ASTM E1450-2009 Standard Test Method for Tension Testing of Structural Alloys in Liquid Helium《液氦中结构合金抗拉试验的标准试验方法》.pdf

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1、Designation: E 1450 09Standard Test Method forTension Testing of Structural Alloys in Liquid Helium1This standard is issued under the fixed designation E 1450; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revisi

2、on. 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 test method describes procedures for the tensiontesting of structural alloys in liquid helium. The format issimilar to that

3、of other ASTM tension test standards, but thecontents include modifications for cryogenic testing whichrequires special apparatus, smaller specimens, and concern forserrated yielding, adiabatic heating, and strain-rate effects.1.2 To conduct a tension test by this standard, the specimenin a cryostat

4、 is fully submerged in normal liquid helium (He I)and tested using crosshead displacement control at a nominalstrain rate of 103s1or less. Tests using force control or highstrain rates are not considered.1.3 This standard specifies methods for the measurement ofyield strength, tensile strength, elon

5、gation, and reduction ofarea. The determination of the elastic modulus is treated in TestMethod E 111.NOTE 1The boiling point of normal liquid helium (He I) at sea levelis 4.2 K (269C or 452.1F or 7.6R). It decreases with geographicelevation and is 4.0 K (269.2C or 452.5F or 7.2R) at the NationalIns

6、titute of Standards and Technology in Colorado, 1677 m (5500 ft)above sea level. In this standard the temperature is designated 4 K.1.4 Values stated in SI units are treated as primary. Valuesstated in U.S. customary units are treated as secondary.1.5 This standard does not purport to address all of

7、 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 and determine the applica-bility of regulatory limitations prior to use. See Section 5.2. Referenced Documents2.1 ASTM Standards:2A 370 Tes

8、t Methods and Definitions for Mechanical Testingof Steel ProductsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 8/E 8M Test Methods for Tension Testing of MetallicMaterialsE29 Practice for Using Significant Digits in Test Data toDete

9、rmine Conformance with SpecificationsE83 Practice for Verification and Classification of Exten-someter SystemsE 111 Test Method forYoungs Modulus, Tangent Modulus,and Chord ModulusE 1012 Practice for Verification of Test Frame and Speci-men Alignment Under Tensile and Compressive AxialForce Applicat

10、ion3. Terminology3.1 Definitions:3.1.1 The definitions of terms relating to tension testing thatappear in Terminology E6shall apply here. The definitions inthis section also apply.3.1.2 adiabatic heatingthe internal heating of a specimenresulting from tension testing under conditions such that thehe

11、at generated by plastic work cannot be quickly dissipated tothe surrounding cryogen.3.1.3 adjusted length of the reduced sectionthe length ofthe reduced section plus an amount calculated to compensatefor strain in the fillet region.3.1.4 axial strainthe average of the longitudinal strainsmeasured at

12、 opposite or equally spaced surface locations on thesides of the longitudinal axis of symmetry of the specimen.Thelongitudinal strains are measured using two or more strain-sensing devices located at the mid-length of the reducedsection.3.1.5 bending strainthe difference between the strain atthe sur

13、face of the specimen and the axial strain (the bending1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.04 onUniaxial Testing.Current edition approved June 1, 2009. Published August 2009. Originallyapproved in

14、1992. Last previous edition approved in 2003 as E 1459 03.2For referenced ASTM standards, 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.1Co

15、pyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.strain varies around the circumference and along the reducedsection of the specimen).3.1.6 Dewara vacuum-insulated container for cryogenicfluids.3.1.7 discontinuous yielding stress, sithe

16、peak stress atthe initiation of the first measurable serration on the curve ofstress-versus-strain.3.1.7.1 DiscussionThe parameter siis a function of testvariables and is not a material constant.3.1.8 gage lengththe original distance between gagemarks made on the specimen for determining elongation

17、afterfracture.3.1.9 length of the reduced sectionthe distance betweenthe tangent points of the fillets that bound the reduced section.3.1.10 maximum bending strainthe largest value of bend-ing strain in the reduced section of the specimen.3.1.10.1 DiscussionMaximum bending strength is calcu-lated fr

18、om strains measured at two, three, or more circumfer-ential positions, and at each of two different longitudinalpositions.3.1.11 reduced sectionsection in the central portion of thespecimen, which has a cross section smaller than the grippedends.3.1.12 tensile cryostata test apparatus for applying t

