1、Designation: D7774 12D7774 17Standard 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 nu
2、mber in 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. Scope Scope*1.1 This test method covers the de
3、termination of dynamic full reversed fatigue properties of plastics in flexure. This method isapplicable to rigid and semi-rigid plastics. Stress and strain levels are below the proportional limit of the material where the strainsand stresses are relatively elastic. Three-point or four-point bending
4、 systems are used to determine these properties.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-pointloading system is used for this procedure.1.2.2 Procedure B, designed for mat
5、erials that use four-point loading systems to determine flexural strength. Four-point loadingsystem is used for this procedure.1.3 Comparative tests can be run in accordance with either procedure, provided that the procedure is found satisfactory for thematerial being tested.1.4 The values stated in
6、 SI units are to be regarded as the standard. The values provided in parentheses are for information only.1.5 This standard 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 an
7、d health practices and determine the applicability of regulatorylimitations prior to use.NOTE 1This standard and ISO 13003 address the same subject matter, but differ in technical content and results cannot be directly compared betweenthe two test methods.1.6 This international standard was develope
8、d in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2
9、.1 ASTM Standards:2D618 Practice for Conditioning Plastics for TestingD638 Test Method for Tensile Properties of PlasticsD790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating MaterialsD792 Test Methods for Density and Specific Gravity (Relative D
10、ensity) 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 Determining Density of PolyethyleneD3479/D3479M Test Method for Tension-Tension Fatigue of Polymer Matr
11、ix Composite MaterialsD4883 Test Method for Density of Polyethylene by the Ultrasound Technique (Withdrawn 2017)3D5947 Test Methods for Physical Dimensions of Solid Plastics SpecimensD6272 Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials
12、 byFour-Point Bending1 This test method is under the jurisdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.10.24 on EngineeringFracture andDesign PropertiesFatigue.Current edition approved July 5, 2012May 1, 2017. Published July 2012May 2017. Last previo
13、us edition approved in 20112012 as D7774 - 11.D7774 - 12.DOI:10.1520/D7774-12. DOI:10.1520/D7774-17.2 For referencedASTM 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 Doc
14、ument Summary page on the ASTM website.3 The last approved version of this historical standard is referenced on www.astm.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becaus
15、eit 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 by ASTM is to be considered the official document.*A Summary of Changes section appears
16、 at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E4 Practices for Force Verification of Testing MachinesE83 Practice for Verification and Classification of Extensometer SystemsE1942 Guide for Evaluating Data
17、 Acquisition Systems Used in Cyclic Fatigue and Fracture Mechanics Testing2.2 ISO Standard:ISO 13003 Fibre-Reinforced PlasticsDetermination of Fatigue Properties Under Cyclic Loading Conditions43. Terminology3.1 DefinitionsDefinitions applying to this test method appear in Terminology D883.3.2 mean
18、strainthe algebraic average of the maximum and minimum strains in one cycle.3.3 mean stressthe algebraic average of the maximum and minimum stresses in one cycle.3.4 R Ratiothe ratio of the minimum stress or strain to the maximum stress or strain that the specimen is loaded.3.5 proportional limitthe
19、 maximum elastic stress or strain exhibited by the material as observed during Test Methods D790(for Procedure A) or Test Method D6272 (for Procedure B).4. Summary of Test Method4.1 Procedure AA specimen of rectangular cross section is braced by two double-sided supports and is loaded by means ofa d
20、ouble-sided loading nose midway between the supports.Asupport span-to-depth ratio of 16:1 is used.The specimen is cyclicallyloaded equally in the positive and negative directions to a specific stress or strain level at a uniform frequency until the specimenruptures or yields. From these tests, fatig
21、ue strengths can be determined at specified numbers of cycles.At least four different stressor strain levels are tested to construct a stress versus number of cycles to failure (S-N) curve or a strain versus number of cyclesto failure (r-N) to determine the flexural endurance limit of the material.4
22、.2 Procedure BA specimen of rectangular cross section is braced by two double-sided supports and is loaded by means oftwo double-sided loading noses, each an equal distance from the adjacent support. Load span-to-support span ratios can be 1:2 or1:3. The specimen is cyclically loaded equally in the
23、positive and negative directions to a specific stress or strain level at a uniformfrequency until the specimen ruptures or yields. From these tests, fatigue strengths can be determined at specified numbers ofcycles. At least four different stress or strain levels are tested to construct a stress ver
24、sus number of cycles to failure (S-N) curveor a strain versus number of cycles to failure (r-N) to determine the flexural endurance limit of the material.5. Significance and Use5.1 These fatigue tests are used to determine the effect of processing, surface condition, stress, and so forth, on the fat
25、igueresistance of plastic material subjected to flexural stress for relatively large numbers of cycles. The results can also be used as aguide for the selection of plastic materials for service under conditions of repeated flexural stress.5.2 Properties can vary with specimen depth and test frequenc
26、y. Test frequency can be 1-25 Hz but it is recommended that afrequency of 5 Hz or less be used.5.3 Material response in fatigue is not identical for all plastics. If a plastic does not exhibit an elastic region, where strain isreversible, plastic deformation will occur during fatigue testing, causin
27、g the amplitude of the programmed load or deformation tochange during testing. In this situation, caution shall be taken when using the results for design as they are generally not indicativeof the true fatigue properties of the material.5.4 The results of these fatigue tests are suitable for applic
