Hello everyone,

I have a question w.r.t. a simple cantilever beam stress study. I am doing a validation prediction using classic beam theory which involves using a Free body diagram, a Shear Force diagram then a Bending Moment Diagram.

When i use hand calculations to determine the maximum bending moment and then the maximum stress (using, max stress = Mc/I), I get a value that is much different from the SW simulation value of the maximum stress. I get 87.69 psi while SW Simulation says 118psi. I have tried every possible configuration of boundary conditions for this. Alternatively however, I used the prediction for a simply supported beam and the results were correct. Can anyone help me with this.

The beam is 600 inches long and the details of the study are in the attached images.

Much Thanks,

David

I'd say there may be a stress concentration at the fixture, since a layer of nodes that cannot move is connected to a layer of nodes that has to move. Refine the mesh, and you should see the large stress get larger and larger, but become packed into a smaller and smaller area. If you extract the stress from the spot closest to the fixture where it is converged (where it stops getting higher when you change the mesh size), then it ought to be closer.

In general, you are not going to be able to get an accurate stress at the boundary of your model, because the boundary conditions are so phony. You have to take your model out past the area you are analyzing.

BTW, if you run this as a beam mesh, I'll bet it agrees with you hand calcs to about 5 decimal places.