1、Designation: D 6272 02 (Reapproved 2008)e1Standard 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 indicate
2、s the year oforiginal adoption or, in the 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.e1NOTEEditorially changed Note 1 in April 2008.1. Scope*1.
3、1 This test method covers the determination of flexuralproperties 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 generally
4、applicable to rigid and semirigid materials. However, flexuralstrength 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 p
5、rocedures:1.2.1 Procedure A, designed principally for materials thatbreak 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 f
6、lexural modulus, unless the materialspecification states otherwise. 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 un
7、its are to be regarded as thestandard. The values provided in parentheses 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 heal
8、th practices and determine the applica-bility of regulatory limitations prior to use.NOTE 1This test method is equivalent to ISO 14125 (Method B).2. Referenced Documents2.1 ASTM Standards:2D 618 Practice for Conditioning Plastics for TestingD 638 Test Method for Tensile Properties of PlasticsD 790 T
9、est Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating MaterialsD 883 Terminology Relating to PlasticsD 4000 Classification System for Specifying Plastic Mate-rialsD 4066 Classification System for Nylon Injection and Ex-trusion Materials (PA)D 5947 Test
10、Methods for Physical Dimensions of SolidPlastics SpecimensE4 Practices for Force Verification of Testing MachinesE83 Practice for Verification and Classification of Exten-someter SystemsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 ISO Standard:
11、3ISO 14125 (Method B)3. Terminology3.1 Definitions: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 l
12、oading noses),each an equal distance from the adjacent support point. Thedistance between the loading noses (the load span) is either one1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Curre
13、nt edition approved April 1, 2008. Published July 2008. Originallyapproved in 1998. Last previous edition approved in 2002 as D 6272 - 02.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
14、information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (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,
15、 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.third 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 for certai
16、n 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.5. Significance and Use5.1 Flexural properties determined by this test method areespec
17、ially 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 limits imposed by Test MethodD 790. The major difference between four point and three pointbending modes is the location of the maximum bendingmom
18、ent and maximum axial fiber stress. In four point bendingthe maximum axial fiber stress is uniformly distributed be-tween the loading noses. In three point bending the maximumaxial fiber stress is located immediately under the loading nose.5.3 Flexural properties may vary with specimen depth,tempera
19、ture, atmospheric conditions, and the difference in rateof straining specified in Procedures A and B.5.4 Before proceeding with this test method, referenceshould be made to the specification of the material being tested.Any test specimen preparation, conditioning, dimensions, ortesting parameters co
20、vered in the material specification, orboth, shall take precedence over those mentioned in this testmethod. If there are no material specifications, then thesedefault conditions apply. Table 1 in Classification D 4000 liststhe ASTM materials standards that currently exist.6. Apparatus6.1 Testing Mac
21、hineA 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 6 1 % of maximum loadexpected to be measured. It shall be equipped with a deflectionmeasuring device. The
22、 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 cros
23、shead rate used. The accuracy of the testing machineshall be verified in accordance with Practices E4.6.2 Loading Noses and SupportsThe loading noses andsupports shall have cylindrical surfaces. In order to avoidexcessive indentation, or failure due to stress concentrationdirectly under the loading
24、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 interestedparties. When other loading noses and supports are used theymust comply with the following requirements: they shall be atleast 3.2 mm (18 in.) fo
25、r 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 this largeif significant indentation or compressive failure occurs. The arcof the loading noses in contact with the specimen shall besufficiently
26、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 influence the flexural modulus and flexural strengthvalues. The loading noses dimension has the greater influence. Dimen-sions of loading noses
27、 and supports must be specified for materialspecifications.6.3 Deflection Measuring DeviceA properly calibrateddevice to measure the deflection of the beam at the commoncenter of the loading span, that meets or exceeds Practice E83,Class C, shall be used. The device shall automatically andcontinuous
28、ly record the deflection during the test.6.4 MicrometersSuitable 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 semi-rigidplastics may be measured
29、with a hand micrometer with ratchet.A suitable instrument for measuring the thickness of non-rigidFIG. 1 Loading DiagramNOTE 1Default radii 5.0 mm; see 6.2.FIG. 2 Loading Noses and Supports (Example of One ThirdSupport Span)D 6272 02 (2008)e12test specimens shall have: a contact measuring pressure o
30、f 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 sha
31、llconform to the portion of the calibration section of TestMethod D 5947.7. Test Specimen7.1 The specimens may be cut from sheets, plates, ormolded shapes, or may be molded to the desired finisheddimensions. The actual dimensions used in Section 12 (Calcu-lation) shall be measured in accordance with
32、 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 Thermosetting Ma-terials and Certain Materials Used for Electrical Insulation,Including Vulcanized Fiber and Glass Bonded Mica):7.2.1 Mate
33、rials 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 5 and 6). For all tests, thesupport
34、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.) 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 foroverhangin
35、g 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 slippingthrough the supports.NOTE 4Whenever possible, the original surface of the sheet shall beunaltered. However, where testing machine
36、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 location ofthe specimens with reference to the total depth shall be noted. The valueobtained on specimens with machined surfaces may di
37、ffer from thoseobtained on specimens with original surfaces. Consequently, any specifi-cations for flexural properties on the 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 the
38、tension 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 specimendepth exceeds the width, buckling may occur.7.2.2 Materials Less than 1.6 m (116 in.) in ThicknessThespecimen shall be 50.8 m
39、m (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 calculating results presumes that beam width is small incomparison with the support span. Therefore, the formulas do not applyrigorously
40、 to these dimensions.NOTE 7Where 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 6)
41、.7.3 Laminated Thermosetting 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
42、 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 ratio shall be chosen such that failures occur inthe outer fibers of the specimens, due only to the bendingmoment (see Note 8). Three r
43、ecommended 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 be loaded with a large radius loading noses (upto 1.5 times the specimen depth) to prevent premature damageto the outer fibers.7.4 M
44、olding 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 supportspan, resulting in a support span-to-depth ratio of 16 (tolerance+ 4 or 2). Thicker specimens should be avoided if theyexhibit signific
45、ant shrink marks or bubbles when molded.7.5 High-Strength Reinforced Composites, Including HighlyOrthotropic LaminatesThe support span-to-depth ratio shallbe chosen such that failures occur in the outer fibers of thespecimens, due only to the bending moment (Note 8). Threerecommended support span-to
46、-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-to-depth ratios as high as 40:1. Hence, forthese materials, an increase in span-to-depth ratio to 60:1 isrecommended to eliminate s
47、hear effects when modulus data arerequired. It should also be noted that the flexural modulus ofhighly anisotropic laminates is a strong function of ply-stacking sequence and will not necessarily correlate withtensile modulus, that is not stacking-sequence dependent.NOTE 8As a general rule, support
48、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 increased forcomposite laminates having relatively low shear strength in the plane ofthe laminate and relatively high tensile stren
49、gth 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 specimens.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
