1、Designation: D 2990 01Standard Test Methods forTensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics1This standard is issued under the fixed designation D 2990; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 These test methods cover the
3、 determination of tensileand compressive creep and creep-rupture of plastics underspecified environmental conditions (see 3.1.3).1.2 While these test methods outline the use of three-pointloading for measurement of creep in flexure, four-point loading(which is used less frequently) can also be used
4、with theequipment and principles as outlined in Test Methods D 790.1.3 For measurements of creep-rupture, tension is the pre-ferred stress mode because for some ductile plastics rupturedoes not occur in flexure or compression.1.4 Test data obtained by these test methods are relevant andappropriate f
5、or use in engineering design.1.5 The values stated in SI units are to be regarded as thestandard. The values in parentheses are for information only.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 s
6、tandard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. A specific warningstatement is given in 6.8.2.NOTE 1This standard and ISO 899 are similar in content, but are notequivalent.2. Referenced Documents2.1 ASTM Standards
7、:2D 543 Practices for Evaluating the Resistance of Plastics toChemical ReagentsD 618 Practice for Conditioning Plastics for TestingD 621 Test Methods for Deformation of Plastics UnderLoad3D 638 Test Method for Tensile Properties of PlasticsD 695 Test Method for Compressive Properties of RigidPlastic
8、sD 790 Test Methods for Flexural Properties of Unreinforcedand Reinforced Plastics and Electrical Insulating MaterialsD 1822 Test Method for Tensile-Impact Energy to BreakPlastics and Electrical Insulating MaterialsD 2236 Test Method for Dynamic Mechanical Properties ofPlastics by Means of a Torsion
9、al Pendulum3D 4000 Classification System for Specifying Plastic Mate-rialsD 4968 Guide for Annual Review of Test Methods andSpecifications for Plastics3. Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 creep modulusthe ratio of initial applied stress tocreep strain.3.1.2 creep st
10、rainthe total strain, at any given time,produced by the applied stress during a creep test.3.1.2.1 DiscussionThe term creep, as used in this testmethod, reflects current plastics engineering usage. In scientificpractice, creep is often defined to be the nonelastic portion ofstrain. However, this def
11、inition is not applicable to existingengineering formulas. Plastics have a wide spectrum of retar-dation times, and elastic portions of strain cannot be separatedin practice from nonelastic. Therefore, wherever “strain” ismentioned in these test methods, it refers to the sum of elasticstrain plus th
12、e additional strain with time.3.1.3 deformationa change in shape, size or position of atest specimen as a result of compression, deflection, or exten-sion:3.1.4 compressionin a compressive creep test, the de-crease in length produced in the gage length of a test specimen.3.1.5 deflectionin a flexura
13、l creep test, the change inmid-span position of a test specimen.3.1.6 extensionin a tensile creep test, the increase inlength produced in the gage length of a test specimen.3.1.7 slenderness ratiothe ratio of the length of a columnof uniform cross section to its least radius of gyration; forspecimen
14、s of uniform rectangular cross section, the radius ofgyration is 0.289 times the smaller cross-sectional dimension;1These test methods are under the jurisdiction of ASTM Committee D20 onPlastics and are the direct responsibility of Subcommittee D20.10 on MechanicalProperties.Current edition approved
15、 August 10, 2001. Published October 2001. Originallypublished as D 2990 71. Last previous edition D 2990 95. These test methodsand Practice D 2991 replace Practices D 674, which has been discontinued.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Servic
16、e at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken
17、, PA 19428-2959, United States.for specimens of uniform circular cross section, the radius ofgyration is 0.250 times the diameter.3.1.8 stressfor tensile or compressive creep, the ratio ofthe applied load to the initial cross-sectional area; for flexuralcreep, maximum fiber stress is as calculated i
18、n accordance withTest Methods D 790.4. Summary of Test Methods4.1 These test methods consist of measuring the extensionor compression as a function of time and time-to-rupture, orfailure of a specimen subject to constant tensile or compressiveload under specified environmental conditions.5. Signific
