Weekend Special: FEM in FreeCAD for Dummies

[@EngineerJerry]

Thank you for the demo. I have an engineering education but have never worked in the field. However, the FEM result you received was expected. Essentially all of the load is carried by the top surface of the truss. I repeated your example in the same orientation but put fillets on the bottom and got a similar result. If you want more load carried by the bottom member of the truss you would want to flip the geometry vertically and make all the contact points more than point contact. Preferably you would add fillets and avoid those sharp corners. This analysis tells you that you have over engineered the bottom member and could make it much thinner.

[@Jim-Penn]

Good stuff ... way beyond my skill level in FreeCAD but still cool to see this software's capabilities.

[@allandeans3904]

Your problem is caused because you used two fixed constraints at each end. You should only use one constraint fixing the x and y and z movements. The other end should only be fixed in the z direction and be free to move in the x direction (like a roller support). This will prevent fixed end moments being introduced into the analysis

[@kattkushol]

I was also wondering about the same thing. I need to figure out how to apply different types of support conditions in freeCAD.

[@allandeans3904]

It’s been a while since I did this but from memory I believe you should select an edge rather than a surface. Then you can constrain that edge in x,y&z on one end. This creates a pin joint that will not impart momentum to the beam as you need it simply supported. The other end edge should only be constrained in the upper down (y) direction to allow it to be free to move in the x direction when loaded. If you do this the truss should distribute load as you expected. Hope that helps Cheers Allan

[@allandeans3904]

That was meant to be moment not momentum

[@ajarivas72]

@@allandeans3904 I am not sure if you can select and edge to fix its motion, only surfaces can be selected. You have to edit manually the *.inp file written by FreeCAD before executing Calculix. Look for the nodes you desire to fix the motion in the z direction and then run calculix. I just found this channel and like it very much.

[@feroze_bangla]

@@allandeans3904 I was finally able to do it. Selecting an edge worked. All this time I was waiting for FreeCAD to introduce roller and pin supports, just didn't realize they were there to begin with. Thanks.