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Procedures are developed for assessing the influence of various material and processing factors on the fatigue performance of leaf springs. Cyclic material properties, determined from smooth axial specimens of spring steel, are used to determine the level and cyclic stability of residual stresses resulting from mechanical processing as well as the amount of permanent deformation associated with presetting operations. A damage parameter, incorporating material properties, residual stress effects and applied stressing conditions, is used to predict failure location, i.e. surface or subsurface, and lifetime as a function of processing sequence. Predictions are found to be in good agreement with experimental bending results.

The incorporation of reliability theory into a fatigue analysis algorithm is studied. This probabilistic approach gives designers the ability to quantify “real world” variations existing in the material properties, geometry, and loading of engineering components. Such information would serve to enhance the speed and accuracy of current design techniques. An automobile wheel assembly is then introduced as an example of the applications of this durability/reliability design package.