1、Designation: D790 10D790 15Standard Test Methods forFlexural Properties of Unreinforced and Reinforced Plasticsand Electrical Insulating Materials1This standard is issued under the fixed designation D790; the number immediately following the designation indicates the year oforiginal adoption or, in
2、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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1
3、.1 These test methods cover the determination of are used to determine the flexural properties of unreinforced and reinforcedplastics, including high-modulushighmodulus composites and electrical insulating materials in the form of rectangular bars moldeddirectly or cut from sheets, plates, or molded
4、 shapes. These test methods are utilizing a three-point loading system to apply a loadto simply supported beam (specimen). The method is generally applicable to both rigid and semirigid materials. However,semi-rigid materials, but flexural strength cannot be determined for those materials that do no
5、t break or that do not fail yield in the outersurface of the test specimen within the 5.0 % strain limit of these test methods. These test methods utilize a three-point loadingsystem applied to a simply supported beam. A four-point loading system method can be found in Test Method 5.0 % strain limit
6、.D6272.1.1.1 Procedure A, designed principally for materials that break at comparatively small deflections.1.1.2 Procedure B, designed particularly for those materials that undergo large deflections during testing.1.1.3 Procedure A shall be used for measurement of flexural properties, particularly f
7、lexural modulus, unless the materialspecification states otherwise. Procedure B may be used for measurement of flexural strength only. Tangent modulus data obtainedby Procedure A tends to exhibit lower standard deviations than comparable data obtained by means of Procedure B.1.2 Comparative tests ma
8、y be run in accordance with either procedure, provided that the procedure is found satisfactory for thematerial being tested. Test specimens of rectangular cross section are injection molded or, cut from molded or extruded sheets orplates, or cut from molded or extruded shapes. Specimens must be sol
9、id and uniformly rectangular. The specimen rests on twosupports and is loaded by means of a loading nose midway between the supports.1.3 Measure deflection in one of two ways; using crosshead position or a deflectometer. Please note that studies have shownthat deflection data obtained with a deflect
10、ometer will differ from data obtained using crosshead position. The method of deflectionmeasurement shall be reported.NOTE 1Requirements for quality control in production environments are usually met by measuring deflection using crosshead position. However,more accurate measurement may be obtained
11、by using an deflection indicator such as a deflectometer.NOTE 2Materials that do not rupture by the maximum strain allowed under this test method may be more suited to a 4-point bend test. The basicdifference between the two test methods is in the location of the maximum bending moment and maximum a
12、xial fiber stresses. The maximum axial fiberstresses occur on a line under the loading nose in 3-point bending and over the area between the loading noses in 4-point bending. A four-point loadingsystem method can be found in Test Method D6272.1.4 The values stated in SI units are to be regarded as t
13、he standard. The values provided in parentheses are for information only.1.5 The text of this standard references notes and footnotes that provide explanatory material. These notes and footnotes(excluding those in tables and figures) shall not be considered as requirements of the standard.1.6 This s
14、tandard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.NOTE 3These test methods ar
15、e not technically equivalent to ISO 178.This standard and ISO 178 address the same subject matter, but differ intechnical content.1 These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Curren
16、t edition approved April 1, 2010Dec. 1, 2015. Published April 2010January 2016. Originally approved in 1970. Last previous edition approved in 20072010 asD790 07D790 10. 1. DOI: 10.1520/D0790-10.10.1520/D0790-15.This document is not an ASTM standard and is intended only to provide the user of an AST
17、M standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published
18、by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12. Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioni
19、ng Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD883 Terminology Relating to PlasticsD2309 Tests for Rubber PropertyCompression Set Induced by Nuclear Radiation (Withdrawn 1981)3D4000 Classification System for Specifying Plastic MaterialsD4101 Specification for Polypropylen
20、e Injection and Extrusion MaterialsD5947 Test Methods for Physical Dimensions of Solid Plastics SpecimensD6272 Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials byFour-Point BendingE4 Practices for Force Verification of Testing MachinesE6
21、91 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method2.2 ISO Standard:4ISO 178 PlasticsDetermination of Flexural Properties3. Terminology3.1 DefinitionsDefinitions of terms applying to these test methods appear in Terminology D883 and Annex A1A2 of TestMetho
22、d D638.4. Summary of Test Method4.1 A bar test specimen of rectangular cross section rests on two supports in a flat-wise position and is loaded by means of aloading nose located midway between the supports. A support span-to-depth ratio of 16:1 shallUnless testing certain laminatedmaterials (see 7
23、be used unless there is reason to suspect that a larger span-to-depth ratio may be required, as may be the case forcertain laminated materials (see Sectionfor guidance), a support span-to-depth (of specimen) ratio 16:1 shall be used.The specimenis deflected until rupture occurs in the outer surface
24、of the test specimen 7 andor until Note 7 for guidance).a maximum strain (see5.1.6) of 5.0 % is reached, whichever occurs first.4.2 The specimen is deflected until rupture occurs in the outer surface of the test specimen or until a maximum strain (see 12.7)of 5.0 % is reached, whichever occurs first
25、.4.2 Procedure A is designed principally for materials that break at comparatively small deflections and it shall be used formeasurement of flexural properties, particularly flexural modulus, unless the material specification states otherwise. Procedure Aemploys a strain rate of 0.01 mm/mm/min (0.01
26、 in./in./min) and is the preferred procedure for this test method, while ProcedureB employs a strain rate of 0.10 mm/mm/min (0.10 in./in./min).method.4.3 Procedure B is designed principally for those materials that do not break or yield in the outer surface of the test specimenwithin the 5.0 % strai
27、n limit when Procedure A conditions are used. of these test methods and it shall be used for measurementof flexural strength only. Procedure B employs a strain rate of 0.10 mm/mm/min (0.10 in./in./min). Procedure B employs a strainrate of 0.10 mm/mm/min (0.10 in./in./min).4.4 Type I tests utilize cr
28、osshead position for deflection measurement.4.5 Type II tests utilize an instrument (deflectometer) for deflection measurement.4.6 The procedure used and test type shall be reportedNOTE 4Comparative tests may be run in accordance with either procedure, provided that the procedure is found satisfacto
29、ry for the material beingtested. Tangent modulus data obtained by ProcedureAtends to exhibit lower standard deviations than comparable results obtained by means of ProcedureB.5. Significance and Use5.1 Flexural properties as determined by these test methods are especially useful for quality control
30、and specification purposes.5.1 Materials that do not fail by the maximum strain allowed under these test methods (3-point bend) may be more suited toa 4-point bend test. The basic difference between the two test methods is in the location of the maximum bending moment andmaximum axial fiber stresses
31、. The maximum axial fiber stresses occur on a line under the loading nose in 3-point bending and overthe area between the loading noses in 4-point bending. Flexural properties as determined by this test method are especially usefulfor quality control and specification purposes. They include:2 For re
32、ferencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 The last approved version of this historical standard is referenced
33、 on www.astm.org.4 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.D790 1525.1.1 Flexural Stress (f)When a homogeneous elastic material is tested in flexure as a simple beam supported at two pointsand loaded at the midpoi
34、nt, the maximum stress in the outer surface of the test specimen occurs at the midpoint. Flexural stressis calculated for any point on the load-deflection curve using equation (Eq 3) in Section 12 (see Notes 5 and 6).NOTE 5Eq 3 applies strictly to materials for which stress is linearly proportional
35、to strain up to the point of rupture and for which the strains are small.Since this is not always the case, a slight error will be introduced if Eq 3 is used to calculate stress for materials that are not true Hookean materials.The equation is valid for obtaining comparison data and for specificatio
