1、Designation: C394 00 (Reapproved 2008)C394/C394M 13Standard Test Method forShear Fatigue of Sandwich Core Materials1This standard is issued under the fixed designation C394;C394/C394M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision
2、, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers determination of determines the effect of repeated shear loads on sandwich core
3、materials.forceson core material used in sandwich panels. Permissible core material forms include those with continuous bonding surfaces (suchas balsa wood and foams) as well as those with discontinuous bonding surfaces (such as honeycomb).1.2 This test method is limited to test specimens subjected
4、to constant amplitude uniaxial loading, where the machine iscontrolled so that the test specimen is subjected to repetitive constant amplitude force (stress) cycles. Either shear stress or appliedforce may be used as a constant amplitude fatigue variable.1.3 The values stated in either SI units or i
5、nch-pound units are to be regarded separately as the standard. The inch-pound unitsgiven may be approximate.standard. The values stated in each system may not be exact equivalents; therefore, each system shallbe used independently of the other. Combining values from the two systems may result in non
6、-conformance with the standard.Within the text, the inch-pound units are shown in brackets.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practi
7、ces and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C271/C271M Test Method for Density of Sandwich Core MaterialsC273C273/C273M Test Method for Shear Properties of Sandwich Core MaterialsC274/C274M Terminology of Structural Sandwich Co
8、nstructionsD883 Terminology Relating to PlasticsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for Moisture Absorption Properties and Equilibrium Conditioning of Polymer Matrix CompositeMaterialsE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating
9、Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot orProcessE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE456 Terminology Relating to Quality and StatisticsE4E467 PracticesPractice for Force Verification of Testing MachinesVerifi
10、cation of Constant Amplitude Dynamic Forces in anAxial Fatigue Testing SystemE739 Practice for Statistical Analysis of Linear or Linearized Stress-Life (S-N) and Strain-Life (-N) Fatigue DataE1012 Practice for Verification of Testing Frame and Specimen Alignment Under Tensile and Compressive Axial F
11、orceApplicationE1309 Guide for Identification of Fiber-Reinforced Polymer-Matrix Composite Materials in DatabasesE1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in DatabasesE1471 Guide for Identification of Fibers, Fillers, and Core Materials in Computerized Ma
12、terial Property Databases1 This test method is under the jurisdiction of ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.09 on SandwichConstruction.Current edition approved March 1, 2008Oct. 1, 2013. Published April 2008 October 2013. Originally approve
13、d in 1957. Last previous edition approved in 2000 asC394 00(2008) . DOI: 10.1520/C0394-00R08.10.1520/C0394_C0394M13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to t
14、he standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes a
15、ccurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United
16、States12.2 ISO Standards3ISO 13003:2003(E) Fibre-reinforced plastics: Determination of fatigue properties under cyclic loading conditions3. Terminology3.1 Definitions:3.1.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology C274/C274Mdefines terms relat
17、ing to structural sandwich constructions. Terminology D883 defines terms relating to plastics. Terminology E6defines terms relating to mechanical testing. Terminology E456 and Practice E177 define terms relating to statistics. In the eventof a conflict between terms, Terminology D3878 shall have pre
18、cedence over the other terminologies.NOTE 1If the term represents a physical quantity, its analytical dimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard symbology for fundamental dimensions, shown within square brac
19、kets: M for mass,L for length, T for time, for thermodynamic temperature, and nd for non-dimensional quantities. Use of these symbols is restricted to analyticaldimensions when used with square brackets, as the symbols may have other definitions when used without the brackets.3.2 Definitions:3.2.1 c
20、onstant amplitude loading, nin fatigue, a loading in which all of the peak values of force (stress) are equal and all ofthe valley values of force (stress) are equal.3.2.2 fatigue loading transition, nin the beginning of fatigue loading, the number of cycles before the force (stress) reachesthe desi
21、red peak and valley values.3.2.3 force (stress) ratio, R nd, nin fatigue loading, the ratio of the minimum applied force (stress) to the maximum appliedforce (stress), where positive force (stress) corresponds to the tension mode of loading.3.2.4 frequency, f T-1, nin fatigue loading, the number of
22、force (stress) cycles completed in 1 s (Hz).3.2.5 peak, nin fatigue loading, the occurrence where the first 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 val
23、ue of force (stress) required to cause failure of a specimen under quasi-staticloading conditions after the specimen is subjected to fatigue loading.3.2.7 run-out, nin fatigue, an upper limit on the number of force cycles to be applied.3.2.8 spectrum loading, nin fatigue, a loading in which the peak
24、 values of force (stress) are not equal or the valley values offorce (stress) are not equal (also known as variable amplitude loading or irregular loading).3.2.9 valley, nin fatigue loading, the occurrence where the first derivative of the force (stress) versus time changes fromnegative to positive
25、sign; the point of minimum force (stress) in constant amplitude loading.3.2.10 wave form, nthe shape of the peak-to-peak variation of the force (stress) as a function of time.3.3 Symbolsb = width of specimen, mm inCV = coefficient of variation statistic of a sample population for a given property (i
26、n percent)L = length of specimen, mm inN = number of constant amplitude cyclesP = force on specimen, positive for tension mode of loading, N lbR = fatigue force (stress) ratio, minimum-to-maximum cyclic force (stress)Sn1 = standard deviation statistic of a sample population for a given propertyx1 =
27、test result for an individual specimen from the sample population for a given propertyx = mean or average (estimate of mean) of a sample population for a given property = core shear stress, MPa psi4. Summary of Test Method4.1 This test method consists of subjecting a sandwich core to cyclic shear fo
