Dynamic Mechanical Behavior of Titanium Ti-6Al-4V at Transient Large Deformation Manufacturing Processes

Titanium Ti-6Al-4V alloy has been widely used in the aerospace, biomedical, automobile and petroleum industries. However, Ti-6Al-4V is a typical difficult-to-process material owning to its unique physical and mechanical properties which are characterized by low thermal conductivity, low modulus of elasticity, and high yield strength at elevated temperatures. The rapidly rising demand for titanium components demands more efficient manufacturing processes. Material property of Ti-6Al-4V plays an important role in process design and optimization especially for transient large deformations processes such as forming and machining. However, the dynamic mechanical behavior is poorly understood and accurate predictive models have yet to be developed. To obtain meaningful results which reflect the physical mechanisms of large deformation processes, it is essential to study the dynamic mechanical behavior of Ti-6Al-4V. The Johnson-Cook (JC) model has shown to be effective for modeling strain-hardening behavior of metals and it is numerically robust and can easily be used in finite element simulation models. However, the determination of JC model parameters is determined mostly based on split Hopkinson bar pressure (SHPB) test at isothermal conditions, which is very different from those of transient large deformations characterized by quick and high temperature changes. This study focuses on the dynamic mechanical behavior of titanium in transient manufacturing processes. The mechanical behavior of Ti-6Al-4V at large strains and strain rates beyond the isothermal conditions has been studied using the JC model coupled with the adiabatic condition. Heat fraction coefficient and temperature parameter have great effect on Flow stress-strain relationship. A significant drop of the flow stress occurs at large deformations with high strain rates. The flow stress sensitivity to JC strength model parameters was also investigated. The effect of pressure-stress ratio on material failure strain has shown the material may exhibit super plasticity before failure at hydro compression mode.