1、Designation: D6790/D6790M 16Standard Test Method forDetermining Poissons Ratio of Honeycomb Cores1This standard is issued under the fixed designation D6790/D6790M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the sand-wich honeycomb core Poissons ratio from the anticlasticcurvature radii,
3、 see Fig. 1.1.2 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 from the two systems may result in non-conf
4、ormancewith 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 establish appro-priate safety and health practic
5、es and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C271/C271M Test Method for Density of Sandwich CoreMaterialsD883 Terminology Relating to PlasticsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for MoistureAbsorpt
6、ion Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsE122 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 inASTM Test MethodsE456 Terminolog
7、y 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 E456 and Practice E177define terms
8、 relating to statistics. In the event of a conflictbetween terms, Terminology D3878 shall have precedenceover the other terminologies.3.2 Symbols: c = chord measurementCV = coefficient of variation statistic of a sample populationfor a given property (in percent)d = depth measurementRa= anticlastic
9、curvature radiusRc= cylinder radiusSn-1= standard deviation statistic of a sample population fora given propertyx1= 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 propertyv = Poissons rat
10、io4. Summary of Test Method4.1 This test method determines the Poissons ratio ofsandwich honeycomb core by bending the core around acylinder and taking measurements of the anticlastic curvaturethat occurs.5. Significance and Use5.1 Certain sandwich panel analyses require the Poissonsratio of the hon
11、eycomb core. It is not possible to measure thehoneycombs Poissons ratio by conventional methods.5.2 This test method provides a standard method of deter-mining the Poissons ratio of honeycomb core materials fordesign properties, material specifications, research and devel-opment applications, and qu
12、ality assurance.5.3 Factors that influence the Poissons ratio of honeycombcore materials and shall therefore be reported include thefollowing: core material, methods of material fabrication, coregeometry, core thickness, core thickness uniformity, cell wallthickness, specimen geometry, specimen prep
13、aration, andspecimen conditioning.1This test method is under 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 2002. Last pre
14、vious edition approved in 2014 as D6790 - 14. DOI:10.1520/D6790_D6790M-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
15、ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States16. Interferences6.1 The test method described here is one means of obtain-ing the Poissons ratio of honeycomb core. However, this testmethod has not been widely used, and it
16、 is in its conceptualstage.6.2 Material and Specimen PreparationPoor material fab-rication practices and damage induced by improper specimenmachining are known causes of high data scatter for sandwichcores. Important aspects of sandwich core specimen prepara-tion that contribute to data scatter incl
17、ude the existence ofjoints, voids or other core discontinuities, out-of-planecurvature, and surface roughness. Non-uniform edge geometrycan influence the measurement of the chord distance describedin 11.6.6.3 Core GeometryCore-specific geometric factors thataffect Poissons ratio include core cell si
18、ze, uniformity of corecell geometry, core cell wall thickness, core cell wall thicknessuniformity, core thickness, and core thickness uniformity.6.4 EnvironmentResults are affected by the environmentalconditions under which specimens are conditioned, as well asthe conditions under which the core is
19、tested. Specimens testedin various environments can exhibit differences in Poissonsratio.6.5 Specimen-Cylinder ContactResults may vary if thespecimen is too rigid in bending to permit intimate contact ofits surface with the cylinder along the specimen center linewithout fracturing the core. Use of a
20、 larger cylinder radius isrecommended if the midpoints of two parallel ends of the corespecimen cannot be made to contact the standard cylinderusing light hand pressure.6.6 Measurement DevicesMeasurements for anticlasticcurvature depth described in 11.6 may be affected by the widthof the scale descr
21、ibed in 7.3 where it contacts the specimen.7. Apparatus7.1 Micrometers and Calipers-Amicrometer having a flatanvil interface, or a caliper of suitable size, shall be used. Theaccuracy of the instrument(s) shall be suitable for reading towithin 0.5 % of the sample length, width and thickness. Fortypi
22、cal specimen geometries, an instrument with an accuracyof 60.025 mm 60.001 in. is desirable for thicknessmeasurement, whereas an instrument with an accuracy of60.25 mm 60.01 in. is desirable for length and widthmeasurement.7.2 CylindersA cylinder shall be utilized to bend the coreto a defined radius
23、 of curvature. Standard tests shall utilize acylinder of 305 mm 12 in. radius. This radius is generallyacceptable for testing of cores up to 25 mm 1.0 in. inthickness. A larger cylinder radius shall be used if the mid-points of two parallel ends of the core specimen cannot bemade to contact the stan
24、dard cylinder using light hand pressurewithout fracturing the core. Tests conducted using non-standard cylinder radii must be designated as such, with thecylinder radius reported with any test results.7.3 ScaleA scale is required that is capable of measuringlength with an accuracy of 61mm60.05 in.7.