19、ensileforces to test specimens in cryogenic environments (Fig. 1).4. Significance and Use4.1 Tension tests provide information on the strength andductility of materials under uniaxial tensile stresses. Thisinformation may be useful for alloy development, comparisonand selection of materials, and qua

20、lity control. Under certaincircumstances, the information may also be useful for design.4.2 The force-time and force-extension records for alloystested in liquid helium using displacement control are serrated(1).3Serrations are formed by repeated bursts of unstableplastic flow and arrests. The unsta

21、ble plastic flow (discontinu-ous yielding) is a free-running process occurring in localizedregions of the reduced section at higher than nominal rates ofstrain with internal specimen heating. Examples of serratedstress-strain curves for a typical austenitic stainless steel withdiscontinuous yielding

22、 are shown in Fig. 2.4.3 A constant specimen temperature cannot be maintainedat all times during tests in liquid helium. The specimentemperature at local regions in the reduced section risestemporarily above 4 K during each discontinuous yieldingevent (see Fig. 2), owing to adiabatic heat. The numbe

23、r ofevents and the magnitude of the associated drops in magnitudeof force are a function of the material composition and otherfactors such as specimen size and test speed. Typically, alteringthe mechanical test variables can modify but not eliminate thediscontinuous yielding (2-4). Therefore, tensil

24、e property mea-surements of alloys in liquid helium (especially tensilestrength, elongation, and reduction of area) lack the usualsignificance of property measurements at room temperaturewhere deformation is more nearly isothermal and discontinu-ous yielding typically does not occur.4.4 The stress-s

25、train response of a material tested in liquidhelium depends on whether force control or displacementcontrol is used (3). Crosshead displacement control is specifiedin this standard since the goal is material characterization byconventional methods. The possibility of a different and lessfavorable ma

26、terial response must be taken into account whendata are used for design in actual applications subject toforce-controlled conditions.3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.FIG. 1 Schematic Illustration of Typical Cryostat for Tension Testin

27、g at 4 KE14500925. Hazards5.1 Several precautions must be observed in the use ofcryogenic fluids and equipment. Skin or eye contact withcryogens will freeze and destroy tissue. The appropriateprotection may require goggles, clothing without pockets orcuffs, gloves, and tongs for handling cold specim

28、ens. Cryo-genic containers that are internally pressurized or evacuated arepotentially hazardous in that damage or leaks can produceexplosions or implosions. Also, when liquids evaporate togases, there is a huge volume increase; therefore asphyxiationis a potential threat where liquid nitrogen or li

29、quid heliumevaporates in rooms that are not properly ventilated. Safetyguidelines pertaining to the use of liquid helium and othercryogenic fluids are considered elsewhere in more detail (5).6. Apparatus6.1 Test MachinesUse a test machine that meets therequirements of Practices E4regarding verificat

30、ion of forceaccuracy. Know the test machine compliance (displacementper unit of applied force of the apparatus itself). Measure thecompliance by coupling the force train without including aspecimen, by replacing the specimen with a rigid block, or byusing a special calibration specimen. Then, measur

31、e the com-pliance at a low force and at the highest force used to qualifythe machine, as directed in 6.4.1 of this test method.6.2 System DesignTypically, alloys in liquid helium ex-hibit double or triple their ambient strengths. For the samespecimen geometry, higher forces must be applied to thecry

32、ostat, test specimen, force train members, and grips atcryogenic temperatures. Since many conventional test ma-chines have a maximum force of 100 kN (22 480 lbf) or less,it is recommended that the apparatus be designed to accom-modate one of the small specimens cited in 8.2.2 of this testmethod.6.3

33、Construction MaterialsMany construction materials,including the vast majority of ferritic steels, are brittle at 4 K.To prevent service failures, fabricate the grips and otherforce-train members using strong, tough, cryogenic alloys.Materials that have low thermal conductivity are desirable toreduce

34、 heat flow. Austenitic stainless steels (AISI 304LN),maraging steels (200, 250, or 300 grades, with nickel plating toprevent rust), and extra-low-interstitial (ELI) grade titaniumFIG. 2 Typical Engineering Stress-Strain Curves and Specimen Temperature Histories, at Four Different Nominal Strain Rate

