1、Designation: D 790 071Standard Test Methods forFlexural Properties of Unreinforced and Reinforced Plasticsand Electrical Insulating Materials1This standard is issued under the fixed designation D 790; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1NOTERemoved resear
3、ch report footnote from Section 14 editorially in September 2008.1. Scope*1.1 These test methods cover the determination of flexuralproperties of unreinforced and reinforced plastics, includinghigh-modulus composites and electrical insulating materials inthe form of rectangular bars molded directly
4、or cut from sheets,plates, or molded shapes. These test methods are generallyapplicable to both rigid and semirigid materials. However,flexural strength cannot be determined for those materials thatdo not break or that do not fail in the outer surface of the testspecimen within the 5.0 % strain limi
5、t of these test methods.These test methods utilize a three-point loading system appliedto a simply supported beam. A four-point loading systemmethod can be found in Test Method D 6272.1.1.1 Procedure A, designed principally for materials thatbreak at comparatively small deflections.1.1.2 Procedure B
6、, designed particularly for those materialsthat undergo large deflections during testing.1.1.3 Procedure A shall be used for measurement of flexuralproperties, particularly flexural modulus, unless the materialspecification states otherwise. Procedure B may be used formeasurement of flexural strengt
7、h only. Tangent modulus dataobtained by Procedure A tends to exhibit lower standarddeviations than comparable data obtained by means of Proce-dure B.1.2 Comparative tests may be run in accordance with eitherprocedure, provided that the procedure is found satisfactory forthe material being tested.1.3
8、 The values stated in SI units are to be regarded as thestandard. The values provided in brackets are for informationonly.1.4 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-
9、priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1These test methods are not technically equivalent to ISO 178.2. Referenced Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 638 Test Method for Tensile P
10、roperties of PlasticsD 883 Terminology Relating to PlasticsD 4000 Classification System for Specifying Plastic Mate-rialsD 4101 Specification for Polypropylene Injection and Ex-trusion MaterialsD 5947 Test Methods for Physical Dimensions of SolidPlastics SpecimensD 6272 Test Method for Flexural Prop
11、erties of Unrein-forced and Reinforced Plastics and Electrical InsulatingMaterials by Four-Point BendingE4 Practices for Force Verification of Testing MachinesE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ISO Standard:3ISO 178 PlasticsDeterminat
12、ion of Flexural Properties3. Terminology3.1 DefinitionsDefinitions of terms applying to these testmethods appear in Terminology D 883 and Annex A1 of TestMethod D 638.4. Summary of Test Method4.1 A bar of rectangular cross section rests on two supportsand is loaded by means of a loading nose midway
13、between the1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.10 on MechanicalProperties.Current edition approved Sept. 1, 2007. Published October 2007. Originallyapproved in 1970. Last previous edition approved in 20
14、03 as D 790 03.2For 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 American National Standards In
15、stitute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.supports. A support span-to-depth rati
16、o of 16:1 shall be usedunless there is reason to suspect that a larger span-to-depthratio may be required, as may be the case for certain laminatedmaterials (see Section 7 and Note 7 for guidance).4.2 The specimen is deflected until rupture occurs in theouter surface of the test specimen or until a
17、maximum strain(see 12.7) of 5.0 % is reached, whichever occurs first.4.3 Procedure A employs a strain rate of 0.01 mm/mm/min0.01 in./in./min and is the preferred procedure for this testmethod, while Procedure B employs a strain rate of 0.10mm/mm/min 0.10 in./in./min.5. Significance and Use5.1 Flexur
18、al properties as determined by these test methodsare especially useful for quality control and specificationpurposes.5.2 Materials that do not fail by the maximum strainallowed under these test methods (3-point bend) may be moresuited to a 4-point bend test. The basic difference between thetwo test
19、methods is in the location of the maximum bendingmoment and maximum axial fiber stresses. The maximum axialfiber stresses occur on a line under the loading nose in 3-pointbending and over the area between the loading noses in 4-pointbending.5.3 Flexural properties may vary with specimen depth,temper
20、ature, atmospheric conditions, and the difference in rateof straining as specified in Procedures A and B (see also Note7).5.4 Before proceeding with these test methods, referenceshould be made to the ASTM specification of the materialbeing tested. Any test specimen preparation, conditioning,dimensio
21、ns, or testing parameters, or combination thereof,covered in the ASTM material specification shall take prece-dence over those mentioned in these test methods. Table 1 inClassification System D 4000 lists the ASTM material speci-fications that currently exist for plastics.6. Apparatus6.1 Testing Mac
22、hine A properly calibrated testing ma-chine that can be operated at constant rates of crosshead motionover the range indicated, and in which the error in the loadmeasuring system shall not exceed 61 % of the maximum loadexpected to be measured. It shall be equipped with a deflectionmeasuring device.
