1、Designation: D6772/D6772M 16Standard Test Method forDimensional Stability of Sandwich Core Materials1This standard is issued under the fixed designation D6772/D6772M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the year of last
2、 revision. 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 core dimensional stability in the two plan dimensions.1.2 The v
3、alues 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-conformancewith the stand
4、ard.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 practices and determine the
5、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 MoistureAbsorption Prop-erties and E
6、quilibrium 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 Terminology Relating to Quality
7、 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 relating to statisti
8、cs. In the event of a conflictbetween terms, Terminology D3878 shall have precedenceover the other terminologies.3.2 Symbols:3.2.1 CVcoefficient of variation statistic of a samplepopulation for a given property (in percent)3.2.2 Li initial (pre-test) measured dimension3.2.3 Lfpost-heating measured d
9、imension3.2.4 Sn-1standard deviation statistic of a sample popula-tion for a given property3.2.5 xItest result for an individual specimen from thesample population for a given property3.2.6 xmean or average (estimate of mean) of a samplepopulation for a given property4. Summary of Test Method4.1 Thi
10、s test method consists of placing a small piece ofsandwich core material in an elevated temperature environmentfor a specified period of time. After cooling, the dimensionalchanges in the planar dimensions are measured and comparedto the initial measurements taken prior to thermal exposure,both imme
11、diately after heating and after re-conditioning. Atypical honeycomb core specimen is shown in Fig. 1.5. Significance and Use5.1 Sandwich panel cores may change planar dimensionswhen heated. This phenomenon can be associated with theeffects of heating upon the core material itself, as well aschanges
12、in core moisture content resulting from the heatingcycle. It is prudent to know if this may be problematic withregard to the intended final part dimensions.5.2 This test method provides a standard method of charac-terizing the dimensional stability of sandwich core materialsfor design properties, ma
13、terial specifications, research anddevelopment applications, and quality assurance.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
14、 April 2016. Originallyapproved in 2002. Last previous edition approved in 2015 as D6772 15. DOI:10.1520/D6772_D6772M-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, refe
15、r to the standards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States15.3 Factors that influence dimensional stability of sandwichcore materials and shall therefore be reported include thefollowin
16、g: core material, methods of material fabrication, coregeometry, core thickness, core thickness uniformity, cell wallthickness, specimen geometry, specimen preparation, heatingand cooling environments (including temperatures and humid-ity levels), and specimen conditioning (both prior to and afterhe
17、ating).6. Interferences6.1 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 include
18、the existence ofjoints, voids or other core discontinuities, out-of-planecurvature, and surface roughness.6.2 Core GeometryCore-specific geometric factors thataffect dimensional stability include core cell size, uniformity ofcore cell geometry, core cell wall thickness, core cell wallthickness unifo
19、rmity, core thickness, and core thickness uni-formity.6.3 EnvironmentResults are affected by the environmentalconditions (including both temperatures and humidity levels)under which specimens are pre-conditioned, the elevatedtemperature exposure environment, the re-conditioning envi-ronment after he
20、ating, as well as the conditions under whichthe planar dimensional measurements are taken. Specimenstested in various environments can exhibit differences indimensional stability.7. Apparatus7.1 Micrometers and CalipersA micrometer having a flatanvil interface, or a caliper of suitable size, shall b
21、e used. Theaccuracy of the instrument(s) shall be suitable for reading towithin 0.5 % of the sample length, width and thickness. Fortypical 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
22、 mm 60.01 in. is desirable for length and widthmeasurement.7.2 Balance or Weighing ScaleAn analytical balance orweighing scale is required that is capable of measuring themass of the core material accurately to 60.5 %.7.3 OvenAn air-circulating oven is required that shall becapable of maintaining th
23、e required temperature to within63C65 F.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 designed experiment. Forstatistically significant data, consult the proced
24、ures outlined inPractice E122. Report the method of sampling.8.2 Test Specimens:8.2.1 Core ThicknessStandard test specimens shall utilize13 mm 0.50 in. thick core. When assessing dimensionalstability characteristics of core used in specific sandwichconstructions, it is recommended to test the actual
25、 corethickness used in the end application. Tests conducted usingnon-standard core thicknesses must be designated as such, withthe core thickness reported with any test results.8.2.2 Core Planar GeometryCore test specimens shall beapproximately 450 mm 18 in. by 900 mm 36 in. in theplanar dimensions.