28、rce parallel to the plane of its faces. The force istransmitted to the core through loading plates which are bonded directly to the core (unlike the static core shear test, Test MethodC273/C273M, bonding of loading plates to facesheets bonded to the core is not permitted). The number of force (stres
29、s) cyclesat which failure occurs for a specimen subjected to a specific force (stress) ratio and force (stress) magnitude is determined.NOTE 2This test method may be used as a guide to conduct shear fatigue testing of sandwich panels consisting of facesheets and core with the TestMethod C273/C273M l
30、oading plates bonded to the facesheets.4.2 The only acceptable failure modes for shear fatigue of sandwich core materials are those which are internal to the sandwichcore. Failure of the loading plate-to-core bond is not an acceptable failure mode.3 Available from International Organization for Stan
31、dardization (ISO), 1, ch. de la Voie-Creuse, CP 56, CH-1211 Geneva 20, Switzerland, http:/www.iso.org.C394/C394M 1325. Significance and Use5.1 UsuallyOften the most critical stress to which a sandwich panel core is subjected is shear. The effect of repeated shearstresses on the core material can be
32、very important.important, particularly in terms of durability under various environmentalconditions.5.2 TheseThis test methods providemethod provides a standard method of obtaining the sandwich core shear fatigueproperties.response. Uses include screening candidate core materials for a specific appl
33、ication, developing a design-specific coreshear cyclic stress limit, and core material research and development.NOTE 3This test method may be used as a guide to conduct spectrum loading. This information can be useful in the understanding of fatigue behaviorof core under spectrum loading conditions,
34、 but is not covered in this standard.5.3 Factors that influence core fatigue response and shall therefore be reported include the following: core material, coregeometry (density, cell size, orientation, etc.), specimen geometry and associated measurement accuracy, specimen preparation,specimen condi
35、tioning, environment of testing, specimen alignment, loading procedure, loading frequency, force (stress) ratio andspeed of testing (for residual strength tests).NOTE 4If a sandwich panel is tested using the guidance of this standard, the following may also influence the fatigue response and should
36、be reported:facing material, adhesive material, methods of material fabrication, adhesive thickness and adhesive void content. Further, core-to-facing strength maybe different between precured/bonded and co-cured facings in sandwich panels with the same core and facing materials.6. Interferences6.1
37、Material and Specimen PreparationPoor material fabrication practices and damage induced by improper specimenmachining are known causes of high data scatter in composites in general. Specific material factors that affect sandwich coreinclude variability in core density and degree of cure of core bond
38、ing adhesive. For this particular core shear test, thickness of theadhesive bond to honeycomb core (adhesive-filled depth into the honeycomb core cells), core misalignment/distortion/damage, orbonding surface roughness may affect the core shear strength and fatigue life.6.2 System AlignmentUnintende
39、d loading eccentricities will cause premature failure. Every effort should be made to eliminateundesirable eccentricities from the test system. Such eccentricities may occur as a result of misaligned grips, poor specimenpreparation, or poor alignment of the bonded loading plates and loading fixture.
40、 If there is any doubt as to the alignment inherentin a given test machine, then the alignment should be checked following the general philosophical approach described in TestMethod E1012.6.3 GeometrySpecific geometric factors that affect core shear fatigue response include core cell geometry (shape
41、, density,orientation), core thickness, specimen shape (L/b ratio), and adhesive thickness.6.4 EnvironmentResults are affected by the environmental conditions under which the tests are conducted. Specimens testedin various environments can exhibit significant differences in both fatigue life and fai
42、lure mode. Critical environments must beassessed independently for each adhesive and core material tested. If possible, test the specimen under the same fluid exposurelevel used for conditioning. However, cases such as elevated temperature testing of a moist specimen place unrealistic requirementson
43、 the capabilities of common testing machine environmental chambers. In such cases, the mechanical test environment may needto be modified, for example, by testing at elevated temperature with no fluid exposure control, but with a specified limit on timeto failure from withdrawal from the conditionin
44、g chamber.6.5 Loading FrequencyResults may be affected by specimen heating if the test is run at too high a cyclic loading rate. Highcyclic rates may induce heating due to material damping, and may cause variations in specimen temperature and properties of thecore. Varying the cyclic frequency durin
45、g the test is generally not recommended, as the response may be sensitive to the frequencyutilized and the resultant thermal history.6.6 Force (Stress) RatioResults may be affected by the force (stress) ratio under which the tests are conducted.6.7 Loading ModeResults may be affected by the mode of
46、loading (tension versus compression).6.8 Failure ModeIn some sandwich applications the effective shear strength of the core may be limited by the strength of thecore-to-facing interface. In these cases it may be appropriate to test a sandwich panel representative of the intended application.7. Appar
47、atus7.1 MicrometersThe micrometer(s) shall use a flat anvil interface on machined edges or very smooth-tooled surfaces. Theaccuracy of the instrument(s) shall be suitable for reading to within 1 % of the sample length, width and thickness. For typicalspecimen geometries, an instrument with an accura
48、cy of 625 m 60.001 in. is desirable for thickness, length and widthmeasurement.7.2 Test FixturesUse either the tension or compression tension loading fixture described in Test Method C273/C273Mdepending on the specified mode of loading.C394/C394M 1337.3 Fatigue Testing Machine, Machineany standard c
49、onstant load fatigue testing machine capable of applying a direct stressto the specimen and equipped with a counter. The load measuring system used shall have an accuracy of 61 % of the indicatedvalue.The accuracy of the test machine shall be verifiedThe testing machine shall be in accordance with PracticesPractice E4E467.and shall satisfy the following requirements:7.3.1 Drive MechanismThe testing machine drive mechanism shall be capable of imparting to the movable head a controlledvelocity with respect to the statio
