instantaneous modulus

[Muzialis]

Hi All,

let me wish you a very happy 2008.

I am dealing at the moment with a sound wave propagation problem for a composite structure whose static rersponse is very well predicted by an ANSYS model we have put together.
To determine the speed of sound of the contained liquid we are requested though to determine the instantaneous elastic modulus (i guess the transient response before the static equilibrium is reached, is it correct?), which is something I do not know anything about.We have experimental measures so would be really a pity not to try a prediction, which is rather poor using the static modulus.
Has anyone any experience in the field or any good advice?

Thank you very much.

Kindest Regards

Muzialis

[Jorgen]

Hi Muzialis,

I agree that the instantaneous modulus can be higher than the static (equilibrium) modulus. If you know experimentally that they are different, then that difference is likely caused by viscoelastic behavior of your composite material.

If you want to predict the difference then you need to use a viscoelastic model, and calibrate the model using Dynamic Mechanical Analysis (DMA) data or some other dynamic data.

- Jorgen

[Muzialis]

Jorgen,

thank you as usual for your reply.
Would you mind spending a further line on what is intended by DMA, as I am not sure I know what it is?

Thank you ever so much.

Kindest Regards

Marco

[Jorgen]

DMA = Dynamic Mechanical Analysis is a simple way to determine the viscoelastic properties (storage modulus and loss modulus) of material. You can also determine the behavior using traditional experiments. The value of DMA is that is done on smaller specimens and is typically cheaper. It might not be possible, however, to use this experimental technique for your composite.

- Jorgen

[Muzialis]

Jorgen,

thank you very much for this clarification.

All the best

Muzialis