Viscoelastic material

[Dr. Ahmad Chihadeh]

Dear Colleagues,

Following the derivations of the Linear Viscoelasticity in the Version 8.6 Theory Manual and looking at subroutine viscoe

the formula
qi(i,n) = exp_n*qi(i,n) + dq_n*(ee(i) - en(i))

shouldnt be
qi(i,n) = mu_n*exp_n*qi(i,n) + dq_n*(ee(i) - en(i))
?

as eqn. 9.37 in the manual
s(t) = 2G[mu_0 e(t) + mu_1 h(t)]

Best regards
Ahmad

[Prof. R.L. Taylor]

I believe it is correct as coded. If you multiplied as you state the left and right would be inconsistent by the mu value.

[Dr. Ahmad Chihadeh]

but dq_n is also multiplied by mu_n

do n = 1,nv
        mu_n  = d(2*n+49)
        dtau  = dt/d(2*n+50)

        dq_n = mu_n * hvisc(dtau,exp_n)
        gfac = gfac + dq_n
        mu_0 = mu_0 + mu_n

!       Update history and compute viscoelastic deviatoric stress
        do i = 1,ntm
          qi(i,n) = exp_n*qi(i,n) + dq_n*(ee(i) - en(i))
          sig(i)  = sig(i) + qi(i,n)
        end do ! i
      end do ! n

[Prof. S. Govindjee]

I tried a simple creep test computation and did not get the result I was expecting.  I will have a further look at the coding to see if there is an error or if my expectation was flawed.  Attached is my input file, where I was expecting the displacement to double upon relaxation.

[PS: There is a printing error in elements/material/inmate.f, whereby the volumetric viscoelastic parameters are not being printed to the output file.]