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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 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.

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.

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.