1、Designation: C 480/C 480M 08Standard Test Method forFlexure Creep of Sandwich Constructions1This standard is issued under the fixed designation C 480/C 480M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revision
2、. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the creepcharacteristics and creep rate of flat sandwich constructionsloaded in flexur
3、e, at any desired temperature. Permissible corematerial forms include those with continuous bonding surfaces(such as balsa wood and foams) as well as those withdiscontinuous bonding surfaces (such as honeycomb).1.2 The values stated in either SI units or inch-pound unitsare to be regarded separately
4、 as standard. Within the text theinch-pound units are shown in brackets. The values stated ineither SI units or inch-pound units are to be regarded separatelyas standard. The values stated in each system may not be exactequivalents; therefore, each system shall be used independentlyof the other. Com
5、bining values from the two systems mayresult in non-conformance with the standard.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 d
6、etermine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 274 Terminology of Structural Sandwich ConstructionsC 393/C 393M Test Method for Core Shear Properties ofSandwich Constructions by Beam FlexureD 883 Terminology Relating to PlasticsD 3878
7、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 FlexureE6 Terminology Relating to Methods of Mecha
8、nical Test-ingE 122 Practice for Calculating Sample Size to Estimate,With Specified Precision, the Average for a Characteristicof a Lot or ProcessE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 1309 Guide for Identificat
9、ion of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE 1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases3. Terminology3.1 DefinitionsTerminology D 3878 defines terms relatingto high-modulus fibers and their composites. TerminologyC 27
10、4 defines terms relating to structural sandwich construc-tions. Terminology D 883 defines terms relating to plastics.Terminology E6defines terms relating to mechanical testing.Terminology E 456 and Practice E 177 define terms relating tostatistics. In the event of a conflict between terms, Terminolo
11、gyD 3878 shall have precedence over the other terminologydocuments.3.2 Symbols:3.2.1 Adistance between pivot point and point of appliedforce on the specimen3.2.2 bspecimen width3.2.3 Bdistance from pivot point to center of gravity ofthe loading arm3.2.4 ccore thickness3.2.5 CRIcreep rate at time, ii
12、3.2.6 dsandwich total thickness3.2.7 dinitial static deflection under the same load and atthe same temperature3.2.8 Dtotal deflection at time, t3.2.9 Ffapplied facing stress3.2.10 Fsapplied core shear stress3.2.11 Mdistance between point and weight point3.2.12 nnumber of specimens3.2.13 pmass of loa
13、ding plate and rod3.2.14 Papplied force3.2.15 Slength of support span3.2.16 wmass of lever arm1This specification is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved Sept. 1, 20
14、08. Published October 2008. Originallyapproved in 1961. Last previous edition approved in 2005 as C 480 99(2005).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
15、 standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.17 Wmass of weight (including tray mass)4. Summary of Test Method4.1 This test method consists of subjecting a beam ofsandwich co
16、nstruction to a sustained force normal to the planeof the sandwich, using either a 3-point or a 4-point loadingfixture. Deflection versus time measurements are recorded.4.2 For long beam specimens conforming to Test MethodD 7249/D 7249M, the only acceptable failure modes for sand-wich facesheet stre
17、ngth are those which are internal to one ofthe facesheets. Failure of the sandwich core or the core-to-facesheet bond preceding failure of one of the facesheets is notan acceptable failure mode for this specimen configuration.4.3 For short-beam specimens conforming to Test MethodC 393/C 393M, the on
18、ly acceptable failure modes are coreshear or core-to-facing bond. Failure of the sandwich facingpreceding failure of the core or core-to-facing bond is not anacceptable failure mode for this specimen configuration.4.4 Careful post-test inspection of the specimen is requiredas facing failure occurrin
19、g in proximity to the loading pointscan be caused by local through-thickness compression or shearfailure of the core that precedes failure of the facing.5. Significance and Use5.1 The determination of the creep rate provides informa-tion on the behavior of sandwich constructions under constantapplie
