You will have to give us considerably more information for anyone to be able to help you.
Recommend starting with something simple that you can calculate and post it here with both the calcs and analysis setup along with a description of the issue.
Also, look at the validation examples In the software to see that it had been checked. Most times the issue is setup or interpretation. For example using stress at a singularity as a measuring point.
The plate dimension
Length = 200mm
Thickness = 5mm
The force given on the plate surface area is 49N
With A extruded cut of hole with 1mm depth and 25mm of diameter which I had defined as fixed geometry.
1. You are comparing a 2d problem to a 3d problem. Is that a fair comparison? You may want to consider making the problems more consistent.
2. You are comparing results at what looks like a singularity to your hand calc. You may want to look at our article on blog.hawkridgesys.com about mesh convergence.
3. From a setup perspective, use a split line instead of a cut for your restraint.
4. I don't see any documentation of your assumptions for your calcs or your simulation. This may help you understand the differences,
I'm having a hard time understanding what you're trying to model and what you're calculating by hand, but from what I understand:
You have a plate you a uniform surface load on top and the plate is supported by a circular rod at the center. If so, then here are my thoughts:
For your FEM:
- You cut into the material to get your surface region. Removing material (as well as creating sharp reentrant corners) will greatly amplify stress.
- It doesn't seem as if you performed a convergence study; your results don't have any error tied to them.
- You've modeled the support with a fixed constraint. Does the real system behave as a fixed constraint?
For your hand calculations:
- You're calculating your shear stress using F/A. That's "average" shear, whereas you need to calcualte maximum shear. In other words, you're assuming a constant shear stress distribution through the thickness, when this is not the case.
- You don't consider bending stresses at all.
- If you're going to do this with a 2D assumption, you need to apply axi-symmetric assumptions.