Abstract
The author suggests a method for determining the effect of wire or bar curvature on allowable stresses in helical springs, based on the endurance properties of the material. The method is based on the assumption, in agreement with available fatigue-test data, that stress-concentration effects produced by wire curvature may be neglected in calculating the static component of applied stress; also, it is assumed that the relation between the static- and variable-stress components at failure follows a linear law. On this basis, charts are given for determining maximum allowable stress as a function of spring index, ratio of minimum to maximum stress, and ratio between yield point and endurance limit. The effect of sensitivity of the material to stress concentration is taken into account by introducing a sensitivity-index q. Results calculated by means of the equations given show good agreement with results from tests of springs of different indexes. Some of the limitations of the method are discussed, and suggestions are made for future testing work.
