Iso Chronous curve

Thanks Vijay

                  for giving me guide lines but my altimate aim is to the finding of devlopment of iso chronous curve for creep buckling.and for that while studing nonlinear strees strain curve we know that as in non linear stage the what is the value of stress and strain at time T=0 and time T=t? is the any formula for the Et and Es in non linear stress and strain?...and which procedure for calulation foe Et and Es?

Regards

Asit Rathod