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

[peteroznewman]

 

When you know how a revolute joint connection works, then you know to ignore the stress for a few diameters around the hole. Yes, it is plain wrong on the surface of the hole since it applies tension forces on the opposite side of the hole to the true solution, but this is fine if you know that and are willing to accept the trade-off to get accurate forces in a short amount of time. Remember that Saint-Venant’s principle tells us that the difference in stress in the link a large distance from the hole will become very small, even when the stress at the hole surface is just plain wrong.

In the simple Static Structural analysis I suggested, stress at the hole becomes fairly accurate, with the trade-off that the stress at the other end has become just plain wrong. But this is fine if you know that and ignore the stress at the other end. The bearing load applies forces in the radial direction only with a cosine fall off. Nodes have a force weighting of cosine(angle) between 0 and +/-90 degrees and the sum of the forces in the chosen direction equal the assigned value. As I mentioned, a bearing load is a good approximation for the load distribution of a close fitting pin in a hole and has the benefit of being quick and easy to use. I described the most accurate method of calculating stress in the hole and you are welcome to use that when needed but know that it will take more time.  In many cases, the extra time is not warranted.

There are several methods to get accurate stress near the hole.  A third method is to use Inertia Relief, which is available in Ansys. It will also use the Bearing Load in a Static Structural analysis so will give the same stress around the hole as the Static Structural analysis with the Bearing Load and the Fixed Support, but will not produce the wrong stress at the fixed support end. Click on Analysis Settings to turn Inertia Relief On. Watch this video for more information on Inertia Relief.