1、Designation: E2368 10 (Reapproved 2017)Standard Practice forStrain Controlled Thermomechanical Fatigue Testing1This standard is issued under the fixed designation E2368; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of l
2、ast revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers the determination of thermome-chanical fatigue (TMF) properties of materials under uniaxiallyloade
3、d strain-controlled conditions. A “thermomechanical”fatigue cycle is here defined as a condition where uniformtemperature and strain fields over the specimen gage sectionare simultaneously varied and independently controlled. Thispractice is intended to address TMF testing performed insupport of suc
4、h activities as materials research anddevelopment, mechanical design, process and quality control,product performance, and failure analysis. While this practiceis specific to strain-controlled testing, many sections willprovide useful information for force-controlled or stress-controlled TMF testing
5、.1.2 This practice allows for any maximum and minimumvalues of temperature and mechanical strain, and temperature-mechanical strain phasing, with the restriction being that suchparameters remain cyclically constant throughout the durationof the test. No restrictions are placed on environmental facto
6、rssuch as pressure, humidity, environmental medium, and others,provided that they are controlled throughout the test, do notcause loss of or change in specimen dimensions in time, andare detailed in the data report.1.3 The use of this practice is limited to specimens and doesnot cover testing of ful
7、l-scale components, structures, orconsumer products.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.5 This international standard was developed in accor-dance with internationally recognized principles on standard-ization
8、established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E3 Guide for Preparation of Metallographic SpecimensE4 Pra
9、ctices for Force Verification of Testing MachinesE83 Practice for Verification and Classification of Exten-someter SystemsE111 Test Method for Youngs Modulus, Tangent Modulus,and Chord ModulusE112 Test Methods for Determining Average Grain SizeE220 Test Method for Calibration of Thermocouples ByComp
10、arison TechniquesE337 Test Method for Measuring Humidity with a Psy-chrometer (the Measurement of Wet- and Dry-Bulb Tem-peratures)E467 Practice for Verification of Constant Amplitude Dy-namic Forces in an Axial Fatigue Testing SystemE606 Test Method for Strain-Controlled Fatigue TestingE1012 Practic
11、e for Verification of Testing Frame and Speci-men Alignment Under Tensile and Compressive AxialForce ApplicationE1823 Terminology Relating to Fatigue and Fracture Testing3. Terminology3.1 The definitions in this practice are in accordance withdefinitions given in Terminology E1823 unless otherwisest
12、ated.3.2 Definitions:3.2.1 Additional definitions are as follows:3.2.2 stress, stress is defined herein to be the engineeringstress, which is the ratio of force, P, to specimen original crosssectional area, A: 5 P/A (1)The area, A, is that measured in an unloaded condition atroom temperature. See 7.
13、2 for temperature state implications.3.2.3 coeffcient of thermal expansion, the fractionalchange in free expansion strain for a unit change intemperature, as measured on the test specimen.1This practice is under the jurisdiction of ASTM Committee E08 on Fatigue andFracture and is the direct responsi
14、bility of Subcommittee E08.05 on CyclicDeformation and Fatigue Crack Formation.Current edition approved Nov. 1, 2017. Published December 2017. Originallyapproved in 2004. Last previous edition approved in 2010 as E2368101. DOI:10.1520/E2368-10R17.2For referenced ASTM standards, visit the ASTM websit
15、e, 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.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesT
16、his international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade
17、(TBT) Committee.13.2.4 total strain, tthe strain component measured on thetest specimen, and is the sum of the thermal strain and themechanical strain.3.2.5 thermal strain, ththe strain component resultingfrom a change in temperature under free expansion conditions(as measured on the test specimen).
