Super easy beam bending analysis question

[Anonymous]

In order to validate Inventor Stress Analysis, I am doing some simple beam simulation and comparing deflections between the hand calculations and the results from Inventor stress analysis.

I got fairly good results with a cantilever beam, but when I did a beam with both ends fixed my hand calculation gave a deflection that was 50% greater than the Inventor results.

The "beam" which I used for the calculation is fixed on both ends:

Thickness: 1.5 in

Width: 37.75 in

Length: 58.75 in

Material: 6061 AL with E = 9993 ksi

I put a gravity load on the model and got a good match with the hand calculation.

When I added a 500 lb load in the middle of the beam, results no longer matched.

I used the textbook equations for a beam fixed at both ends:

deflection = (wL^4)/384EL  (1)

deflection = (WL^3)/192EL  (2)

The first equation is for the gravity load where w is the load per unit length and wL equals the weight of the beam.

The second equation uses W for the point load which is 500 lb at the midpoint of the beam.

My hand calculations show:

Deflection from beam weight: 0.0016 in

Deflection due to the 500 lb load: 0.0050 in

Total max. deflection: 0.0066 in

The inventor simulation shows .004 in deflection.

I am looking for help to see if I am doing something wrong?  I have fairly high confidence in my hand calculations, but I am very new to simulations, so any help would be appreciated.

[Binga]

Hello @Anonymous
Welcome to the Autodesk Community!

Are you using which environment to do the analysis? Stress Analysis or Frame Analysis?
Can you post some pictures of your simulation configuration?

[swalton]

Did you select a line or edge at the center of your beam to apply the 500 lb load? 

If you just selected the beam face, Inventor assumes that you have applied a distributed load of 500 lbs to that face. 

[Anonymous]

Thanks for the reply!

I am using Stress Analysis environment

I have attached my configuration and results as a screenshot.

[Anonymous]

I tried to do a point load and thought I attached to the center point of the plate.

I just tried sketching a line in through the centerline and attaching the load to it, but it did not seem to recognize the line.  Is there a proper method for attaching a load to a line?

[Anonymous]

This is my problem!

I made a small thin extrusion at the midpoint and the results came out great.

There has to be a more elegant way to place a load at the midpoint but I am not seeing it.

[swalton · Accepted solution]

You will have to create a Split on the face where you want the load.  That will give you an edge to select with the load command.

See my attached IV2014 part.

[Anonymous]

That was exactly my problem. I was unfamiliar with the split command.  One more question for future simulations: What would be the best method to apply a point load?

[swalton · Accepted solution]

  You may be able to create a workpoint in the CAD model and select it with the FEA tools. 

If not, use the split command to create a vertex or a very small area where you want your point load.

[Anonymous]

I could not get the load to attach to a work point, but I was able to do another split and create a vertex.

This has been a big help.

Thanks again!