1、Designation: C297/C297M 16Standard Test Method forFlatwise Tensile Strength of Sandwich Constructions1This standard is issued under the fixed designation C297/C297M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last
2、revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope1.1 This test method determines the flatw
3、ise tensile strengthof the core, the core-to-facing bond, or the facing of anassembled sandwich panel. Permissible core material formsinclude those with continuous bonding surfaces (such as balsawood and foams) as well as those with discontinuous bondingsurfaces (such as honeycomb).1.2 The values st
4、ated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system are not exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.1.2.1 Wit
5、hin 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 applica-bility
6、 of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C271/C271M Test Method for Density of Sandwich CoreMaterialsD792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD883 Terminology Relating to PlasticsD2584 Test Method for
7、Ignition Loss of Cured ReinforcedResinsD2734 Test Methods for Void Content of Reinforced PlasticsD3039/D3039M Test Method for Tensile Properties of Poly-mer Matrix Composite MaterialsD3171 Test Methods for Constituent Content of CompositeMaterialsD3878 Terminology for Composite MaterialsD5229/D5229M
8、 Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precisi
9、on, 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 Statistics3. Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites, as well
10、 as termsrelating to sandwich constructions. Terminology D883 definesterms relating to plastics. Terminology E6 defines termsrelating to mechanical testing. Terminology E456 and PracticeE177 define terms relating to statistics. In the event of aconflict between terms, Terminology D3878 shall have pr
11、ece-dence over the other terminologies.3.2 Symbols:3.2.1 Across-sectional area of a test specimen3.2.2 CVcoefficient of variation statistic of a samplepopulation for a given property (in percent)3.2.3 eedge tolerance between specimen and loadingblocks3.2.4 Fzftuultimate flatwise tensile strength3.2.
12、5 Pmaxmaximum force carried by test specimen beforefailure3.2.6 Sn-1 standard deviation statistic of a sample popula-tion for a given property3.2.7 xitest result for an individual specimen from thesample population for a given property3.2.8 xmean or average (estimate of mean) of a samplepopulation f
13、or a given property1This 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 1952. Last previous edition a
14、pproved in 2015 as C297/C297M 15).DOI: 10.1520/C0297_C0297M-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 ASTM websit
15、e.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14. Summary of Test Method4.1 This test method consists of subjecting a sandwichconstruction to a uniaxial tensile force normal to the plane ofthe sandwich. The force is transmitted to
16、the sandwich throughthick loading blocks, which are bonded to the sandwich facingsor directly to the core.4.2 The only acceptable failure modes for flatwise tensilestrength are those which are internal to the sandwich construc-tion. Failure of the loading block-to-sandwich bond is not anacceptable f
17、ailure mode.5. Significance and Use5.1 In a sandwich panel, core-to-facing bond integrity isnecessary to maintain facing stability and permit load transferbetween the facings and core. This test method can be used toprovide information on the strength and quality of core-to-facing bonds. It can also
18、 be used to produce flatwise tensilestrength data for the core material. While it is primarily used asa quality control test for bonded sandwich panels, it can also beused to produce flatwise tensile strength data for structuraldesign properties, material specifications, and research anddevelopment
19、applications.5.2 Factors that influence the flatwise tensile strength andshall therefore be reported include the following: facingmaterial, core material, adhesive material, methods of materialfabrication, facing stacking sequence and overall thickness,core geometry (cell size, cell wall thickness),
20、 core density,adhesive thickness, specimen geometry, specimen preparation,specimen conditioning, environment of testing, specimenalignment, loading procedure, speed of testing, facing voidcontent, adhesive void content, and facing volume percentreinforcement. Properties that may be derived from this
21、 testmethod include flatwise tensile strength.6. Interferences6.1 Material and Specimen PreparationPoor material fab-rication practices, lack of control of fiber alignment, anddamage induced by improper specimen machining are knowncauses of high data scatter in composites in general. Specificmateria
22、l factors that affect sandwich composites include vari-ability in core density and degree of cure of resin in both facingmatrix material and core bonding adhesive. Important aspectsof sandwich panel specimen preparation that contribute to datascatter are incomplete or nonuniform core bonding to faci
23、ngs,misalignment of core and facing elements, the existence ofjoints, voids or other core and facing discontinuities, out-of-plane curvature, facing thickness variation, and surface rough-ness.6.2 System AlignmentExcessive bending will cause pre-mature failure. Every effort should be made to elimina
24、te excessbending from the test system. Bending may occur as a result ofmisaligned grips, poor specimen preparation, or poor align-ment of the loading blocks and loading fixture. If there is anydoubt as to the alignment inherent in a given test machine, thenthe alignment should be checked as discusse
25、d in Test MethodD3039/D3039M.6.3 GeometrySpecific geometric factors that affect sand-wich flatwise tensile strength include core cell geometry, corethickness, specimen shape (square or circular), adhesivethickness, facing thickness, and facing per-ply thickness.6.4 EnvironmentResults are affected by
26、 the environmentalconditions under which the tests are conducted. Specimenstested in various environments can exhibit significant differ-ences in both strength behavior and failure mode. Criticalenvironments must be assessed independently for each facing,adhesive and core material tested.6.5 Conditi
27、oningAs it is inappropriate to bond a moisture-conditioned specimen to the loading blocks, it is necessary toperform the bonding operation prior to such conditioning. Thepresence of the loading blocks will affect the degree ofmoisture intake into the specimen, in comparison to a non-bonded sample.7.
