Hello,

I'm simulating bolt tightening in Abaqus, however, every time I apply rotation to any of the parts in the model (either the nut or the rod), they expand. 

I've applied the rotation in different ways and all of them produce expansion: Rotation BC, Moment, two opposite surface traction forces...

I have also included rigid shells around the bolt head and applied the BC to the reference point... It also expands.

Can someone explain me why is this the case? is there any violation of the principles when a body rotates in Abaqus?

Also, how can I model body rotation without expansion?

Many thanks in advance.