25、4 Straight EdgeA straight edge is required that iscapable of measuring length with an accuracy of 61mm60.05 in.8. Sampling and Test Specimens8.1 SamplingTest at least five specimens per test condi-tion unless valid results can be gained through the use of fewerspecimens, such as in the case of a des
26、igned experiment. Forstatistically significant data, consult the procedures outlined inPractice E122. Report the method of sampling.8.2 Test Specimens:8.2.1 Core GeometryCore test specimens shall be square.The length and width should be great enough to obtain ananticlastic curvature when the specime
27、n is bent over thecylinder. A specimen size of 300 by 300 mm 12 by 12 in. inplanar dimensions is recommended. For honeycomb cores, theplanar dimension cross-section is defined to be in the facingplane (in regard to the orientation that the core would be placedin a structural sandwich construction) a
28、nd is perpendicular tothe orientation of the cell walls. Larger specimen sizes may berequired if the cylinder radius is larger than 305 mm 12 in.8.2.2 Core ThicknessVarious core thicknesses should betested.Acore thickness of 13 mm (0.50 in.) is recommended asa starting thickness.8.2.3 Core Preparati
29、on and MachiningPrepare the corematerial samples so that the facing plane surfaces are parallelto each other and perpendicular to the sides of the core. Takeprecautions when cutting specimens from large sheets of corematerial to avoid notches, undercuts, rough or uneven surfacesdue to inappropriate
30、machining methods. Record and report thecore material specimen cutting preparation method.8.3 LabelingLabel the test specimens so that they will bedistinct from each other and traceable back to the sheet oforigin, and will neither influence the test nor be affected by it.9. Calibration9.1 The accura
31、cy of all measuring equipment shall havecertified calibrations that are current at the time of use of theequipment.FIG. 1 Anticlastic CurvatureD6790/D6790M 16210. Conditioning10.1 The recommended pre-test condition is effective mois-ture equilibrium at a specific relative humidity as establishedby T
32、est Method D5229/D5229M; however, if the test requestordoes not explicitly specify a pre-test conditioning environment,no conditioning is required and the test specimens may betested as prepared.10.2 The pre-test specimen conditioning process, to includespecified environmental exposure levels and re
33、sulting moisturecontent, shall be reported with the test data.NOTE 1The term “moisture,” as used in Test Method D5229/D5229M, includes not only the vapor of a liquid and its condensate, butthe liquid itself in large quantities, as for immersion.10.3 If no explicit conditioning process is performed,
34、thespecimen conditioning process shall be reported as “uncondi-tioned” and the moisture content as “unknown.”11. Procedure11.1 Parameters to be Specified Before Test:11.1.1 The specimen sampling method, specimen geometry,and conditioning travelers (if required).11.1.2 The properties and data reporti
35、ng format desired.NOTE 2Determine specific material property, accuracy, and datareporting requirements prior to test for proper selection of apparatus.11.1.3 The environmental conditioning parameters.11.2 General Instructions:11.2.1 Report any deviations from this test method, whetherintentional or
36、inadvertent.11.2.2 If core material density is to be reported, then obtainthese samples from the same sheet of core material beingtested. Density may be evaluated in accordance with TestMethod C271/C271M.11.2.3 Following final core material specimen machining,but before conditioning and testing, mea
37、sure the specimenlength and width in the planar dimensions at three places. Thethickness of the specimen shall be measured at four locationsand recorded as the average of the four measurements. Theaccuracy of these measurements shall be within 0.5 % of thedimension. Measure the specimen length and w
