1、Designation: E1450 16Standard Test Method forTension Testing of Structural Alloys in Liquid Helium1This standard is issued under the fixed designation E1450; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision
2、. 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 of
3、 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 tensile cr
4、yostat is fully submerged in normal liquid helium(He I) and tested using crosshead displacement control at anominal strain rate of 103mm/mm/s or less. Tests using forcecontrol or high strain rates are not considered.1.3 This standard specifies methods for the measurement ofyield strength, tensile st
5、rength, elongation, and reduction ofarea. The determination of the Youngs modulus is treated inTest Method E111.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 N
6、ationalInstitute 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 addr
7、ess all of 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:
8、2A370 Test Methods and Definitions for Mechanical Testingof Steel ProductsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE29 Practice for Using Significant Digits in Test Dat
9、a toDetermine Conformance with SpecificationsE83 Practice for Verification and Classification of Exten-someter SystemsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodE111 Test Met
10、hod for Youngs Modulus, Tangent Modulus,and Chord ModulusE1012 Practice for Verification of Testing Frame and Speci-men Alignment Under Tensile and Compressive AxialForce Application3. Terminology3.1 Definitions of Terms Common to Mechanical Testing3.1.1 The definitions of mechanical testing terms t
11、hat ap-pear in the Terminology E6 apply to this test method. Theseterms include bending strain, elongation, extensometer, force,gauge length, proportional limit, reduced section, reduction ofarea, stress-strain diagram, tensile strength, andYoungs modu-lus.3.1.2 In addition, the following common ter
12、ms from Termi-nology E6 are defined: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 discontinuous yielding, nin a uniaxial test, a hesita-tion or fluctuation of force observed at the onset of pl
13、asticdeformation, due to localized yielding.3.1.4.1 DiscussionThe stress-strain curve need not appearto be discontinuous.3.1.5 discontinuous yielding stress, ithe peak stress at theinitiation of the first measurable serration on the curve ofstress-versus-strain.3.1.5.1 DiscussionThe parameter iis a
14、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 E28.04 onUniaxial Testing.Current edition approved Nov. 15, 2016. Published February 2017. Originallyapprov
15、ed in 1992. Last previous edition approved in 2009 as E1450 09. DOI:10.1520/E1450-16.2For 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
16、page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for
17、 theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.1.6 gauge length, nthe original length of that portion ofthe specimen over which strain, elongation, or change of lengthis determined.3.1.6.1 D
18、iscussionTypically, this length is also the dis-tance between gauge marks, if gauge marking is used tofacilitate measurement of the elongation after fracture.3.1.6.2 DiscussionWhen sensing extension or motionwith a gauge length that is predetermined by the specimengeometry or specific test method, t
19、hen only resolution andstrain error for the specified gauge length should determine theclass of the extensometer system.3.1.7 length of the reduced sectionthe distance betweenthe tangent points of the fillets that bound the reduced section.3.1.8 reduced sectionthe central portion of the specimenthat
20、 has a cross section smaller than the gripped ends.3.1.8.1 DiscussionThe cross section is uniform withinprescribed tolerances.3.2 Definitions of Terms Specific to This Standard:3.2.1 adiabatic heatingthe internal heating of a specimenresulting from tension testing under conditions such that theheat
21、generated by plastic work cannot be quickly dissipated tothe surrounding cryogen.3.2.2 Dewara vacuum-insulated container for cryogenicfluids.3.2.3 tensile cryostata test apparatus for applying tensileforces to test specimens in cryogenic environments Fig. 1.4. Significance and Use4.1 Tension tests p
22、rovide 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 for design.4.2 The force-time a
23、nd force-extension records for somealloys tested in liquid helium using displacement control areoften serrated (1).3Serrations are formed by repeated bursts ofunstable plastic flow and arrests. The unstable plastic flow(discontinuous yielding) is a free-running process occurring inlocalized regions
24、of the reduced section at higher than nominalrates of strain with internal specimen heating. Examples ofserrated stress-strain curves for a typical austenitic stainlesssteel with discontinuous yielding are shown in Fig. 2.4.3 A constant specimen temperature cannot be maintainedat all times during te
25、sts 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 heating. The number ofevents and the magnitude of the associated drops in magnitudeof force are a function of the
26、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 tensilestrength, elongation, and
27、 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 control or displace
28、ment3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.FIG. 1 Schematic Illustration of Typical Tensile Cryostat for Tension Testing at 4 KE1450 162control is used (3). Crosshead displacement control is specifiedin this standard since the goal is mater
29、ial characterization byconventional methods. The possibility of a different and lessfavorable material response must be taken into account whendata are used for design in actual applications subject toforce-controlled conditions.5. Hazards5.1 Several precautions must be observed in the use ofcryogen
30、ic 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 specimens. Cryo-genic containers that are internally pressurized or evacuated arepotentially
31、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 liquid heliumevaporates in rooms that are not properly ventilated. Safetyguidelines perta
32、ining 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 E4 regarding verification of forceaccuracy.NOTE 2Because it is important to minimize heat loss from the dewa
33、rthrough the cryogenic test frame (Fig. 1), the cross-sections of thesecomponents are often smaller than they would be in a conventional testmachine.Adrawback to these smaller cross sections is that the complianceof the test frame, (displacement per unit of applied force), can beunacceptably large.