35、s,for AISI 304L Stainless Steel Tested in Liquid Helium (4)E1450093alloys (Ti-6Al-4V and Ti-5Al-2.5Sn) have been used withproper design, for grips, pull rods, and cryostat frames.Nonmetallic materials (for example, glass-epoxy composites)are excellent insulators and are sometimes used for compres-si

36、on members.6.4 Alignment:6.4.1 Proper system alignment is essential to avoid bendingstrains in the tension tests.6.4.2 Single-Specimen ApparatusFor a conventionalsingle-specimen cryostat, the machine and grips should becapable of applying force to a precisely machined calibrationspecimen so that the

37、 maximum bending strain does not exceed10 % of the axial strain. Reduce bending strain to an acceptablelevel by making proportional adjustments to a cryostat havingalignment capability, or by using spacing shims to compensatean unadjustable fixture. Calculate the strain based on readingstaken while

38、the calibration specimen is subjected to a lowforce, as well as at the highest force for which the machine andforce train are being qualified. Procedures for measuringspecimen alignment are given in Practice E 1012.NOTE 2This requirement will minimize contributions from the testapparatus to the bend

39、ing strain. Tests performed with a qualified apparatusmay still vary in amount of bending strain owing to small variations in theproposed test specimen configurations, or differences in machining.6.4.3 Multiple-Specimen ApparatusFor this type of cry-ostat the alignment depends on the type of fixture

40、s used.Measure and record the maximum bending strain.6.4.4 Qualify the apparatus by making axiality measure-ments at room temperature and at 4 K. To perform axiality testsof the apparatus, the specimen form should be the same as thatused during cryogenic tests, and the specimen concentricityshould b

41、e as nearly perfect as possible. No plastic strain shouldoccur in the reduced section of the alignment specimen duringapplication of force. In some cases this may necessitate the useof a relatively stiff, high-strength calibration specimen.6.4.4.1 For cylindrical specimens, calculate the maximumbend

42、ing strain defined in 3.1.10 from the strains measured atthree circumferential positions, at each of two different longi-tudinal positions (if length permits). Measure the strains withthree electrical-resistance strain gages, extensometers, or clipgages equally spaced around the reduced section of t

43、hespecimen. The two longitudinal positions should be as far apartas possible, but not closer than one diameter to a fillet.6.4.4.2 For specimens of square or rectangular cross sec-tion, measure the strain at the center of two parallel (opposite)faces, or in the case of thin cross sections, at the ce

44、nter of thetwo broad faces.6.4.4.3 For conventional threaded or pinned grips, evaluatethe effect of specimen bias as follows. Repeat the axialitymeasurements with the specimen rotated 180, but with thegrips and pull rods retained in their original positions. Thencalculate the maximum bending strain

45、and the strain at thespecimen axis as the average of the two readings at the sameposition relative to the machine. If other grips or methods areused to evaluate the effect of specimen bias it should bedescribed in the report.6.4.5 Strain-Averaging TechniqueNonaxiality of appliedforce (which may be i

46、ntroduced due to the machining of thetest specimens) is usually sufficient to introduce errors intension tests at small strains when strain is measured at onlyone position on the specimen. Therefore measure strains atthree equally spaced (or, if good alignment has been achieved,at least two opposing

47、) positions within the reduced section.Report the average of the strains from the two or threepositions centered on the reduced section. This section may bemore appropriate under the strain gage section since it isreferring to measurement of strain during the test and notalignment.6.5 Gripping Mecha

48、nismsThe choice of gripping mecha-nism to be used is influenced by specimen type. The mecha-nisms described in Test Methods E 8/E 8M are satisfactory at 4K, but cryogenic materials must be used in the construction ofcomponents to avoid failure in service.6.6 Dimension-Measuring DevicesFor measuring

49、the di-mensions of specimens, use a micrometer or other device thatis accurate and precise to at least one-half of the smallest unitto which a given dimension must be measured.6.7 Cryostats and Support Apparatus:6.7.1 CryostatsA Dewar capable of retaining liquid he-lium is required. In general, cryostat force-application framesfor existing test machines must be custom-built, but they mayaccommodate commercially available Dewars. The cryostatmay employ adjustable force-columns to facilitate alignment.Several practical designs, including turret-di