1、Designation: C 365/C 365M 05Standard Test Method forFlatwise Compressive Properties of Sandwich Cores1This standard is issued under the fixed designation C 365/C 365M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of las
2、t revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method covers the determinati
3、on of compres-sive strength and modulus of sandwich cores. These propertiesare usually determined for design purposes in a directionnormal to the plane of facings as the core would be placed ina structural sandwich construction. The test procedures pertainto compression in this direction in particul
4、ar, but also can beapplied with possible minor variations to determining compres-sive properties in other directions. Permissible core materialforms include those with continuous bonding surfaces (such asbalsa wood and foams) as well as those with discontinuousbonding surfaces (such as honeycomb).1.
5、2 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. Within the text theinch-pound units are shown in brackets. The values stated ineach system are not exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfr
6、om the two systems may result in nonconformance with thestandard.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 appl
7、ica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 271 Test Method for Density of Sandwich Core MaterialsC 274 Terminology of Structural Sandwich ConstructionsD 883 Terminology Relating to PlasticsD 3878 Terminology for Composite MaterialsD 5229/D 5229M Te
8、st Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 122 Practice for Calculation of Sample Size. Within aSpecified Tolerable Er
9、ror, the Average for Characteristic ofa 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 Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE 1434 Guide for Recor
10、ding Mechanical Test Data of Fiber-Reinforced Composite Materials in DatabasesE 1471 Guide for Identification of Fibers, Fillers, and CoreMaterials in Computerized Material Property Databases3. Terminology3.1 DefinitionsTerminology D 3878 defines terms relatingto high-modulus fibers and their compos
11、ites. TerminologyC 274 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 bet
12、ween terms, TerminologyD 3878 shall have precedence over the other terminologies.3.2 Symbols:A = cross-sectional area of a test specimenCV = coefficient of variation statistic of a sample populationfor a given property (in percent)Ezfc= flatwise compressive modulusFzfcu= ultimate flatwise compressiv
13、e strengthFzfc0.02= flatwise compressive strength at 2 % LVDT/compressometer deflectionPmax= maximum force carried by test specimen beforefailureP0.02= force carried by test specimen at 2 % LVDT/compressometer deflection1This test method is under the jurisdiction of ASTM Committee D30 onComposite Ma
14、terials and is the direct responsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved Oct. 1, 2005. Published October 2005. Originallyapproved in 1955. Last previous edition approved in 2003 as C 365 03.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
15、orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Sn1= standard de
16、viation statistic of a sample population fora given propertyt = thickness of a test specimenx1= 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 propertyd = LVDT or compressometer deflection
17、szfc0.02= flatwise compressive stress at 2 % LVDT/compressometer deflection4. Summary of Test Method4.1 This test method consists of subjecting a sandwich coreto a uniaxial compressive force normal to the plane of thefacings as the core would be placed in a structural sandwichconstruction. The force
18、 is transmitted to the sandwich coreusing loading platens attached to the testing machine.5. Significance and Use5.1 Flatwise compressive strength and modulus are funda-mental mechanical properties of sandwich cores that are usedin designing sandwich panels. Deformation data can be ob-tained, and fr
19、om a complete force versus deformation curve, itis possible to compute the compressive stress at any appliedforce (such as compressive stress at proportional limit force orcompressive strength at the maximum force) and to computethe effective modulus of the core.5.2 This test method provides a stand
20、ard method of obtain-ing the flatwise compressive strength and modulus for sand-wich core structural design properties, material specifications,research and development applications, and quality assurance.5.3 In order to prevent local crushing at the edges of somehoneycomb cores, it is often desirab
21、le to stabilize the edgeswith a suitable material, such as a thin layer of resin or thinfacings. Flatwise compressive strength data may be generatedusing either stabilized specimens (reported as stabilized com-pression strength) or non-stabilized specimens (reported asbare compression strength). It
22、is customary aerospace industrypractice to determine compression modulus only when usingstabilized specimens.5.4 Factors that influence the flatwise compressive strengthand shall therefore be reported include the following: corematerial, methods of material fabrication, core geometry (cellsize), cor
23、e density, specimen geometry, specimen preparation,specimen conditioning, environment of testing, specimenalignment, loading procedure, and speed of testing.6. Interferences6.1 Material and Specimen PreparationPoor materialfabrication practices and damage induced by improper speci-men machining are
24、known causes of high data scatter incomposites and sandwich structures in general. A specificmaterial factor that affects sandwich cores is variability in coredensity. Important aspects of sandwich core specimen prepa-ration that contribute to data scatter include the existence ofjoints, voids or ot
25、her core discontinuities, out-of-plane curva-ture, and surface roughness.6.2 System AlignmentNon-uniform loading over the sur-face of the test specimen may cause premature failure. Non-uniform loading may result from non-uniform specimen thick-ness, failure to locate the specimen concentrically in t
26、hefixture, or system or fixture misalignment.6.3 GeometrySpecific geometric factors that affect sand-wich flatwise compressive strength include core cell geometry,core thickness, and specimen shape (square or circular).Flatwise compressive strength and modulus measurements areparticularly sensitive
27、to thickness variations over the cross-sectional area of the specimen, which can cause local loadingeccentricities, as well as toe regions in the force versusdisplacement curves due to specimen seating.6.4 EnvironmentResults are affected by the environmen-tal conditions under which specimens are con
