1、Designation: D 6416/D 6416M 01 (Reapproved 2007)Standard Test Method forTwo-Dimensional Flexural Properties of Simply SupportedSandwich Composite Plates Subjected to a DistributedLoad1This standard is issued under the fixed designation D 6416/D 6416M; the number immediately following the designation
2、 indicates 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method determines the two-
3、dimensional 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 procedur
4、e of Test Method C 393,where concentrated loads induce one-dimensional, simplebending in beam 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 compo
5、sed of 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
6、 are not exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibil
7、ity 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:2C 274 Terminology of Structural Sandwich ConstructionsC 365 Test Method for Flatwise Compressive P
8、roperties ofSandwich CoresC 393 Test Method for Flexural Properties of SandwichConstructionsD 792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD 2584 Test Method for Ignition Loss of Cured ReinforcedResinsD 2734 Test Methods for Void Content of Reinfor
9、ced Plas-ticsD 3171 Test Methods for Constituent Content of CompositeMaterialsD 3878 Terminology for Composite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 251 Test Methods for Performance Characteristics ofMetallic Bonded
10、 Resistance Strain GagesE 1237 Guide for Installing Bonded Resistance StrainGages2.2 ASTM Adjunct:Sandwich Plate Test Fixture and Hydromat Pressure Blad-der, ASTM D 6416/D 6416M33. Terminology3.1 Terminology D 3878 defines terms relating to high-modulus fibers and their composites. Terminology C 274
11、defines terms relating to structural sandwich constructions.Terminology E6defines terms relating to mechanical testing.In the event of a conflict between terms, Terminology D 3878shall have precedence over the other terminology standards.3.2 Definitions of Terms Specific to This Standard:3.2.1 bendi
12、ng stiffness, 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.
13、3.2.3 face sheet, nthe outermost layer or composite com-ponent of a sandwich construction, generally thin and of high1This 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
14、 approved Jan. 1, 2007. Published January 2007. Originallyapproved in 1999. Last previous edition approved in 2001 as D 6416/D6416M 01e1.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume i
15、nformation, refer to the standards Document Summary page onthe ASTM website.3Detailed drawings for the fabrication of the 500mm test fixture and pressurebladder shown in Fig. 3 and Fig. 4 are available from ASTM Headquarters. OrderAdjunct No. ADJD6416.1Copyright ASTM International, 100 Barr Harbor D
16、rive, PO Box C700, West Conshohocken, PA 19428-2959, United States.density, which resists most of the edgewise loads and flatwisebending moments: synonymous with face, skin, and facing.3.2.4 footprint, nthe enclosed area of the face sheetsurface of a sandwich panel in contact with the pressurebladde
17、r 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 essentiallythe same properties in
18、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, yet pliable closedcontainer fill
19、ed 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 with shear rigidity.3.2.10 test
20、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 the length andwidth of the test p
21、anel 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 ex= normal face sheet strain, x component.3.3.6 ey= normal face sheet strain, y component.3.3.7 f = f
22、ace 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 pressure.3.3.12 f = width of the un
23、loaded 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 ve= experimentally determined deflection at centerof test panel.4. Summary of Test Method4.1 Asquare test panel is simply supported on all four edgesand unifo
24、rmly 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 subjected to awell-defined distr
25、ibuted 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. Since the pressure bladder
26、 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 face-sheet surface. Atypical
27、 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 method can be used tocompare the
28、 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 failure mecha-nisms of sandw
29、ich 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 code for use asstructural d
30、esign 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. Interferences6.1 Material and Specime
31、n 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 variability in core density an
32、d 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 non-squareness of adjacent
33、 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 significant effect ontest re
34、sults. 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 axis. Given the fixtureitself
35、has sufficient rigidity, erroneous conclusions about panelstrength and stiffness might be drawn if insufficient torque hasbeen applied to the fasteners securing the lower panel edgeD 6416/D 6416M 01 (2007)2support frame. In general, panels with more flexural rigidityand shear rigidity require more b
36、olt torque to approach simplesupport.6.3 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 theabsolute load applied b
37、y 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 shapes)and (2) the pressure is
38、 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 the observedstrains and
39、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 effective contact area can be ca
40、lculated 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. Calibration tests using
41、 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 properedge support and c
42、onstraint.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 also result if the pressu
43、re 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 is anartifact of the test.
44、 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-side panel surface.To minim
45、ize 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 be inconformance with Prac
46、tices E4and 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 controlled velocity with
47、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 device shall be essentiallyfre
48、e 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 strength evaluation, orbo
49、th, 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 circular cross-section,12.7 mm 0.5 in.
