Journal of Materials Processing Technology 173 (2006) 252–259 Constitutive model of the alloy 2117-T4 at low strain rates and temperatures H.V. Mart´ ınez a,∗ , D. Coupard b , F. Girot b a GINUMA, Pontificia Bolivariana University, A.A. 56006 Medell´ ın, Colombia b LAMEFIP-ENSAM, Esplanade des Arts et M´ etiers, 33405 Talence Cedex, France Received 16 July 2004; received in revised form 16 July 2004; accepted 26 May 2005 Abstract This paper relates the cold forming of the alloy 2117-T4 and the description of a constitutive model for low temperatures and plastic strain rates. The characterization of the alloy was done by cylinder upsetting aided by a finite element code (FORGE2 ® ) and following an inverse approach. Taking into account the assumptions associated to the software, the parameters of the Hansel–Spittel and hyperboloid-type models were identified assuming a von Mises material. © 2005 Elsevier B.V. All rights reserved. Keywords: 2117-T4 aluminum alloy; Cylinder upsetting; Viscoplasticity; Hansel–Spittel constitutive model 1. Introduction Actual trends in metals forming processes are character- ized by increasing demands for complex shapes and close tolerances. Numerical simulation of forming operations can be helpful in understanding the effect of process parame- ters on the product quality. It can also be used to validate a tool design. The quality of the numerical results is strongly related to the material properties and friction conditions at the die/workpiece interface. Numerous models have been developed to take into account both the material flow stress and friction conditions. Such models often comprise several parameters to estimate from simple mechanical tests (ten- sile, compression, torsion, ring test, ...). This paper relates the constitutive model for low temperatures and plastic strain rates of the 2117-T4 aluminium alloy. This material is com- monly used in aeronautical applications [1], i.e. for riveting operations. Taking into account the initial geometry of the rivet, i.e. a length of 7.14 mm and a diameter of 4.76 mm, a cylinder upsetting test has been chosen instead of a classical tensile ∗ Corresponding author. Tel.: +574 415 9195; fax: +574 411 2372. E-mail address: hadervm@upb.edu.co (H.V. Mart´ ınez). test. Nevertheless, compression testing does not directly give access to the material flow characteristics. For example, the boundary conditions give rise to a multiaxial stress state pre- venting a simple and direct interpretation of the results. The stress state is often triaxial in the sample volume due to bar- reling and biaxial on the free surfaces [2]. Interpretation of the upsetting test by analytical methods such as those used for tensile testing can thus exceptionally be considered when friction at the die/workpiece interface is very restricted. How- ever, during a lubricated cylinder upsetting of a sample with a height to diameter ratio greater or equal to 1.5, the force is mainly influenced by the material rheology and not much by the friction coefficient, whereas the barreling of the deformed and relaxed cylinder is sensitive to friction but not much to the material rheology [3]. With this remark, rheology and tri- bology can thus be identified separately. The force is used to determine the rheological parameters for any kind of friction condition and the geometry enables the evaluation of the fric- tion coefficient with the material parameters provided by the first identification. In this study, a thin MoS 2 solid lubricant layer was sprayed at the die/workpiece interface in order to (a) minimize the friction coefficient and (b) approach as much as possible a homogeneous upsetting test for which friction has a little 0924-0136/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2005.05.056