Fu = facesheet ultimate strength (tensile or compressive)Fs = core shear allowable strengthFc = core compression allowable strengthk = core shear strength factor to ensure facing failurek = core shear strength factor to ensure facesheet failurel = length of loading spanL = length of suppor
20、t spanlpad = length of loading padn = number of specimensP = applied forcePmax = maximum force carried by test specimen before failureSn1 = standard deviation statistic of a sample population for a given property = facing stress = facesheet stresst = facing thicknesst = facesheet thicknessx1 = test
21、result for an individual specimen from the sample population for a given propertyx = mean or average (estimate of mean) of a sample population for a given property4. Summary of Test Method4.1 This test method consists of subjecting a long beam of sandwich construction to a bending moment normal to t
22、he plane ofthe sandwich, using a 4-point loading fixture. Deflection and strain versus force measurements are recorded.4.2 The only acceptable failure modes for sandwich facesheet strength are those which are internal to one of the facesheets.Failure of the sandwich core or the core-to-facesheet bon
23、d preceding failure of one of the facesheets is not an acceptable failuremode. Careful post-test inspection of the specimen is required as facingfacesheet failure occurring in proximity to the loadingpoints can be caused by local through-thickness compression or shear failure of the core that preced
24、es failure of thefacing.facesheet.5. Significance and Use5.1 Flexure tests on flat sandwich construction may be conducted to determine the sandwich flexural stiffness, the core shearstrength, and shear modulus, or the facingsfacesheetscompressive and tensile strengths. Tests to evaluate core shear s
25、trength mayalso be used to evaluate core-to-facingcore-to-facesheet bonds.5.2 This test method is limited to obtaining the strength and stiffness of the sandwich panel facings,facesheets, and to obtainingload-deflection data for use in calculating sandwich beam flexural and shear stiffness using Sta
26、ndard Practice D7250/D7250M. Dueto the curvature of the flexural test specimen when loaded, facesheet compression strength from this test may not be equivalentto the facesheet compression strength of sandwich structures subjected to pure edgewise (in-plane) compression.5.3 Core shear strength and sh
27、ear modulus are best determined in accordance with Test Method C273C273/C273M providedbare core material is available. Test Method C393C393/C393M may also be used to determine core shear strength. StandardPractice D7250/D7250M may be used to calculate the flexural and shear stiffness of sandwich bea
28、ms.D7249/D7249M 1825.4 This test method can be used to produce facingfacesheet strength data for structural design allowables, materialspecifications, and research and development applications; it may also be used as a quality control test for bonded sandwich panels.5.5 Factors that influence the fa
29、cingfacesheet strength and shall therefore be reported include the following: facingfacesheetmaterial, core material, adhesive material, methods of material fabrication, facingfacesheet stacking sequence and overallthickness, core geometry (cell size), core density, adhesive thickness, specimen geom
30、etry, specimen preparation, specimenconditioning, environment of testing, specimen alignment, loading procedure, speed of testing, facingfacesheet void content,adhesive void content, and facingfacesheet volume percent reinforcement. Further, facingfacesheet strength may be differentbetween precured/
31、bonded and co-cured facesheets of the same material.NOTE 2Concentrated forces on beams with thin facingsfacesheets and low density cores can produce results that are difficult to interpret, especiallyclose to the failure point. Wider loading blocks and rubber pressure pads may assist in distributing
32、 the forces.NOTE 3To ensure that simple sandwich beam theory is valid, a good rule of thumb for the four-point bending test is the span length divided by thesandwich thickness should be greater than 20 (L/d 20) with the ratio of facingfacesheet thickness to core thickness less than 0.1 (t/c 0.1).6.
