Determination of Yield Locus of Sheet Metal at Elevated Temperatures: A Novel Concept for Experimental Set-Up


Article Preview

The constant demand of increasing performances and safety in vehicle industry has led significant innovations in the materials used in sheet metal forming processes. In particular, multiphase steels and lightweight alloys have known higher and higher importance, thanks to the development of new stamping processes at elevated temperatures, which guarantee, at the same time, better formability, lower springback and more accurate micro-structural control in the formed sheets. With respect to these aspects, the correct design and optimization of the new processes cannot prescind of the mechanical characterization of materials in biaxial stress conditions, especially when it strongly varies according to the stress and temperature. In this paper, a novel experimental set-up is presented for determining the in-plane yield locus of sheet metals at elevated temperatures. A cruciform specimen, whose geometry was optimized by numerical simulation, is used for the study of the yield locus in the range of biaxial tensile stresses. The test machine concept is based on punch-wedge mechanism, which uses the vertical movement of the press for the deformation of the specimen along two perpendicular axes. In the first part of the paper, the optimization of the cruciform specimen by thermo-mechanical FE analyses is outlined. Details on the experimental set-up are then given with the description of the apparatus, the measurement of plastic strains and the heating system for tests at elevated temperatures.



Main Theme:

Edited by:

F. Micari, M. Geiger, J. Duflou, B. Shirvani, R. Clarke, R. Di Lorenzo and L. Fratini




A. Ghiotti et al., "Determination of Yield Locus of Sheet Metal at Elevated Temperatures: A Novel Concept for Experimental Set-Up", Key Engineering Materials, Vol. 344, pp. 97-104, 2007

Online since:

July 2007




[1] M. Geiger, M. Merklein, C. Hoff: Basic Investigation on the Hot Stamping Steel 22MnB5, Sheet Metal 2005 Conference, Proceedings (2005), pp.795-802, (2005).


[2] L.G. Aranda, P. Ravier, Y. Chastel: Hot Stamping of Quenchable Steels: Material Data and process Simulations, IDDRG 2003 Conference, Proceedings (2003), pp.166-164, (2003).


[3] M. Suehiro, K. Kusumi, T. Miyakoshi, J. Maki, M. Ohogami: Properties of Aluminium-coated Steels for Hot-forming, Nippon Steel Technical Report N. 88 July (2003).


[4] Makinouchi, A., Teodosiu, C., Nakagawa, T., 1998, Advance in FEM Simulation and its Related Technologies in Sheet Metal Forming, Annals of the CIRP, 47/2: 641-649.


[5] D. Lorenz, K. Roll: Modelling and Analysis of Integrated Hotforming and quenching Processes, Sheet Metal 2005 Conference, Proceedings (2005), pp.787-794, (2005).


[6] P. Hein, A Global Approach of the Finite Element Simulation of Hot Stamping, Sheet Metal 2005 Conference, Proceedings (2005), pp.763-770, (2005).


[7] T. Sokolowski, K. Gerke, M. Ahmetoglu, T. Altan, Evaluation of tube formability and material characteristics: hydraulic bulge testing of tubes, J. Mat. Process. Tech., 98, 2000, 34-40.


[8] G. Gutscher, H. -C. Wu, G. Ngaile, T. Altan, Determination of flow stress for sheet metal forming using the viscous pressure bulge (VPB) test, J. Mat. Process. Tech., 146, 2004, 1-7.


[9] G. Ferron, A. Makinde, Design and development of a biaxial strength testing device, Journal of Testing and Evaluation, 16 (1988) 253-256.


[10] A. Makinde, L. Thibodeau, K.W. Neale, Development of an apparatus for biaxial testing using cruciform specimens, Experimental Mechanics, 32 (1992) 138-144.


[11] E. Hoferlin, A. Van Bael, P. Van Houtte, G. Steyaert, C. De Mare´, Biaxial tests on cruciform specimens for the validation of crystallographic yield loci, International Journal of Material Processing Technology, 80-81 (1998) 545-550.


[12] D.E. Green, K.W. Neale, S.R. MacEwen, A. Makinde, R. Perrin, Experimental investigation of the biaxial behaviour of an aluminium sheet, Intern. Journal of Plasticity, 20 (2004) 1677-1706.


[13] M. Geiger, G Van der Heyd, M. Merklein, W. Hubnatter, Novel concept of experimental setup for characterization of plastic yielding of sheet metal at elevated temperatures, Advanced Materials Research, 6-8, pp.657-664, (2005).


[14] A. Ghiotti, S. Valotto, Internal Report, DIMEG 06/2006, in Italian.