1、Designation: C394/C394M 16Standard Test Method forShear Fatigue of Sandwich Core Materials1This standard is issued under the fixed designation C394/C394M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revision. A
2、 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 determines the effect of repeated shearforces on core material used in sandwich panels. Permissiblecore material form
3、s include those with continuous bondingsurfaces (such as balsa wood and foams) as well as those withdiscontinuous bonding surfaces (such as honeycomb).1.2 This test method is limited to test specimens subjectedto constant amplitude uniaxial loading, where the machine iscontrolled so that the test sp
4、ecimen is subjected to repetitiveconstant amplitude force (stress) cycles. Either shear stress orapplied force may be used as a constant amplitude fatiguevariable.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system ma
5、y not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard. Within the text, the inch-pound units areshown in brackets.1.4 This standard does not purport to address all of thesafety c
6、oncerns, 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 regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C271/C271M Test Method for Density o
7、f Sandwich CoreMaterialsC273/C273M Test Method for Shear Properties of SandwichCore MaterialsD883 Terminology Relating to PlasticsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsE6 T
8、erminology Relating to Methods of 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 Sta
9、tisticsE467 Practice for Verification of Constant Amplitude Dy-namic Forces in an Axial Fatigue Testing SystemE739 Practice for StatisticalAnalysis of Linear or LinearizedStress-Life (S-N) and Strain-Life (-N) Fatigue DataE1012 Practice for Verification of Testing Frame and Speci-men Alignment Under
10、 Tensile and Compressive AxialForce Application2.2 ISO Standards3ISO 13003:2003(E) Fibre-reinforced plastics: Determinationof fatigue properties under cyclic loading conditions3. Terminology3.1 Definitions:3.1.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites, as
11、 well as terms relatingto sandwich constructions. Terminology D883 defines termsrelating to plastics. Terminology E6 defines terms relating tomechanical testing. Terminology E456 and Practice E177define terms relating to statistics. In the event of a conflictbetween terms, Terminology D3878 shall ha
12、ve precedenceover the other terminologies.NOTE 1If the term represents a physical quantity, its analyticaldimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions, shown within square
13、 brackets: Mfor mass, L for length, T for time, for thermodynamic temperature,and nd for non-dimensional quantities. Use of these symbols is restrictedto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets.3.2 Definitions:1Thi
14、s 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 1957. Last previous edition approved in 2013 as C394
15、 13. DOI:10.1520/C0394_C0394M-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 website.3Available from Internationa
16、l Organization for Standardization (ISO), 1, ch. dela Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.1 constant amplitude loading, nin fatigue, a loading inwhi
17、ch all of the peak values of force (stress) are equal and allof the valley values of force (stress) are equal.3.2.2 fatigue loading transition, nin the beginning offatigue loading, the number of cycles before the force (stress)reaches the desired peak and valley values.3.2.3 force (stress) ratio, R
18、nd, nin fatigue loading, theratio of the minimum applied force (stress) to the maximumapplied force (stress), where positive force (stress) correspondsto the tension mode of loading.3.2.4 frequency, f T-1, nin fatigue loading, the number offorce (stress) cycles completed in 1 s (Hz).3.2.5 peak, nin
19、fatigue loading, the occurrence where thefirst derivative of the force (stress) versus time changes frompositive to negative sign; the point of maximum force (stress)in constant amplitude loading.3.2.6 residual strength, ML-1T-2, nthe value of force(stress) required to cause failure of a specimen un
20、der quasi-static loading conditions after the specimen is subjected tofatigue loading.3.2.7 run-out, nin fatigue, an upper limit on the number offorce cycles to be applied.3.2.8 spectrum loading, nin fatigue, a loading in whichthe peak values of force (stress) are not equal or the valleyvalues of fo
21、rce (stress) are not equal (also known as variableamplitude loading or irregular loading).3.2.9 valley, nin fatigue loading, the occurrence where thefirst derivative of the force (stress) versus time changes fromnegative to positive sign; the point of minimum force (stress)in constant amplitude load
22、ing.3.2.10 wave form, nthe shape of the peak-to-peak varia-tion of the force (stress) as a function of time.3.3 Symbolsb = width of specimen, mm inCV = coefficient of variation statistic of a sample populationfor a given property (in percent)L = length of specimen, mm inN = number of constant amplit
23、ude cyclesP = force on specimen, positive for tension mode of loading,N lbR = fatigue force (stress) ratio, minimum-to-maximumcyclic force (stress)Sn1= standard deviation statistic of a sample population fora given propertyx1= test result for an individual specimen from the samplepopulation for a gi
24、ven propertyx = mean or average (estimate of mean) of a samplepopulation for a given property = core shear stress, MPa psi4. Summary of Test Method4.1 This test method consists of subjecting a sandwich coreto cyclic shear force parallel to the plane of its faces. The forceis transmitted to the core
25、through loading plates which arebonded directly to the core (unlike the static core shear test,Test Method C273/C273M, bonding of loading plates tofacesheets bonded to the core is not permitted). The number offorce (stress) cycles at which failure occurs for a specimensubjected to a specific force (
26、stress) ratio and force (stress)magnitude is determined.NOTE 2This test method may be used as a guide to conduct shearfatigue testing of sandwich panels consisting of facesheets and core withthe Test Method C273/C273M loading plates bonded to the facesheets.4.2 The only acceptable failure modes for
