ASTM D7774-2012 8897 Standard Test Method for Flexural Fatigue Properties of Plastics《塑料抗折疲劳性能的标准试验方法》.pdf

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1、Designation: D7774 12Standard Test Method forFlexural Fatigue Properties of Plastics1This standard is issued under the fixed designation D7774; 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

2、parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.NoteBalloted equations and text were included editorially and the year date changed on July 5, 2012.1. Scope1.1 This test method covers the determination of

3、dynamicfull reversed fatigue properties of plastics in flexure. Thismethod is applicable to rigid and semi-rigid plastics. Stress andstrain levels are below the proportional limit of the materialwhere the strains and stresses are relatively elastic. Three-pointor four-point bending systems are used

4、to determine theseproperties.1.2 This test method can be used with two procedures:1.2.1 Procedure A, designed for materials that use three-point loading systems to determine flexural strength. Three-point loading system is used for this procedure.1.2.2 Procedure B, designed for materials that use fo

5、ur-point loading systems to determine flexural strength. Four-point loading system is used for this procedure.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 b

6、e 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

7、 and determine the applica-bility of regulatory limitations prior to use.NOTE 1This standard and ISO 13003 address the same subject matter,but differ in technical content and results cannot be directly comparedbetween the two test methods.2. Referenced Documents2.1 ASTM Standards:2D618 Practice for

8、Conditioning Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating MaterialsD792 Test Methods for Density and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD8

9、83 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 Meth

10、od for Density of Polyethylene by theUltrasound TechniqueD5947 Test Methods for Physical Dimensions of SolidPlastics SpecimensD6272 Test Method for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating Materialsby Four-Point BendingE4 Practices for Force Verification o

11、f Testing MachinesE83 Practice for Verification and Classification of Exten-someter SystemsE1942 Guide for Evaluating Data Acquisition SystemsUsed in Cyclic Fatigue and Fracture Mechanics Testing2.2 ISO Standard:ISO 13003 Fibre-Reinforced PlasticsDetermination ofFatigue Properties Under Cyclic Loadi

12、ng Conditions33. Terminology3.1 DefinitionsDefinitions applying to this test methodappear in Terminology D883.3.2 mean strainthe algebraic average of the maximumand minimum strains in one cycle.3.3 mean stressthe algebraic average of the maximum andminimum stresses in one cycle.3.4 R Ratiothe ratio

13、of the minimum stress or strain to themaximum stress or strain that the specimen is loaded.3.5 proportional limitthe maximum elastic stress or strainexhibited by the material as observed during Test MethodsD790 (for Procedure A) or Test Method D6272 (for ProcedureB).1This test method is under the ju

14、risdiction of ASTM Committee D20 on Plasticsand is the direct responsibility of Subcommittee D20.10.24 on Engineering andDesign Properties.Current edition approved July 5, 2012. Published July 2012. Last previousedition approved in 2011 as D7774 - 11. DOI:10.1520/D7774-12.2For referenced ASTM standa

15、rds, 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.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor,

16、New York, NY 10036, http:/www.ansi.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Test Method4.1 Procedure AA specimen of rectangular cross sectionis braced by two double-sided supports and is loaded by meansof a d

17、ouble-sided loading nose midway between the supports.A support span-to-depth ratio of 16:1 is used. The specimen iscyclically loaded equally in the positive and negative directionsto a specific stress or strain level at a uniform frequency untilthe specimen ruptures or yields. From these tests, fati

18、guestrengths can be determined at specified numbers of cycles. Atleast 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 theflexural endurance limit of the material.4.

