Size effect on the high strain rate micro/meso-tensile behaviors of pure titanium foil

Abstract

The influence of size effect on deformation behaviors at quasi-static strain rate has been widely studied in recent years. However, there is little research about size effect on deformation behaviors of metal foils at high strain rate. To clarify how the size effect influences the deformation behavior of metal foils over a wide range of strain rate, the tensile tests at different strain rates of pure titanium foil with various grain sizes were originally conducted using material testing system (MTS) and a specially designed Split Hopkinson Tension Bar. It is found that microstructure evolution and fracture mechanism show great differences between quasi-static and dynamic tensile tests. Moreover, size effect on flow stress of pure titanium foil also shows obvious distinctions between quasi-static and dynamic tensile tests and this phenomenon was well explained by the proposed twinning refinement physics model. Furthermore, the uniform strain for pure titanium foil is larger at high strain rate than that at quasi-static strain rate, and a larger uniform strain for pure titanium foil with larger grains was observed at high strain rate. A modified Johnson-Cook model coupling effects of grain size and strain rate was proposed to predict the flow stress of pure titanium foil, and the prediction matched well with the experimental results.

Keywords

• Size effect
• Micro/meso-scale tension
• Micro-forming
• High strain rate
• Pure titanium foil