1、Designation:D 671 93Standard Test Method forFlexural Fatigue of Plastics by Constant-Amplitude-of-Force1This standard is issued under the fixed designation D 671;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revisi
2、on.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers the determination of the effectof repetitions of the same magnitude of flexural stress onplastics by fixed-ca
3、ntilever type testing machines,designed toproduce a constant-amplitude-of-force on the test specimeneach cycle.1.2 The values stated in SI units are to be regarded as thestandard.The values given in parentheses are for informationonly.1.3 This standard does not purport to address all of thesafety pr
4、oblems,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.2.Referenced Documents2.1 ASTM Standards:D 618 Practice for Conditioning Plastics a
5、nd ElectricalInsulating Materials for Testing2D 4000 Classification System for Specifying Plastic Mate-rials33.Summary of Test Method3.1 This test method measures the ability of a material toresist deterioration from cyclic stress.The test results providedata on the number of cycles of stress to pro
6、duce specimenfailure by fracture,softening,or reduction in stiffness byheating as a result of internal friction(damping).4.Significance and Use4.1 The flexural fatigue test provides information on theability of rigid plastics to resist the development of cracks orgeneral mechanical deterioration of
7、the material as a result ofa relatively large number of cycles of constant amplitude offorce.4.2 This test method is useful to determine the effect ofvariations in material,stress,and environmental conditions onthe ability of a material to resist deterioration resulting fromrepeated stress.It may al
8、so be used to provide data for use asa guide to design and selection of materials for service underconditions of repeated stress.4.3 The results are suitable for direct application in designonly when all design factors including magnitude and mode ofstress,size and shape of part,ambient and part tem
9、perature,heat transfer conditions,cyclic frequency,and environmentalconditions are comparable to the test conditions.4.4 The results obtained from testing machines other thanthe type described here may not agree due to differences inspecimen size and geometry,testing machine speeds,heattransfer,mate
10、rial fabrication,etc.4.5 The type of machine covered in this test method issuitable for determining the fatigue strength for a range ofmean stress in flexure.However,for plastic materials,whichcreep and stress relax,the effect of a mean stress other thanzero is to cause relaxation so that the stress
11、 cycle tends toapproach the condition of complete reversal of stress.4.6 Tests of thin sheet yield results which vary with thethickness of the sheet(Note 1).Because of this fact thethickness of the sheet shall be specified when reporting resultsof tests of thin sheet;and all comparisons of different
12、 materials,or selection of materials on the basis of fatigue strength,shallbe made from results of tests of standard specimens or tests inwhich the same thickness of sheet is used for all materials.NOTE1For the purposes of this test a thin sheet shall be defined as asheet less than 7.6 mm(0.3 in.)in
13、 thickness or a material for which theratio of the modulus of elasticity to the fatigue limit is less than 100.Thereason for these restrictions is that thin sheets and materials having a lowmodulus of elasticity are bent so much under the required loads that thefatigue specimen cannot(in the deflect
14、ed position)be considered a straightbeam and hence the following equation is not accurate:S 5 Mc/Iwhere:S=stress in outer fiber,M=bending moment(PL),c=distance from neutral axis to outer fiber,andI=moment of inertia.1This test method is under the jurisdiction ofASTM Committee D-20 on Plasticsand is
15、the direct responsibility of Subcommittee D20.10 on Mechanical Properties.Current edition approved Oct.15,1993.Published December 1993.Originallypublished as D 671 42 T.Last previous edition D 671 90.2Annual Book of ASTM Standards,Vol 08.01.3Annual Book of ASTM Standards,Vol 08.03.1Copyright ASTM In
16、ternational,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.NOTICE:This standard has either been superceded and replaced by a new version or discontinued.Contact ASTM International(www.astm.org)for the latest information.4.7 In any plastic part fatigue may be frequency dependent.Data should not be extrapolated to other frequencies unless thefrequency response is known.4.8 In any plastic having appreciable damping,fatigue isdependent on the heat transfer of the spe