28、ation in design only when the specimen test conditions realisticallysimulate service conditions or some methodology of accounting for service conditions is available and clearly defined.5.5 This procedure accommodates various specimen preparation techniques. Comparison of results obtained from speci
29、mensprepared in different manners shall not be considered comparable unless equivalency has been demonstrated.6. Apparatus6.1 Testing MachineThe testing machine shall essentially meet the specifications of Test Method D790 except as describedbelow. The error in the deflection measuring system shall
30、not exceed 60.5 % of the maximum deflection. The machine shall beable to execute sinusoidal or square/trapezoidal load or deflection programs at the specified test frequency and maintain an errorof 61 % or less of the maximum programmed load or deflection.6.2 Recording EquipmentCalibrated equipment
31、must be used to record the following information during testing at a dataacquisition rate and filter in accordance with Guide E1942:6.2.1 Load versus time,6.2.2 Deflection versus time, and6.2.3 Number of cycles.4 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor,
32、 New York, NY 10036, http:/www.ansi.org.D7774 1726.3 MicrometersApplicable apparatus in accordance with Test Methods D5947 shall be used to measure the width andthickness of the test specimen.6.4 Bending Fixture6.4.1 Procedure AAthree-point bending fixture shall be used.Adouble-sided loading nose an
33、d two double-sided supports arerequired for this procedure. One side loads or supports the top of the specimen and the other loads or supports the bottom of thespecimen. The dimensions of both sides shall be identical. The radii of the noses and supports will be in accordance with TestMethod D790. A
34、n example of a fixture configuration for Procedure A is shown in Fig. 1. This fixture has a support span range of50.8 to 254 mm (2 to 10 in.) at 50.8 mm (2 in.) intervals.6.4.1.1 The supports are set to simply support the specimen using minimal pressure to hold the specimen in place. The specimensha
35、ll be long enough so that the ends do not slip from the supports during testing.6.4.2 Procedure BFour-point bending fixture shall be used. Two double-sided loading noses and two double-sided supportsare required for this procedure. One side loads or supports the top of the specimen and the other loa
36、ds or supports the bottom ofthe specimen. The dimensions of both sides shall be identical. The radii of the noses and supports will be in accordance with TestMethod D6272. Load-span-to-support-span ratios shall be set at 1:2 or 1:3. An example of a 1:3 load-span-to-support-span ratiofixture configur
37、ation for Procedure B is shown in Fig. 2. This fixture has a load span range of 50.8 to 101.6 mm (2 to 4 in.) anda support span range of 101.6 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 specimen using minimal pressure to hold the sp
38、ecimen in place. The specimenshall be long enough so that the ends do not slip from the supports during testing.7. Sampling, Test Specimens, and Test Units7.1 Specimens shall be taken from samples that accurately represent the material or design that is being tested.7.2 The specimens can be cut from
39、 sheets, plates, or molded shapes, or can be molded to the desired finished dimensions. Theactual dimensions used for calculations shall be measured in accordance with Test Methods D5947.7.3 Procedure ASpecimen dimensions, shape, surfaces, and limitations shall be in compliance with Test Method D790
40、. Thespecimen shall be long enough to allow for overhanging on each end of at least 10 % of the support span, but in no case less than12.8 mm 164 (12 in.). Overhang shall be sufficient to prevent the specimen from slipping through the supports.7.4 Procedure BSpecimen dimensions, shape, surfaces, and
41、 limitations shall be in compliance with Test Method D6272. Thistest method only covers specimens with 1:2 or 1:3 load span-to-support span ratios. The specimen shall be long enough to allowfor overhanging on each end of at least 10 % of the support span, but in no case less than 12.8 mm (12 in.). O
42、verhang shall besufficient to prevent the specimen from slipping through the supports.7.5 Specimens that do not naturally fail in the load span during testing can be made thinner in the gauge area to promote failurein the load span. The reduced width of the specimen shall be used to calculate the te
43、st stress or strain.7.6 Samples cut from non-uniform thick molded part sections shall be machined equally and minimally on both sides to createa uniform thickness in the support span. It must be noted that machining the thickness of plastic can change the mechanicalproperties and caution shall be ta
44、ken when applying the results to design.7.7 It is recommended that density measurements be taken from each sample in the support span in accordance with TestMethods D792, Test Method D1505, Practice D2839 or Test Method D4883 to ensure that the process used to fabricate thespecimens creates consiste
45、nt and uniform material.FIG. 1 Three-Point Fixture for Flexural Fatigue TestsD7774 1738. Number of Test Specimens8.1 At least three test specimens shall be tested at each of the four stress or strain levels (minimum of twelve specimens for eachtest). For additional sample sizes consult Table 1 of Te
46、st Method D3479/D3479M.8.2 In the case of anisotropic materials, a single direction shall be chosen and maintained for all stress or strain levels.9. Calibration and Standardization9.1 All equipment shall be calibrated in accordance with the manufacturers specifications and Practice E4.9.2 Specimens
47、 for each test shall be identically processed and prepared for accurate results.10. Conditioning10.1 ConditioningCondition the test specimens in accordance with Procedure A of Practice D618 unless otherwise specifiedby contract or the relevant ASTM material specification. Condition time is specified
48、 as a minimum. Temperature and humiditytolerances shall be in accordance with Section 7 of Practice D618 unless specified differently by contract or material specification.10.2 Test ConditionsConduct the tests at the same temperature and humidity used for conditioning with tolerances inaccordance wi
49、th Section 7 of Practice D618 unless otherwise specified by contract or the relevant ASTM material specification.11. Procedure11.1 Specimen MeasurementsTake measurements of all specimens. Measure and record the depth and width of the specimento the nearest 0.03 mm (0.001 in.) at the center of the support span. For specimens less than 2.54 mm (0.100 in.) in depth, measurethe depth to the nearest 0.003 mm (0.0001 in.). Take three different measurements of each dimension at the midpoint of the supportspan and average the resulting measurements. These measureme
