____________________ * Corresponding author: University Technology Centre in Gas Turbine Transmission Systems, ITRC Building, The University of Nottingham, University Park, Nottingham NG7 2RD UK, chris.bennett@nottingham.ac.uk A FINITE ELEMENT ANALYSIS OF ERRORS IN AXISYMMETRIC ISOTHERMAL AND GLEEBLE COMPRESSION TESTING OF Ti-6Al-4V C. J. Bennett 1* , S. B. Leen 2 , P. H. Shipway 1 1 Department of Mechanical, Materials and Manufacturing Engineering University of Nottingham, Nottingham NG7 2RD, UK 2 Mechanical and Biomedical Engineering, College of Engineering and Informatics, National University of Ireland, Galway ABSTRACT: Coupled thermo-mechanical finite element modelling of both the isothermal axisymmetric and Gleeble compression testing of Ti-6Al-4V has been carried out in order to give insight into errors which occur when generating flow stress data for process modelling by these methods. A strain-rate and temperature-dependent Norton-Hoff material model is used to represent the material in the analyses and also for calculation of relative stress error. Significant errors are predicted for both testing methods caused by interface friction between the platens and the specimen and plastically- induced heat generation. An axial temperature profile is also predicted in the Gleeble test specimen from resistance heating which increases deformation at the axial centre of the specimen and introduces further errors. Stress errors of up to 25% are predicted. KEYWORDS: compression, Gleeble, titanium, plastic deformation, finite element 1 INTRODUCTION For the modelling of manufacturing processes involving large deformations, an extensive amount of plastic (flow stress) data is required. Typically, hot isothermal compression testing is used to generate flow stress data for finite element modelling [1, 2]; this technique is suitable for modelling processes such as sheet forming, rolling and extrusion where the temperature of the workpiece is held approximately constant throughout the process. However, for manufacturing processes involving rapid heating rates and large deformations such as friction welding, the use of other compression testing methods such as those involving Gleeble thermo- mechanical simulators is becoming more prevalent [3, 4] due to their ability to generate rapid heating rates in specimens. It is important when material testing is carried out for finite element modelling that the material data accurately represent the material properties pertinent to the process being modelled and that any systematic errors in the testing procedure are understood and accounted for when generating the material dataset. 2 MODEL DEVELOPMENT Coupled thermo-mechanical modelling of the compression testing of the titanium alloy, Ti-6Al-4V has been carried out using the DEFORM-2D finite element software for both the axisymmetric isothermal compression process and compression testing using a Gleeble thermo-mechanical simulator The specimen geometry is identical for both types of test, namely cylinders 12 mm in length and 8mm in diameter. In light of the specimen geometry; the modelling can be approximated using an axisymmetric element formulation assuming that there is no misalignment between the specimen and the platens and there are no geometry errors or other initial inhomegeinities which could skew the specimen as these effects cannot be accounted for in the model. The outline of the finite element model is shown in Figure 1 and the main basis of the model is identical for both types of testing method. However for the Gleeble modelling, a resistance heating model is first run to generate the axial temperature profile that is present during the test; this is achieved by applying a current flux to the top die and a zero voltage to the bottom die. DOI 10.1007/s12289-010-0977-8 © Springer-Verlag France 2010 Int J Mater Form (2010) Vol. 3 Suppl 1:1155 1158 –