1、Designation: D 6272 02Standard Test Method forFlexural Properties of Unreinforced and Reinforced Plasticsand Electrical Insulating Materials by Four-Point Bending1This standard is issued under the fixed designation D 6272; the number immediately following the designation indicates the year oforigina
2、l adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method covers the determination of flexuralproperties
3、of unreinforced and reinforced plastics, includinghigh-modulus composites and electrical insulating materials inthe form of rectangular bars molded directly or cut from sheets,plates, or molded shapes. These test methods are generallyapplicable to rigid and semirigid materials. However, flexuralstre
4、ngth cannot be determined for those materials that do notbreak or that do not fail in the outer fibers. This test methodutilizes a four point loading system applied to a simplysupported beam.1.2 This test method may be used with two procedures:1.2.1 Procedure A, designed principally for materials th
5、atbreak at comparatively small deflections.1.2.2 Procedure B, designed particularly for those materialsthat undergo large deflections during testing.1.2.3 Procedure A shall be used for measurement of flexuralproperties, particularly flexural modulus, unless the materialspecification states otherwise
6、. Procedure B may be used formeasurement of flexural strength.1.3 Comparative tests may be run according to eitherprocedure, provided that the procedure is found satisfactory forthe material being tested.1.4 The values stated in SI units are to be regarded as thestandard. The values provided in pare
7、ntheses are for informa-tion only.1.5 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-priate safety and health practices and determine the applica-bility of regulatory limita
8、tions prior to use.NOTE 1This test method is equivalent to, but not identical toISO 14125 (Method B).2. Referenced Documents2.1 ASTM Standards:D 618 Practice for Conditioning Plastics for Testing2D 638 Test Method for Tensile Properties of Plastics2D 790 Test Method for Flexural Properties of Unrein
9、forcedand Reinforced Plastics and Electrical Insulating Materi-als2D 883 Terminology Relating to Plastics2D 4000 Classification System for Specifying Plastic Mate-rials3D 4066 Classification System for Nylon Injection and Ex-trusion Materials (PA)3D 5947 Test Methods for Physical Dimensions of Solid
10、Plastic Specimens2E4 Practices for Force Verification of Testing Machines4E83 Practice for Verification and Classification of Exten-someters4E 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method52.2 ISO Standard:6ISO 14125 (Method B)3. Terminology3.1 Defin
11、itions:3.1.1 Definitions of terms applying to these test methodsappear in Terminology D 883 and Annex A2 of Test MethodD 638.4. Summary of Test Method4.1 A bar of rectangular cross section rests on two supportsand is loaded at two points (by means of two loading noses),each an equal distance from th
12、e adjacent support point. Thedistance between the loading noses (the load span) is either onethird or one half of the support span (see Fig. 1). A supportspan-to-depth ratio of 16:1 shall be used unless there is reasonto suspect that a larger span-to-depth ratio may be required, asmay be the case fo
13、r certain laminated materials (see Section 7and Note 8 for guidance).4.2 The specimen is deflected until rupture occurs in theouter fibers or until the maximum fiber strain (see 12.7)of5%is reached, whichever occurs first.1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsa
14、nd is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Current edition approved April 10, 2002. Published June 2002. Originallypublished as D 6272 98. Last previous edition D 6272 00.2Annual Book of ASTM Standards, Vol 08.01.3Annual Book of ASTM Standards, Vol 08.02.4Annual
15、Book of ASTM Standards, Vol 03.01.5Annual Book of ASTM Standards, Vol 14.02.6Available from American National Standards Institute, 25 W. 43rd St., 4thFloor, New York, NY 10036.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO B
16、ox C700, West Conshohocken, PA 19428-2959, United States.5. Significance and Use5.1 Flexural properties determined by this test method areespecially useful for quality control and specification purposes.5.2 This test method may be more suited for those materialsthat do not fail within the strain lim
17、its imposed by Test MethodD 790. The major difference between four point and three pointbending modes is the location of the maximum bendingmoment and maximum axial fiber stress. In four point bendingthe maximum axial fiber stress is uniformly distributed be-tween the loading noses. In three point b
