Compression Springs - Buckling

Compression springs can be prone to buckling. In a traditional way, the length of a compression spring decreases under the effect of an axial loading. Below a critical length, some springs can bend laterally instead of continuing to decrease length: it is buckling. The length below which the phenomenon appears is called critical buckling length LK.

A compression spring must be dimensioned so that it does not buckle laterally during its use. By using the spring with lengths higher than LK, there is no problem of buckling. The critical length of buckling LK is function of the geometry of the spring (L0/D) and of the type of end fixations of the spring. LK is thus independent of the theoretically acceptable maximum stress in the body of the spring. DIN standard counts 5 support cases. It associates with each one of them a different value of the end fixation constant n.

End fixation constant (DIN standard)

Critical length LK can be graphicaly determined or starting from the following formulation (DIN standards):

If   ν L0 / D < π [ (2m + 1) / (m + 2)]0.5 then LK = 0 (no risk of buckling)

Else

with μ = E / ( 2G ) -1.

Buckling curve

The springs for which it is not possible to ensure buckling strength must be maintained in a boring or by an axis. But it then occurs a friction and a reduction of the fatigue resistance.




Manuel Paredes