18、th5 T (2)NOTE 1For some materials, may be nonlinear over the temperaturerange of interest.3.2.6 mechanical strain, mthe strain component resultingwhen the free expansion thermal strain (as measured on the testspecimen) is subtracted from the total strain.m5 t2 th(3)3.2.7 elastic strain, elthe strain
19、 component resultingwhen the stress is divided by the temperature-dependentYoungs Modulus (in accordance with Test Method E111).el5 /ET! (4)3.2.8 inelastic strain, inthe strain component resultingwhen the elastic strain is subtracted from the mechanical strain.in5 m2 el(5)3.2.9 strain ratio, Rthe ra
20、tio of minimum mechanicalstrain to the maximum mechanical strain in a strain cycle.R 5 min/max(6)3.2.10 mechanical strain/temperature true phase angle,for the purpose of assessing phasing accuracy, this isdefined as the waveform shift (expressed in degrees) betweenthe maximum temperature response as
21、 measured on the speci-men and the maximum mechanical strain response. For refer-ence purpose, the angle is considered positive if thetemperature response maximum leads the mechanical strainresponse maximum by 180 or less, otherwise the phase angleis considered to be negative.3.2.11 in-phase TMF, (
22、= 0)a cycle where the maximumvalue of temperature and the maximum value of mechanicalstrain occur at the same time (see Fig. 1a).3.2.12 out-of-phase (anti-phase) TMF, ( = 180)a cyclewhere the maximum value of temperature leads the maximumvalue of mechanical strain by a time value equal to12 the cycl
23、eperiod (see Fig. 1b).4. Significance and Use4.1 In the utilization of structural materials in elevatedtemperature environments, components that are susceptible tofatigue damage may experience some form of simultaneouslyvarying thermal and mechanical forces throughout a givencycle. These conditions
24、are often of critical concern becausethey combine temperature dependent and cycle dependent(fatigue) damage mechanisms with varying severity relating tothe phase relationship between cyclic temperature and cyclicmechanical strain. Such effects can be found to influence theevolution of microstructure
25、, micromechanisms of degradation,and a variety of other phenomenological processes that ulti-mately affect cyclic life. The strain-controlled thermomechani-cal fatigue test is often used to investigate the effects ofsimultaneously varying thermal and mechanical loadings underidealized conditions, wh
26、ere cyclic theoretically uniform tem-perature and strain fields are externally imposed and controlledthroughout the gage section of the specimen.5. Test Apparatus5.1 Testing MachineAll tests shall be performed in a testsystem with tension-compression loading capability and veri-fied in accordance wi
27、th Practices E4 and E467. The test system(test frame and associated fixtures) shall be in compliance withthe bending strain criteria specified in Practices E606, E1012,and E467. The test system shall be able to independentlycontrol both temperature and total strain. In addition it shall becapable of
28、 adding the measured thermal strain to the desiredmechanical strain to obtain the total strain needed for theindependent control.5.2 Gripping FixturesAny fixture, such as those specifiedin Practice E606, is acceptable provided it meets the alignmentcriteria specified in Practice E606, and the specim
29、en failswithin the uniform gage section. Specimens with threaded endstypically tend to require more effort than those with smoothshank ends to meet the alignment criteria; for this reason,smooth shank specimens are preferred over specimens withthreaded ends. Fixtures used for gripping specimens shal
30、l bemade from a material that can withstand prolonged usage,particularly at high temperatures. The design of the fixtureslargely depends upon the design of the specimen. Typically, acombination of hydraulically-actuated collet grips and smoothshank specimens provide good alignment and high lateralst
31、iffness.5.3 Force TransducerThe force transducer shall be placedin series with the load train and shall comply with thespecifications in Practices E4 and E467.5.4 ExtensometersAxial deformation in the gage sectionof the specimen should be measured with an extensometer. Theextensometers (including op
32、tical extensometers, using an ap-propriate calibration procedure) should qualify as Class B-2 orbetter in accordance with Practice E83.5.5 Transducer CalibrationAll transducers shall be cali-brated in accordance with the recommendations of the respec-tive manufacturers. Calibration of each transduce
33、r shall betraceable to the National Institute of Standards and Technology(NIST).5.6 Heating DeviceSpecimen heating can be accom-plished by various techniques including induction, directresistance, radiant, or forced air heating. In all such cases,active specimen cooling (for example, forced air) can
