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Hello all,

I am trying to simulate the behaviour of a structure that goes through thermal stress. The temperature is applied through a time dependent expression and the temperature goes from 293K to 1436K. The study done is time dependent.

My structure is a thin film with a gage section made of silicon nitride over a silicon substrate. From the measurements of my devices, I know there is a tensile residual stressof 390MPa on the thin film, however, whenever I use the "initial stress feature" and input a 390MPa as the value when I check the stress on my structures at time 0s I get values of about 2.7E9. There are no other loads applied to the device. The only added boundary condtion comes from constraining the 4 points at the corners of the device. I do notunderstand why my stress levels get bumped so high. I check the initial conditions of my model and it does show the whole film prestressed to 390MPa

I have read that the "initial stress" function is kind of confusing as well, so I tried to apply a statitc study that brought my temperature down from 950K to 293K, which generated a stress of 390MPa in my results and then use that result as my input for a second study where i try to do what i mentioned above. However, the same thing happens when I put my simulation at 0s my stress then becomes really low to about 2.7MPa. I have tried several approaches and combinations of options but none of them give me the result I believe I should be getting.

I am attaching my .mph file any help is appreciated