Learning Forum

[Stefan Weitz]

Hello Everyone,

 

I am trying to model the stress- and strainfields in a layered system after fabrication, therefore I am recreating the fabrication process to see which internal stress acts after fabrication.
During fabrication a plain material is glued on the layered system, this step I did recreate by ekill and later ealive. However, after the ealive command and emergance of the glued material the geometry deforms which I don't understand. It seems like the connections between the layers are suddenly gone (I defined beforehand all connections of each layer as connected). Layers seem to intersect and overlap between each other. Next to it, the internal stress changes completly, high stress suddenly appear in the region where the adhesive is modeled.

In the image you see the first prinzipial stress before and after adding the material to the system with ealive at a temperature of 22°C.

Does somebody know why my geometry is deforming and why the stress is suddenly changeing?

[Gary Stofan]

It appears as if the Contact is penetrating / pushing through each other. 
I would start with confirming by using Contact Tracker(s). Note this is not the same as Contact Tool.
Contact Trackers are inserted on the Solution Information. 
Contact Trackers allow you to graph the number of contacting elements vs time (and many other quantites).

As far as why the contact is pentrating through, it can be several reasons.
 - Time stepping is too fast.
 - Inaccurate material properties. 

 

[Stefan Weitz]

Can you please clarify what Contact Tracker is? My software is in german and I can't tell which one you actually mean, I tried the following:
Solution > contact tool > Status (gives me that my interfaces are bonded)
Solution > contact tool > Penetration (gives me small penetrations which are seemingly not connect to the high stress)

I simplified the model further (removed ekill and other mechanics) to have the plain volume. Since I have to add some mechanics to get the simulation running, I added a small block next to my geometry which is displaced by 10µm. The original structure is not supposed to move. Here something odd happens, the original structures moves several mm away and somewhat tilts. It seems like its on an orbit or so. Moreover the high stresses remain in the adhesive layer. 

After some testing, I found that the reference temperatures for the different materials effect the high stress and this odd discplacement. 

 

After changeing all the reference temperatures to "by environment". The situation enhances but there are still stresses (mainly in normal X direction but also in Y and Z) as well as an odd shift of the structure. (In this case the penetration of the interface equals 0)
Can you tell me where the stress could come from? And why is the structure moveing?

Many thanks for your help! :)

[Gary Stofan]

 

 

Here is the Contact Tracker path…

 

It seems the model is moving unexpectedly. 

I would start by using all linear material (Steel) to make sure you have the mechanics / constraints / contacts set correctly. 

 

Gary