20、d force. Creep is defined as deflection under constantforce over a period of time beyond the initial deformation as aresult of the application of the force. Deflection data obtainedfrom this test method can be plotted against time, and a creeprate determined. By using standard specimen constructions
21、 andconstant loading, the test method may also be used to evaluatecreep behavior of sandwich panel core-to-facing adhesives.5.2 This test method provides a standard method of obtain-ing flexure creep of sandwich constructions for quality control,acceptance specification testing, and research and dev
22、elop-ment.5.3 Factors that influence the sandwich construction creepresponse and shall therefore be reported include the following:facing material, core material, adhesive material, methods ofmaterial fabrication, facing stacking sequence and overallthickness, core geometry (cell size), core density
23、, core thick-ness, adhesive thickness, specimen geometry, specimen prepa-ration, specimen conditioning, environment of testing, speci-men alignment, loading procedure, speed of testing, facingvoid content, adhesive void content, and facing volume percentreinforcement. Further, facing and core-to-fac
24、ing strength andcreep response may be different between precured/bonded andco-cured facesheets of the same material.6. Interferences6.1 The interferences listed in Test Methods C 393/C 393Mand D 7249/D 7249M are also applicable to this test method.7. Apparatus7.1 Micrometers and CalipersA micrometer
25、 having a flatanvil interface, or a caliper of suitable size, shall be used. Theinstruments(s) shall have an accuracy of 625 m 60.001 in.for thickness measurement, and an accuracy of 6250 m60.010 in. for length and width measurements.NOTE 1The accuracies given above are based on achieving measure-me
26、nts that are within1%ofthesample length, width and thickness.7.2 Loading FixturesThe fixture for loading the specimenshall be a 3-point loading configuration that conforms to eitherTest Method D 7249/D 7249M (for a long beam test) or to TestMethod C 393/C 393M (for a short beam test) except that aco
27、nstant force shall be applied by means of weights and a leversystem. Fig. 1 shows a lever and weight-loading apparatus thathas been found satisfactory.7.3 Deflectometer (LVDT)The deflection of the specimenshall be measured in the center of the support span by aproperly calibrated device having an ac
28、curacy of 60.025 mm60.001 in. or better.7.4 Conditioning ChamberWhen conditioning materialsat non-laboratory environments, a temperature/vapor-levelcontrolled environmental conditioning chamber is required thatshall be capable of maintaining the required temperature towithin 63C 65F and the required
29、 relative humidity levelto within 63 %. Chamber conditions shall be monitored eitheron an automated continuous basis or on a manual basis atregular intervals (a minimum of once daily checks are recom-mended).7.5 Environmental Test ChamberAn environmental testchamber is required for test environments
30、 other than ambienttesting laboratory conditions. This chamber shall be capable ofmaintaining the gage section of the test specimen at therequired test environment during the mechanical test.8. Sampling and Test Specimens8.1 SamplingTest at least five specimens per test condi-tion unless valid resul
31、ts can be gained through the use of fewerspecimens, as in the case of a designed experiment. Forstatistically significant data, consult the procedures outlined inPractice E 122. Report the method of sampling.8.2 Geometry, Facing, Core:8.2.1 Core or Core-to-Facing Failure Mode DesiredThetest specimen
32、 configuration shall be a sandwich construction ofa size and proportions conforming to the flexure test specimendescribed in Test Method C 393/C 393M. The standard speci-men configuration should be used whenever the specimendesign equations in Section 8.2.3 of C 393/C 393M indicatethat a core of cor
33、e-to-facing bond failure mode is expected. InFIG. 1 Creep Test Apparatus and Loading SystemC 480/C 480M 082cases where the standard C 393/C 393M specimen configura-tion will not produce a desired failure, a non-standard speci-men shall be designed to produce a core or bond failure mode.8.2.2 Faceshe
34、et Failure Mode DesiredThe test specimenconfiguration shall be a sandwich construction of a size andproportions conforming to the flexure test specimen describedin Test Method D 7249/D 7249M. A non-standard 3-pointloading specimen configuration shall be designed per Section8.2.3 of D 7249/D 7249M to