19、2 Procedure BA specimen of rectangular cross sectionis braced by two double-sided supports and is loaded by meansof two double-sided loading noses, each an equal distance fromthe adjacent support. Load span-to-support span ratios can be1:2 or 1:3. The specimen is cyclically loaded equally in theposi

20、tive and negative directions 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. At least four different stress orstrain levels are tested to construct a stress versus nu

21、mber ofcycles to failure (S-N) curve or a strain versus number ofcycles to failure (r-N) to determine the flexural endurance limitof the material.5. Significance and Use5.1 These fatigue tests are used to determine the effect ofprocessing, surface condition, stress, and so forth, on thefatigue resis

22、tance of plastic material subjected to flexural stressfor relatively large numbers of cycles. The results can also beused as a guide for the selection of plastic materials for serviceunder conditions of repeated flexural stress.5.2 Properties can vary with specimen depth and test fre-quency. Test fr

23、equency can be 1-25 Hz but it is recommendedthat a frequency of 5 Hz or less be used.5.3 Material response in fatigue is not identical for allplastics. If a plastic does not exhibit an elastic region, wherestrain is reversible, plastic deformation will occur duringfatigue testing, causing the amplit

24、ude of the programmed loador deformation to change during testing. In this situation,caution shall be taken when using the results for design as theyare generally not indicative of the true fatigue properties of thematerial.5.4 The results of these fatigue tests are suitable for appli-cation in desi

25、gn only when the specimen test conditionsrealistically simulate service conditions or some methodologyof accounting for service conditions is available and clearlydefined.5.5 This procedure accommodates various specimen prepa-ration techniques. Comparison of results obtained from speci-mens prepared

26、 in different manners shall not be consideredcomparable unless equivalency has been demonstrated.6. Apparatus6.1 Testing MachineThe testing machine shall essentiallymeet the specifications of Test Method D790 except as de-scribed below. The error in the deflection measuring systemshall not exceed 60

27、.5 % of the maximum deflection. Themachine shall be able to execute sinusoidal or square/trapezoidal load or deflection programs at the specified testfrequency and maintain an error of 61 % or less of themaximum programmed load or deflection.6.2 Recording EquipmentCalibrated equipment must beused to

28、 record the following information during testing at adata acquisition rate and filter in accordance with GuideE1942:6.2.1 Load versus time,6.2.2 Deflection versus time, and6.2.3 Number of cycles.6.3 MicrometersApplicable apparatus in accordance withTest Methods D5947 shall be used to measure the wid

29、th andthickness of the test specimen.6.4 Bending Fixture6.4.1 Procedure AA three-point bending fixture shall beused. A double-sided loading nose and two double-sidedsupports are required for this procedure. One side loads orsupports the top of the specimen and the other loads or supportsthe bottom o

30、f the specimen. The dimensions of both sides shallbe identical. The radii of the noses and supports will be inaccordance with Test Method D790. An example of a fixtureFIG. 1 Three-Point Fixture for Flexural Fatigue TestsD7774 122configuration for Procedure A is shown in Fig. 1. This fixturehas a sup

31、port span range of 50.8 to 254 mm (2 to 10 in.) at 50.8mm (2 in.) intervals.6.4.1.1 The supports are set to simply support the specimenusing minimal pressure to hold the specimen in place. Thespecimen shall be long enough so that the ends do not slip fromthe supports during testing.6.4.2 Procedure B

32、Four-point bending fixture shall beused. Two double-sided loading noses and two double-sidedsupports are required for this procedure. One side loads orsupports the top of the specimen and the other loads or supportsthe bottom of the specimen. The dimensions of both sides shallbe identical. The radii

33、 of the noses and supports will be inaccordance with Test Method D6272. Load-span-to-support-span ratios shall be set at 1:2 or 1:3. An example of a 1:3load-span-to-support-span ratio fixture configuration for Pro-cedure B is shown in Fig. 2. This fixture has a load span rangeof 50.8 to 101.6 mm (2

34、to 4 in.) and a support span range of101.6 to 203.2 mm (4 to 8 in.), both at 50.8 mm (2 in.)intervals.6.4.2.1 The supports are set to simply support the specimenusing minimal pressure to hold the specimen in place. Thespecimen shall be long enough so that the ends do not slip fromthe supports during

35、 testing.7. Sampling, Test Specimens, and Test Units7.1 Specimens shall be taken from samples that accuratelyrepresent the material or design that is being tested.7.2 The specimens can be cut from sheets, plates, or moldedshapes, or can be molded to the desired finished dimensions.The actual dimensi

