Force reaction at symmetry plane

[assafwei]

Hi,

I am having some difficulty understanding the force reactions in a symmetry plane.
I am running a half symmetry model, fixed at one end, displacement BC on the other end - it is a two parts assembly - the model is cut in half in the middle and a symmetry BC is placed on the symmetry plane faces, the BCs are all half symmetric (symmetric loading and geometry).
After the solve is done I plot the reaction forces on all BCs (fixed, displacement and symmetry). The fixed reaction and displacement reaction pretty much sums up in the Z direction (the displacement direction - mismatch of about 0.2 N out of 540 N), but there is an added force reaction in the Y direction (normal to the symmetry plane) of about 200 [N]which summs up to a total imbalance of total reactions (fixed BC Vs. Displacement) of about 40 [N].
To my understanding, when I will run a full model anslysis without this symmetry - the imbalance will cancel (I will run it when I get to it, too many projects...) but I am a bit confused regarding the implications of this "imbalance" on the half symmetry model results.
Any input will be much appreciated.

See attched image for a simplified representation of the simulation.

Thanks.

 

[Shu Jiang PEng SE]

For symmetrical structure with symmetrical load, symmetrical force should present on the symmetrical internal force. In your case the force is due to the Poisson ratio. Try change Poisson ratio to zero then the force will be gone.

 

[assafwei]

Hi,

Thanks for the quick input.

Changing Poisson's ration to 0 didnt change alot (reduced the reaction at the symmetry BC by about 10% but still considerable reaction at the symmetry BC).