A column buckling problem? 1

[becma27]

| |
|---|
thirty | |
pounds | | fixed with threads all around
of weight |---|
| |

I have included a picture of my problem. Someone told me they thought it was a column buckling pproblem but I'm not sure. the vertical plate on the left will have somewhere around thirty pounds of weight on it and it needs to attach and be aligned very precise with the plate on the right. I want to use pins in between with threads on either side to separate. My worry is that since the right plate is only made of 5/8 thick magnesium it can't hold the force or might warp. What type of equations should I use for this and what suggestions does anyone have?

becma27

 

[meintsi]

Is this what your trying to show?

| | | |
| |STUD| |
| | | |
| | | |
|W |P| |P| But how are the ends
|E |L| |L| supported????
|I |A| |A|
|G |T| |T|
|H |E| |E|
|T |1| |2|
| | | |
| |STUD| |
| | | |

 

[meintsi]

Darn thing looked straight in the preview.

 

[becma27]

So did mine! Yeah, you got it right meintsi. the right plate is circular and bolts to the back of a telescope. The left plate is not fixed at all accept through the studs.

 

[becma27]

Anyone have the equations for this?

 

[TVP]

From Materials Selection in Mechanical Design by M. F. Ashby (excellent book published by Butterworth-Heinemann):

If sufficiently slender, an elastic column, loaded in compression, fails by elastic buckling at a critical load Fcrit. This load is determined by end constraints (degree of fixity). And end may be constrained in position and direction, or it may be free to rotate but not translate, or it may sway without rotation, or it may sway and rotate. The addition of a bending moment M reduces the buckling load.

Fcrit = [n^2 * pi^2 * E * I] / L^2

where n is the # of half-wavelengths in the buckled shape (basically a constant that depends on end constraints)

E is the elastic modulus of the material

I is the second moment of area of the section

L is the length of the section

You need to figure out what the constraint is in order to know what n should be:

n = 0.5 for fixed at one end, free to translate at the other end
n = 1 for free to rotate but not translate
n = 1 for fixed at one end and free to translate at the other
n = 1.5 for fixed at one end and free to rotate at the other
n = 2 for fixed at both ends

I'm still baffled by your drawing, so I don't want to hazard a guess on what to use. Good luck.

 

[meintsi]

becma27..

Sorry, been gone for a couple of days.

If I understand that both plates are vertical (and parelell) and that the right plate (cirular) is fixed at all sides, then your condition is one of a simple beam in bending, where the load applied is a couple (magnitude of weight times gravity).

Depending on how many bolts are holding the two pieces together, the worst case deflection plane will defined via a funtion of the distance of the bolt from the couple center vs. the verticality of the bolt. You may have to check more than one plane. - hope that makes some sense

If the plates are not vertical, additional points forces must be included in the solution.