1、544 KSME International Journal Vol.IZ No.4,pp.544 552,1998 A Study on Deformation Characteristics of the Plane Strain Punch Stretching Test Youngsuk Kim*and Dongwon Jung*(Received July 21,1997)Recently,a new simple test method called plane strain stretching(PSS)test has been developed to evaluate th
2、e stamping formability of sheet materials.From the previous studies,the PSS test has been proved to have a good reproducibility and Io show good correlation with the press performance.In order to clarify the deformation characteristic of the PSS test and to investigate the effect of material and pro
3、cess variables on the performance of the PSS test,3-dimensional finite element simulations for the PSS test were performed and its results are compared with those of experiments.Key Words:Stamping Formability,Sheet Material,Plane Strain Punch Stretching Test,Finite Element Simulation 1.Introduction
4、The stamping process plays an important role in the automotive industry.Various deformation modes such as stretching,drawing,bending,or a combination of these occur during the stamping process.Currently,there are several kinds of experimental and simulative tests that duplicate well each deformation
5、 mode occurring in the stamping process,as discussed in(Ghosh.et.al.,1984).Among these simulative tests,the Erichsen cup test,Swift cup drawing test,and the hemis-pherical punch stretching test(LDH report,1990)are frequently used to evaluate the material for-inability.However,these test methods some
6、times produce poor data reproducibility and unrealistic evaluation,especially for the zinc-coated steel sheets which are widely used in car bodies for their excellent anticorrosion property,in order lo successfully obtain the desired shape of a panel,it is necessary to avoid forming failures such as
7、 local necking and shape inaccuracy and to assure the stamping formability of sheet material.*Department of Mechanical Engineering,Kyung-pook National University.*Department of Mechanical Engineering,Jaeju National University.Recently,two simple and effective test methods have been developed to eval
8、uate the stamping formability of sheet materials.One is the new Ohio State University Formability test(Saunders and Wagoner,1993;Sub and Wagoner)and the other is the Kims plane strain stretching test(Kim,et al.,1993;Kim and Park,1994a;Kim and Park 1994b),In the OSU formability test a long rectangula
9、r specimen is uniformly stretched under the action of a long,small radius of cylin-derical punch until the failure of the specimen occurs in plane strain deformation mode.Some finite element simulations were performed to investigate the effect of the tool geometry and the specimen size on the deform
10、ation characteristic.Therein,the optimum condition of these parame-ters is ascertained(Saunders and Wagoner,1993;Sub and Wagoner,1993).However,in the PSS test,a specially designed cylindrical punch is used to assure a plane strain stretching deformation at overall area of the rec-tangular specimen w
11、ith a proper width.In the PSS test the specimen width of 126ram,critical width,for punch geometry of 70ram in width and 70mm in length with punch corner radius of 5ram yields a plane strain deformation of the specimen for various automotive sheet materials including high strength steel sheet and alu
12、minum sheet A Study on Deformation Characteristics of the Plane Strain Punch Stretching Test 545(Kim,et al.,1993).The limiting punch height(LPH)value measured at plane strain fl-acture is used as a measure of material formability.The PSS test showed good reproducibility for various automotive sheet
13、materials and good correlation with press performances.The characteristic of the PSS test can be clar-ified by investigating the effect of the material and process variables on the results of the PSS test.However,due to the limitation on the arbitrary assignment of the material and process variables
14、 in the:real experiments the numerical virtual test with properly designed variables should be fie-quently referred.The finite element method(FEM)with robust calculation procedures and extensive verification of the results could be suit-ed for this purpose(Saunders and Wagoner,1993;Sub and Wagoner,1
15、993;Park and Lee,1994;Yoshida et al.,1993).Due to significant advances in the simulation of sheet metal forming processes using FEM it is now possible to make realistic analyses of sheet metal forming opera-tions that taking the material and process vari-ables into account.In this paper,the detailed
16、 characteristics of the PSS test are studied by using the commercially available 3 dimensional stamping simulation FEM code,namely the explicit dynamic code PAM-STAMP version 2.1(PAM-STAMP,1992).The effect of material variables(material anisotropy parameter and work hardening expo-nent)and process variables(specimen width and coefficient of friction)on the strain distributions and the LPH values would be simulated,and then the numerical results will be compared with experimental ones.2.Finite El