28、 Apparatus7.1 Micrometers and CalipersA micrometer witha4to7 mm 0.16 to 0.28 in. nominal diameter ball-interface or a flatanvil interface shall be used to measure the specimen thick-ness. A ball interface is recommended for thickness measure-ments when facings are bonded to the core and at least one
29、surface is irregular (e.g., the bag-side of a thin facing laminatethat is neither smooth nor flat). A micrometer or caliper with aflat anvil interface is recommended for thickness measure-ments when facings are bonded to the core and both surfacesare smooth (e.g., tooled surfaces).Amicrometer or cal
30、iper witha flat anvil interface shall be used for measuring length andwidth, as well as the specimen thickness when no facings arepresent. The use of alternative measurement devices is permit-ted if specified (or agreed to) by the test requestor and reportedby the testing laboratory. The accuracy of
31、 the instruments shallbe suitable for reading to within1%ofthesample dimensions.For typical specimen geometries, an instrument with an accu-racy of 60.025 mm 60.001 in. is adequate for the length,width, and thickness measurements.7.2 Loading FixturesThe loading fixtures shall be self-aligning and sh
32、all not apply eccentric loads.Asatisfactory typeof apparatus is shown in Fig. 1. A dual-pin connection oruniversal joint shall be attached to each loading block tominimize any moments imparted to the test specimen. Theloading blocks shall be sufficiently stiff to keep the bonded coreor facings essen
33、tially flat under load. Loading blocks 40 to50 mm 1.5 to 2.0 in. thick have been found to performsatisfactorily. Recommended dimensions and tolerances for theloading blocks are provided in Fig. 2.7.3 Testing MachineThe testing machine shall be in ac-cordance with Practices E4 and shall satisfy the f
34、ollowingrequirements:7.3.1 Testing Machine ConfigurationThe testing machineshall 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
35、head. TheC297/C297M 162velocity of the movable head shall be capable of beingregulated in accordance with 11.6.7.3.3 Force IndicatorThe testing machine force-sensingdevice shall be capable of indicating the total force beingcarried by the test specimen. This device shall be essentiallyfree from iner
36、tia lag at the specified rate of testing and shallindicate the force with an accuracy over the force range(s) ofinterest of within 61 % of the indicated value.7.4 Conditioning ChamberWhen conditioning materialsat non-laboratory environments, a temperature/vapor-levelcontrolled environmental conditio
37、ning chamber is required thatshall be capable of maintaining the required temperature towithin 63C65 F 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.7.5 Environmental Test
38、ChamberAn environmental testchamber is required for test environments 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 Sampli
39、ngTest at least five specimens per test condi-tion unless valid 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 GeometryTest specime
40、ns shall have a square or cir-cular cross section, and shall be equal in thickness to thesandwich panel thickness. Recommended dimensions andtolerances for the core specimens are provided in Fig. 3.Minimum specimen facing areas for various types of corematerials are as follows:8.2.1 Continuous Bondi
41、ng Surfaces (for example, balsawood, foams)The minimum facing area of the specimen shallbe 625 mm21.0 in.2, and the minimum width or diameter ofthe loading blocks shall be 25 mm 1.0 in. Recommendedtolerances for the core specimens are provided in Fig. 3.8.2.2 Discontinuous Cellular Bonding Surfaces
42、(forexample, 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 and speci-men dimensions are recommended in Table 1 for the morecommon cell sizes. These are intended to provide approxi-mately 60 cel
43、ls minimum in the test specimen. The largestfacing area listed in the table (5625 mm29.0 in.2) is apractical maximum for this test method. Cores with cell sizeslarger than 9 mm 0.375 in. may require a smaller number ofcells to be tested in the specimen.8.3 Specimen Preparation and MachiningSpecimenp
44、reparation 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-lubricated precision sawing, milling, or gr
45、ind-ing. The use of diamond tooling has been found to beextremely effective for many material systems. Edges shouldbe flat and parallel within the specified tolerances. Record andreport the specimen cutting preparation method.8.4 LabelingLabel the test specimens so that they will bedistinct from eac
46、h other and traceable back to the panel oforigin, and will neither influence the test nor be affected by it.8.5 Loading Fixture BondingThe loading blocks shall bebonded to the core or facings of the test specimen using asuitable adhesive. To minimize thermal exposure effects uponthe existing core-to
47、-facing bonds, it is recommended that theassembly bonding temperature be at room temperature, or atleast 28 C 50 F lower than that at which the sandwich wasoriginally bonded. Similarly, the assembly bonding pressureshall not be greater than the original facing-to-core bondingpressure. It is recommen
48、ded to bond the specimens to theloading blocks using a suitable bonding fixture (e.g. one witha deep 90 v-shaped notch and a corner undercut) that providessupport and alignment to the assembly during the entirebonding process. Take care to ensure that the specimen andblocks do not move during the bo
49、nding process. Permissibletolerances for the bonded assembly are provided in Fig. 4.Edge tolerances (e) between the specimen and loading blockedges, as well as those between loading block edges, shall meetthe requirements of Fig. 4 along each side of the specimen.Loading block edge parallelism requirements in Fig. 4 may beFIG. 1 Flatwise Tension Test SetupC297/C297M 163satisfied through the use of a bonding fixture which meets theparallelism requirements throughout the supporting surfaces. .FIG. 2 Loading Block Dimensions and T
