Experimental Critical Buckling Load

  • #1
2
0
Hi guys,

I was wondering could I get some help with determining the experimental critical buckling load of a pinned ended strut. I am hoping to compare predicted values from Euler buckling and Perry Robertson to experimental values. I have carried out a experiment where by I applied a axial load to the strut and recorded both the horizontal and vertical displacement. From this data can I apply a formula to give me the critical buckling load? Or is the critical buckling load simply the highest value recorded in the experiment?

Thanks for any help!
 

Answers and Replies

  • #2
OldEngr63
Gold Member
732
51
Assuming that your strut was initially straight (so that it would actually buckle rather than simply bend), then make a plot of load as a function of axial displacement. You should see a pronounced "knee" in the curve. That is the buckling load. It is not the highest load recorded because most post-buckled columns continue to support the load and the load rises slowly.
 
  • #3
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Thanks for the reply,

There is no clearly defined "knee" in some of my samples. Is there anymore accurate way to determine the "knee" rather then doing it by eye? I am just trying to keep my experimental errors to a minimum.

upload_2015-1-14_22-56-12.png
 
  • #4
SteamKing
Staff Emeritus
Science Advisor
Homework Helper
12,796
1,668
Thanks for the reply,

There is no clearly defined "knee" in some of my samples. Is there anymore accurate way to determine the "knee" rather then doing it by eye? I am just trying to keep my experimental errors to a minimum.

View attachment 77667
If you look at the test results for Sample 1, I would say the 'knee' is clearly defined when the test load is approx. 350-360 Newtons. Where the applied load is relatively constant, the test piece undergoes a measurable change in deflection, which suggests that some sort of inelastic behavior is occurring. The other two samples do not appear to exhibit the same behavior.

Of course, a lot of information about the test pieces and the test set up have not been disclosed.
 
  • #5
OldEngr63
Gold Member
732
51
What is the material and what is your geometry (length, width, etc. for the test specimens)?
Did your experiments result in a permanent set, or were they fully elastic? (Buckling is an elastic phenomenon; plastic deformation puts an end to all questions of buckling.)

I don't think we can help you very much without this data.
 

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