Modeling temperature dependent material properties

Hey guys,

I am new to FEATool trying to evaluate its features before purchasing a commercial license. I tried to adapt the following test case to the best of my abilities from the Tutorial

"Resistive Heating in a Tungsten Filament"

I am trying to set up a model simulating the thermal behavior of a ceramic PTC heating element.

The basic model works, but I did not have success yet in respecting the temperature dependent behavior of the electrical resistance in PTC ceramics, which is highly un-linear around a certain temperature, the so called Curie-temperature.

Ideally this should be built through a table of measured values and interpolation, but for now I tried to work with logical expressions.

For the conductivity value in the "Conductivity Media DC" equation I tried to enter the following:

(T<473)*100 + (T>=473)*(T<475)*10 + (T>=475)*1

Expected behavior:
T<473K -> 100 S/m
T between 473K and 475K -> 10 S/m
T>475K -> 1 S7m

I also entered the entire expression in the source term "Q" of the "Heat Transfer" equation, but judging from the error I receive, I didn't even get that far.

"Could not evaluate the expression "(((aSubExpr(:,1)<473).*100)".
Please check and make sure that it is a valid expression."

test.fea

Thank you for reporting, the error seems to be due to an issue with the expression parsing, in this particular case something with the blank spaces. If you remove **all** blank spaces from the "ht:Q" coefficient it will run (but not converge in this particular case), and/or adding it as a named model "Coefficient/Expression" (instead of entering it directly into the equation edit fields.

This issue will be fixed in the next update/release (as it should not be sensitive to whitespace).