1、Designation:D79017Standard 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 the case of
2、 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*1.1 These test meth
3、ods are used to determine the flexuralproperties of unreinforced and reinforced plastics,includinghigh modulus composites and electrical insulating materialsutilizing a three-point loading system to apply a load to asimply supported beam(specimen).The method is generallyapplicable to both rigid and
4、semi-rigid materials,but flexuralstrength cannot be determined for those materials that do notbreak or yield in the outer surface of the test specimen withinthe 5.0%strain limit.1.2 Test specimens of rectangular cross section are injectionmolded or,cut from molded or extruded sheets or plates,or cut
5、from molded or extruded shapes.Specimens must be solid anduniformly rectangular.The specimen rests on two supports andis loaded by means of a loading nose midway between thesupports.1.3 Measure deflection in one of two ways;using crossheadposition or a deflectometer.Please note that studies have sho
6、wnthat deflection data obtained with a deflectometer will differfrom data obtained using crosshead position.The method ofdeflection measurement shall be reported.NOTE1Requirements for quality control in production environmentsare usually met by measuring deflection using crosshead position.However,m
7、ore accurate measurement may be obtained by using andeflection indicator such as a deflectometer.NOTE2Materials that do not rupture by the maximum strain allowedunder 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
8、 maximumbending moment and maximum axial fiber stresses.The maximum axialfiber stresses occur on a line under the loading nose in 3-point bending andover the area between the loading noses in 4-point bending.A four-pointloading system method can be found in Test Method D6272.1.4 The values stated in
9、 SI units are to be regarded as thestandard.The values provided in parentheses are for informa-tion only.1.5 The text of this standard references notes and footnotesthat provide explanatory material.These notes and footnotes(excluding those in tables and figures)shall not be consideredas requirement
10、s of the standard.1.6 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 limitations prior to use.
11、NOTE3This standard and ISO 178 address the same subject matter,but differ in technical content.1.7 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Sta
12、ndards,Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade(TBT)Committee.2.Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD883 Terminology Relating to PlasticsD400
13、0 Classification System for Specifying Plastic Materi-alsD4101 Specification for Polypropylene Injection and Extru-sion MaterialsD5947 Test Methods for Physical Dimensions of SolidPlastics SpecimensD6272 Test Method for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insula
14、ting Materi-als by Four-Point BendingE4 Practices for Force Verification of Testing MachinesE83 Practice for Verification and Classification of Exten-someter Systems1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.1
15、0 on MechanicalProperties.Current edition approved July 1,2017.Published July 2017.Originally approvedin 1970.Last previous edition approved in 2015 as D790 152.DOI:10.1520/D0790-17.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.
16、For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.*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 StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards,Guide