19、ance and Use5.1 Data from creep and creep-rupture tests are necessary topredict the creep modulus and strength of materials underlong-term loads and to predict dimensional changes that mayoccur as a result of such loads.5.2 Data from these test methods can be used: (1)tocompare materials, (2) in the
20、 design of fabricated parts, (3)tocharacterize plastics for long-term performance under constantload, and ( 4) under certain conditions, for specificationpurposes.5.3 Before proceeding with this test method, referenceshould be made to the specification of the material being tested.Any specimen prepa
21、ration, conditioning, dimensions, and/ortesting parameters covered in the material specification shalltake precedence over those mentioned in this test method,except in cases where to do so would conflict with the purposefor conducting testing. If there are no material specifications,then the defaul
22、t conditions apply.6. Apparatus6.1 Tensile Creep:6.1.1 GripsThe grips and gripping technique shall bedesigned to minimize eccentric loading of the specimen.Swivel or universal joints shall be used beyond each end of thespecimen.6.1.2 It is recommended that grips permit the final centeringof the spec
23、imen prior to applying the load. Grips that permit adisplacement of the specimen within the grips during loadapplication are not suitable.6.2 Compressive Creep:6.2.1 AnvilsParallel anvils shall be used to apply the loadto the unconfined-type specimen (see 8.2). One of the anvils ofthe machine shall
24、preferably be self-aligning and shall, in orderthat the load may be applied evenly over the face of thespecimen, be arranged so that the specimen is accuratelycentered and the resultant of the load is through its center.Suitable arrangements are shown in Fig. 1 and Fig. 2 of TestMethods D 621.6.2.2
25、Guide TubeA guide tube and fixtures shall be usedwhen testing slender specimens (see 8.3) to prevent buckling.A suitable arrangement is shown in Fig. 1. The guide tube is a3.2-mm (0.125-in.) Schedule 40 stainless steel pipe nippleapproximately 150 mm (6 in.) long reamed to 6.860 60.025-mm (0.270 6 0
26、.001-in.) inside diameter.6.3 Flexural Creep:6.3.1 Test RackA rigid test rack shall be used to providesupport of the specimen at both ends with a span equal to 16( + 4, 2) times the thickness of the specimen. In order toavoid excessive indentation of the specimen, the radius of theFIG. 1 A Compressi
27、ve Creep Apparatus Including Details When Used in an Environmental ChamberD2990012support shall be 3.2 mm (0.125 in). Sufficient space must beallowed below the specimen for dead-weight loading at mid-span.6.3.2 StirrupA stirrup shall be used which fits over thetest specimen from which the desired lo
28、ad may be suspendedto provide flexural loading at mid-span. In order to preventexcessive indentation or failure due to stress concentrationunder the stirrup, the radius of the stirrup shall be 3.2 mm(0.125 in.). Connection between stirrup and weight shall bemade in a manner to avoid nonuniform loadi
29、ng caused bymisalignment or rack not being level.6.3.3 A suitable arrangement is shown in Fig. 2.6.4 Loading SystemThe loading system must be so de-signed that the load applied and maintained on the specimen iswithin 6 1 % of the desired load. The loading mechanism mustallow reproductively rapid and
30、 smooth loading as specified in11.3. In creep-rupture tests, provision must be made to ensurethat shock loading, caused by a specimen failure, is nottransferred to other specimens undergoing testing.6.4.1 Loading systems that provide a mechanical advantagerequire careful design to maintain constant
31、load throughout thetest. For example, lever systems must be designed so that theload does not change as the lever arm moves during the test.6.5 Extension, Compression, and Deflection Measurement:6.5.1 The extension or compression of specimen gagelength under load shall be measured by means of any de
32、vicethat will not influence the specimen behavior by mechanical(undesirable deformation, notches, etc.), physical (heating ofspecimen, etc.), or chemical effects. Preferably the extensionshall be measured directly on the specimen, rather than by gripseparation. Anvil displacement may be used to meas
33、ure com-pression. If extension measurements are made by grip separa-tion, suitable correction factors must be determined, so thatstrain within the gage length may be calculated. These correc-tion factors are dependent on the geometry of the specimen andits drawing behavior, and they must be measured
34、 with respectto these variables.6.5.2 The deflection of the specimen at mid-span shall bemeasured using a dial gage (with loading springs removed,with its measuring foot resting on stirrup) or a cathetometer.6.5.3 The accuracy of the deformation measuring deviceshall be within 6 1 % of the deformati