18、ending the maximumaxial fiber stress is located immediately under the loading nose.5.3 Flexural properties may vary with specimen depth,temperature, atmospheric conditions, and the difference in rateof straining specified in Procedures A and B.5.4 Before proceeding with this test method, referencesh
19、ould be made to the specification of the material being tested.Any test specimen preparation, conditioning, dimensions, ortesting parameters covered in the material specification, orboth, shall take precedence over those mentioned in this testmethod. If there are no material specifications, then the
20、sedefault conditions apply. Table 1 in Classification D 4000 liststhe ASTM materials standards that currently exist.6. Apparatus6.1 Testing MachineA 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
21、loadmeasuring system shall not exceed 6 1 % of maximum loadexpected to be measured. It shall be equipped with a deflectionmeasuring device. 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 specim
22、en duringtesting, or appropriate corrections shall be made. The loadindicating mechanism shall be essentially free from inertial lagat the crosshead rate used. The accuracy of the testing machineshall be verified in accordance with Practices E4.6.2 Loading Noses and SupportsThe loading noses andsupp
23、orts shall have cylindrical surfaces. In order to avoidexcessive indentation, or failure due to stress concentrationdirectly under the loading noses, the radii of the loading nosesand supports shall be 5.0 6 0.1 mm (0.197 6 0.004 in.) unlessotherwise specified or agreed upon between the interestedpa
24、rties. When other loading noses and supports are used theymust comply with the following requirements: they shall be atleast 3.2 mm (18 in.) for all specimens, and for specimens 3.2mm (18 in.) or greater in depth, the radius of the supports maybe up to 1.6 times the specimen depth. They shall be thi
25、s largeif significant indentation or compressive failure occurs. The arcof the loading noses in contact with the specimen shall besufficiently large to prevent contact of the specimen with thesides of the noses (see Fig. 2).NOTE 2Test data have shown that the loading noses and supportdimensions can
26、influence the flexural modulus and flexural strengthvalues. The loading noses dimension has the greater influence. Dimen-sions of loading noses and supports must be specified for materialspecifications.6.3 Deflection Measuring DeviceA properly calibrateddevice to measure the deflection of the beam a
27、t the commoncenter of the loading span, that meets or exceeds Practice E83,Class C, shall be used. The device shall automatically andcontinuously record the deflection during the test.6.4 MicrometersSuitable micrometers for measuring thewidth and thickness of the test specimen to an incrementaldiscr
28、imination of at least 0.025 mm (0.001 in.) should be used.All width and thickness measurements of rigid and semi-rigidplastics may be measured with a hand micrometer with ratchet.A suitable instrument for measuring the thickness of non-rigidtest specimens shall have: a contact measuring pressure of
29、256 2.5 kPa (3.6 6 0.036 psi), a movable circular contact foot6.35 6 0,025 mm (0.250 6 0.001 in.) in diameter and a fixedanvil 6.35 6 0,025 mm (0.250 6 0.001 in.) in diameter andbeing parallel to the contact foot within 0.005 mm (0.0002 in.)over the entire foot area. Flatness of foot and anvil shall
30、conform to the portion of the calibration section of TestMethod D 5947.FIG. 1 Loading DiagramNOTE 1Default radii 5.0 mm; see 6.2.FIG. 2 Loading Noses and Supports (Example of One ThirdSupport Span)D62720227. Test Specimen7.1 The specimens may be cut from sheets, plates, ormolded shapes, or may be mo
31、lded to the desired finisheddimensions. The actual dimensions used in Section 12 (Calcu-lation) shall be measured in accordance with Test MethodD 5947.NOTE 3Any necessary polishing of specimens shall be done only inthe lengthwise direction of the specimen.7.2 Sheet Materials (Except Laminated Thermo
32、setting Ma-terials and Certain Materials Used for Electrical Insulation,Including Vulcanized Fiber and Glass Bonded Mica):7.2.1 Materials 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 thes
33、pecimen shall be the thickness of the sheet, and the depth shallnot exceed the width (see Notes 5 and 6). For all tests, thesupport span shall be 16 (tolerance 6 1) times the depth of thebeam. Specimen width shall not exceed one fourth of thesupport span for specimens greater than 3.2 mm (18 in.) in