28、ditioned, as wellas the conditions under which the tests are conducted. Speci-mens tested in various environments can exhibit significantdifferences in both strength behavior and failure mode. Criticalenvironments must be assessed independently for each corematerial tested.7. Apparatus7.1 Micrometer
29、s and CalipersA micrometer having a flatanvil interface, or a caliper of suitable size, shall be used. Theaccuracy of the instrument(s) shall be suitable for reading towithin 1 % of the sample length and width (or diameter) andthickness. For typical specimen geometries, an instrument withan accuracy
30、 of 612 m 60.0005 in. is desirable for thicknessmeasurement, whereas an instrument with an accuracy of6250 m 60.010 in. is acceptable for length and width (ordiameter) measurement.7.2 Loading PlatensForce shall be introduced into thespecimen using one fixed flat platen and one spherical seat(self-al
31、igning) platen. The platens shall be well-aligned andshall not apply eccentric forces. A satisfactory type of appara-tus is shown in Figs. 1 and 2. The platen surfaces shall extendbeyond the test specimen periphery. If the platens are notsufficiently hardened, or simply to protect the platen surface
32、s,a hardened plate (with parallel surfaces) can be insertedbetween each end of the fixture and the corresponding platen.7.3 Testing MachineThe testing machine shall be inaccordance with Practices E4and shall satisfy the followingrequirements:7.3.1 Testing Machine ConfigurationThe testing machineshal
33、l have both an essentially stationary head and a movablehead.7.3.2 Drive MechanismThe testing machine drive mecha-nism shall be capable of imparting to the movable head acontrolled velocity with respect to the stationary head. Thevelocity of the movable head shall be capable of beingregulated in acc
34、ordance with 11.5.7.3.3 Force IndicatorThe testing machine load-sensingdevice shall be capable of indicating the total force beingcarried by the test specimen. This device shall be essentiallyfree from inertia lag at the specified rate of testing and shallindicate the force with an accuracy over the
35、 force range(s) ofinterest of within 61 % of the indicated value.7.4 Crosshead Displacement IndicatorThe testing ma-chine shall be capable of monitoring and recording the cross-head displacement (stroke) with a precision of at least 61%.If machine compliance is significant, it is acceptable toC 365/
36、C 365M 052measure the displacement of the movable head using an LVDT,compressometer, or similar device with 61 % precision ondisplacement. A transducer and rod setup, shown in Figs. 1 and2, has been found to work satisfactorily. In the example shown,a small hole is drilled in the center of the core
37、specimen and inthe bottom loading platen, and a transducer rod is insertedthrough the hole, such that it contacts the upper loading platen.NOTE 1Bonded resistance strain gages are not usually consideredsatisfactory for measuring strain in this application because of theirstiffness. The reinforcing e
38、ffect of bonding gages to some cores can leadto large errors in measurement of strain.7.5 Conditioning ChamberWhen conditioning materialsat non-laboratory environments, a temperature/vapor-levelcontrolled environmental conditioning chamber is required thatshall be capable of maintaining the required
39、 temperature towithin 63C 65F and the required relative humidity levelto within 63 %. Chamber conditions shall be monitored eitheron an automated continuous basis or on a manual basis atregular intervals.7.6 Environmental Test ChamberAn environmental testchamber is required for test environments oth
40、er 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 results c
41、an 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 GeometryTest specimens shall have a square or cir-cular cross-section not exceeding 10 000 m
42、m216.0 in.2, andshall be equal in thickness to the sandwich core thickness.Minimum specimen cross-sectional areas for various types ofcore materials are as follows:NOTE 2The specimens cross-sectional area is defined in the facingplane, in regard to the orientation that the core would be placed in as
43、tructural sandwich construction. For example, for a honeycomb core thecross-sectional area is defined in the plane of the cells, which isperpendicular to the orientation of the cell walls.8.2.1 Continuous Bonding Surfaces (for example, BalsaWood, Foams)The minimum facing area of the specimenshall be
44、 625 mm21.0 in.2.8.2.2 Discontinuous Cellular Bonding Surfaces (for ex-ample, Honeycomb)The required facing area of the speci-men is dependent upon the cell size, to ensure a minimumnumber of cells are tested. Minimum facing areas are recom-mended in Table 1 for the more common cell sizes. These are
45、intended to provide approximately 60 cells minimum in the testspecimen. The largest facing area listed in the table (5625mm29.0 in.2) is a practical maximum for this test method.Cores with cell sizes larger than 9 mm 0.375 in. may requirea smaller number of cells to be tested in the specimen.8.3 Spe
46、cimen Preparation and MachiningPrepare the testspecimens so that the loaded surfaces will be parallel to eachFIG. 1 Platen, Transducer, and Rod Setup FIG. 2 Close-up of Specimen Between Loading PlatensC 365/C 365M 053other and perpendicular to the sides of the specimen. Takeprecautions when cutting
47、specimens from large sheets of coreto avoid notches, undercuts, and rough or uneven surfaces dueto inappropriate machining methods. Obtain final dimensionsby water-lubricated precision sawing, milling, or grinding. Theuse of diamond tooling has been found to be extremelyeffective for many material s
48、ystems. Record and report thespecimen cutting preparation method.NOTE 3In order to prevent local crushing at the edges of somehoneycomb cores, it is often desirable to reinforce the edges with asuitable material. In such instances, the edges may be dipped in a thinlayer of resin, or thin facings may
49、 be bonded to the core. When either ofthese stabilization techniques is used, the test shall be reported as astabilized compression test, and the method, configuration, and process ofstabilization utilized shall be reported. When honeycomb cell edges arenot stabilized, the test shall be reported as a bare compression test. It iscustomary aerospace industry practice to determine compression modulusonly when using stabilized specimens.NOTE 4Testing of core materials with typical manufacturing thick-ness tolerances (60.08 to 60.13 mm 60.003
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