FEA x Analytical

[Henry26]

Hello everyone,

I've performed an FEA and a hand calculation of a beam under simple load:

Diameter: 20mm
Lenght: 200mm
Load: 1kN

Thus:
I: 7850mm^4
Stress: 254MPa

FEA (solid):

http://files.engineering.com/getfile.aspx?folder=1386a2e6-49e0-4fa8-a1a8-d266f2fcf2b9&file=Max.JPG

Beam element:

http://files.engineering.com/getfil...52e6-43ca-ab93-1b5f67f91a06&file=max_beam.JPG

It's very simple calculation, but in FEA I had a doubt about how to understand where is the exactly main stress.
In this situation it's easy to find the exactly region with the main stress, because I can find the result through a simple hand calculation but and if the geometry isn't simple with several radius?
As you can see, the beam element gave me the exactly value in the exactly region which doesn't happen with FEA (solid).

Software used: Creo Simulate
Mesh: 0.5mm

Thanks in advance:
Henry.

 

[rb1957]

how did you constrain the solid model ? if you constrain all freedoms at all nodes you are overly constraining the model, and get spurious results.

the solid model is going to give you a lot more local results than the beam model ... it'll detect the local stresses due to a point load, that the beam model doesn't

another day in paradise, or is paradise one day closer ?

 

[Henry26]

Thanks for your answer rb1957,

I really constrained all freedoms at one of the extreme. Do you know how could I improve this condition ir order to get a result more accurate?

Henry.

 

[rb1957]

constrain all nodes in the axial direction, let's call it "x"

constrain one node (any, maybe the one at the center) in the other two directions, "y" and "z" and in "Rx" (or take out Rx as a couple of y or z forces.

another day in paradise, or is paradise one day closer ?

 

[aerostress82]

It is probably due to your applied load in the solid model. Assuming you have a "perfectly symmetrical" mesh at your load application face of your cylinder, you should divide your 1kN force by the number of the "perfectly symmetrical" nodes on that face and apply distributed load on the whole face.

Constraining all the nodes might be fine in this case. In Nastran, if you were to use CBEAM element for your bar element application, your solid model would probably match these results then.

Think of your beam element, and imagine it as a solid model. What is your actual boundary condition on that beam and how can u represent this in solid FEA?

If you can't work this out, I would advise you to try this with an I-beam. That will teach you more..

Spaceship!!
Aerospace Engineer, M.Sc. / Aircraft Stress Engineer

 

[Henry26]

Thank you guys, for all answers.

 

[aerostress82]

Did u figure it out? Could you get the same results finally?

Spaceship!!
Aerospace Engineer, M.Sc. / Aircraft Stress Engineer