I am trying to find out the maximum stress on a cantilever beam which is subjected a force of 1250 N. The beam is a circular hollow tube:

- - Inner diameter: 82.9 mm.
- - Outer diameter: 88.9 mm.
- - Length= 47 mm.

My theoretical calculations states that the maximum stress is equal to 3.49 MPa, and it should be located at the top and bottom surfaces near the fixture points where the bending moment is maximum. Since it is a short beam, I have also considered the shear stress and its maximum value at the neutral axis is equal to 3.11 MPa. However, FEA results show that the maximum stress is equal to 15.56 MPa as shown in the figure below.

I have observed that FEA yields accurate results for long beams but its results are inaccurate when the beam is short.

Does anyone have any idea why this problem is happening? I would really appreciate it if you could help me.

Could you please examine the other result like stress along x,y or z axis