FEA Constraint Help

[Andrew Brockbank]

Hi, please see the attached drawing. I've set up an FEA for a part (a rocker for a monoshcok suspension system) and constrained the rod as described in the photo. Please can someone explain to me why the part is able to complete an FEA analysis rather than spinning around indefinitely? Many thanks

 

[FEA way]

Which FEA software did you use for this analysis ? Some programs have soft springs option enabled by default (especially CAD-embedded FEA modules). This feature stabilizes rigid body motions of the model.

It's also important what these types of boundary conditions actually mean (which DOFs they constrain) in this particular software.

 

[Andrew Brockbank]

Fusion360. The constraint is frictionless, which just prevents any movements between surfaces in the normal direction. Therefore the rod can spin. The part cannot move in the axial direction of the rod, but can rotate freely around the rod, and without F1 and F2 creating equal moments I wouldn't expect the results to converge.

 

[FEA way]

I don't use Fusion360 but I'm pretty sure that it automatically applies soft springs to underconstrained models just like stress analysis module in Inventor does. Check the analysis settings.

 

[rb1957]

agree with above … somehow your code is balancing your structure with some constraint. In NASTRAN its called "AutoSPC" … can be very dangerous.

Are there tutorials YT videos for this ?

another day in paradise, or is paradise one day closer ?

 

[Andrew Brockbank]

Cheers guys, I'll look into it. In SOLIDWORKS the same operation causes tiny displacements although the model still runs. Strange that Autodesk is providing such different results.

 

[rb1957]

the SW result is just as troubling … if the loads and constraints don't balance then the FEA shouldn't solve.

another day in paradise, or is paradise one day closer ?