1、Designation: D2990 09D2990 17Standard Test Methods forTensile, Compressive, and Flexural Creep and Creep-Rupture of Plastics 1This standard is issued under the fixed designation D2990; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 These test method
3、s cover the determination of tensile and compressive creep and creep-rupture of plastics under specifiedenvironmental conditions (see 3.1.33.2).1.2 WhileIn these test methods outline the use of three-point loading three-point loading, as described in Test Methods D790,is used for measurement of cree
4、p in flexure, four-point loading (which is used less frequently) can also be used with flexure.However, four-point loading using the equipment and principles as outlined described in TestD6272 Methodsis D790.alsopermitted as an option.1.3 For measurements of creep-rupture, tension is the preferred s
5、tress mode because for some ductile plastics rupture does notoccur in flexure or compression.1.4 Test data obtained by these test methods are relevant and appropriate for use in engineering design.1.5 The values stated in SI units are to be regarded as the standard. The values in parentheses are for
6、 information only.1.6 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 and health practices and determine the applicability of regulatorylimitations prior to use
7、. A specific warning statement is given in 6.8.2.NOTE 1This standard and ISO 899 Parts 1 and 2 address the same subject matter, but differ in technical content (and results cannot be directlycompared between the two test methods). ISO 899 Part 1 addresses tensile creep and creep to rupture and ISO 8
8、99 Part 2 addresses flexural creep.Compressive creep is not addressed in ISO 899.2. Referenced Documents2.1 ASTM Standards:2D543 Practices for Evaluating the Resistance of Plastics to Chemical ReagentsD618 Practice for Conditioning Plastics for TestingD638 Test Method for Tensile Properties of Plast
9、icsD695 Test Method for Compressive Properties of Rigid PlasticsD790 Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating MaterialsD883 Terminology Relating to PlasticsD1822 Test Method for Tensile-Impact Energy to Break Plastics and Electrical Insul
10、ating MaterialsD4000 Classification System for Specifying Plastic MaterialsD4065 Practice for Plastics: Dynamic Mechanical Properties: Determination and Report of ProceduresD4968 Practice for Annual Review of Test Methods and Specifications for PlasticsD5947 Test Methods for Physical Dimensions of S
11、olid Plastics SpecimensD6272 Test Method for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials byFour-Point Bending1 These test methods are under the jurisdiction of ASTM Committee D20 on Plastics and are the direct responsibility of Subcommittee D20.10
12、on Mechanical Properties.Current edition approved Sept. 1, 2009March 1, 2017. Published September 2009March 2017. Originally approved in 1971. Last previous edition approved in 20012009as D2990 - 01.D2990 - 09. DOI: 10.1520/D2990-09.10.1520/D2990-17.2 For referencedASTM standards, visit theASTM webs
13、ite, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indicatio
14、n of what changes have been made to the previous version. Becauseit 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 consid
15、ered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions:3.1.1 For definitions of terms used in this test method and asso
16、ciated with plastics issues refer to the terminology contained instandard D883.3.2 Definitions of Terms Specific to This Standard:3.2.1 creep modulusthe ratio of initial applied stress to creep strain.3.2.2 creep strainthe total strain, at any given time, produced by the applied stress during a cree
17、p test.3.2.2.1 DiscussionThe term creep, as used in this test method, reflects current plastics engineering usage. In scientific practice, creep is often definedto be the nonelastic portion of strain. However, this definition is not applicable to existing engineering formulas. Plastics have awide sp
18、ectrum of retardation times, and elastic portions of strain cannot be separated in practice from nonelastic. Therefore,wherever “strain” is mentioned in these test methods, it refers to the sum of elastic strain plus the additional strain with time.3.2.3 deformationa change in shape, size or positio
19、n of a test specimen as a result of compression, deflection, or extension:3.2.4 compressionin a compressive creep test, the decrease in length produced in the gagegauge length of a test specimen.3.2.5 deflectionin a flexural creep test, the change in mid-span position of a test specimen.3.2.6 extens
