1、Designation: C 297/C 297M 04Standard Test Method forFlatwise Tensile Strength of Sandwich Constructions1This standard is issued under the fixed designation C 297/C 297M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of l
2、ast 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 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. 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 valuesfrom the two syst
5、ems 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 applica-bility of r
6、egulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 274 Terminology of Structural Sandwich ConstructionsD 792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD 883 Terminology Relating to PlasticsD 2584 Test Method for Ignition
7、 Loss of Cured ReinforcedResinsD 2734 Test Method for Void Content of Reinforced Plas-ticsD 3039/D 3039M Test Method for Tensile Properties ofPolymer Matrix Composite MaterialsD 3171 Test Method for Constituent Content of CompositeMaterialsD 3878 Terminology for Composite MaterialsD 5229/D 5229M Tes
8、t 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 Choice of Sample Size to Estimate aMeasure of Quality for a
9、 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 Recording Mechanical Test Data of Fiber-Rein
10、forced 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 composites. TerminologyC 274 defines terms re
11、lating 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, TerminologyD 3878 shall hav
12、e 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)1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct re
13、sponsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved May 1, 2004. Published May 2004. Originallyapproved in 1952. Last previous edition approved in 1999 as C 297 94 (1999).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Se
14、rvice 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.Fzftu= ultimate flatwise tensile strengthP
15、max= maximum force carried by test specimen beforefailureSn-1= standard deviation statistic of a sample population fora given propertyx1= 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 pr
16、operty4. 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 the sandwich throughthick loading blocks, which are bonded to the sandwich facingsor directly to the core.4.2
17、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 failure mode.5. Significance and Use5.1 In a sandwich panel, core-to-facing bond integrity isnecessary to maint
18、ain 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 be used to produce flatwise tensilestrength data for the core material. While it is primarily used asa qualit
19、y control test for bonded sandwich panels, it can also beused to produce flatwise tensile strength data for structuraldesign properties, material specifications, and research anddevelopment applications.5.2 Factors that influence the flatwise tensile strength andshall therefore be reported include t
20、he following: facingmaterial, core material, adhesive material, methods of materialfabrication, facing stacking sequence and overall thickness,core geometry (cell size), core density, adhesive thickness,specimen geometry, specimen preparation, specimen condi-tioning, environment of testing, specimen
21、 alignment, loadingprocedure, speed of testing, facing void content, adhesive voidcontent, and facing volume percent reinforcement. Propertiesthat may be derived from this test method include flatwisetensile strength.6. Interferences6.1 Material and Specimen PreparationPoor materialfabrication pract
22、ices, lack of control of fiber alignment, anddamage induced by improper specimen machining are knowncauses of high data scatter in composites in general. Specificmaterial factors that affect sandwich composites include vari-ability in core density and degree of cure of resin in both facingmatrix mat
23、erial and core bonding adhesive. Important aspectsof sandwich panel specimen preparation that contribute to datascatter are incomplete or nonuniform core bonding to facings,misalignment of core and facing elements, the existence ofjoints, voids or other core and facing discontinuities, out-of-plane
24、curvature, facing thickness variation, and surface rough-ness.6.2 System AlignmentExcessive bending will cause pre-mature failure. Every effort should be made to eliminate excessbending from the test system. Bending may occur as a result ofmisaligned grips, poor specimen preparation, or poor align-m
25、ent of the bonding blocks and loading fixture. If there is anydoubt as to the alignment inherent in a given test machine, thenthe alignment should be checked as discussed in Test MethodD 3039/D 3039M.6.3 GeometrySpecific geometric factors that affect sand-wich flatwise tensile strength include core
26、cell geometry, corethickness, specimen shape (square or circular), adhesive thick-ness, facing thickness, and facing per-ply thickness.6.4 EnvironmentResults are affected by the environmen-tal conditions under which the tests are conducted. Specimenstested in various environments can exhibit signifi
27、cant differ-ences in both strength behavior and failure mode. Criticalenvironments must be assessed independently for each facing,adhesive and core material tested.6.5 ConditioningAs it is inappropriate to bond amoisture-conditioned specimen to the bonding blocks, it isnecessary to perform the bondi
28、ng operation prior to suchconditioning. The presence of the bonding blocks will affectthe degree of moisture intake into the specimen, in comparisonto a non-bonded sample.7. Apparatus7.1 MicrometersThe micrometer(s) shall use a 4- to 5-mm0.16- to 0.20-in. nominal diameter ball-interface on irregular
