FEM- Cowper-Symond Equations

hi, i came to this model in my FEM.
Does anyone know about the cowper-symond model? There is an equation for scaling out the yield stress.
In this equation it require 2 strain rate parameters, C, P. If my speed of projectile impact is around 200m/s wad should the C, P are??
If anyone know wad i am saying, pls help. thanks. thanks for your sharing.
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