20、ionin a tensile creep test, the increase in length produced in the gagegauge length of a test specimen.3.2.7 slenderness ratiothe ratio of the length of a column of uniform cross section to its least radius of gyration; for specimensof uniform rectangular cross section, the radius of gyration is 0.2
21、89 times the smaller cross-sectional dimension; for specimens ofuniform circular cross section, the radius of gyration is 0.250 times the diameter.3.2.8 stressfor tensile or compressive creep, the ratio of the applied load to the initial cross-sectional area; for flexural creep,maximum fiber stress
22、is as calculated in accordance with Test Methods force to a unit area of the test specimenD790.3.2.8.1 DiscussionTensile and compressive stress is determined based on the original cross sectional area of the specimen. Three and four pointflexure tests produce both tensile and compressive stresses in
23、 the specimen. The flexural stress is taken to be the maximum outerfiber stress.4. Summary of Test Methods4.1 These test methods consist of measuring the extension or compression as a function of time and time-to-rupture, or failureof a specimen subject to constant tensile or compressive load under
24、specified environmental conditions.5. Significance and Use5.1 Data from creep and creep-rupture tests are necessary to predict the creep modulus and strength of materials under long-termloads and to predict any dimensional changes that may will potentially occur as a result of such loads.5.2 Data fr
25、om these test methods can be used: are suitable for use: (1) to compare materials, (2) in the design of fabricated parts,(3) to characterize plastics for long-term performance under constant load, and (4) under certain conditions, for specificationpurposes.5.3 Before proceeding with this test method
26、, reference shall be made to the specification of the material being tested. Anyspecimen preparation, conditioning, dimensions, and/or testing parameters covered in the material specification shall takeprecedence over those mentioned in this test method, except in cases where to do so would conflict
27、 with the purpose for conductingtesting. If there are no material specifications, then the default conditions apply.6. Apparatus6.1 Tensile Creep:6.1.1 GripsThe grips and gripping technique shall be designed to minimize eccentric loading of the specimen. Swivel oruniversal joints shall be used beyon
28、d each end of the specimen.6.1.2 It is recommended that grips permit the final centering of the specimen prior to applying the load. Grips that permit adisplacement of the specimen within the grips during load application are not suitable.6.2 Compressive Creep:6.2.1 AnvilsParallel anvils shall be us
29、ed to apply the load to the unconfined-type specimen (see 8.2). One of the anvils of themachine shall preferably be self-aligning and shall, in order that the load be applied evenly over the face of the specimen, bearranged so that the specimen is accurately centered and the resultant load is throug
30、h its center.D2990 1726.2.2 Guide TubeA guide tube and fixtures shall be used when testing slender specimens (see 8.3) to prevent buckling. Asuitable arrangement is shown in Fig. 1. The guide tube is a 3.2-mm (0.125-in.) Schedule 40 stainless steel pipe nippleapproximately 150 mm (6 in.) long reamed
31、 to 6.860 6 0.025-mm (0.270 6 0.001-in.) inside diameter.6.3 Flexural Creep:6.3.1 Test RackA rigid test rack shall be used to provide support of the specimen at both ends with a span equal to 16( + 4, 2) times the thickness of the specimen. In order to avoid excessive indentation of the specimen, th
32、e radius of the supportshall be 3.2 mm (0.125 in). Sufficient space must be allowed below the specimen for dead-weight loading at mid-span.6.3.2 StirrupA stirrup shall be used which fits over the test specimen from which the desired load shall be suspended toprovide flexural loading at mid-span. In
33、order to prevent excessive indentation or failure due to stress concentration under thestirrup, the radius of the stirrup shall be 3.2 mm (0.125 in.). Connection between stirrup and weight shall be made in a mannerto avoid nonuniform loading caused by misalignment or rack not being level.6.3.3 A sui
34、table arrangement is shown in Fig. 2.6.4 Loading SystemThe loading system must be so designed that the load applied and maintained on the specimen is within61 % of the desired load. The loading mechanism must allow reproductively rapid and smooth loading as specified in 11.3. Increep-rupture tests,