29、surfaces such as the bag-side of a facing laminate, and a flatanvil interface on machined edges or very smooth-tooledsurfaces. The accuracy of the instrument(s) shall be suitable forreading to within 1 % of the sample length, width andthickness. For typical specimen geometries, an instrument withan
30、accuracy of 625 mm 60.001 in. is desirable for thickness,length and width measurement.7.2 Loading FixturesThe loading fixtures shall be self-aligning and shall not apply eccentric loads.Asatisfactory typeof apparatus is shown in Fig. 1. The loading blocks shall besufficiently stiff to keep the bonde
31、d core or facings essentiallyflat under load. Loading blocks 40 to 50 mm 1.5 to 2.0 in.thick have been found to perform satisfactorily. Permissibletolerances for the loading blocks (along with alignment re-quirements) are provided in Fig. 2.7.3 Testing MachineThe testing machine shall be inaccordanc
32、e with Practices E4and shall satisfy the followingrequirements: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 acontrolle
33、d velocity with respect to the stationary head. Thevelocity of the movable head shall be capable of beingregulated in accordance with 11.6.7.3.3 Load IndicatorThe testing machine load-sensingdevice shall be capable of indicating the total force beingcarried by the test specimen. This device shall be
34、 essentiallyfree from inertia lag at the specified rate of testing and shallC 297/C 297M 042indicate 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/va
35、por-levelcontrolled environmental conditioning chamber is required thatshall be capable of maintaining the required 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 a
36、tregular intervals.7.5 Environmental Test 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 tes
37、t.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, as in the case of a designed experiment. Forstatistically significant data, consult the procedures outlined inPractice E 122. Report the
38、method of sampling.8.2 GeometryTest specimens shall have a square or cir-cular cross-section, and shall be equal in thickness to thesandwich panel thickness. Minimum specimen facing areas forvarious types of core materials are as follows:8.2.1 Continuous Bonding Surfaces (for example, balsawood, foa
39、ms)The minimum facing area of the specimenshall be 625 mm21.0 in.2.8.2.2 Discontinuous Cellular Bonding Surfaces (for ex-ample, honeycomb)The required facing area of the specimenis dependent upon the cell size, to ensure a minimum numberof cells are tested. Minimum facing areas are recommended inTab
40、le 1 for the more common cell sizes. These are intended toprovide approximately 60 cells minimum in the test specimen.The largest facing area listed in the table (5625 mm29.0 in.2)is a practical maximum for this test method. Cores with cellsizes larger than 9 mm 0.375 in. may require a smallernumber
41、 of cells to be tested in the specimen.8.3 Specimen 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
42、methods. Obtain final dimen-sions by water-lubricated precision sawing, milling, or grind-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 prepara
43、tion method.8.4 LabelingLabel the 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.8.5 Loading Fixture BondingThe loading blocks shall bebonded to the core or facings of the test specimen u
44、sing asuitable adhesive. To minimize thermal exposure effects uponthe existing core-to-facing bonds, it is recommended that theassembly bonding temperature be at room temperature, or atleast 28C 50F lower than that at which the sandwich wasoriginally bonded. Similarly, the assembly bonding pressures
45、hall not be greater than the original facing-to-core bondingpressure. Permissible tolerances for the bonded assembly(along with alignment requirements) are provided in Fig. 2.9. Calibration9.1 The accuracy of all measuring equipment shall havecertified calibrations that are current at the time of us
46、e of theequipment.10. Conditioning10.1 Standard Conditioning ProcedureUnless a differentenvironment is specified as part of the experiment, conditionthe test specimens in accordance with Procedure C of TestMethod D 5229/D 5229M, and store and test at standardlaboratory atmosphere (23 6 3C 73 6 5F an
47、d 50 6 5%relative humidity).11. Procedure11.1 Parameters to Be Specified Before Test:11.1.1 The specimen sampling method, specimen geometry,and conditioning travelers (if required).11.1.2 The properties and data reporting format desired.NOTE 1Determine specific material property, accuracy, and datar
48、eporting requirements prior to test for proper selection of instrumentationand data recording equipment. Estimate the specimen strength to aid intransducer selection, calibration of equipment, and determination ofequipment settings.11.1.3 The environmental conditioning test parameters.FIG. 1 Flatwis
49、e Tension Test SetupC 297/C 297M 04311.1.4 If performed, sampling method, specimen geometry,and test parameters used to determine facing density andreinforcement volume.11.2 General Instructions:11.2.1 Report any deviations from this test method, whetherintentional or inadvertent.11.2.2 If specific gravity, density, facing reinforcement vol-ume, or facing void volume are to be reported, then obtainthese samples from the same panels being tested. Specificgravity and density may be evaluated in accordance with TestMethods D 792. Volume
