For example, \sigma^2/a+\tau^2/b=k^2

where a(\rho)=4/3*\rho^4/(1-\rho), b(\rho)\rho^3, \rho - relative density, \sigma - medium pressure, \tau - Mises stress intensity, k - yield strength, can be function of the strain rate, for example k=k0*H^v, H - the intensity of the irreversible shear strain rates, v - material const.

tnx for u answer