Cantilever Beam Deflection Results Does't Agree with Theory

[JosephX]

Hi all

I was doing a cantilever beam static loading analysis. I need to find its deflection with loads added. Then, the result from Abaqus will be used to compare with the result from theory equation. However, my result from abaqus is so weird and has a huge difference with theory result. I cannot figure it out.

My beam has the length 0.6m, width 0.02m and height 0.001m. The material is Steel with E=2.23e11 v=0.3 and density is 7833.33kg/m^3. So, its own weight was simulated as a pressure force on the beam that is 76.845N/m^2. All units used SI meter.

However, Abaqus gave me the tip deflection which is 6.16. According to my Unit system, it will be 6.16 meters which is weird and theory gave me 6.55cm Then, I tried to load a 0.4905N force at tip. Abaqus generated a 14.9 meters ... and Theory gave me 9.5cm.

Anyone know the issue? Please help me and Thanks in advance.

I attached my ipt.file here.

https://skydrive.live.com/redir?resid=E5B452EC1A481E70!13845&authkey=!AGOrMV6M8cUR4us

 

[IceBreakerSours]

This seems like homework. Please look at the FAQs.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[DanStro]

IceBreakerSours is right, we won't give student answers to homework. And since it's not clear whether or not this is a student post I'll only give some guidance. Pay attention to your elements and their formulation. Look at how increasing the element count affects the results. Also look at the geometric order of them and how they affect the results.

I've modeled what you've described (with the exception that I used a gravity load and not a pressure) and the result from Abaqus matches exactly the hand calculated value (6.65cm).

HTH,
Dan

Han primo incensus

 

[JosephX]

Thanks IceBREAKERsours and DanStro

This is my very initial part of my whole project. This part should help me to get through the Abaqus. Unfortunately, I cannot even find the right answer of this simple case.

Actually, I read many tutorials on this topic and followed the procedures to do my case. However, I still cannot get right answer so far. I think this part work should not have many different places with most of basic tutorials. Only thing I think it is special is that this beam is a very thin so it would cause a large deflection. Therefore, the method would have slightly difference and need to be tweaked. Could you tell me is there any special treatment on the procedure?

Do I need to write the plastic property into the materials section due to large deflection?

Thanks
JosephX

 

[JosephX]

And I also did vibration analysis. The Natural frequency and mode shape all matched the theory but only deflection.

 

[DanStro]

You do not need to change anything with the material definition (i.e. add plasticity) Try what I suggested and you'll be able to figure it out.

Han primo incensus

 

[JosephX]

Thanks DanStro

Yes the geometric order in mesh section was changed to Quadratic before. It would cause the issue on "attempt to generate many increments" if the NL opened.

And I have done a optimization analysis on the number of nodes. It gave me an optimized number of nodes that can have stable results.

the mode you made is in 3D or 2D?

Joseph

 

[DanStro]

I did it in 3D.

Han primo incensus

 

[JosephX]

most of time, I got 6.297e-3 at tip now. That is too small.

 

[IceBreakerSours]

As DanStro suggested, increasing the number of elements and/or the order of the elements should help. Also, make sure your units are consistent.

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083

 

[IceBreakerSours]

Perhaps you are making a mistake during post-processing. How did you find your nodal displacement?

http://www.eng-tips.com/faqs.cfm?fid=376

http://www.eng-tips.com/faqs.cfm?fid=1083