Stress Terms of a Visco Hypoelastic formulation for FEA.

Hi all,




I am implementing visco-hypoelasticity in my FEA code for my research as


given in the 4.8.6 ANSYS manual.




I have relaxation only in the shear modulus and not in the pressure. The


manual doesn't give the explicit expression for the shear elastic stress


term and the pressure stress term. I extrapolated the expressions from what


is given, and the code is not working properly. Can you please tell me if


the following expressions for the shear elastic stress and the pressure term


is right?
If not, please let me know the equations of the pressure part and the elastic stress part.







- Shear Elastic Stress (Sinf)




S(inf,n+1) = Delta(R)*S(inf,n)*Delta(R)' +


4*G(inf)*Delta(R,n+1/2)*Delta(strain,n+1/2)*Delta(R,n+1/2)'






- Pressure Term




P(n+1) = P(n)**1* + 2*K*trace(Delta(strain,n+1/2))**1*






where,




Delta(R), Delta(R,n+1/2) are given expressions in section 4.8.6


G(inf) is shear modulus at infinite time


Delta(train,n+1/2) is the incremental strain at time step n+1/2, expression


given in section 4.8.6


trace(Delta(strain,n+1/2)) is the trace of the above matrix


*1* is a unit matrix r identity tensor.




Please share whatever you feel. I will be of help and thanks in advance.