ESDU Engineer

ESDU 06024 Dynamic characteristics of cylindrical helical springs.
Part 1: deformation, stresses and stability

Springs are often an essential part of the machine design process, providing the force return in linkage or cam follower systems. ESDU 06024 is the first in a series that deals with the dynamic characteristics of cylindrical helical springs, comprising both tension/compression and torsion springs. This Data Item deals with the deformation of the spring coil, the stresses induced in the coil and the stability of the coil due to the action of external forces and moments.

In general the loads on the spring consist of an axial force, with a line of action along a vertical axis, and a moment acting in a plane perpendicular to the vertical axis. The assumptions and limitations that relate to the calculation procedure are defined, together with the prescribed loading conditions that are assumed to apply to the spring, and consist of the following:

(a) the cross-section of the wire is constant,
(b) the helix angle remains small (normally less than 8° to 10°),
(c) the spring material is not stressed beyond its elastic limit,
(d) the stress condition of all cross-sections of the working coils is the same (a consequence of axial symmetry),
(e) the deflection of the spring under load remains small (normally less than a quarter of the mean diameter of the coil), and
(f) the resultant force that is loading the spring acts along the spring vertical axis, i.e. the geometrical centre-line, and also the loading moment acts in a plane perpendicular to the vertical axis.

The Data Item derives all the equations used for determination of the spring deformation, the stresses induced in the spring wire and the transverse loading on the spring. The form design of the spring ends is defined since it affects the loading characteristics. The elastic stability of compression and torsion springs is discussed and formulae given for ensuring stability. The Item contains design data for which, within observance of the assumptions and limitations, the given methods of calculation yield very close approximations to the values obtained in practice.

RELATED DATA ITEMS

ESDU 82008
Elastic stresses and deflections of helical compression and tension springs of round wire.

ESDU 82012
Nested helical compression springs of round wire (to be used in conjunction with Data Item No. 82008).

ESDU 83002
Allowable stresses for helical compression and tension springs of round wire.

ESDU 83003
Notes on the design of helical compression and tension springs of round wire.

Queries regarding this article should be directed to Chris Loughton, Head of the Mechanical Motion and System Dynamics Group: chris.loughton@ihs.com

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