1、Designation: E 1450 03Standard 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 (e) 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 cryosta
4、t 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, elo
5、ngation, 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 NationalIn
6、stitute 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 o
7、f 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:A 370 Tes
8、t Methods and Definitions for Mechanical Testingof Steel Products2E4 Practices for Force Verification of Testing Machines3E6 Terminology Relating to Methods of Mechanical Test-ing3E8 Test Methods for Tension Testing of Metallic Materials3E8M Test Methods for Tension Testing of Metallic Mate-rials Me
9、tric3E29 Practice for Using Significant Digits in Test Data toDetermine Conformance with Specifications4E83 Practice for Verification and Classification of Exten-someter System3E 111 Test Method forYoungs Modulus, Tangent Modulus,and Chord Modulus3E 1012 Practice for Verification of Specimen Alignme
10、ntUnder Tensile Loading33. 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 condi
11、tions such that theheat 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 longitudin
12、al strainsmeasured at 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 betwee
13、n the strain atthe surface of the specimen and the axial strain (the bendingstrain 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 peak stress atthe initiation of the
14、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.1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.0
15、4 onUniaxial Testing.Current edition approved August 10, 2003. Published September 2003. Origi-nally approved in 1992. Last previous edition approved in 1998 as E 1459 92(1998).2Annual Book of ASTM Standards, Vol 01.03.3Annual Book of ASTM Standards, Vol 03.01.4Annual Book of ASTM Standards, Vol 14.
16、02.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.8 gage lengththe original distance between gagemarks made on the specimen for determining elongation afterfracture.3.1.9 length of the reduced sectionthe distance betweenthe tang
17、ent 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 from strains measured at two, three, or more circumfer-ential positions, and at
18、 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 tensileforces to test specimens in cryogenic environments (Fig. 1).4. Signific
19、ance 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 quality control. Under certaincircumstances, the information may also be useful
20、for design.4.2 The force-time and force-extension records for alloystested in liquid helium using displacement control are serrated(1).5Serrations are formed by repeated bursts of unstableplastic flow and arrests. The unstable plastic flow (discontinu-ous yielding) is a free-running process occurrin
21、g 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 are shown in Fig. 2.4.3 A constant specimen temperature cannot be maintained
22、at 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 number ofevents and the magnitude of the associated drops in magnitudeof force are
23、 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, tensile property mea-surements of alloys in liquid helium (especially tensilestreng
24、th, 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-strain response of a material tested in liquidhelium depends on whether force
25、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 material response must be taken into account whendata are used for design in ac
26、tual applications subject toforce-controlled conditions.5. 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, gl
27、oves, and tongs for handling cold specimens. 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 pote
28、ntial threat where liquid nitrogen or liquid 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 therequire
29、ments of Practices E4regarding verification 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 sp
30、ecial calibration specimen. Then, measure 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,
31、 higher forces must be applied to thecryostat, 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,5The boldface numbers in parentheses refer to the list of references at the end ofthis tes
32、t method.FIG. 1 Schematic Illustration of Typical Cryostat for TensionTestingat4KE1450032it 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 Construction MaterialsMany construction materials,including the vast majority of
33、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 heat flow. Austenitic stainless steels (AISI 304LN),maraging steels (200, 250, o
34、r 300 grades, with nickel plating toprevent rust), and extra-low-interstitial (ELI) grade titaniumalloys (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 ar
35、e sometimes used for compres-sion 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
36、calibrationspecimen so that the 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 strai
37、n based on readingstaken while 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 fro
38、m the testapparatus to the bending 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
39、 depends on the type of fixtures 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
40、 specimen concentricityshould be as nearly perfect as possible. No plastic strain shouldFIG. 2 Typical Engineering Stress-Strain Curves and Specimen Temperature Histories, at Four Different Nominal Strain Rates,for AISI 304L Stainless Steel Tested in Liquid Helium (4)E1450033occur in the reduced sec
41、tion 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 maximumbending strain defined in 3.1.10 from the strains measured atthree circumferential po
42、sitions, 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 thespecimen. The two longitudinal positions should be as far apartas possible, but
43、 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 center of thetwo broad faces.6.4.4.3 For conventional threaded or pinned grips, eva
44、luatethe 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 and the strain at thespecimen axis as the average of the two readings at the same
45、position 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 introduced due to the machining of thetest specimens) is usually sufficient to int
46、roduce 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) positions within the reduced section.Report the average of the strains from the
47、 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 MechanismsThe choice of gripping mecha-nism to be used is influenced by specimen type.
48、 The mecha-nisms described in Test Methods E8andE8Mare satisfactoryat 4 K, but cryogenic materials must be used in the constructionof components to avoid failure in service.6.6 Dimension-Measuring DevicesFor measuring the di-mensions of specimens, use a micrometer or other device thatis accurate and
49、 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-disc designs formultiple-specimen testing with a single cooling, are discussedin Refs