33、Interferences6.1 Material and Specimen PreparationPoor material fabrication practices and damage induced by improper specimenmachining are known causes of high data scatter in composites and sandwich structures in general. A specific material factor thataffects sandwich cores is variability in core
34、density. Important aspects of sandwich core specimen preparation that contribute todata scatter include the existence of joints, voids or other core discontinuities, out-of-plane curvature, and surface roughness.6.2 GeometrySpecific geometric factors that affect sandwich facingfacesheet strength inc
35、lude facingfacesheet thickness, corecell geometry, and facingfacesheet surface flatness (toolside or bagside surface in compression).6.3 EnvironmentResults are affected by the environmental conditions under which specimens are conditioned, as well as theconditions under which the tests are conducted
36、. Specimens tested in various environments can exhibit significant differences inboth strength behavior and failure mode. Critical environments must be assessed independently for each specific combination ofcore material, facingfacesheet material, and core-to-facingcore-to-facesheet interfacial adhe
37、sive (if used) that is tested.6.4 Core MaterialIf the core material has insufficient shear or compressive strength, it is possible that the core may locallycrush at or near the loading points thereby resulting in facesheet failure due to local stresses. In other cases, facingfacesheet failurecan cau
38、se local core crushing. When there is both facingfacesheet and core failure in the vicinity of one of the loading points itcan be difficult to determine the failure sequence in a post-mortem inspection of the specimen as the failed specimens look verysimilar for both sequences.7. Apparatus7.1 Microm
39、eters and CalipersA micrometer having a flat anvil interface, or a caliper of suitable size, shall be used. Theinstrument(s) shall have an accuracy of 625 m 60.001 in. for thickness measurement, and an accuracy of 6250 m 60.010in. for length and width measurement.NOTE 4The accuracies given above are
40、 based on achieving measurements that are within 1 % of the sample length, width and thickness.7.2 Loading Fixtures7.2.1 Standard ConfigurationThe standard loading fixture shall consist of a 4-point loading configuration with two supportbars that span the specimen width located below the specimen, a
41、nd two loading bars that span the specimen width located on thetop of the specimen (Fig. 1), The force shall be applied vertically through the loading bars, with the support bars fixed in placein the test machine. The standard loading fixture shall have the centerlines of the support bars separated
42、by a distance of 560 mm22.0 in. and the centerlines of the loading bars separated by a distance of 100 mm 4.0 in.7.2.2 Non-Standard ConfigurationsAll other loading fixture configurations (see Fig. 2) are considered non-standard anddetails of the fixture geometry shall be documented in the test repor
43、t. Figs. 3-5 show typical test fixtures. Non-standard 3- and4-point loading configurations have been retained within this standard a) for historical continuity with previous versions of TestMethod C393C393/C393M, b) because some sandwich panel designs require the use of non-standard loading configur
44、ations toachieve facesheet failure modes, and c) load-deflection data from non-standard configurations may be used with Standard PracticeD7250/D7250M to obtain sandwich beam flexural and shear stiffnesses.FIG. 1 Test Specimen and FixtureD7249/D7249M 1837.2.3 Support and Loading BarsThe bars shall be
45、 designed to allow free rotation of the specimen at the loading and supportpoints. The bars shall have sufficient stiffness to avoid significant deflection of the bars under load; any obvious bowing of the barsConfiguration Support Span (S) Load Span (L)Standard 4-Point 560 mm 22.0 in. 100 mm 4.0 in
46、.Non-Standard 3-Point (Mid-span)S 0.04-Point (Quarter-Span)S S/24-Point (Third-Span)S S/3FIG. 2 Loading ConfigurationsFIG. 3 Standard 4-Point Loading ConfigurationFIG. 4 3-Point Mid-Span Loading Configuration (Non-Standard)D7249/D7249M 184or any gaps occurring between the bars and the test specimen
47、during loading shall be considered significant deflection. Therecommended configuration has a 25 mm 1.0 in. wide flat steel loading block to contact the specimen (through rubber pressurepads) and is loaded via either a cylindrical pivot (see Fig. 3) or a V-shaped bar riding in a V-groove in the top
48、of the flat-bottomedsteel loading pad. The tips of the V-shaped loading bars shall have a minimum radius of 3 mm 0.12 in. The V-groove in theloading pad shall have a radius larger than the loading bar tip and the angular opening of the groove shall be such that the sidesof the loading bars do not co
49、ntact the sides of the V-groove during the test. Loading bars consisting of 25 mm 1.0 in. diametersteel cylinders may also be used, but there is a greater risk of local specimen crushing with cylindrical bars. Also, the load andsupport span lengths tend to increase as the specimen deflects when cylindrical loading bars without V-grooved loading pads areused (e.g., rolling supports).7.2.4 Pressure PadsRubber pressure pads having a Shore A durometer of 60, a width of 25 mm 1.0 in., a nominal thicknessof 3 mm 0.125 in. and spa