27、shear fatigue ofsandwich core materials are those which are internal to thesandwich core. Failure of the loading plate-to-core bond is notan acceptable failure mode.5. Significance and Use5.1 Often the most critical stress to which a sandwich panelcore is subjected is shear. The effect of repeated s
28、hear stresseson the core material can be very important, particularly interms of durability under various environmental conditions.5.2 This test method provides a standard method of obtain-ing the sandwich core shear fatigue response. Uses includescreening candidate core materials for a specific app
29、lication,developing a design-specific core shear cyclic stress limit, andcore material research and development.NOTE 3This test method may be used as a guide to conduct spectrumloading. This information can be useful in the understanding of fatiguebehavior of core under spectrum loading conditions,
30、but is not covered inthis standard.5.3 Factors that influence core fatigue response and shalltherefore be reported include the following: core material, coregeometry (density, cell size, orientation, etc.), specimen geom-etry and associated measurement accuracy, specimenpreparation, specimen conditi
31、oning, environment of testing,specimen alignment, loading procedure, loading frequency,force (stress) ratio and speed of testing (for residual strengthtests).NOTE 4If a sandwich panel is tested using the guidance of thisstandard, the following may also influence the fatigue response and shouldbe rep
32、orted: facing material, adhesive material, methods of materialfabrication, adhesive thickness and adhesive void content. Further, core-to-facing strength may be different between precured/bonded and co-curedfacings in sandwich panels with the same core and facing materials.6. Interferences6.1 Materi
33、al and Specimen PreparationPoor material fab-rication practices and damage induced by improper specimenmachining are known causes of high data scatter in compositesin general. Specific material factors that affect sandwich coreinclude variability in core density and degree of cure of corebonding adh
34、esive. For this particular core shear test, thicknessof the adhesive bond to honeycomb core (adhesive-filled depthinto the honeycomb core cells), core misalignment/distortion/damage, or bonding surface roughness may affect the coreshear strength and fatigue life.6.2 System AlignmentUnintended loadin
35、g eccentricitieswill cause premature failure. Every effort should be made toeliminate undesirable eccentricities from the test system. Sucheccentricities may occur as a result of misaligned grips, poorspecimen preparation, or poor alignment of the bonded loadingplates and loading fixture. If there i
36、s any doubt as to thealignment inherent in a given test machine, then the alignmentC394/C394M 162should be checked following the general philosophical ap-proach described in Test Method E1012.6.3 GeometrySpecific geometric factors that affect coreshear fatigue response include core cell geometry (sh
37、ape,density, orientation), core thickness, specimen shape (L/bratio), and adhesive thickness.6.4 EnvironmentResults are affected by the environmentalconditions under which the tests are conducted. Specimenstested in various environments can exhibit significant differ-ences in both fatigue life and f
38、ailure mode. Critical environ-ments must be assessed independently for each adhesive andcore material tested. If possible, test the specimen under thesame fluid exposure level used for conditioning. However,cases such as elevated temperature testing of a moist specimenplace unrealistic requirements
39、on the capabilities of commontesting machine environmental chambers. In such cases, themechanical test environment may need to be modified, forexample, by testing at elevated temperature with no fluidexposure control, but with a specified limit on time to failurefrom withdrawal from the conditioning
40、 chamber.6.5 Loading FrequencyResults may be affected by speci-men heating if the test is run at too high a cyclic loading rate.High cyclic rates may induce heating due to material damping,and may cause variations in specimen temperature and prop-erties of the core. Varying the cyclic frequency duri
41、ng the testis generally not recommended, as the response may be sensi-tive to the frequency utilized and the resultant thermal history.6.6 Force (Stress) RatioResults may be affected by theforce (stress) ratio under which the tests are conducted.6.7 Loading ModeResults may be affected by the mode of
42、loading (tension versus compression).6.8 Failure ModeIn some sandwich applications the ef-fective shear strength of the core may be limited by the strengthof the core-to-facing interface. In these cases it may beappropriate to test a sandwich panel representative of theintended application.7. Appara
43、tus7.1 MicrometersThe micrometer(s) shall use a flat anvilinterface on machined edges or very smooth-tooled surfaces.The accuracy of the instrument(s) shall be suitable for readingto within1%ofthesample length, width and thickness. Fortypical specimen geometries, an instrument with an accuracyof 625
44、 m 60.001 in. is desirable for thickness, length andwidth measurement.7.2 Test FixturesUse either the tension or compressiontension loading fixture described in Test Method C273/C273Mdepending on the specified mode of loading.7.3 Testing MachineThe testing machine shall be in ac-cordance with Practi
45、ce E467 and shall satisfy the followingrequirements:7.3.1 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 accordance w
46、ith 11.7.7.3.2 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 inertia lag at the specified rate of testing and shallindicate the force with an accuracy over the force r
47、ange(s) ofinterest to within 61 % of the indicated value.7.3.3 CounterThe testing machine shall be capable ofcounting cycles of applied load.7.4 Conditioning ChamberWhen conditioning materialsin non-laboratory environments, a temperature/vapor-levelcontrolled environmental conditioning chamber is re
48、quired 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 atregular intervals.7.5 Environmental Test ChamberAn environm
49、ental 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.7.6 Thermocouple and Temperature Recording Devices,capable of reading specimen temperature to 60.5C 61.0F.8. Sampling and Test Specimens8.1 SamplingFor statistically significant data, the proce-dures outlined in Practice E122 should be consulted. Astatistically significant