34、 be usedto achieve desired cooling rates provided that the temperaturerelated specifications in 7.4 are satisfied.NOTE 2If induction is used, it is advisable to select a generator witha frequency sufficiently low to minimize “skin effects” (for example,preferential heating on the surface and near su
35、rface material with respectto the bulk, that is dependent on RF generator frequency) on the specimenduring heating.5.7 Temperature Measurement SystemThe specimen tem-perature shall be measured using thermocouples in contact withthe specimen surface in conjunction with an appropriatetemperature indic
36、ating device or non-contacting sensors thatE2368 10 (2017)2are adjusted for emisivity changes by comparison to a refer-ence such as thermocouples.NOTE 3Direct contact between the thermocouple and the specimen isimplied and shall be achieved without affecting the test results (forexample, test data f
37、or a specimen when initiation occurred at the point ofcontact of the thermocouple shall be omitted from consideration). Com-monly used methods of the thermocouple attachment are: resistance spotwelding (outside the gage section), fixing by binding or pressure.NOTE 4Under inductive heating, thermocou
38、ple wires may act as heatsinks, and can thus lower the local specimen surface temperature. Thiseffect may be substantial at high temperatures. (1)5.7.1 Calibration of the temperature measurement systemshall be in accordance with Method E220.5.8 Data Acquisition SystemA computerized system ca-pable o
39、f carrying out the task of collecting and processingforce, extension, temperature, and cycle count data digitally isrecommended. Sampling frequency of data points shall besufficient to ensure correct definition of the hysteresis loopFIG. 1 Schematics of Mechanical Strain and Temperature for In- and
40、Out-of-Phase TMF TestsE2368 10 (2017)3especially in the regions of reversals. Different data collectionstrategies will affect the number of data points per cycleneeded, however, typically 200 points per cycle are required.5.9 Alternatively, an analog system capable of measuringthe same data may be u
41、sed and would include:5.9.1 An X-Y-Y recorder used to record force, extension,and temperature hysteresis loops,5.9.2 A strip-chart recorder for several time-dependent pa-rameters: force, extension and temperature,5.9.3 A peak detector per signal, and5.9.4 A cycle counter.NOTE 5The recorders may be r
42、eplaced with storage devices capableof reproducing the recorded signals either in photographic or analog form.These devices are necessary when the rate of recorded signals is greaterthan the maximum slew-rate of the recorder. They allow permanentrecords to be reproduced subsequently at a lower rate.
43、6. Specimens6.1 Specimen Design ConsiderationsAll specimen de-signs shall be restricted to those featuring uniform axial gagesections, as these specimen designs offer a reasonable con-tinuum volume for testing. Tubular specimens are preferred tosolid specimen designs because they will tend to facili
44、tatethermal cycling due to lower material mass and will reduce thepotential for unwanted radial temperature gradients duringthermal cycling (see 7.4.5).6.2 Specimen GeometrySpecific geometries of tubularspecimens will vary depending upon materials and testingneeds. One of the more critical dimension
45、s is wall thickness,which should be large enough to avoid instabilities duringcyclic loading and thin enough to maintain a uniform tempera-ture across the specimen wall. For polycrystalline materials, atleast 10 to 20 grains should be present through the thickness ofthe wall to preserve isotropy. In
46、 order to determine the grainsize of the material metallographic samples should be preparedin accordance with Methods E3 and the average grain sizeshould be measured according to Test Method E112. Repre-sentative examples of tubular specimens, which have beensuccessfully used in TMF testing, are inc
47、luded in Fig. 2.Further general guidance regarding specific geometric detailscan be gained from the uniform gage section specimen designspresented in E606. Solid specimen designs such as thosepresented in Practice E606 are also permitted. However, careshall be taken to ensure that radial temperature
48、 gradients duringthermal cycling are not excessive; see 7.4.4 and associatednote.NOTE 6For tubular specimens, wall thicknesses (WT) and outerdiameters (OD) that fall in the following range are often found acceptable:5 0), the mechanical componentof loading should be gradually ramped to its minimum a
49、bsolutevalue such that this value is reached at the appropriatetemperature in the thermal cycle; at this point, the properlyphased TMF cycle is immediately commenced. For large totalstrain amplitude tests, the mechanical component of strain maybe increased to its final amplitude over multiple cycles toprevent overshoot. Such a gradual increase may also berequired for materials that exhibit a serrated yielding phenom-enon.7.10 Monitoring the TestThe specimen temperature andtotal strain shall be monitored during the
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