ASTM_E_2218_-_15.pdf

Designation:E221815Standard Test Method forDetermining Forming Limit Curves1This standard is issued under the fixed designation E2218;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last 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 method gives the procedure for constructing aforming limit curve(FLC)for a metallic sheet material byusing a hemispherical deformation punch test and a uniaxialtension test to quantitatively simulate biaxial stretch and deepdrawing processes.1.2 FLCs are useful in evaluating press performance bymetal fabrication strain analysis.1.3 The method applies to metallic sheet from 0.5 mm(0.020 in.)to 3.3 mm(0.130 in.).1.4 The values stated in SI units are to be regarded as thestandard.The inch-pound equivalents are approximate.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.Referenced Documents2.1 ASTM Standards:2A568/A568M Specification for Steel,Sheet,Carbon,Structural,and High-Strength,Low-Alloy,Hot-Rolled andCold-Rolled,General Requirements forE6 Terminology Relating to Methods of Mechanical TestingE8/E8M Test Methods for Tension Testing of Metallic Ma-terialsE517 Test Method for Plastic Strain Ratio r for Sheet MetalE646 Test Method for Tensile Strain-Hardening Exponents(n-Values)of Metallic Sheet MaterialsE2208 Guide for Evaluating Non-Contacting Optical StrainMeasurement Systems3.Terminology3.1 Terminology E6 shall apply including the special termsused in this method shown in 3.2.3.2 Definitions:3.2.1 biaxial stretchinga mode of metal sheet forming inwhich positive strains are observed in all directions at a givenlocation.3.2.1.1 DiscussionSee Fig.1.3.2.2 deep drawinga metal sheet forming operation inwhich strains on the sheet surface are positive in the directionof the punch travel(e1)and negative at 90 to that direction.3.2.2.1 DiscussionDeep drawing,see Fig.1,occurs in thewalls of a drawn cylinder or the corner walls of a deep drawnpart when the flange clamping force is sufficient to restrainmetal movement and wrinkling,while permitting the punch topush the center area of the blank into the cavity of the die.Strain conditions that can cause wrinkling or thickening areshown in Fig.2.3.2.2.2 DiscussionIn forming a square pan shape,metalfrom an area of the flange under a reduced clamping force ispulled into the die to form the side wall of the part.3.2.3 forming limit diagram(FLD)a graph on which themeasured major(e1)and associated minor(e2)strain combi-nations are plotted to develop a forming limit curve.3.2.3.1 DiscussionSee Fig.2.3.2.4 forming limit curve(FLC)an empirically derivedcurve showing the biaxial strain levels beyond which localizedthrough-thickness thinning(necking)and subsequent failureoccur during the forming of a metallic sheet.3.2.4.1 Discussion See Fig.3.3.2.4.2 DiscussionThe curve of Fig.3 is considered theforming limit for the material when the metal is subjected to astamping press operation.It was obtained for a drawing qualityaluminum killed steel sheet.The curve of Fig.3 correlates withthe upper curve of Fig.2,a generic curve representing ametallic sheet material with a FLDoof 40%.3.2.4.3 DiscussionThe strains are given in terms of per-cent major and minor strain measured after forming a series oftest specimen blanks by using a grid pattern.The gauge lengthsbefore and after forming the part are measured to obtain the1This method is under the jurisdiction of ASTM Committee E28 on MechanicalTesting and is the direct responsibility of Subcommittee E28.02 on Ductility andFormability.Current edition approved Oct.1,2015.Published December 2015.Originallypublished in 2002.Last previous edition approved in 2014 as E2218141.DOI:10.1520/E2218-152For 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 percent strain.The curve for negative(e2)strains will generallyfollow a constant surface area relationship to the associated(e1)strain.3.2.4.4 DiscussionThe range of possible major strain(e1)is from 0%to over 200%.The range of possible minor strain(e2)is from 40%to over+60%.3.2.5 limiting dome height(LDH)testan evaluative testfor metal sheet deformation capability employing a hemi-spherical punch and a circumferential clamping force sufficientto prevent metal in the surrounding flange from being pulledinto the die cavity.3.3 Definitions of Terms Speci