1、Designation: E2712 15Standard Test Methods forBulge-Forming Superplastic Metallic Sheet1This standard is issued under the fixed designation E2712; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number
2、in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 These test methods describe procedures for determiningthe biaxial formability of a superplastic metallic sheet in acircular die.1.2 The intent
3、 of these test methods are primarily to be usedas tests of superplasticity as measured by the ability to form toa prescribed depth in a die cavity without rupturing. These testmethods can also be used to generate material for the measure-ment of cavitation in the formed part. These can be used asgo/
4、no go criteria for qualification to a specification.1.3 These test methods have been used successfully withaluminum alloys. The use of these test methods on other metalsshould be verified.1.4 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in t
5、hisstandard.1.5 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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.
6、Referenced Documents2.1 ASTM Standards:2E2448 Test Method for Determining the Superplastic Prop-erties of Metallic Sheet Materials3. Summary of Test Method3.1 Two methods of bulge forming are included in these testmethods.3.1.1 In the first test method, the sheet is formed into a dieof a fixed depth
7、 as prescribed in a specification. If it touches thebase of the die without rupturing, then it is considered to havemet the specification.3.1.2 In the second test method, the depth of the die isreduced so that the material fills the die.Aportion excised fromthe center of the formed part may be exami
8、ned for internalcavitation within the sheet.4. Significance and Use4.1 When a superplastic material is regularly being used inindustrial production, it is often convenient to use the bulge testto qualify a batch or heat lot to an acceptance criterion.Comparing these test methods with Test Method E24
9、48, thebulge test does not require a machined coupon, it is moreconvenient to perform, and it most closely simulates themultiaxial stresses and strains present in forming parts. Thesetest methods do not measure the intrinsic superplastic proper-ties of a material. Test Method E2448 should be used in
10、 thatinstance.5. Apparatus5.1 The bulge test consists of forming a sheet of materialinto a right circular cylindrical die using pressurized gas. Theapparatus is shown in Fig. 1. The die cavity has a 100-mmdiameter and a specified depth in a vessel suitably designed forthe pressure and temperature en
11、visaged for the test.The surfacefinish of the die cavity shall be RA=0.4 m.5.2 The depth of the die (X in Fig. 1), may be varied bymeans of inserts or other methods to the depth set by thespecification. For convenience, a series of inserts of differentheights may be installed in the die to provide d
12、ifferent depthsaccording to the bulge test requirements.NOTE 1Adepth of 55 mm has been successfully used on superplastic-forming (SPF) 5083 aluminum alloy.5.2.1 The insert shall allow the free passage of gas aroundits periphery to the exhaust hole in the die.5.3 The die entry radius is 5 mm. A lower
13、 plate with acontrol thermocouple may be moved to press against the die.The plate has a gas seal bead 0.7 mm high by 8 mm wide anda 136-mm inside diameter. A gas pressurization system with agauge or other suitable means of measuring pressure anddetecting sheet failure shall be provided at the lower
14、plate toform the material into the cavity. The pressure tolerance up to1 MPa shall be 650 kPa, and above 1 MPa shall be 65%ofpressure.An exhaust port in the die may be connected either to1This test method is under the jurisdiction of ASTM Committee E28 onMechanical Testing and is the direct responsi
15、bility of Subcommittee E28.02 onDuctility and Formability.Current edition approved May 1, 2015. Published July 2015. Originally approvedin 2009. Last previous edition approved in 2009 as E2719091. DOI: 10.1520/E2712-15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact A
16、STM 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 States1the atmosphere or to a secon
17、d gas pressurization system thatprovides a back pressure to the forming sheet.5.4 The apparatus is provided with a means of heating it tothe specified temperature for the material being tested. Usually,it is enclosed in a furnace equipped with doors opening in thefront. The allowed tolerance between
18、 indicated and nominaltest temperature is 63C up to 700C and 66C above 700C.The apparatus is provided with a means of moving the die orlower plate to insert and remove sheets of material and also toprovide a force on the plate to counteract the force exerted bythe pressurized gas. Usually, it is ins
19、talled in a hydraulic pressor clamping mechanism.6. Procedure6.1 Dome Rupture Test:6.1.1 Clean a sheet of superplastic material sized at least160 by 160 mm so that it is free of surface contaminants. Thedie and plate shall be clean and free of any lubricant. Nolubricant shall be used in the test unl
20、ess specifically required bythe lot acceptance criteria. If desired, the rolling direction maybe marked in one corner of the specimen.NOTE 2The presence of lubricant greatly affects the depth to whichthe material forms before rupturing. Although very important forproduction, lubricant adds an unnece
