Table of Contents

Materials and Structure





A failure mode that must be taken into account when components are used in compression is buckling. The diagram shows a strut that is long compared to its diameter. The two ends of the strut can rotate but are constrained to stay on the same vertical line. A load, F, applied to the strut causes an initial elastic response, the strut decreasing in length as the load is increased in accordance with Hooke's law. As the load F is increased one of two outcomes may result. If the rod remains stable against buckling (remains straight) the yield stress,
sy, of the material may be passed and the strut will deform plastically and retain a deformed length when the force is removed. For a slender rod it is more probable that the rod deflects elastically in a transverse direction when a force FCr = p2EI/L2 is reached, where E is Young's modulus, I the geometric moment of inertia, and L the length of the strut. Provided the transverse deformation does not cause the material to plastically deform, removal of the load in this buckling case will cause the strut to return to its initial length and shape. In general, for a slender strut the stress at which buckling occurs is lower than sy and this is the limiting strength factor in compression loading.

From: Polakowski and Ripling,
"Strength and Structure of Engineering Materials,"
Prentice Hall (1966)