×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# rod buckling calculation2

## rod buckling calculation

(OP)
Can anyone give me the calculations (or send me to a site) necessary to compute the critical buckling stress for a hydraulic cylinder.

Thanks,
Calman

### RE: rod buckling calculation

Any respectible cylinder manufacturer catalog should include the formulas for buckling calculations. You can use any other mechanical engineering habdbook such as Machinery's Handbook. Goggle search should give results too.

### RE: rod buckling calculation

(OP)
I've been looking in Machinery's Handbook and it gives me the calculations for a structural column (i.e. Euler's formula), but I don't know how to relate that to a cylinder. For example, what to substitute for your "k" and "l" values. The google search turned up nothing.

Calman

### RE: rod buckling calculation

calcultr

I didn't use buckling analysis for a long time. But the info in Mchinery's handbook should be enough. You can also look at any machine design book such a Shigley, Norton. This is a very basic subject. What version of Macinery's handbook you have?

### RE: rod buckling calculation

(OP)
I have the 24th ed.  It shows the formula P=(pi^2*I*E)/l^2.
I just don't know what to use for the effective length "l".
The cylinder is mounted by two pins (one at end of rod, the other at rear of cyl.) and the open center-center is 202".

Anyway,

### RE: rod buckling calculation

The effective length will be the maximum piston rod length between the piston head (with the seals) and the support guide (with the seals) in the cylinder body. The worst case is when the piston rod is not extended meaning when its most length is still inside the cylinder and the piston starts its pushing. Your "problem" is to decide what type of "ending" you have (fixed, free etc). Here, a manufacturer technical info may help. To be on the safe side you can take the "both ends free" case.

### RE: rod buckling calculation

(OP)
Since the cylinder is supported at the two extremes (rod end and rear end), I don't understand why the effective length wouldn't be the distance from pineye to pineye when the rod is fully extended.

Wouldn't the worst case be when the rod is fully extended out of the cylinder?  That seems to be the most likely time for buckling failure to occur.

So let's say I used the "both ends free" case. What would that make my "k" factor?

Thanks

### RE: rod buckling calculation

In Euler formula there is no "K". Look at page 251 at the bottom of the table and use the "Both ends rounded" you can see that all you need is:

E - Modulus of elasticity
I - Rod section ineria = Pi*d^4/64
l - column maximum length

P=((Pi)^2*I*E)/(L^2)

### RE: rod buckling calculation

(OP)
So then what should my "l" be? You were saying earlier that it is from the piston to the rod bearing surface. But shouldn't it be taken from pin to pin when the cylinder is fully extended?

### RE: rod buckling calculation

I am not familiar with the cylinder design. Is it open on the side where the rod extend from? Is the rod supported or guided between the two "pins"? If not then you are correct.

### RE: rod buckling calculation

(OP)
There is no support b/t pins. Well, that should definitely

### RE: rod buckling calculation

2
hi there
eulers formula can be adapted for cylinders,

Fcr = pi2 x E X I/L2 ----- (eULERS )
sub. pi x d4/64 for I ( solid round shaft )
and 2.07 x 10*5 foe E (steel )

Fcr = pi*3 x d*4 x 2.07 x 10*5/l*2 x 64

then Fcr = d*4 x 10*5/l*2
then d*4 = Fcr x l*2/1 x 10*5

d = 4th root of Fcr x l*2/1 x 10*5
where Fcr = critical force in newtons
E = modulus of elasticity, N/mm*2
I = moment of inertia of rod mm*4
l = effective length

this gives rod dia for criticalforce, that is the force at which the rod may start to buckle, you must apply a safety factor to be sur that it doe's not collapse

d >  4th root of Fa x l*2 x sf/1 x 10*5

Fa is allowable force in newtons
sf is safety factor
-
example.
cyl is 125mm dia p = 20Mpa extended rod 1000mm fixed at bottom free at end load factor 1,5  sf is 4

cyl force  = 0,7854x(125)*2x20
= 2,45x10*5 N
Fa = 2,45x10*5x1,5
3,68x10*5 N
rod l = 1000x4
= 4000mm
d = 4th root 3,68x10*5x(4000)*2x4/1x10*5
d = 125mm dia rod
I hope this was of help to you.

greye.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a partâ€™s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!