35、provision must be made to ensure that shock loading, caused by a specimen failure, is not transferred to otherspecimens undergoing testing.6.4.1 Loading systems that provide a mechanical advantage require careful design to maintain constant load throughout the test.For example, lever systems must be
36、 designed so that the load 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 gagegauge length under load shall be measured by means of any device thatwill not influence the specimen behavior by
37、 mechanical (undesirable deformation, notches, etc.), physical (heating of specimen,etc.), or chemical effects. Preferably the extension shall be measured directly on the specimen, rather than by grip separation.Anvildisplacement may be used It is permissible to use anvil displacement to measure com
38、pression. If extension measurements are madeby grip separation, suitable correction factors must be determined, so that strain within the gage length can be calculated. gaugelength is calculable. These correction factors are dependent on the geometry of the specimen and its drawing behavior, and the
39、ymust be measured with respect to these variables.6.5.2 The deflection of the specimen at mid-span shall be measured using a dial gagegauge (with loading springs removed, withits measuring foot resting on stirrup) or a cathetometer.6.5.3 The accuracy of the deformation measuring device shall be with
40、in 6 1 % of the deformation to be measured.FIG. 1 A Compressive Creep Apparatus Including Details When Used in an Environmental ChamberD2990 1736.5.4 Deformation measuring devices shall be calibrated against a precision micrometer screw or other suitable standard underconditions as nearly identical
41、as possible with those encountered in the test. Caution is necessary when using deformationmeasuring devices whose calibration is subject to drifting with time and is dependent on temperature and humidity.6.5.5 Deformation measuring devices shall be firmly attached to or seated on the specimen so th
42、at no slippage occurs. Electricalresistance gagesgauges are suitable only if the material tested will permit perfect adhesion to the specimen and if they areconsistent with 6.5.1.6.6 Time MeasurementThe accuracy of the time measuring device shall be 6 1 % of the time-to-rupture or failure or theelap
43、sed time of each creep measurement, or both.6.7 Temperature Control and Measurement:6.7.1 The temperature of the test space, especially close to the gagegauge length of the specimen, shall be maintained within62C by a suitable automatic device and shall be stated in reporting the results.NOTE 2The t
44、hermal contraction and expansion associated with small temperature changes during the test may produce changes in the apparent creeprate, especially near transition temperatures.6.7.2 Care must be taken to ensure accurate temperature measurements over the gagegauge length of the specimen throughoutt
45、he test. The temperature measuring devices shall be checked regularly against temperature standards and shall indicate thetemperature of the specimen gagegauge area.6.7.3 Temperature measurements shall be made at frequent intervals, or continuously recorded to ensure an accuratedetermination of the
46、average test temperature and compliance with 6.7.1.6.8 Environmental Control and Measurement:6.8.1 When the test environment is air, the relative humidity shall be controlled to within 6 5 % during the test unless otherwisespecified, or unless the creep behavior of the material under testing has bee
47、n shown to be unaffected by humidity. The controllingand measuring instruments shall be stable for long time intervals and accurate to within 61 %. (The control of relative humidityis known to be difficult at temperatures much outside the range of 10 to 40C (50 to 100F).)FIG. 2 Flexural Creep Test A
48、pparatusD2990 1746.8.2 The composition of the test environment shall be maintained constant throughout the test. (WarningSafety precautionsshall be taken to avoid personal contact, to eliminate toxic vapors, and to guard against explosion hazards in accordance with anypossible hazardous nature of th
49、e particular environment being used.)6.9 Vibration ControlCreep tests are quite sensitive to shock and vibration. The location of the apparatus, the test equipment,and mounting shall be so designated that the specimen is isolated from vibration. Multiple-station test equipment must be ofsufficient rigidity so that no significant deflection occurs in the test equipment during creep or creep-rupture testing. Duringtime-to-rupture or failure, means to prevent jarring of other test specimens by the falling load from a failed test specimen shall beprovided b
