Viscoelastic analysis for pdms material in ANSYS

[rahulkishor]

Hi,

I wanted to perform an analysis using ansys to find out the dissipation of acoustic wave in pdms material. So I found that pdms being a viscoelastic material, we need to perform a nonlinear analysis with the prony series for shear and volumetric modulus entered in the viscoelastic properties for the pdms material. The acoustic wave load was of the frequency 100MHz, so I performed a transient analysis in ansys for a time equal to 250ns with substep of 0.5ns. But after running for a while the analysis terminated due to nonconvergence.

Can anyone help me to solve this issue
1. Is it right to set the viscoelastic properties for pdms to study its acoustic wave dissipation
2. If the first one makes sense, how can I make sure that I get a result out of the transient analysis that I perform

Pls if any one could help me!

Thanks in advance!

[Jorgen]

1) Sure you can use a linear viscoelasticity model to study the wave propagation response
2) Are you sure you apply appropriate boundary conditions?

-Jorgen

[rahulkishor]

1) Sure you can use a linear viscoelasticity model to study the wave propagation response
2) Are you sure you apply appropriate boundary conditions?

-Jorgen

Many thanks for your reply, Jorgen.

1) Is it a "linear" viscoelastic modelling? Cos what I observe is that when I enter the prony series (relative modulii and relaxation time), the analysis becomes nonlinear due to material nonlinearities. Just thought of confirming the same.
2) My model is a Surface acoustic wave generated out of a piezoelectric substrate which now is propagating and I place a pdms material on the path of the wave propagation. I havnt applied any boundary conditions for the pdms material instead some boundary conditions (piezoelectric) and loads(input voltage) for acoustic wave generation was applied. Could you please tell me if there is some mistake.

The prony constants which I used are:
TB,PRONY,4,,1,SHEAR
TBDATA,1,0.989,1e-4

TB,PRONY,4,,1,BULK
TBDATA,1,0.9423,1e-4

Now for the transient analysis I have done the following:
1) time at end of load step=250ns (acoustic wave frequency being 100MHz ->10ns)
2)Number of substeps = 500 (time step size=0.5ns)

I have seen from some materials that they perform 2 load steps and all. But I didnt understand the rationale. Could you please help me with this.

NB: If there are some good materials for ANSYS viscoelastic transient analysis. Could you share it?