35、 achieve a facing failure mode.The standard 4-point loading D 7249/D 7249M specimen con-figuration may be used if a suitable creep loading apparatus isused.8.3 Compression Side FacingUnless otherwise specifiedby the test requestor, the bag-side facing of a co-curedcomposite sandwich panel shall be p
36、laced as the upper,compression-loaded facing during test, as facing compressionstrength is more sensitive to imperfections typical of bag-sidesurfaces (for example, intra-cell dimpling) than is facingtension strength. Creep response is expected to follow the sametrends as static strength.8.4 Specime
37、n Preparation and MachiningSpecimenpreparation is extremely important for this test method. Takeprecautions when cutting specimens from large panels to avoidnotches, undercuts, rough or uneven surfaces, or delaminationsdue to inappropriate machining methods. Obtain final dimen-sions by water-lubrica
38、ted precision sawing, milling, or grind-ing. The use of diamond coated machining tools has beenfound to be extremely effective for many material systems.Edges should be flat and parallel within the specified toler-ances. Record and report the specimen cutting preparationmethod.8.5 LabelingLabel the
39、test specimens so that they will bedistinct from each other and traceable back to the panel 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 theequipme
40、nt10. Conditioning10.1 The recommended pre-test specimen condition is ef-fective moisture equilibrium at a specific relative humidity perD 5229/D 5229M; however, if the test requestor does notexplicitly specify a pre-test conditioning environment, condi-tioning is not required and the test specimens
41、 may be tested asprepared.10.2 The pre-test specimen conditioning process, to includespecified environmental exposure levels and resulting moisturecontent, shall be reported with the test data.NOTE 2The term moisture, as used in Test Method D 5229/D 5229M,includes not only the vapor of a liquid and
42、its condensate, but the liquiditself in large quantities, as for immersion.10.3 If no explicit conditioning process is performed, 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
43、.1 The specimen sampling method, specimen geometry,and conditioning travelers (if required).11.1.2 The loading fixture support span (and loading span ifa 4-point loading configuration is used).11.1.3 The force, P, to be applied to the specimen and themaximum time for the test.11.1.4 The properties a
44、nd data reporting format desired.11.1.5 The environmental conditioning test parameters.11.1.6 The nominal thicknesses of the facing materials.NOTE 3Determine specific material property, accuracy, and datareporting requirements prior to test for proper selection of instrumentationand data recording e
45、quipment. Estimate the maximum specimen deflec-tion to aid in transducer selection, calibration of equipment, and determi-nation of equipment settings.11.2 General Instructions:11.2.1 Report any deviations from this test method, whetherintentional or inadvertent.11.2.2 Condition the specimens as req
46、uired. Store the speci-mens in the conditioned environment until test time, if the testenvironment is different than the conditioning environment.11.2.3 Before testing, measure and record the specimenlength, width and thickness at three places in the test section.Measure the specimen length and widt
47、h with an accuracy of6250 m 60.010 in. Measure the specimen thickness withan accuracy of 625 m 60.001 in. Record the dimensions tothree significant figures in units of millimeters inches.11.3 Measure and record the length of the support andloading spans.11.4 The weight required to apply the specifie
48、d force to thespecimen by the 3-point loading lever system shown in Fig. 1may be calculated as follows:W 5P p! A wBM(1)where:W = mass of weight (including tray mass), N lb,P = force applied to specimen, N lb,p = mass of loading plate and rod, N lb,w = mass of lever arm, N lb,A = distance between piv
49、ot point and point of appliedforce on the specimen, mm in.B = distance from pivot point to center of gravity of theloading arm, mm in., andM = distance between pivot point and weight point, mm,11.5 Test EnvironmentIf possible, test the specimen underthe same fluid exposure level used for conditioning. However,cases such as elevated temperature testing of a moist specimenplace unrealistic requirements on the capabilities of commontesting machine environmental chambers. In such cases, themechanical test environme