36、n purposes, but only up to a maximum fiber strain of 5 % in the outer surfaceof the test specimen for specimens tested by the procedures described herein.NOTE 6When testing highly orthotropic laminates, the maximum stress may not always occur in the outer surface of the test specimen.5 Laminatedbeam
37、 theory must be applied to determine the maximum tensile stress at failure. If Eq 3 is used to calculate stress, it will yield an apparent strength basedon homogeneous beam theory. This apparent strength is highly dependent on the ply-stacking sequence of highly orthotropic laminates.5.1.2 Flexural
38、Stress for Beams Tested at Large Support Spans (f)If support span-to-depth ratios greater than 16 to 1 are usedsuch that deflections in excess of 10 % of the support span occur, the stress in the outer surface of the specimen for a simple beamis reasonably approximated using equation (Eq 4) in 12.3
39、(see Note 7).NOTE 7When large support span-to-depth ratios are used, significant end forces are developed at the support noses which will affect the moment ina simple supported beam. Eq 4 includes additional terms that are an approximate correction factor for the influence of these end forces in lar
40、ge supportspan-to-depth ratio beams where relatively large deflections exist.5.1.3 Flexural Strength (fM)Maximum flexural stress sustained by the test specimen (see Note 6) during a bending test. Itis calculated according to Eq 3 or Eq 4. Some materials that do not break at strains of up to 5 % give
41、 a load deflection curve thatshows a point at which the load does not increase with an increase in strain, that is, a yield point (Fig. 1, Curve b), Y. The flexuralstrength is calculated for these materials by letting P (in Eq 3 or Eq 4) equal this point, Y.5.1.4 Flexural Offset Yield StrengthOffset
42、 yield strength is the stress at which the stress-strain curve deviates by a given strain(offset) from the tangent to the initial straight line portion of the stress-strain curve. The value of the offset must be given wheneverthis property is calculated.NOTE 8Flexural Offset Yield Strength may diffe
43、r from flexural strength defined in 5.1.3. Both methods of calculation are described in the annex toTest Method D638.5 For a discussion of these effects, see Zweben, C., Smith, W. S., and Wardle, M. W., “Test Methods for Fiber Tensile Strength, Composite Flexural Modulus and Propertiesof Fabric-Rein
44、forced Laminates, “Laminates,” Composite Materials: Testing and Design (Fifth Conference), ASTM STP 674, 1979, pp. 228262.NOTE 1Curve a: Specimen that breaks before yielding.Curve b: Specimen that yields and then breaks before the 5 % strain limit.Curve a: Specimen that breaks before yielding.c: Spe
45、cimen thatCurve b: Specimen that yields and then breaks before the 5 % strain limit.Curve c: Specimen that neither yields nor breaks before the 5 % strain limit.FIG. 1 TypicalTypical Curves of Flexural Stress (f) Versus Flexural Strain (f)D790 1535.1.5 Flexural Stress at Break (fB)Flexural stress at
46、 break of the test specimen during a bending test. It is calculatedaccording to Eq 3 or Eq 4. Some materials give a load deflection curve that shows a break point, B, without a yield point (Fig.1, Curve a) in which case fB = fM. Other materials give a yield deflection curve with both a yield and a b
47、reak point, B (Fig. 1,Curve b). The flexural stress at break is calculated for these materials by letting P (in Eq 3 or Eq 4) equal this point, B.5.1.6 Stress at a Given StrainThe stress in the outer surface of a test specimen at a given strain is calculated in accordancewith Eq 3 or Eq 4 by letting
48、 P equal the load read from the load-deflection curve at the deflection corresponding to the desiredstrain (for highly orthotropic laminates, see Note 6).5.1.7 Flexural Strain, fNominal fractional change in the length of an element of the outer surface of the test specimen atmidspan, where the maxim
49、um strain occurs. Flexural strain is calculated for any deflection using Eq 5 in 12.4.5.1.8 Modulus of Elasticity:5.1.8.1 Tangent Modulus of ElasticityThe tangent modulus of elasticity, often called the “modulus of elasticity,” is the ratio,within the elastic limit, of stress to corresponding strain. It is calculated by drawing a tangent to the steepest initial straight-lineportion of the load-deflection curve and using Eq 6 in 12.5.1 (for highly anisotropic composites, see Note 15).NOTE 9Shear deflections can seriously reduce the apparent mo
