Dynamic Multi-Axial Loading Response and Constitutive/Damage Modeling of Titanium and Titanium Alloys

Abstract

Research ObjectivesTitanium alloys, and ceramics encapsulated in titanium alloys are considered for next generation of lightweight tanks. The objectives of this research project are to obtain responses of newly developed economical, but with much higher Oxygen content, Ti6Al-4V alloys, determine the suitability of existing constitutive relations to model these responses, and to determine material constants for these models (e.g., JC and KHL models) for incorporation in computer codes for penetration simulation.These objectives are being achieved through uniaxial loading experiments over a wide range of strain rates and temperatures in the first year of funding, and through multi-axial loading experiments over a wide strain rate range and a wide temperature range in the second and third year of funding, respectively. ApproachUniaxial compressive experiments, over a wide range of strain rates and temperatures, are used to determine material constants for two constitutive models (Johnson-Cook and Khan-Huang-Liang); experiments are performed on several titanium (Ti-6Al-4V) alloys. The results from these models are correlated to these experimental data to demonstrate the flexibility in each model. Most other investigators who have performed similar studies, stopped at this stage. The approach taken by other scientists is not right because if correlations are done with the same experiments from which the material constants are determined, then correlations should be always good for any constitutive model. We have gone one step further, which is very desirable, if not required, to validate a constitutive model. In the phase of the current year of funding, multi-axial loading experiments (e.g. dynamic torsion followed by dynamic compression using Kolsky or split Hopkinson bar technique, uniaxial compression followed by biaxial compression, etc) have been performed and compared to predictions from these two constitutive models to establish validity of these two models over a wide ranges of strain rates and temperatures. BackgroundSince the introduction of titanium and titanium alloys around 1950, they have become important materials for aerospace, energy, and chemical industries. They are used chiefly for parts that require good corrosion resistance, moderate strength up to 588 K, and lightweight. Titanium alloys, especially Ti-6Al-4V, an α+β type titanium alloy is largely used alloy in many industries because of its extremely attractive properties like high specific strength, good deformability, reasonable ductility and ability to withstand high temperatures and resistance to corrosion. It is primarily used in aero-engine, gas turbines and other applications. The development of a relatively economical Ti-6Al-4V alloy, with a low interstitial content has prompted a lot of interest in its possible use in armor tanks because of improved ductility, whereas the conventional more expensive Ti6Al-4V alloy has been used primarily in aerospace components chiefly because of its high strength to weight ratio. This advantage has al...