Learning Forum

[fares abbara]

Hello,

I have an elastic tube that i would like to add certain material properties to it, taken from literature. The tube is assumed to be hyper elastic with tabulated stress-strain data. The stress-strain graph is non-linear, but it was assumed to have to linear parts with different Young's Moduli. I am testing the model on transient by applying a cyclic loading, however, i need to add density and Young's modulus readings. The density part if covered, but i don't know how to go about the Young's modulus specification given that i have two different moduli (before and after a certain strain reading on the graph). the material is also assumed to be anisotropic.

 

[peteroznewman]

Hello Fares,

This data looks suspect.  Stress is usually zero at zero strain.  This data is far from zero stress at zero strain.

[fares abbara]

Hello Mr. peteroznewman,

That's true, i've noticed that. Unfortunately, this was the best data i have managed to get my hands on to impliment on my model. However, i did a curve fitting of a 9-Parameter Mooney Rivlin Model, and managed to get a fit as shown in the picture i attached.

[peteroznewman]

The negative slope is problematic. That will lead to instabilities during the solution.

I suggest you discard the stress-strain data below a strain value of 0.03 and fit a lower order curve to the remaining points. That should eliminate the negative slope.

[fares abbara]

Thank you for your suggestion, Sir.

 

I have done as you said and the model ran smoothly. However, i have ran into an issue when probing stress and acceleration in the solution. I created 4 coordinates (2 on the outer surface and 2 on the inner surface of the tube), and i assigned those coordinates to the probes accordingly. However, while the probes on the outer surface displayed results, the inner probes do not seem to be generating results. i tried several times to update the solution, but to no avail. I attached a screenshot to show the positions of the coordinates and the solution section. As you can see CTP and CTP_2 probes are showing results while CSP and CSP_2 are not.

[peteroznewman]

Slice the geometry to create a vertex at the location of the coordinate systems. The vertex will move with the elements as they change shape while the coordinate system stays in place while the elements move away from that point.