1、Designation: D6416/D6416M 01 (Reapproved 2012)Standard Test Method forTwo-Dimensional Flexural Properties of Simply SupportedSandwich Composite Plates Subjected to a DistributedLoad1This standard is issued under the fixed designation D6416/D6416M; the number immediately following the designation ind
2、icates theyear of original adoption or, in the case of revision, 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 determines the two-dimen
3、sional flex-ural properties of sandwich composite plates subjected to adistributed load. The test fixture uses a relatively large squarepanel sample which is simply supported all around and has thedistributed load provided by a water-filled bladder. This type ofloading differs from the procedure of
4、Test Method C393, whereconcentrated loads induce one-dimensional, simple bending inbeam specimens.1.2 This test method is applicable to composite structures ofthe sandwich type which involve a relatively thick layer of corematerial bonded on both faces with an adhesive to thin-facesheets composed of
5、 a denser, higher-modulus material, typi-cally, a polymer matrix reinforced with high-modulus fibers.1.3 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 n
6、ot exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of
7、 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:2C274 Terminology of Structural Sandwich ConstructionsC365/C365M Test Method for Flatwise Compressive Pro
8、p-erties of Sandwich CoresC393 Test Method for Flexural Properties of SandwichConstructionsD792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD2584 Test Method for Ignition Loss of Cured ReinforcedResinsD2734 Test Methods for Void Content of Reinforced
9、Plas-ticsD3171 Test Methods for Constituent Content of CompositeMaterialsD3878 Terminology for Composite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE251 Test Methods for Performance Characteristics of Me-tallic Bonded Resis
10、tance Strain GaugesE1237 Guide for Installing Bonded Resistance Strain Gages2.2 ASTM Adjunct:Sandwich Plate Test Fixture and Hydromat Pressure Blad-der, ASTM D6416/D6416M33. Terminology3.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology C274 de-fines
11、 terms relating to structural sandwich constructions. Ter-minology E6 defines terms relating to mechanical testing. Inthe event of a conflict between terms, Terminology D3878 shallhave precedence over the other terminology standards.3.2 Definitions of Terms Specific to This Standard:3.2.1 bending st
12、iffness, nthe sandwich property whichresists bending deflections.3.2.2 core, na centrally located layer of a sandwichconstruction, usually low density, which separates and stabi-lizes the facings and transmits shear between the facings andprovides most of the shear rigidity of the construction.3.2.3
13、 face sheet, nthe outermost layer or composite com-ponent of a sandwich construction, generally thin and of highdensity, which resists most of the edgewise loads and flatwisebending moments: synonymous with face, skin, and facing.1This test method is under the jurisdiction of ASTM Committee D30 onCo
14、mposite Materials and is the direct responsibility of Subcommittee D30.09 onSandwich Construction.Current edition approved Aug. 1, 2012. Published December 2012. Originallyapproved in 1999. Last previous edition approved in 2007 as D6416/D6416M 01(2007). DOI: 10.1520/D6416_D6416M-01R12.2For referenc
15、ed 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.3Detailed drawings for the fabrication of the 500mm test fixture and press
16、urebladder shown in Fig. 3 and Fig. 4 are available from ASTM Headquarters. OrderAdjunct No. ADJD6416.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.4 footprint, nthe enclosed area of the face sheetsurface of a sandwich panel in
17、 contact with the pressurebladder during loading.3.2.5 hydromat, na pressure bladder with a square perim-eter fabricated from two square pieces of industrial beltingwhich are superposed and clamped at the edges with through-bolted, mild steel bar stock.3.2.6 isotropic material, na material having es
18、sentiallythe same properties in any direction.3.2.7 orthotropic material, na material in which a prop-erty of interest, at a given point, possesses three mutuallyperpendicular planes of symmetry, which taken together definethe principal material coordinate system.3.2.8 pressure bladder, na durable,
19、yet pliable closedcontainer filled with water, or other incompressible fluid,capable of conforming to the contour of a normally loaded testpanel when compressed against its face sheet surface by a testmachine.3.2.9 shear stiffness, nthe sandwich property which re-sists shear distortions: synonymous
