ASTM_D_7791_-_12.pdf

Designation:D779112Standard Test Method forUniaxial Fatigue Properties of Plastics1This standard is issued under the fixed designation D7791;the number immediately following the designation indicates 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.1.Scope1.1 This test method covers the determination of dynamicfatigue properties of plastics in uniaxial loading.This methodis applicable to rigid and semi-rigid plastics.Uniaxial loadingsystems with tension and compression capabilities are used todetermine these properties.Stress and strain levels are belowthe proportional limits of the material where the strains andstresses are relatively elastic.1.2 This test method can be used with two procedures:1.2.1 Procedure A,fatigue testing in tension.1.2.2 Procedure B,fatigue testing in compression,only forrigid plastics.1.3 Comparative tests can be run in accordance with 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 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 health practices and determine the applica-bility of regulatory limitations prior to use.NOTE1There is no known ISO equivalent to this standard.2.Referenced Documents2.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD695 Test Method for Compressive Properties of RigidPlasticsD792 Test Methods for Density and Specific Gravity(Rela-tive Density)of Plastics by DisplacementD883 Terminology Relating to PlasticsD1505 Test Method for Density of Plastics by the Density-Gradient TechniqueD2839 Practice for Use of a Melt Index Strand for Deter-mining Density of PolyethyleneD3479/D3479M Test Method for Tension-Tension Fatigueof Polymer Matrix Composite MaterialsD4883 Test Method for Density of Polyethylene by theUltrasound TechniqueD5947 Test Methods for Physical Dimensions of SolidPlastics SpecimensE4 Practices for Force Verification of Testing MachinesE83 Practice for Verification and Classification of Exten-someter SystemsE466 Practice for Conducting Force Controlled ConstantAmplitude Axial Fatigue Tests of Metallic MaterialsE1942 Guide for Evaluating Data Acquisition Systems Usedin Cyclic Fatigue and Fracture Mechanics Testing3.Terminology3.1 DefinitionsDefinitions of terms applying to this testmethod appear in Terminology D883.3.2 Definitions:3.2.1 compressive proportional limitmaximum elasticstress or strain exhibited by a material in compression asobserved in Test Method D695.3.2.2 mean strainalgebraic average of the maximum andminimum strains in one cycle.3.2.3 mean stressalgebraic average of the maximum andminimum stresses in one cycle.3.2.4 R ratioratio of the minimum stress or strain to themaximum stress or strain that the specimen is loaded.3.2.5 tensile proportional limitmaximum elastic stress orstrain exhibited by a material in tension as observed in TestMethod D638.4.Summary of Test Method4.1 Procedure AA specimen of rectangular or circularcross section is gripped by the ends of the specimen,pulledequally in opposite directions,and released back to its originalposition or load.The specimen is cyclically loaded in tensionto a specific stress or strain level at a uniform frequency untilthe specimen ruptures or yields.From these tests,fatiguestrengths can be determined at specified numbers of cycles.At1This test method is under the jurisdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Current edition approved April 1,2012.Published May 2012.DOI:10.1520/D7791-12.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 least,four different stress or strain levels are tested to constructa stress versus number of cycles to failure(S-N)curve or astrain versus number of cycles to failure(r-N)to determine theuniaxial endurance limit of the material in tension.4.2 Procedure BA specimen of rectangular or circularcross section is compressed equally from opposite directionsand released back to its original position or load.The specimenis cyclically loaded in compression to a specific stress or strainlevel at a uniform frequency until the specimen ruptures oryields.From these tests,fatigue strengths can be determined atspecified numbers of cycles.