Elastic Buckling 1

[LeonhardEuler]

This seems like an elementary question, but I've always wondered about it and have scoured the internet to no avail. Perhaps it is too simple for Mech of materials books to explain.

My question is how does a compression member buckle with a purely axial load. Is this due to inherent initial out of straightness, which means the load actually isn't purely axial and does have eccentricity and moment, or is this due to poissons effect where the axial load creates a lateral stress?

 

[JStephen]

If you're interested in topics such as this, I suggest getting Timoshenko's "History of the Strength of Materials", which, at last check, was available pretty cheap as a Dover paperback.