26、 For honeycomb cores, the planar dimensioncross section is defined to be in the facing plane (in regard tothe orientation that the core would be placed in a structuralsandwich construction) and is perpendicular to the orientationof the cell walls. For honeycomb cores the 450-mm 18-in.dimension is th
27、e cores ribbon or L direction. Other dimensionscan be used, but must be reported. Smaller specimens may beused if oven size is limited.8.2.3 Core Preparation and MachiningPrepare the corematerial samples so that the facing plane surfaces are parallelto each other and perpendicular to the sides of th
28、e core. Takeprecautions when cutting specimens from large sheets of corematerial to avoid notches, undercuts, rough or uneven surfacesdue to inappropriate machining methods. Record and report thecore material specimen cutting preparation method.8.3 LabelingLabel the test specimens so that they will
29、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 accuracy of all measuring equipment shall havecertified calibrations that are current at the time of use of theequipment.10. Conditioning10.1 Pre-test
30、environmental conditioning requirements shallbe specified by the test requestor. The recommended pre-testcondition is effective moisture equilibrium at a specific relativehumidity as established by Test Method D5229/D5229M;however, if the test requestor does not explicitly specify apre-test conditio
31、ning environment, no conditioning is requiredand the test specimens may be tested as prepared.10.2 The pre-test specimen conditioning process, to includespecified environmental exposure levels and resulting moisturecontent, shall be reported with the test data.NOTE 1The term “moisture,” as used in T
32、est Method D5229/D5229Mincludes not only the vapor of a liquid and its condensate, but the liquidFIG. 1 Dimensional Stability SpecimenD6772/D6772M 162itself in large quantities, as for immersion.10.3 If no explicit pre-test conditioning process isperformed, the pre-test specimen conditioning process
33、 shall bereported as “unconditioned” and the moisture content as“unknown.”10.4 Post-heating environmental conditioning requirementsshall be specified by the test requestor. The recommendedpost-heating condition is moisture content equivalency to thatafter pre-test conditioning, which is obtained by
34、re-conditioning the specimen in the same conditioning environ-ment used for pre-conditioning for an equivalent duration. Ifthe test requestor does not explicitly specify a re-conditioningenvironment, no re-conditioning is required.10.5 The specimen re-conditioning process, to includespecified enviro
35、nmental exposure levels, shall be reported withthe test data.10.6 If no explicit re-conditioning process is performed, thespecimen re-conditioning process shall be reported as “uncon-ditioned” and the moisture content as “unknown.”11. Procedure11.1 Parameters to be Specified Before Test:11.1.1 The s
36、pecimen sampling method, specimen geometry,and conditioning travelers (if required).11.1.2 The properties and data reporting format desired.NOTE 2Determine specific material property, accuracy, and datareporting requirements prior to test for proper selection of apparatus.11.1.3 The environmental pr
37、e-conditioning and re-conditioning parameters.11.2 General Instructions:11.2.1 Report any deviations from this test method, whetherintentional or 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 e
38、valuated in accordance with TestMethod C271/C271M.11.2.3 Following final core material specimen machining,but before conditioning and testing, measure the specimenlength and width in the planar dimensions at three places. Thethickness of the specimen shall be measured at four locationsand recorded a
39、s the average of the four measurements. Theaccuracy of these measurements shall be within 0.5 % of thedimension. Measure the specimen length and width with anaccuracy of 60.25 mm 60.010 in. Measure the specimenthickness with an accuracy of 60.025 mm 60.001 in.Record the dimensions to three significa
40、nt figures in units ofmillimeters inches. If the specimen warps, it may be flattenedwhile making the measurements.11.2.4 Determine the mass of the specimen with an accu-racy of 60.5 %.11.3 Condition the specimens as required. Store the speci-mens in the conditioned environment until test time, if th
41、e testenvironment is different than the conditioning environment.Record the total time that the specimens are exposed to theconditioning environment.11.4 Following final specimen conditioning, but beforetesting, re-measure the specimen length, width, and thicknessas in 11.2.3, and re-measure the spe
42、cimen mass as in 11.2.4.11.5 Mark the specimen in eight locations as shown in Fig.1. For honeycomb core, it is recommended that the cells bepotted with a resin at the eight locations and then marked (seeFig. 2). Recommended dimensional locations for the eightmarkings are shown in Fig. 3.11.6 Measure
43、 the dimensions between the marked locationswith an accuracy of 60.25 mm 60.010 in. Make threemeasurements in one direction and three measurements in theother direction, as shown in Fig. 3.11.7 Preheat the oven to 175 6 3 C 350 6 5 F and placethe specimen flat on a wire-mesh-type shelf. Other temper
44、a-tures may be used but must be reported.11.8 After 90 min exposure in the oven, remove the speci-men from the oven and allow to cool in the specifiedre-conditioning environment.11.9 When the specimen is at room temperature, re-measurethe six dimensions as in 11.6 and record as the immediatepost-hea
45、ting dimensions. The immediate post-heating dimen-sional changes reflect the combined effects of heating anddrying upon the core dimensional stability.11.10 Re-condition the specimen in the same conditioningenvironment used to pre-condition the specimen, for at leastthe same total time recorded in 1
46、1.3.11.11 Re-measure the six dimensions as in 11.6, and recordas the final post-heating dimensions. The final post-heatingdimensional changes reflect the effects of heating upon thecore, as the final moisture content should approximate the pre-conditioned moisture content.12. Validation12.1 Property
47、 values shall not be calculated for any speci-men that contains some obvious flaw described in 6.1, unlesssuch flaw constitutes a variable being studied. Retests shall beperformed for any specimen on which values are not calcu-lated.FIG. 2 Potted Honeycomb CellD6772/D6772M 16313. Calculations13.1 Di
48、mensional ChangesCalculate the dimensionalchanges as follows, for both the initial post-heating measure-ments and the final post-heating measurements:percent change 5Lf2 Li!Li3100 %! (1)where:Li= initial (pre-test) measured dimension, andLf= post-heating measured dimension.13.2 StatisticsFor each se
49、ries of tests, calculate averagevalue, standard deviation and coefficient of variation (inpercent) for the average specimen dimensional change in eachof the two directions (both initial and final post-heating):x 5Si51nxi22 nx2Dn (2)Sn215Si51nxi22 nx2Dn 2 1! (3)CV 5 100 3 Sn21x (4)where:x = sample mean (average) specimen dimensional changein each direction;Sn-1= sample standard deviation in each direction;CV = sample coefficient of variation, %;n = number of specimens; andxI= measured or derived property.14. Repor