23、 The stiffness of the testing machine shall besuch that the total elastic deformation of the system does notexceed 1 % of the total deflection of the test specimen duringtesting, or appropriate corrections shall be made. The loadindicating mechanism shall be essentially free from inertial lagat the
24、crosshead rate used. The accuracy of the testing machineshall be verified in accordance with Practices E4.6.2 Loading Noses and SupportsThe loading nose andsupports shall have cylindrical surfaces. The default radii of theloading nose and supports shall be 5.0 6 0.1 mm 0.197 60.004 in. unless otherw
25、ise specified in an ASTM materialspecification or as agreed upon between the interested parties.When the use of an ASTM material specification, or an agreedupon modification, results in a change to the radii of theloading nose and supports, the results shall be clearly identifiedas being obtained fr
26、om a modified version of this test methodand shall include the specification (when available) from whichthe modification was specified, for example, Test MethodD 790 in accordance with Specification D 4101.6.2.1 Other Radii for Loading Noses and SupportsWhenother than default loading noses and suppo
27、rts are used, in orderto avoid excessive indentation, or failure due to stress concen-tration directly under the loading nose, they must comply withthe following requirements: they shall have a minimum radiusof 3.2 mm 18 in. for all specimens. For specimens 3.2 mm orgreater in depth, the radius of t
28、he supports may be up to 1.6times the specimen depth. They shall be this large if significantindentation or compressive failure occurs. The arc of theloading nose in contact with the specimen shall be sufficientlylarge to prevent contact of the specimen with the sides of thenose. The maximum radius
29、of the loading nose shall be nomore than four times the specimen depth.6.3 Micrometers Suitable micrometers for measuring thewidth and thickness of the test specimen to an incrementaldiscrimination of at least 0.025 mm 0.001 in. should be used.All width and thickness measurements of rigid and semiri
30、gidplastics may be measured with a hand micrometer with ratchet.A suitable instrument for measuring the thickness of nonrigidtest specimens shall have: a contact measuring pressure of25 6 2.5 kPa 3.6 6 0.36 psi, a movable circular contact foot6.35 6 0.025 mm 0.250 6 0.001 in. in diameter and a lower
31、fixed anvil large enough to extend beyond the contact foot inall directions and being parallel to the contact foot within 0.005mm 0.002 in. over the entire foot area. Flatness of foot andanvil shall conform to the portion of the Calibration section ofTest Methods D 5947.7. Test Specimens7.1 The spec
32、imens may be cut from sheets, plates, ormolded shapes, or may be molded to the desired finisheddimensions. The actual dimensions used in Section 4.2, Cal-culation, shall be measured in accordance with Test MethodsD 5947.NOTE 2Any necessary polishing of specimens shall be done only inthe lengthwise d
33、irection of the specimen.TABLE 1 Flexural StrengthMaterial Mean, 103psiValues Expressed in Units of %of 103psiVrAVRBrCRDABS 9.99 1.59 6.05 4.44 17.2DAP thermoset 14.3 6.58 6.58 18.6 18.6Cast acrylic 16.3 1.67 11.3 4.73 32.0GR polyester 19.5 1.43 2.14 4.05 6.08GR polycarbonate 21.0 5.16 6.05 14.6 17.