35、on to be measured.6.5.4 Deformation measuring devices shall be calibratedagainst a precision micrometer screw or other suitable standardunder conditions as nearly identical as possible with thoseencountered in the test. Caution is necessary when usingFIG. 2 Flexural Creep Test ApparatusD2990013defor
36、mation measuring devices whose calibration is subject todrifting with time and is dependent on temperature andhumidity.6.5.5 Deformation measuring devices shall be firmly at-tached to or seated on the specimen so that no slippage occurs.Electrical resistance gages are suitable only if the materialte
37、sted will permit perfect adhesion to the specimen and if theyare consistent with 6.5.1.6.6 Time MeasurementThe accuracy of the time measur-ing device shall be 6 1 % of the time-to-rupture or failure orthe elapsed time of each creep measurement, or both.6.7 Temperature Control and Measurement:6.7.1 T
38、he temperature of the test space, especially close tothe gage length of the specimen, shall be maintained within 62C by a suitable automatic device and shall be stated inreporting the results.NOTE 2The thermal contraction and expansion associated with smalltemperature changes during the test may pro
39、duce changes in the apparentcreep rate, especially near transition temperatures.6.7.2 Care must be taken to ensure accurate temperaturemeasurements over the gage length of the specimen throughoutthe test. The temperature measuring devices shall be checkedregularly against temperature standards and s
40、hall indicate thetemperature of the specimen gage area.6.7.3 Temperature measurements shall be made at frequentintervals, or continuously recorded to ensure an accuratedetermination of the average test temperature and compliancewith 6.7.1.6.8 Environmental Control and Measurement:6.8.1 When the test
41、 environment is air, the relative humidityshall be controlled to within 6 5 % during the test unlessotherwise specified, or unless the creep behavior of thematerial under testing has been shown to be unaffected byhumidity. The controlling and measuring instruments shall bestable for long time interv
42、als and accurate to within 6 1%.(The control of relative humidity is known to be difficult attemperatures much outside the range of 10 to 40C (50 to100F).)6.8.2 The composition of the test environment shall bemaintained constant throughout the test. Warning: Safetyprecautions should be taken to avoi
43、d personal contact, toeliminate toxic vapors, and to guard against explosion hazardsin accordance with any possible hazardous nature of theparticular environment being used.6.9 Vibration ControlCreep tests are quite sensitive toshock and vibration. The location of the apparatus, the testequipment, a
44、nd mounting shall be so designated that thespecimen is isolated from vibration. Multiple-station testequipment must be of sufficient rigidity so that no significantdeflection occurs in the test equipment during creep or creep-rupture testing. During time-to-rupture or failure, means toprevent jarrin
45、g of other test specimens by the falling load froma failed test specimen shall be provided by a suitable net orcushion.7. Reagents7.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications o
46、f the Commit-tee on Analytical Reagents of the American Chemical Society,where such specifications are available.4Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.7.2 Purity o
47、f WaterUnless otherwise indicated, referencesto water shall be understood to mean distilled water or water ofequal purity.7.3 Specified ReagentsShould this test method be refer-enced in a material specification, the specific reagent to be usedshall be as stipulated in the specification.7.4 Standard
48、ReagentsA list of standard reagents is alsoavailable in Test Method D 543.8. Test Specimens8.1 Test specimens for tensile creep measurements shall beeither Type I or Type II as specified in Test Method D 638.Inaddition to these, specimens specified in Test Method D 1822may be used for creep-rupture
49、testing. Tabs may be trimmed tofit grips, as long as the gripping requirements in 6.1.1 are met.8.2 Specimens for unconfined compressive creep tests maybe suitably prepared in the manner described in Test MethodD 695, except that the length should be increased so that theslenderness ratio lies between 11 and 15. The standard testspecimen shall be in the form of a right cylinder or prism.Preferred specimen cross sections are 12.7 by 12.7 mm (0.50by 0.50 in.) or 12.7 mm (0.50 in.) in diameter. Surfaces of thetest specimens shall be plane and parallel.8.3 T