38、idth with anaccuracy of 6 0.25 mm 6 0.010 in. Measure the specimenthickness with an accuracy of 6 0.025 mm 6 0.001 in.Record the dimensions to three significant figures in units ofmillimetres inches.11.3 Condition the specimens as required. Store the speci-mens in the conditioned environment until t
39、est time, if the testenvironment is different from the conditioning environment.11.4 Following final specimen conditioning, but beforetesting, re-measure the specimen length, width, and thicknessas in 11.2.3. Mark the midpoint along each of the specimenedges with an accuracy of 6 1mm6 0.05 in. (ensu
40、ring themarking medium will neither influence the test nor be affectedby it).11.5 Bend the honeycomb core specimen around the cylin-der of known radius, making sure the midpoints of two parallelends of the specimen contact the cylinder. If the ends of thespecimen cannot be made to contact the standa
41、rd cylinderusing light hand pressure without fracturing the core, a largercylinder radius shall be used to determine the Poissons ratio.11.6 With the specimen bent around the cylinder, place thestraight edge (specified in 7.4) across the midpoints of the twoedges of the specimen not in contact with
42、the cylinder (asshown in Fig. 2) and measure the chord distance, c. Using themeasured chord distance, locate and mark the midpoint of thestraight edge (as shown in Fig. 2) with an accuracy of 6 1mm6 0.05 in. Position the scale (specified in 7.3)atthemidpoint of the straight edge (as shown in Fig. 2)
43、 and measurethe depth, d. Take care to avoid imparting transverse forces tothe specimen when positioning the straight edge and scale, assuch loading can affect the chord distance and depth measure-ments.12. Validation12.1 Property values shall not be calculated for any speci-men that contains some o
44、bvious flaw described in 6.2, unlesssuch flaw constitutes a variable being studied. Resets shall beperformed for any specimen on which values are not calcu-lated.FIG. 2 MeasurementsD6790/D6790M 16313. Calculations13.1 Poissons RatioCalculate the anticlastic curvatureradius, Ra, and Poissons ratio, v
45、, of the specimens as follows:Ra54 d21c28 dv 5RcRa(1)(see Fig. 2)where:v = Poissons ratio,Ra= anticlastic curvature radius,Rc= cylinder radius,c = chord measurement, andd = depth measurement.13.2 StatisticsFor each series of test samples, calculateaverage value, standard deviation, and coefficient o
46、f variation(in percent) for Poissons ratio:x 5Si51nXiDn(2)Sn215!Si51nxi22 nx2Dn 2 1!(3)CV 5 100 3Sn21x(4)where:x = sample mean (average),Sn-1= sample standard deviation,CV = sample coefficient of variation, %,n = number of specimens, andx1= measured or derived property.14. Report14.1 Report the foll
47、owing information, or references point-ing to other documentation containing this information, to themaximum extent applicable (reporting of items beyond thecontrol of a given testing laboratory, such as might occur withmaterial details or specimen fabrication parameters, shall bethe responsibility
48、of the requestor):14.1.1 The revision level or date of issue of this test method.14.1.2 The name(s) of the test operator(s).14.1.3 Any variations to this test method, anomalies noticedduring testing, or equipment problems occurring during testing.14.1.4 Identification of all the materials constituen
49、t to thesandwich core specimen tested, including for each: materialspecification, material type, manufacturers materialdesignation, manufacturers batch or lot number, source (if notfrom manufacturer), date of certification, and expiration ofcertification.14.1.5 Description of the fabrication steps used to preparethe sandwich core specimen including: fabrication start date,fabrication end date, process specification(s), and a descriptionof the equipment used.14.1.6 Method of preparing the test specimen, inc
