Prony Series in ANSYS

[Ingrid]

Does anyone know anything about Prony series in ANSYS?? I´ve made a few experiments and have managed to import the data (Shear modulus) into ANSYS.

One problem with my experiments is that they only cover a short period of time. Is there any way to recalculate the time for a much much longer time period?

While creating prony series in ANSYS I have tried to vary the time constants (st_1, st_2 etc.) and by doing so managed to obtain different prony series. Is there anyway to know how to vary these inputs? I´ve just randomly tried different numbers.

One thing I´ve noticed is that all time constants (tau) are pretty much the same, is that wrong?

Ingrid

[sq]

If all the time constants (tau) were exactly the same, you'd have a one-element Prony series, whose relaxation strength was equal to the sum of the individual strengths. Kind of redundant, really. There should be some separation between them.

In general, when a Prony series is defined, the time constants are specified in such a way that they span some range of times usually on a logarithmic scale (consider how relaxation graphs are plotted). For example, separate the time constants by decades (e.g., 0.01, 0.1, 1, 10, 100, and so on), which is usual, or maybe something like factors of two (1, 2, 4, 8, 16).

In any case, the Prony series time constants of your model should correspond to the time scales of your experiments. For example, if your experiment was 100 seconds long, you can't really say anything about what happens at 1000 seconds. If your sampling rate was 1 Hz (i.e., your first record is at one second), you couldn't say anything detailed about what happens in the 0.1 second timescale.

Given a rheologically simple material, there is, as always, the possibility of using time-temperature superposition to extend the time scales of your experiments. This involves developing what is usually called a "master curve."

[Ingrid]

Thank you for your help.

Is there any way to use Prony series in ANSYS Workbench? I´m not to familiar with ordinary ANSYS. If not, how do you use the prony series in ordinary ANSYS?

Ingrid

[chiduk]

Hi..
This is chidu..,
U can model prony series in ANSYS ..,
1st u have to get MAXWELL table.. and u will get some 99 constants where u have to fill it up all cell by numerical values .. each cell describes one parameter relating viscoelasticity..,
and u have to assume time in decades as 1 10 100 1000 for shear or bulk modulus decay ( where u feel the change of specimen occurs).., and u have to get summing terms which is purely based on u r best assumption .. and it has to be sum of 1 ..