34、depth. 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 end 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 slippi
35、ngthrough the supports.NOTE 4Whenever possible, the original surface of the sheet shall beunaltered. However, where testing machine limitations make it impossibleto follow the above criterion on the unaltered sheet, one or both surfacesshall be machined to provide the desired dimensions, and the loc
36、ation ofthe specimens with reference to the total depth shall be noted. The valueobtained on specimens with machined surfaces may differ from thoseobtained on specimens with original surfaces. Consequently, any specifi-cations for flexural properties on the thicker sheets must state whether theorigi
37、nal surfaces are to be retained or not. When only one surface wasmachined, it must be stated whether the machined surface was on thetension or compression side of the beam.NOTE 5Edgewise tests are not applicable for sheets that are so thinthat specimens meeting these requirements cannot be cut. If s
38、pecimendepth exceeds the width, buckling may occur.7.2.2 Materials Less than 1.6 m (116 in.) in ThicknessThespecimen shall be 50.8 mm (2 in.) long by 12.7 mm (12 in.)wide, tested flatwise on a 25.4-mm (1-in.) support span.NOTE 6Use of the formulas for simple beams cited in these testmethods for calc
39、ulating results presumes that beam width is small incomparison with the support span. Therefore, the formulas do not applyrigorously to these dimensions.NOTE 7Where machine sensitivity is such that specimens of thesedimensions cannot be measured, wider specimens or shorter supportspans, or both, may
40、 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 6).7.3 Laminated Thermosetting Materials and Sheet andPlate Materials Used for Electrical Insulation, IncludingVulcanized Fiber and Glass-Bonded MicaFor paper-baseand fab
41、ric-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 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 rat
42、io shall be chosen such that failures occur inthe outer fibers of the specimens, due only to the bendingmoment (see Note 8). Three recommended support span-to-depth ratios are 16, 32, and 40 to 1. When laminated materialsexhibit low compressive strength perpendicular to the lamina-tions, they shall
43、be loaded with a large radius loading noses (upto 1.5 times the specimen depth) to prevent premature damageto the outer fibers.7.4 Molding Materials (Thermoplastics and Thermosets)The recommended specimen for molding materials is 127 by12.7 by 3.2 mm (5 by12 by18 in.) tested flatwise on a supportspa
44、n, resulting in a support span-to-depth ratio of 16 (tolerance+ 4 or 2). Thicker specimens should be avoided if theyexhibit significant shrink marks or bubbles when molded.7.5 High-Strength Reinforced Composites, Including HighlyOrthotropic LaminatesThe support span-to-depth ratio shallbe chosen suc
45、h that failures occur in the outer fibers of thespecimens, due only to the bending moment (Note 8). Threerecommended support span-to-depth ratios are 16:1, 32:1, and40:1. However, for some highly anisotropic composites, sheardeformation can significantly influence modulus measure-ments, even at span
46、-to-depth ratios as high as 40:1. Hence, forthese materials, an increase in span-to-depth ratio to 60:1 isrecommended to eliminate shear effects when modulus data arerequired. It should also be noted that the flexural modulus ofhighly anisotropic laminates is a strong function of ply-stacking sequen
47、ce and will not necessarily correlate withtensile modulus, that is not stacking-sequence dependent.NOTE 8As a general rule, support span-to-depth ratios of 16 to 1 aresatisfactory when the ratio of the tensile strength to shear strength is lessthan 8 to 1, but the support span-to-depth ratio must be
48、 increased forcomposite laminates having relatively low shear strength in the plane ofthe laminate and relatively high tensile strength parallel to the supportspan.8. Number of Test Specimens8.1 At least five specimens shall be tested for each sample inthe case of isotropic materials or molded speci
49、mens.8.2 For each sample of anisotropic material in sheet form, atleast five specimens shall be tested for each of the followingconditions. Recommended conditions are flatwise and edge-wise tests on specimens cut in lengthwise and crosswisedirections of the sheet. For the purposes of this test, “length-wise” shall designate the principal axis of anisotropy and shallbe interpreted to mean the direction of the sheet known to bestronger in flexure. “Crosswise” shall be the sheet directionknown to be the weaker in flexure and shall be at 90 to thelengthwise