36、ons used for calculations shall be measuredin accordance with Test Methods D5947.7.3 Procedure ASpecimen dimensions, shape, surfaces,and limitations shall be in compliance with Test Method D790.The specimen shall be long enough to allow for overhangingon each end of at least 10 % of the support span

37、, but in no caseless than 12.8 mm 164 (12 in.). Overhang shall be sufficient toprevent the specimen from slipping through the supports.7.4 Procedure BSpecimen dimensions, shape, surfaces,and limitations shall be in compliance with Test MethodD6272. This test method only covers specimens with 1:2 or

38、1:3load span-to-support span ratios. The specimen shall be longenough to allow for overhanging on each end of at least 10 %of the support span, but in no case less than 12.8 mm (12 in.).Overhang shall be sufficient to prevent the specimen fromslipping through the supports.7.5 Specimens that do not n

39、aturally fail in the load spanduring testing can be made thinner in the gauge area to promotefailure in the load span. The reduced width of the specimenshall be used to calculate the test stress or strain.7.6 Samples cut from non-uniform thick molded part sec-tions shall be machined equally and mini

40、mally on both sides tocreate a uniform thickness in the support span. It must be notedthat machining the thickness of plastic can change the me-chanical properties and caution shall be taken when applyingthe results to design.7.7 It is recommended that density measurements be takenfrom each sample i

41、n the support span in accordance with TestMethods D792, Test Method D1505, Practice D2839 or TestMethod D4883 to ensure that the process used to fabricate thespecimens creates consistent and uniform material.8. Number of Test Specimens8.1 At least three test specimens shall be tested at each ofthe f

42、our stress or strain levels (minimum of twelve specimensfor each test). For additional sample sizes consult Table 1 ofTest Method D3479/D3479M.8.2 In the case of anisotropic materials, a single directionshall be chosen and maintained for all stress or strain levels.9. Calibration and Standardization

43、9.1 All equipment shall be calibrated in accordance with themanufacturers specifications and Practice E4.9.2 Specimens for each test shall be identically processedand prepared for accurate results.10. Conditioning10.1 ConditioningCondition the test specimens in accor-dance with Procedure A of Practi

44、ce D618 unless otherwisespecified by contract or the relevant ASTM material specifica-tion. Condition time is specified as a minimum. Temperatureand humidity tolerances shall be in accordance with Section 7FIG. 2 Four-Point Fixture for Flexural Fatigue TestsD7774 123of Practice D618 unless specified

45、 differently by contract ormaterial specification.10.2 Test ConditionsConduct the tests at the same tem-perature and humidity used for conditioning with tolerances inaccordance with Section 7 of Practice D618 unless otherwisespecified by contract or the relevant ASTM material specifica-tion.11. Proc

46、edure11.1 Specimen MeasurementsTake measurements of allspecimens. Measure and record the depth and width of thespecimen to the nearest 0.03 mm (0.001 in.) at the center of thesupport span. For specimens less than 2.54 mm (0.100 in.) indepth, measure the depth to the nearest 0.003 mm (0.0001 in.).Tak

47、e three different measurements of each dimension at themidpoint of the support span and average the resulting mea-surements. These measurements shall be made in accordancewith Test Methods D5947.11.2 Apparatus Setup:11.2.1 Procedure A:11.2.1.1 Determine and set the support span. Measure thespan accu

48、rately to the nearest 0.1 mm (0.004 in.) for spans lessthan 63 mm (2.5 in.). For spans greater than or equal to 63 mm(2.5 in.), measure to the nearest 0.3 mm (0.012 in.). Use theactual measured span for all calculations.11.2.1.2 Position the three-point bend fixture so that the loadnose and load axi

49、s of the testing machine are co-axial. Thisinsures that no moments are created on the apparatus and thatthe load is being applied directly at the midpoint of the fixture.11.2.1.3 Position the specimen on the supports so that theload nose and midpoint of the specimen are aligned and thebottom face of the specimen is perpendicular to the loadingaxis.11.2.2 Procedure B:11.2.2.1 Determine and set the support span and the loadspan. Measure the spans accurately to the nearest 0.1 mm(0.004 in.) for spans less than 63 mm (2.5 in.). For spansgreater than or equal to 6