Time step in Linear Viscoelasticity model

[infinity_95]

Hello everyone,

I have a basic doubts related to Linear viscoelasticity model described in FEAP theory manual.  It is mentioned that the recursive formula is stable for small and large time steps but will the solution change if delta t is changed?

for example I'm trying to solve a axisymmetric vertical thick cylinder problem with linear viscoelastic model and I'm trying  to measure displacement over time under gravity (1g) load.  Will my solution change if delta t is changed?. What is the criteria for selecting delta t. will it depend on my prony series coefficients?. how can I validate my FEA results?.

[Prof. R.L. Taylor]

The model will require time increments that are in the range of the exponentials in the Prony models.  THus, solution will be dependent on time increments used.  For very small time increments your solution should be like the initial moduli, if time incremenets are too large then the solution will be like the equilibrium moduli.

[infinity_95]

Thank you very much for your reply Professor.

so if i use time increments similar to particular relaxation time (say jth element) of  maxwell element in generalized maxwell model, it will respond based on the modulus of that jth element ?. Is my understanding correct?

Basically Im using a relaxation modulus which is varying between 10^-8 sec to 10^8 secs and fitted the curve to a 16 parameter prony series. I have literature data which uses Schaperys approach(transforming time parameter) to get approximate solutions and Im trying to use your recursive formula to get time dependent solution. In my view, solutions based on recursive formula makes sense but I how can i justify my results?