Hydraulic Cylinder Buckling
Hydraulic Cylinder Buckling
(OP)
I am trying to determine the buckling load for a custom built hydraulic cylinder. Of course my fist thought is to use Euler's equation but I'm thinking that only applies to cross sections that are constant.
Since it is custom, the manufacturer has been of no help.
Another engineer here at work claims that he has saw some equations developed by a manufacturer (possibly Parker?) but can't recall who or where.
Any help is appreciated.
Since it is custom, the manufacturer has been of no help.
Another engineer here at work claims that he has saw some equations developed by a manufacturer (possibly Parker?) but can't recall who or where.
Any help is appreciated.





RE: Hydraulic Cylinder Buckling
RE: Hydraulic Cylinder Buckling
Regards
DAve Hall
RE: Hydraulic Cylinder Buckling
Secondly, I suspect most hydraulic cylinders don't count as "thin walled" for buckling. Anyway, if it's pressurized, the cylinder wall isn't in compression.
RE: Hydraulic Cylinder Buckling
It can become a little complicated as most real world problems are.
RE: Hydraulic Cylinder Buckling
Just thought I'd mention it.
Regards,
-Mike
RE: Hydraulic Cylinder Buckling
- Elastic bulging of cylinder causing blow-by.
- Yield of the cylinder wall.
- Clevis rupture.
- Pin shear.
FEA is your safest bet without a test rig.
RE: Hydraulic Cylinder Buckling
FEA is only good if you validate the model. The best way is to do testing which costs a lot of money. A more cost efficient way to analyse the actuator is to use hand analysis. There are many many methods to substantiate the actuator. For example: lug analysis, beam column (there may be beam column effects due to lateral deflection at load), etc. A good number cruncher can finish this analysis in a fraction of the time it takes to complete a valid FEA.
FEA can very easily fool you. I've seen models with results that impart torsion just due to the mesh (a slightly canted mesh), contact that incorrectly transfers loads, non-linear models with way way to much deflection (the adjacent structure would have failed, but not noticed during the model runs), incorrect mesh densities that produce unconservative (and conservative) results. I can go on and on.
RE: Hydraulic Cylinder Buckling
Of course FEA has to be interpreted correctly, but that also goes for the results you get using any of the equations required to analyse the system by hand.
Perfect world - scribble, FEA, Test, repeat. Imperfect world - as many of those steps as you can.
LewTam Inc.
Petrophysicist, Head Stockman, Gun Welder, Gun Shearer, Ski Instructor, Drama Coach.
RE: Hydraulic Cylinder Buckling
I looked up some analysis of landing gear retract actuators for rpmiller. The column stability is analyzed using beam column methods. The column uses two diffent section properties. This method used two pages of analysis. The equivalent FEA would take much more time and effort. Remember, beam column analysis take into account the nonlinear aspect of loaded columns.
For many people, the analysis method of choice is FEA. I feel many people also trust the results without question. I believe this is dangerous (especially for aircraft analysis). Note that aircraft analysis uses FEA all the time (mostly couse grid models for developing loads or fine grid for complex parts). Fortunately the results are validated and correlated.
Rpmiller, hopefully I provided constructive input for you. I apologize for standing on the soapbox; however, I believe FEA is not the answer for your problem. If you are interested I can lay out the beam analysis method for you.
RE: Hydraulic Cylinder Buckling
Bosch Rexroth have excellent literature on this for selecting a cylinder stroke. You may be able to adapt this to your cylinder.
RE: Hydraulic Cylinder Buckling
On that note, thanks to all for their replies.
But back to Kwan's soapbox, I actually enjoyed the FEA discussion on the side. It's given me some real insight about how others think/feel about FEA.
Thanks again.