Strain rate and temperature dependent strain localization of a near α titanium alloy

The tensile response of a near α Ti3Al2.5V alloy, conceived for jet engine fan containment applications, is characterized by Digital Image Correlation (DIC) technique at quasi-static 0.001 s⁻¹, medium rate 12 s⁻¹ and high strain rates 700 s⁻¹-3000 s⁻¹ at room temperature and elevated temperatures 100°C and 200°C. The material is found to present noticeable strain rate sensitivity. Observations indicate that the dynamic true strain rate in the necking cross-section can reach values up to 10,000 s⁻¹ due to strain localization. True stress-strain relationship beyond necking at high strain rates presents limited rate dependent response, however, there is clearly no locking of strain rate effect from medium rate to high rates. A series of tests undertaken at elevated temperatures indicate that the higher temperature results in a higher true strain rate for corresponding values of true strain. Experimental results from quasi-static test condition to high strain rates are used to determine an appropriate constitutive model for finite element simulations of the tensile experiments. The model accurately predicts the experimentally dynamic macroscopic force-time response and local true stress-strain relationship, and reveals the increasing trend of true strain rate evolution and decreasing trend of dynamic amplification evolution in good agreement with the experimental measurements with the average absolute relative error less than 8.4 % and the Pearson correlation coefficient larger than 0.957.