Abstract
The demand on more accurate Wahl's stress correction factor for a suspension coil spring is growing stronger as the initial pitch angle becames larger with the strengthened spring material in recent years. This research committee performed the following activities under such circumstances.
1) Clarification of the precondition of the conventional coil spring characteristic formula, and comprehension of an application limit;
a) Numerical analysis comparison was executed on three patterns of the derivation process of correction factor formulas after clarifying the derivation precondition of the each formula. A. M. Wahl, A. Röver, J. K. Wood, E. Honegger, O. Göhner, P. Henrici, C. J. Ancker & J. N. Goodier, M. Bergsträsser, D. G. Sopwith.
b) The formula of Bergsträsser which is adopted in the DIN standard and the formula of Wahl were compared.
c) The correction factor diagram was summarized on the formula which takes the effect of the initial pitch angle into account.
2) Calculation of the stress and deflection correction factor by FEA;
a) Linear FEA for a 1/4 circle beam was executed using the solid element, and the accuracy of a stress correction factor formula was verified.
b) Nonlinear FEA for one turn of active coil with different pitch angles were executed using the solid element, and the influence of a pitch angle was investigated.
c) The presumed correction factor formula of stress and deflection was derived using Design of Experiments and FEA, and the correction factor diagram was created.
3) Suggestion of better FEA modeling;
a) FEA by the beam element was executed on an actual coil spring, and the essential points of the beam element FEA were proposed by comparing with experimental results.
b) The tendency of the stress correction factor derived from the beam element FEA was studied. Moreover, end turn contact conditions with a coil seat was examined.
