Calculate buckling of a hydraulic cylinder

[paintballJim]

I am attempting to calculate the buckling strength of a hydraulic cylinder and have a question. My book shows that I should use the weakest moment of Inertia section bu8t it would seem that that would be inaccurate. The rod inertia is about 1/4 of the tube. So the question is, do I figure the cylinder as the full length being of the rod and pinned at both ends. Or do I just calculate the buckling strength of the rod and figure the tube end is fixed knowing that the tube is much stiffer than the rod? Or is there a better option. I plan to run a solid-doesn't-Works simulation as well, but I would like to make my mind work a little as well and compare.

Thanks

Jim

 

[racookpe1978]

No!

The most dangerous point is the rod at maximum height from the cylinder, right?

Thus, you have a hollow cylinder (figure out the actual collapse strength of that cylinder as if it were a true hollow cylinder, not as if it were filled with a pressurized oil.)
Then, the rod is NOT fixed in the cylinder, but is a supported-but-collapsible-thin rod restrained only by the oil seal around the piston head and oil-filled opening in one end of the cylinder, and by the rod itself and its oil seal. So, it will act as a hinged thin rod about the oil seals - which are themselves NOT a rigid sliding structural device. They are mobile mechanical devices.

So your thin rod will most likely collapse at the middle of the total length - which, unfortunately, is also at the point of highest stress for an eccentric load and the lowest resistance to overturning and the point of maximum flexibility.

 

[desertfox]

Hi

Go to page 16 of this link

http://www.boschrexroth-us.com/coun...ducts/02_cylinders/a_downloads/9535233846.pdf

 

[desertfox]

Sooty on page 18 it does buckling calculation

 

[braddles90]

Det Norske Veritas have a standard that explains how they want hydraulic cylinder strength to be calculated for approval, including an acceptable buckling calculation - standard is available at this link:

https://exchange.dnv.com/publishing...nv.com/publishing/tap/2009-10/TAP5-778-93.pdf

The structural guy's at our work suggested buckling calcs were 'classically' performed by modelling the cylinder as a cylindrical rod, with the effective length being the distance between clevis pins (if the cylinder was clevis-pin mounted at each end, not sure how conservative the method is for trunnion mounts and other types).

That DNV link is a good method that I found to compare to other methods suggested and get a feel for the results, such as the Parker catalogue above.

 

[paintballJim]

Thank you guys for the answers and links. I was calculating the strengths of the tube as just the tube. Wasn't sure about the connection as 4" of the rod is still in the tube at full extension, with rings at top and bottom.

 

[dvd]

You may want to investigate the use of a stop tube if buckling is a concern. Talk to your cylinder supplier application engineer.

 

[Neilmo]

Hi,

`Roark's Formulas for Stress & Strain` has a formula for buckling which takes account of the cylinder and rod inertias.