21、ssary variable to the test method,which is why it should not generally be used. It follows that the apparentsuperplasticity of a material in the bulge test is less than what can beaccomplished in a production environment; however, the bulge test is onlyused as a pass/fail criteria, not as a quantita
22、tive test to replicate actualforming conditions.6.1.2 Before testing, bring the vessel up to the desiredtemperature. Place the sheet onto the lower plate, and thenmechanically clamped the plate to the die with sufficient forceto prevent gas leakage or the sheet drawing across the sealduring the test
23、.6.1.3 Start the test as soon as the thermocouple reaches theminimum temperature in the range specified, and record thetime taken. The temperature shall be within the tolerancespecified in Section 5 from the time from initiation of applyinggas pressure until the termination of test or fracture.NOTE
24、3The SPF properties of some materials can be highly depen-dent on the thermal history before forming. In this case, a different heatingprofile may be specified, recorded, and controlled for the test to allowoptimum forming conditions to be realized. This is especially true whenrecrystallization or o
25、ther metallurgical phenomena occur.6.1.4 Apply a specified gas pressure to the underside of thesheet. For convenience, the pressure is usually constant;however, a variable pressure/time profile may be specified ifrequired. In general, maintain the pressure on the die side of thesheet (back pressure)
26、 at atmospheric pressure via the exhaustvent. In some cases, however, a constant or variable backpressure may be used. Record the forming and back pressures.NOTE 4The pressure is dependent on the alloy being tested, sheetFIG. 1 Bulge-Forming ApparatusE2712 152thickness, and other factors. A pressure
27、 of 0.15 t MPa has been usedsuccessfully on 5083 aluminum alloy at 773K, where t is the sheetthickness in millimetres.NOTE 5Backpressure minimizes cavitation in the sheet during form-ing and may be especially important for some aluminum alloys.6.1.5 Continue the test until the sheet ruptures, as ind
28、icatedby a sudden drop in pressure in the gas system. Release theforming pressure, back pressure, and clamp load immediately.The time taken to failure may be recorded. If after a suitablelength of time, as determined by experience, the sheet has notruptured, then it has deemed to have fully formed i
29、n the die.6.1.6 Remove the coupon from the apparatus and allow it tocool on a flat surface.6.2 Cavitation Test:6.2.1 For this test, choose a sufficiently shallow die so thatthe sheet will form into the entire shape of the die withoutrupturing. The depth of the die determines the amount ofsuperplasti
30、c strain the material undergoes measured at thecenter of the formed cup. Record the die depth on a certifica-tion of conformance.6.2.2 The test procedure is the same as for the rupture testexcept in this case it is halted after a specified time, when thepart has fully formed into the whole die cavit
31、y. The time maybe established from computer analysis or prior testing ofsimilar sheet, and is easily determined by those practiced in theart of SPF.7. Analysis7.1 Dome Rupture TestExamine the dome for evidencethat it touched the base of the die, indicated by the formationof a flat circular area on t
32、he crown of the dome. This area willnormally not be the area of rupture. If it touched the base, itmet the criteria; if it ruptured without forming a flat area at thecrown, it is considered to have failed the criteria.7.2 Cavitation TestExise a coupon 10 by 10 mm from thecenter of the formed cup. Ex
33、amine it for cavitation. Themethod used to determine cavitation is not part of this testmethod and shall be specified on the bulge test acceptancecriteria.7.3 The superplastic strain of the sample is defined as:eSPF5t02 t1!t13100 %! (1)where:t0= initial thickness measured at the center of the initia
34、lblank andt1= final thickness measured in the same place on theformed cup.8. Report8.1 The following shall be reported:8.1.1 Specimen identification,8.1.2 Material certification,8.1.3 Blank initial thickness and sheared size,8.1.4 Temperature of the test,8.1.5 Strain rate, variable pressure/time par
35、ameters, or theconstant pressure used, and8.1.6 Depth of the die (X in Fig. 1).8.2 For the dome rupture test, the following should bereported:8.2.1 Statement that the specimen passed or failed thespecification height.8.3 For the cavitation test, the following should be reported:8.3.1 Method used to
36、determine cavitation,8.3.2 Amount of cavitation expressed as a volumepercentage, and8.3.3 Superplastic strain.9. Precision and Bias9.1 No information is presented about either the precision orbias of these test methods for bulge-forming superplasticmaterials since these tests are nonquantitative.10.
37、 Keywords10.1 constant strain rate; metallic materials; metallic sheetmaterials; superplastic forming; superplastic forming proper-ties; superplastic properties; temperature; true strain; true stressASTM International takes no position respecting the validity of any patent rights asserted in connect
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