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Buckling of Hydraulic Cylinder

Question asked by Fred Lampela on Feb 16, 2009
Latest reply on Feb 17, 2009 by Fred Lampela
I have a quiestion for you experts out there. I am currently working on a rather large hydralic cylinder, the engineer here has a spreadsheet for calculating buckling using Euler's formula, mostly concerned with rod dia., so in the spreadsheet we are using the extended length of the cylinder & the rod diameter for the entire length of the extended cyl. This 6" bore cyl operates at 4500 PSI has an extended length of 201.25". So the spreadsheet says we need a 5.16" rod dia to achieve a 2:1 factor of safety. I ran the cylinder with a 4.500" dia rod in simulation, & then ran a rod 5.160 dia. of the extended length to compare against what the spreadsheet was telling us.
In the cylinder I restrained both end clevis's and applied 4500 PSI load to the inside cyl wall & the piston face. The pins were free to rotate in the clevis bores. & gravity applied, with cylinder in a horizontal position. I was careful to have the wear ring supports in the proper locations on the piston & gland to simulate the actual support.
In the rod simulation I fixed one clevis, applied a load of 127,235 lbs to the other clevis, again gravity applied & pins able to rotate in the clevis bores. I have attached JPG's of the simulations, cyinder & 5.160" rod.
Now the question: Is the hydraulic cylinder bucking in simulation reliable enough to say, yes a 4.500" cylinder rod adequate? Or shoud I continue to rely on Eulers formula for column buckling on hydralic cylinders. My though is that the way we are calculating with the spreadsheet isn't considering the added strength the cylinder tube adds for buckling considerations.
I ran the rod simulation with a 4.500" dia on the rod also & stresses were near 40,000 psi., so a 4.500 column the ext length doesn't cut it, but a 5.160" does, and the cyl simulation with a 4.500" rod is very close to the stresses in the 5.160" rod.
Any thoughts? Are the simulation methods I am using the right way to approach this?