Do you know about the paper :

'Experimental and numerical analysis of high strain rate response of Ti-6Al-4V titanium alloy'. Available from: https://www.researchgate.net/publication/46251930_Experimental_and_numerical_analysis_of_high_strain_rate_response_of_Ti-6Al-4V_titanium_alloy [accessed Jun 21, 2016].

Here you find the Cowper-Symonds overstress power law including the rate dependence of thematerial. rate Epsilon-plast= D(R-1)exp (n), where D and n are material parameters with the values D = 77850 and n=3.575.

Article Experimental and numerical analysis of high strain rate resp...

thank you sir will try it