Problem thermal stress in Mecway 9

waluyo

I did the heat transfer analysis (thermal steady state) in Mecway 8 (element tri3), then transfer temperatures from solution.

By using the temperatures, then I continued the analysis to static analysis (static analysis), having thermal expansion and stress thermal loading. When I run, it said tri3 is not supported in this analysis, then I changed the elements to tri6 (by using mesh tool - change shape). The result in Mecway 8 is as expected, the structure is expanding due to the temperature loading.

However, when I opened in Mecway 9, it seems not correct. I run in Mecway 7 also ok.

Is this a bug in Mecway 9 or the behavior in element is changed?

Victor

The change is that version 8 and earlier calculated thermal stress using a single average temperature over the whole element but version 9 interpolates the temperature at each integration point which is more accurate. That means non-uniform temperature fields within elements were hidden in version 8 but are apparent in version 9.

This model will give incorrect results in all versions because the midside nodes without temperatures default to the reference temperature - ie no thermal stress. To correct it, use the same tri6 elements in the thermal model as the static model.

waluyo

Thank you Victor,
I rerun the heat transfer after changing to tri6 elements (from tri3), then creating a static model with thermal stress. Yes, it works and showing the same displacement contour as shown in previous one. Perhaps this converts to a better and more accurate result as you have explained.

Victor

Though it looks similar, this new displacement is about double what it was before. The maximum is now 1.3e-8 m compared to 6.7e-9 m without the midside nodes included. That's because without temperatures on the midside nodes, half the nodes of each element were contributing a 0 to the average temperature change so the thermal strain was about half what it should have been.