1、Designation:E244811Standard Test Method forDetermining the Superplastic Properties of Metallic SheetMaterials1This standard is issued under the fixed designation E2448;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last
2、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 test method describes the procedure for determin-ing the superplastic forming properties(SPF)of a metallicsheet material.It
3、 includes tests both for the basic SPF proper-ties and also for derived SPF properties.The test for basicproperties encompasses effects due to strain hardening orsoftening.1.2 This test method covers sheet materials with thicknessesof at least 0.5 mm but not greater than 6 mm.It characterizesthe mat
4、erial under a uni-axial tensile stress condition.NOTE1Most industrial applications of superplastic forming involve amulti-axial stress condition in a sheet;however it is more convenient tocharacterize a material under a uni-axial tensile stress condition.Testsshould be performed in different orienta
5、tions to the rolling direction of thesheet to ascertain initial anisotropy.1.3 This method has been used successfully between strainrates of 10-5to 10-1per second.1.4 This method has been used successfully on Aluminumand Titanium alloys.The use of the method with other metalsshould be verified.1.5 T
6、he values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate
7、safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE21 Test Methods for Elevated Temperature Tensi
8、on Tests ofMetallic MaterialsE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE646 Test Method for Tensile Strain-Hardening Exponents(n-Values)of Metallic Sheet MaterialsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3.Terminol
9、ogy3.1 DefinitionsDefinitions such as gage length(L and L0),true stress(),true strain(),normal engineering stress(S),andengineering strain(e)are defined in Terminology E6.Thus,5 lnL/L0!5 S11e!NOTE2Engineering stress S and strain e are only valid up to the pointof necking or instability of cross sect
10、ion.For superplastic deformation,thecoupon undergoes an essentially uniform and constant neck along itslength,and S and e are assumed in this standard to be valid.However atthe junction to the clamp sections of the coupon the cross section reducesfrom the original value to the final value,over a len
11、gth of approximately4%at each end.Also,there are local small instabilities of cross sectionover the gauge length.These contribute to an error in the calculated valuesof and.In the absence of currently available extensometers that couldoperate in the high temperature environment of an SPF test,and ar
12、e tobe inferred from crosshead extension and force.3.2 Symbols Specific To This Standard:V=machine crosshead velocity,the velocity of the travelingmember of the test machine to which one of the coupon clampsis attached =strain rate,measured as:V/L011e!#NOTE3This is an operational definition of strai
13、n rate.m=strain rate sensitivity,defined as(ln )/(ln ).Inpractical terms,m=log(2/1)/log(2/1)under stated testconditions,see 7.2.1.NOTE4The derived term m is widely used to describe the SPFproperties of a material.It should be used with caution,as it is dependenton strain,strain rate and temperature.
14、Many references in the literature donot identify the strain condition at which the readings were taken,or allowmultiple strains to be used in the determination of m.NOTE5Many superplastic alloys exhibit strain hardening.Howeverthe conventional strain hardening exponent n as defined in Test MethodE64
15、6 is not valid for superplastic materials as strain hardening in the latter1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsibility of Subcommittee E28.02 onDuctility and Formability.Current edition approved June 1,2011.Published July 20
16、11.Originally approvedin 2005.Last previous edition approved in 2008 as E244808.DOI:10.1520/E2448-11.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 is usually a coefficient of strain,rather than an expon
