Reply To: How joint force is distributed among fem nodes in transient simulation.

[peteroznewman]

A revolute joint idealizes a pin-hole connection between two bodies to make transient structural models solve much faster while delivering accurate forces. The trade-off for the fast solve is the local bearing stress is not accurate.  There are several ways to obtain more accurate stress near the hole where the pin presses on one side of the hole.

A quick and simple way to improve the accuracy of the stress near the hole is to duplicate the transient structural model of system A to create system B, then replace B with a Static Structural analysis. Suppress the pin and joints, leaving only the link with two holes. Make the far hole a Fixed Support and apply the peak force over time from analysis A as a bearing load on the hole in analysis B, acting along the length of the link. A bearing load will create a good representation of the radial distribution of forces on the hole that add up to the total axial force. You will see the largest force at the top of the hole and the force will reduce to zero at +/- 90 degrees on either side. One advantage of this method is you can have a much more refined mesh because you only have to solve it once. The next method requires the solution to be completed for each time step, so a refined mesh takes much longer to solve.

A more accurate result for the stress near the hole is to delete the revolute joint and replace it with Frictional Contact between the pin and the hole. You might need additional axial contacts to prevent the link sliding off the pin, or the simulation might run without that.  The trade-off for the more accurate stress is it will take much longer to solve. Frictional contact is slightly more accurate than the bearing load because the deformation of the hole can only be to match the cylindrical shape of the pin.  The bearing load mentioned above does not limit the deformation to follow the surface of the pin, because there is no pin. If the wall thickness around the end of the hole was very thin, then that thin section could deform into a non-cylindrical shape under the varying radial bearing load.