20、with shear rigidity.3.2.10 test panel, na square coupon of sandwich construc-tion fabricated for two-dimensional flexural testing: synony-mous with sandwich panel, sandwich composite plate, sand-wich composite panel, and panel test specimen.3.3 Symbols:3.3.1 a = support span of the test fixture or t
21、he length andwidth of the test panel structure between supports.3.3.2 Aeff= effective contact area of the pressure bladderwhen compressed against the test panel.3.3.3 B = test panel bending stiffness.3.3.4 c = core thickness.3.3.5 x= normal face sheet strain, x component.3.3.6 y= normal face sheet s
22、train, y component.3.3.7 f = face sheet thickness.3.3.8 Fm= total normal force applied to a test panel asmeasured by the test machine load cell.3.3.9 h = average overall thickness of the test panel.3.3.10 N = the number of included terms of the series.3.3.11 Pm= experimentally measured bladder press
23、ure.3.3.12 = width of the unloaded border area of a test panelbetween the edge supports and the effective footprint boundary.3.3.13 S = test panel shear stiffness.3.3.14 e= experimentally determined deflection at centerof test panel.4. Summary of Test Method4.1 Asquare test panel is simply supported
24、 on all four edgesand uniformly loaded over a portion of its surface by awater-filled bladder. Pressure on the panel is increased bymoving the platens of the test frame. The test measures thetwo-dimensional flexural response of a sandwich compositeplate in terms of deflections and strains when subje
25、cted to awell-defined distributed load.4.2 Panel deflection at load is monitored by a centrallypositioned LVDT which contacts the tension-side surface.4.3 Load is monitored by both a crosshead-mounted loadcell, in series with the test fixture, and a pressure transducer inthe pressure bladder itself.
26、 Since the pressure bladder is also atall times in series with the load cell and test fixture, theeffective contact area of the pressure field is continuouslymonitored as the load/pressure quotient.4.4 Strain can be monitored with strategically placed straingage rosettes bonded to the tension-side f
27、ace-sheet surface. Atypical arrangement has four rosettes equally spaced along oneof the axes of symmetry of the plate.5. Significance and Use5.1 This test method simulates the hydrostatic loadingconditions which are often present in actual sandwich struc-tures, such as marine hulls. This test metho
28、d can be used tocompare the two-dimensional flexural stiffness of a sandwichcomposite made with different combinations of materials orwith different fabrication processes. Since it is based ondistributed loading rather than concentrated loading, it mayalso provide more realistic information on the f
29、ailure mecha-nisms of sandwich structures loaded in a similar manner. Testdata should be useful for design and engineering, materialspecification, quality assurance, and process development. Inaddition, data from this test method would be useful in refiningpredictive mathematical models or computer
30、code for use asstructural design tools. Properties that may be obtained fromthis test method include:5.1.1 Panel surface deflection at load,5.1.2 Panel face-sheet strain at load,5.1.3 Panel bending stiffness,5.1.4 Panel shear stiffness,5.1.5 Panel strength, and5.1.6 Panel failure modes.6. Interferen
31、ces6.1 Material and Specimen PreparationPoor materialfabrication practices, lack of control of fiber alignment, anddamage induced by improper coupon machining are knowncauses of high material data scatter in composites in general.Specific material factors that affect sandwich composites in-clude var
32、iability in core density and degree of cure of resin inboth face sheet matrix material and core bonding adhesive.Important aspects of sandwich panel specimen preparation thatcontribute to data scatter are incomplete wetout of face sheetfabric, incomplete or nonuniform core bonding of face sheets,the
33、 non-squareness of adjacent panel edges, the misalignmentof core and face sheet elements, the existence of joints or othercore and face sheet discontinuities, out-of-plane curvature, andsurface roughness.6.2 Test Fixture CharacteristicsConfiguration of thepanel edge-constraint structure can have a s
34、ignificant effect ontest results. Correct interpretation of test data depends on thefixture supporting the test panel in such a manner that theboundary conditions consistent with simple support can beassumed to apply. Panel edge support journals must be copla-nar and perpendicular to the loading axi
