thermal stress analysis

[Anonymous]

Hello, i need help for thermal stress analysis. i am totaly new to simulation stuff. i have this scenario where i want to test this simple frame of two rods connected from the bottom.  i have done static stress simulation , but when i want to add temperature( in Thermal Stress study) and apply force its showing me extreme MPa pressures no matter how i try to do it. Can someone tell me the right way to do this.

i want to hold this frame from one side and pull from other side while there is weight on the top and temperature as well which is applied to the top side of left right and top of the frame. i want temperature to come from some kind of source on the frame. metal i am using is cast iron. temperature 300c. pull force 10kg weight 5kg on the top.

i tried many different ways still having same problem. 1500 MPa / over 2000 MPa / over 3000MPa even more 

I am trying to understand here how to setup this simulation and have right results.

what is causing this extreme pressure. I have attached frame pic

[tyler_henderson]

Hi,

Are you only seeing these high stresses after you add the heat source?  Are the stresses reasonable without the heat source?  Can you check the temperatures in Results with the heat source?  Are they extremely high?  If yes, did you make sure to add Convection to the outer surfaces of the frame?  There will be natural convection that allows heat to transfer from the frame to the air, but if you did not add that then the heat will just build up in the frame.

If you still can't get intuitive results, maybe you can post a copy of the Fusion file here so I can take a look at it for you.

Best regards,

[Anonymous]

Thanks for your time and response. 

in static stress all is normal. No high stresses

when i go in thermal stress study enviorment thats where its happening.

for now i am applying temperature to the frame. so temprature is same on the frame.

After alot of search online now i know where i put constrains on the part thats where the pressure is which i dont no why.

i dont know how to apply temprature to the frame from heat source thats why i am appliying temprature to the frame.

i dont know how to setup this study right. 

[tyler_henderson]

Can you post an image of the Results?

[Anonymous]

here are the pics and fusion 360 file i have attached. i dont know if this file contains simulation as well but i have tried to save that as well in the file

[tyler_henderson]

Ok, I took a look at your model and simulation.  There a couple of issues that are easy to fix:

1.  It looks like you had some interferences between the curved bars and the bottom feet.  I see you removed the interference in Simplify by using the Combine tool, but it left holes cut out of the bottom feet (you chose "keep tool body).  If that's how it is actually going to be manufactured then it's fine, but the simulation does not consider how those parts will be attached, like welds for example.  So there are high stresses at the corners of those holes where the parts are trying to separate.  Removing those holes and just having the ends of the curved bars sitting on the top of the feet will help reduce some of that stress.

2. The Convection Load is not doing anything because it cannot reduce the Applied Temperature.  Applied Temperature is for a known temperature at equilibrium, so the solver tries to maintain that temperature on the applied entities no matter what.  If you know that those bodies are at 400 deg C at equilibrium, then you don't need the Convection.  However, if you don't know the equilibrium temperature, then you should apply a Heat Source or Internal Heat along with known Convection (natural convection at 20 deg C ambient is typically around 5 W/(m^2 K). 

3.  The Fixed Constraint on the bottom of Body 2 is preventing that bottom face from expanding due to the high temperature, and consequently, is causing high stresses in that Body.  You're better off using 3 Frictionless constraints (one perpendicular to each direction you want constrained).  This allows that part to expand in 3 directions and still preventing the whole body from moving.  I also recommend adding a Frictionless constraint to the bottom of Body 1, assuming that Body is resting on something rigid (like the ground) rather than floating in space.

The biggest cause of the stress in your model is the heat.  400 deg C (752 deg F) is quite hot and causes a lot of expansion in that steel.  If that temperature is accurate, then the stress results are probably fairly accurate also (theoretically of course). 

I hope this helps.

[Anonymous · Accepted solution]

Thankyou soo much for your help. Finally i have managed to get 780 MPa max pressure on the model. I am new to all this and trying to learn about simulation. i was stuck on this point for more than week, didnt know what was wrong. With your help things are more clear to me now. 

I really appreciate your time and response. Thanks Alot

[tyler_henderson · Accepted solution]

Great, I’m glad I was helpful. Best of luck.