1、Designation: C480/C480M 08 (Reapproved 2015)Standard Test Method forFlexure Creep of Sandwich Constructions1This standard is issued under the fixed designation C480/C480M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of
2、 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.1. Scope1.1 This test method covers the determination of the creepcharacteristics and creep rate of flat sandwich constructionslo
3、aded in flexure, 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 regar
4、ded separately 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
5、the other. Combining 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 p
6、ractices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C274 Terminology of Structural Sandwich ConstructionsC393/C393M Test Method for Core Shear Properties ofSandwich Constructions by Beam FlexureD883 Terminology Relating to Plast
7、icsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsD7249/D7249M Test Method for Facing Properties of Sand-wich Constructions by Long Beam FlexureE6 Terminology Relating to Methods of
8、 Mechanical TestingE122 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 and StatisticsE1309 Guide for Identifica
9、tion of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases3. Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites. TerminologyC274
10、defines terms relating to structural sandwich construc-tions. Terminology D883 defines terms relating to plastics.Terminology E6 defines terms relating to mechanical testing.Terminology E456 and Practice E177 define terms relating tostatistics. In the event of a conflict between terms, TerminologyD3
11、878 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 of theloading arm3.2.4 ccore thickness3.2.5 CRIcreep rate at time, ii3.2.6
12、 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 loading
13、plate and rod3.2.14 Papplied force1This 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 July 1, 2015. Published August 2015. Originallyapproved in 1961. Last p
14、revious edition approved in 2008 as C480/C480M 08.DOI: 10.1520/C0480_C0480M-08R15.2For 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 pag
15、e onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.15 Slength of support span3.2.16 wmass of lever arm3.2.17 Wmass of weight (including tray mass)4. Summary of Test Method4.1 This test method consists of subjecti
16、ng a beam ofsandwich construction 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 MethodD7249/D7249M, the only acceptable failure modes for san
17、d-wich facesheet strength 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 Metho
18、dC393/C393M, the only acceptable failure modes are core shearor core-to-facing bond. Failure of the sandwich facing preced-ing 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 fa
19、cing failure occurring 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
20、 under constantapplied 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 s
21、pecimen constructions 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,
22、 and research and develop-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 (cel
23、l size), core density, corethickness, adhesive thickness, specimen geometry, specimenpreparation, specimen conditioning, environment of testing,specimen alignment, loading procedure, speed of testing,facing void content, adhesive void content, and facing volumepercent reinforcement. Further, facing
24、and core-to-facingstrength and creep response may be different betweenprecured/bonded and co-cured facesheets of the same material.6. Interferences6.1 The interferences listed in Test Methods C393/C393Mand D7249/D7249M are also applicable to this test method.7. Apparatus7.1 Micrometers and CalipersA
25、 micrometer 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
26、 measure-ments 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 D7249/D7249M (for a long beam test) or to TestMethod C393/C393M (for a short beam test) except t
27、hat aconstant 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 havin
28、g an accuracy 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 r
29、equired 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 envir
30、onments 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 vali
31、d results can be gained through the use of fewerspecimens, as in the case of a designed experiment. Forstatistically significant data, consult the procedures outlined inPractice E122. Report the method of sampling.8.2 Geometry, Facing, Core:FIG. 1 Creep Test Apparatus and Loading SystemC480/C480M 08
32、 (2015)28.2.1 Core or Core-to-Facing Failure Mode DesiredThetest specimen configuration shall be a sandwich construction ofa size and proportions conforming to the flexure test specimendescribed in Test Method C393/C393M. The standard speci-men configuration should be used whenever the specimendesig
33、n equations in Section 8.2.3 of C393/C393M indicate thata core of core-to-facing bond failure mode is expected. In caseswhere the standard C393/C393M specimen configuration willnot produce a desired failure, a non-standard specimen shall bedesigned to produce a core or bond failure mode.8.2.2 Facesh
34、eet Failure Mode DesiredThe test specimenconfiguration shall be a sandwich construction of a size andproportions conforming to the flexure test specimen describedin Test Method D7249/D7249M. A non-standard 3-point load-ing specimen configuration shall be designed per Section 8.2.3of D7249/D7249M to
35、achieve a facing failure mode. Thestandard 4-point loading D7249/D7249M specimen configura-tion may be used if a suitable creep loading apparatus is used.8.3 Compression Side FacingUnless otherwise specifiedby the test requestor, the bag-side facing of a co-curedcomposite sandwich panel shall be pla
36、ced 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 Specimen
37、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-lubricate
38、d 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 te
39、st 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 theequipment
40、10. Conditioning10.1 The recommended pre-test specimen condition is ef-fective moisture equilibrium at a specific relative humidity perD5229/D5229M; however, if the test requestor does notexplicitly specify a pre-test conditioning environment, condi-tioning is not required and the test specimens may
41、 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 D5229/D5229M,includes not only the vapor of a liquid and its co
42、ndensate, 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:11.1.1 The
43、 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 and dat
44、a 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 equipme
45、nt. 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 required.
46、 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 width with
47、 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 specified forc
48、e to thespecimen by the 3-point loading lever system shown in Fig. 1may be calculated as follows:W 5P 2 p! A 2 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 pivot
49、 point and point of applied forceon 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 environment may