34、High-compliance test frames can introduce artifacts inthe stress-strain curve that complicate the interpretation of discontinuousyielding. It is often useful to characterize the compliance of the test framebefore use. Measure the compliance by coupling the force train withoutincluding a specimen, by
35、 replacing the specimen with a rigid block, or byusing a special calibration specimen. Then, measure the compliance at alow force and at the highest force expected in use.6.2 System DesignThe apparatus may be designed toaccommodate one of the small specimens cited in 8.2.1 of thistest method.NOTE 32
36、 Typically, alloys in liquid helium exhibit double or tripletheir ambient strengths. For the same specimen geometry, higher forcesmust be applied to the tensile cryostat, test specimen, force train members,FIG. 2 Typical Engineering Stress-Strain Curves and Specimen Temperature Histories, at Four Di
37、fferent Nominal Strain Rates,for AISI 304L Stainless Steel Tested in Liquid Helium (4)E1450 163and grips at cryogenic temperatures. Many conventional test machineshave a maximum force of 100 kN (22 480 lbf) , which may be insufficientfor testing full-size specimens.6.3 Construction MaterialsTo preve
38、nt service failures,fabricate the grips and other force-train members using strong,tough, cryogenic alloys.NOTE 4Many construction materials, including the vast majority offerritic steels, are brittle at 4 K. Materials that have low thermalconductivity are desirable to reduce heat flow. Austenitic s
39、tainless steels(AISI 304LN), maraging steels (200, 250, or 300 grades, with nickelplating to prevent rust), and extra-low-interstitial (ELI) grade titaniumalloys (Ti-6Al-4V and Ti-5Al-2.5Sn) have been used with proper design,for grips, pull rods, and tensile cryostat frames. Nonmetallic materials (f
40、orexample, glass-epoxy composites) are excellent insulators and are some-times used for compression members.6.4 Alignment:6.4.1 Single- and multiple-specimen systems shall meetPractice E1012 Class 10 alignment at room temperature.NOTE 5Proper system alignment is essential to avoid bending strainsin
41、the tension tests. This requirement will minimize contributions from thetest apparatus to the bending strain. Tests performed with a qualifiedapparatus may still vary in amount of bending strain owing to smallvariations in the proposed test specimen configurations, or differences inmachining.6.5 Gri
42、pping MechanismsThe choice of gripping mecha-nism to be used is influenced by specimen type. The mecha-nisms described in Test Methods E8/E8M are satisfactory at 4K, but cryogenic materials shall be used in the construction ofcomponents to avoid failure in service.6.6 Dimension-Measuring DevicesFor
43、measuring the di-mensions of specimens, use a micrometer or other device thatis accurate and precise to at least one-half of the smallest unitto be measured.6.7 Tensile Cryostats and Support Apparatus:6.7.1 Tensile CryostatsThe tensile cryostat may employadjustable force-columns to facilitate alignm
44、ent. A Dewarcapable of retaining liquid helium is required.NOTE 6In general, tensile cryostat force-application frames forexisting test machines are custom-built, but they may accommodatecommercially available Dewars. Several practical designs, includingturret-disc designs for multiple-specimen test
45、ing with a single cooling, arediscussed in Refs (6-10). Stainless steel Dewars are safer (that is, morefracture resistant) than glass Dewars and less expensive than fiberglassDewars. Generally, a single helium Dewar (see Fig. 1) is sufficient forshort-term tensile tests. Also possible is a double-De
46、war arrangement inwhich an outer Dewar of liquid nitrogen surrounds the inner Dewar ofliquid helium.6.7.2 Ancillary EquipmentDewars and transfer lines forliquid helium must be vacuum insulated. Vacuum pumps,pressurized gas, and liquid nitrogen facilities are thereforerequired. After testing, the hel
47、ium may be released to theatmosphere (see Section 5), recycled as a gas, or reliquefied.NOTE 7Recycling or reliquefaction requires large investments inpurification and support systems.6.8 Temperature Maintenance and Liquid-LevelIndicatorsEnsure that specimen remains fully submerged inliquid helium d
48、uring the test.NOTE 8When the specimen is completely immersed, a simpleindicator or meter, instead of a thermocouple can ensure that the specimenremains fully submerged throughout the test. An on-off indicator of thecarbon-resistor type located at some reference point in the tensile cryostatcan be u
49、sed to verify that the liquid level always remains above thespecimen. Alternatively, the liquid level can be continuously monitoredusing a superconducting wire sensor of appropriate length positionedvertically inside the tensile cryostat.6.9 Axial Strain Measurement:6.9.1 Strain-Averaging TechniqueNonaxiality of appliedforce (which may be introduced 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. Therefor
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