35、s. Given the fixtureitself has sufficient rigidity, erroneous conclusions about panelstrength and stiffness might be drawn if insufficient torque hasbeen applied to the fasteners securing the lower panel edgesupport frame. In general, panels with more flexural rigidityand shear rigidity require more
36、 bolt torque to approach simplesupport.D6416/D6416M 01 (2012)26.3 Pressure Bladder CharacteristicsWhen a pressurebladder is used to introduce normal load to a plate, the responseof the plate is dependent on the resulting pressure distribution.The true function of the pressure bladder is to convert t
37、heabsolute load applied by the test machine into a pressure fieldthat can be specified by a relatively simple mathematicalmodel. With the hydromat-style bladder, two simplifyingassumptions are permitted: (1) the shape of the contact area isa readily definable geometric shape (or combination of shape
38、s)and (2) the pressure is constant within the boundaries of thecontact area. The pressure distribution is then characterizedmerely by the magnitude of the pressure and the size of thefootprint. Obviously, the size and shape of the pressure bladderhave a significant effect on test results in terms of
39、 the observedstrains and deflections. Some errors in data interpretation arepossible insofar as the actual pressure distribution differs fromthe simple mathematical model used in calculations.NOTE 1The error in the hydromat model has mainly to do with detailsof the footprint shape, since the effecti
40、ve contact area can be calculated atany time by dividing the absolute applied load by the bladder pressure. Asecondary error arises from the non-zero bending stiffness of the fiber-reinforced industrial belting fabric that results in a narrow band of varyingpressure at the very edge of the footprint
41、. Calibration tests using a steelplate equipped with strain gages are recommended for each bladder unitto verify that the errors in the pressure distribution model are negligible(see Section 9).6.4 TolerancesTest panels need to meet the dimensionaland squareness tolerances specified in 8.2 to ensure
42、 properedge support and constraint.6.5 System AlignmentErrors can result if the panel sup-port structure is not centered with respect to the actuator of thetest machine, or if the plane defined by the panel edge-bearingsurfaces is not perpendicular to the loading axis of the testmachine. Errors can
43、also result if the pressure bladder is notcentered properly with respect to fixture and actuator or if theedges of the bladder clamping bars are not parallel to the paneledge-support journals.6.6 Other System CharacteristicsWhen attempting tomeasure panel surface deflection, an error results which i
44、s anartifact of the test. It arises as normal load is applied, to theextent that the edges of the sandwich specimen are compressedfrom the reactive line loads generated by the upper and lowerpanel support structure. This direct rigid-body addition affectsany LVDT positioned to contact the tension-si
45、de panel surface.To minimize the error, the edges of soft-core panels should bereinforced in accordance with 8.3.2.7. Apparatus7.1 Procedures A, B, and CA schematic diagram illustrat-ing the key components of the test method apparatus appears inFig. 1.7.1.1 Testing MachineThe testing machine shall b
46、e inconformance with Practices E4 and shall satisfy the followingrequirements:7.1.1.1 Testing Machine HeadsThe testing machine shallhave both an essentially stationary head and a movable head.7.1.1.2 Drive MechanismThe testing machine drivemechanism shall be capable of imparting to the movable heada
47、 controlled velocity with respect to the stationary head. Thevelocity of the movable head shall be capable of beingregulated in accordance with 11.3.7.1.1.3 Load IndicatorThe testing machine load-sensingdevice shall be capable of indicating the total load beingcarried by the test specimen. This devi
48、ce shall be essentiallyfree from inertia-lag at the specified rate of testing and shallindicate the load with an accuracy over the load range(s) ofinterest of within 61 % of the indicated value. The loadrange(s) of interest may be fairly low for bending and shearmodulus evaluation or much higher for
49、 strength evaluation, orboth, as required.7.1.2 Loading FixtureAs illustrated in the schematic dia-gram of Fig. 1, the loading fixture has two parts, a rigid,overhead upper panel support structure, which is attached tothe load cell on the load frame crosshead, and a rigid lowerpanel edge support frame which bolts to the upper panelsupport structure at the corners. A square sandwich compositepanel specimen is constrained at the edges when captured fromabove and below by these two fixture elements. All bearingsurfaces are hardened steel rods with a circula