34、1SMC 26.0 4.76 7.19 13.5 20.4AVr= within-laboratory coefficient of variation for the indicated material. It isobtained by first pooling the within-laboratory standard deviations of the testresults from all of the participating laboratories: Sr = (s1)2+(s2)2.+(sn)2/n1/2 then Vr=(Srdivided by the over
35、all average for the material) 3 100.BVr= between-laboratory reproducibility, expressed as the coefficient of varia-tion: SR=Sr2+ SL21/2where SLis the standard deviation of laboratory means.Then: VR=(SRdivided by the overall average for the material) 3 100.Cr = within-laboratory critical interval bet
36、ween two test results = 2.8 3 Vr.DR = between-laboratory critical interval between two test results = 2.8 3 VR.D79007127.2 Sheet Materials (Except Laminated Thermosetting Ma-terials and Certain Materials Used for Electrical Insulation,Including Vulcanized Fiber and Glass Bonded Mica):7.2.1 Materials
37、 1.6 mm 116 in. or Greater in ThicknessFor flatwise tests, the depth of the specimen shall be thethickness of the material. For edgewise tests, the width of thespecimen shall be the thickness of the sheet, and the depth shallnot exceed the width (see Notes 3 and 4). For all tests, thesupport span sh
38、all be 16 (tolerance 61) times the depth of thebeam. Specimen width shall not exceed one fourth of thesupport span for specimens greater than 3.2 mm 18 in. indepth. Specimens 3.2 mm or less in depth shall be 12.7 mm 12in. in width. The specimen shall be long enough to allow foroverhanging on each en
39、d of at least 10 % of the support span,but in no case less than 6.4 mm 14 in. on each end. Overhangshall be sufficient to prevent the specimen from slippingthrough the supports.NOTE 3Whenever possible, the original surface of the sheet shall beunaltered. However, where testing machine limitations ma
40、ke it impossibleto follow the above criterion on the unaltered sheet, one or both surfacesshall be machined to provide the desired dimensions, and the location ofthe specimens with reference to the total depth shall be noted. The valueobtained on specimens with machined surfaces may differ from thos
41、eobtained on specimens with original surfaces. Consequently, any specifi-cations for flexural properties on thicker sheets must state whether theoriginal surfaces are to be retained or not. When only one surface wasmachined, it must be stated whether the machined surface was on thetension or compres
42、sion side of the beam.NOTE 4Edgewise tests are not applicable for sheets that are so thinthat specimens meeting these requirements cannot be cut. If specimendepth exceeds the width, buckling may occur.7.2.2 Materials Less than 1.6 mm 116 in. in ThicknessThe specimen shall be 50.8 mm 2 in. long by 12
43、.7 mm 12 in.wide, tested flatwise on a 25.4-mm 1-in. support span.NOTE 5Use of the formulas for simple beams cited in these testmethods for calculating results presumes that beam width is small incomparison with the support span. Therefore, the formulas do not applyrigorously to these dimensions.NOT
44、E 6Where machine sensitivity is such that specimens of thesedimensions cannot be measured, wider specimens or shorter supportspans, or both, may be used, provided the support span-to-depth ratio is atleast 14 to 1.All dimensions must be stated in the report (see also Note 5).7.3 Laminated Thermosett
45、ing Materials and Sheet andPlate Materials Used for Electrical Insulation, IncludingVulcanized Fiber and Glass-Bonded MicaFor paper-baseand fabric-base grades over 25.4 mm 1 in. in nominalthickness, the specimens shall be machined on both surfaces toa depth of 25.4 mm. For glass-base and nylon-base
46、grades,specimens over 12.7 mm 12 in. in nominal depth shall bemachined on both surfaces to a depth of 12.7 mm. The supportspan-to-depth ratio shall be chosen such that failures occur inthe outer fibers of the specimens, due only to the bendingmoment (see Note 7). Therefore, a ratio larger than 16:1
47、maybe necessary (32:1 or 40:1 are recommended). When laminatedmaterials exhibit low compressive strength perpendicular to thelaminations, they shall be loaded with a large radius loadingnose (up to four times the specimen depth to prevent prematuredamage to the outer fibers.7.4 Molding Materials (Th
48、ermoplastics and Thermosets)The recommended specimen for molding materials is 127 by12.7 by 3.2 mm 5 by12 by18 in. tested flatwise on a supportspan, resulting in a support span-to-depth ratio of 16 (tolerance61). Thicker specimens should be avoided if they exhibitsignificant shrink marks or bubbles
49、when molded.7.5 High-Strength Reinforced Composites, Including HighlyOrthotropic LaminatesThe span-to-depth ratio shall be cho-sen such that failure occurs in the outer fibers of the specimensand is due only to the bending moment (see Note 7). Aspan-to-depth ratio larger than 16:1 may be necessary (32:1 or40:1 are recommended). For some highly anisotropic compos-ites, shear deformation can significantly influence modulusmeasurements, even at span-to-depth ratios as high as 40:1.Hence, for these materials, an
