Experimental and Numerical Prediction of the Static and Dynamic Forming Properties of Ti6Al4V

Abstract

The strain rate dependence of the plastic yield and failure properties displayed by most metals affects energies, forces and forming limits involved in high speed forming processes. In this contribution a technique is presented to assess the influence of the strain rate on the forming properties of Ti6Al4V sheet. In a first step, static and dynamic tensile experiments are carried out using a classical tensile test device and a split Hopkinson tensile bar facility respectively. Next to uniaxial tensile, also purpose-developed plain strain and shear stress samples are tested. The experimental results clearly show that the mechanical behaviour of Ti6Al4V is strain rate dependent. Indeed, with increasing strain rate, plastic stress levels increase, however, this occurs at the expense of the deformation capacity. Subsequently, to allow simulation of forming processes, Johnson-Cook, Swift and Voce material model parameters are determined. Finally, the influence of the strain rate on the forming limits is assessed using the uni-axial tensile test results. Prediction of the initiation of necking in the Ti6Al4V sheets subjected to multi-axial strain states is based on the Marciniak-Kuczynski model. The thus obtained forming limit diagrams (FLDs) show a non-negligible effect of the strain rate. The reduced ductility at higher strain rates is reflected into an unfavourable downward shift of the FLD. Compared with the experimental data, the static FLD is clearly conservative.