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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.

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.

Fatigue characteristics of representative cold-rolled, high strength steels, in gages ranging from 0.072 in. (1.83 mm) to 0.055 in. (1.39 mm), were determined in fully-reversed, axial strain cycling at amplitudes up to 0.01. Alloys were selected from three families of high strength steels: recovery annealed steels, conventional microalloyed steels - nitrogenized steel and rephosphorized steel, and dual phase steel. Cold rolled low-carbon steel provided a comparative baseline. Cyclic stress-strain curves are presented to indicate the degree of cyclic stability achievable by various strengthening mechanisms while relative fatigue resistance is determined from strain-life curves. The implications of these behavioral trends to component down gaging are discussed.

The fatigue behavior of representative classes of high-strength low-alloy and dual phase steel is reviewed. Cyclic properties describing stress-strain and strain-life relations are used to quantitatively assess material variability as well as processing and environmental effects. Examples of the use of this materials information in design analysis and, in particular, component downgaging are then presented.

Significant progress in materials and structures research leading to improved analytical and experimental capabilities for evaluating the mechanical durability of automotive structures is reviewed. Recent experiences in incorporating modern fatigue analysis methodology in easily used computer-based formats are then presented. This is followed by a general discussion of the application of design aids at various points in the product development cycle with emphasis on future trends and needs.

An overview of the current status and emerging trends in durability-related technologies is presented as an introduction to a series of papers covering applications of durability analysis in design. Problems of information management associated with technology integration are discussed along with the probable impact of new design tools on product development and validation.