Deduce torque from computed efforts

[waIkman]

Hello everyone,

I am facing a problem that I have troubles resolving.

I am doing a 2D contact simulation between 2 parts :

Part 2 is constrained at the base. Part 1 has an imposed angle & also a pivot linkage relative to the center of rotation.

Here is the end result:

Now what I am trying to recover is the torque generated by part 1 on part 2 (or vis-versa, doesn't mater).

At the moment, the only way I found to do so is exporting the resultant forces and multiplying it by the lever arm but I have no confidence in the force I am reading. I have tried to plot the forces on 3 different coordinate systems al of which have an X axis that is orthoradial, but this gives me 3 different results so I am a bit lost...

Coud anybody tell me which value I should extract in that case to deduce the torque in the system ? Or is there a way to directly have the torque ? Is there a tutorial I could follow somewhere ?

Thanks to whoever can help on this

Have a great day.

 

[3DDave]

I can't see from the images exactly what is going on. Is the arc rotating about the exact center of what appears to be a perfect radius? In that case the torque will depend on the friction coefficient. If you want to know the amount of torque to leave the notch then the stored energy won't tell that. You need to look at the friction coefficient and the contact force and the direction of the contact normal.

 

[waIkman]

Hello,

Thank you for the reply ! Yes, par 1 is rotating around a common center of part 1 & 2 that is the center of the internal and external radii of part 2. Ok to recover the contact forces but the problem I have is the projection of the contact force "orthoradialy". I've tried to generate different coordinate systems but they seem to be fixed in space when the problem clearly isn't.

Here is the initial positions of the system:

And here it is at the end:

So I think the contact force I am projecting on the coordinate system's X axis ends up not being perfectly orthoradial.

I understand I might not be super clear but I don't know how to explain it in a simpler way >

Thank you for the help anyway

 

[3DDave]

I don't understand the need for anything "orthoradial" in this case - you need to find the cross product of the surface normal unit vector, multiplied by the magnitude of the contact force, with the radial vector to that point from the center of the rotation and add to that the similar friction vector contribution that is acting tangentially at that same point.

There is likely some non-linear solution that allows for friction and displacement vs input torque.

Alternatively, just get the data of displacement vs force on the little bent beam and do the geometry effects in Excel or some other application. You can calculate the displacement vs angular rotation pretty easily; calculate the contact normal to determine the torque and friction.

 

[FEA way]

Can you attach a picture showing the whole model along with applied boundary conditions and loads ? This would help us make further suggestions.

 

[waIkman]

Hello,

The outer part (N°1) has a pivot link as well as a circumferential displacement of 10°:

The inner part is fixed on its central geometry:

Thanks !