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With the renewed current interest in high strength steel and aluminum automotive body and chassis components it has again become important to properly assess the effects of corrosion on the fatigue behavior of structures. The present work summarizes the past work on fatigue and corrosion and presents new results on current automotive materials. The Neuber plasticity correction method, used throughout fatigue software of the ground vehicle industry to account for localized plastic behavior during fatigue, was found to give a very simple and useful technique for the computation of fatigue life of materials in corrosion environments. Data is offered for many common automotive structural materials and a method is given to adapt finite element calculations to compute corrosion fatigue life.

The fatigue overload behavior of single overlap 5754 aluminum spot welds has been investigated. As a baseline, constant amplitude tension-tension tests with an R=0.1 (=Pmin/Pmax) were conducted. These tests were compared both with several different series of high but variable mean constant maximum load tests, and with periodic overload tests. The high mean load tests, tested with maximum loads of 3560N, 2670N, 1780N, and 1330N all showed a significant reduction in the fatigue limit which ranged from less than ½ to almost 1/3 of the baseline fatigue curve. Further, the fatigue limit reduction from the periodic overload tests was below 1/3 of the constant amplitude baseline tests. The results of these tests indicate that mean loads and variable amplitude loading can both have a significant deleterious impact on fatigue life.

The cyclic behavior of single overlap aluminum joints joined through a number of different methods has been investigated using Alcan 5754-O, an alloy that potentially could be used in structural applications. Overlap shear tests of spot welded, clinched and riveted joints are compared on the basis of their fatigue performance. The fatigue response of the spot welded joint was the baseline to which the other fasteners were compared. Test results showed an improvement of approximately 25% for both the mechanical clinch joints and aluminum rivets in fatigue strength at 106 cycles. The most significant improvement in fatigue strength of 100% was found for the self piercing rivets at 106 cycles. The failure behavior of the various joining methods is discussed as well as the surface appearance.

A computer-based technique was used to produce fatigue life predictions for a variety of steels using service histories recorded from several automotive components. The materials considered, both hot and cold-rolled sheets, ranged in yield strength from 200 MPa (30 ksi) to 580 MPa (84 ksi) and included most of the steels currently under consideration for material substitution to achieve vehicle weight reduction. The results of these computations were used to produce estimates of the weight savings potential, in fatigue limited designs, of the substitution of higher strength materials for conventional hot or cold-rolled low carbon steel; the indicated weight savings were from 16 to 50% depending on the nature of the loading of the component. This wide variation in savings is an indication of the importance of design in the engineering for minimum weight. Differences in the fatigue notch sensitivities of the materials were found to be an important factor in the predicted fatigue lives.

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.

Fatigue properties of sheet steels are examined beginning with a brief overview of the more common strengthening mechanisms used in the manufacturing and processing of sheet products. Cyclic and monotonic flow properties are reviewed with a particular emphasis on processing variables. Strength ductility tradeoffs for sheet steels are discussed and several alloy steels are presented in terms of a Neuber-life cure. The fatigue of cast iron is approached as an internally flawed material. Fatigue life predictions are made by comparing the response of similar structure and composition cast steel to that of cast iron and then applying a Neuber analysis to the results. Fatigue results are given for both non-heat-treatable and heat-treatable aluminum alloys. Finally, the role of residual stresses induced by surface treatments is discussed.