Thesis (M.S.)--University of Wisconsin--Madison, 1963. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 60-62).

The reliability of systems relies heavily on accurate fatigue life prediction of related components. Fatigue life prediction is a complicated process requiring the correct methodology to determine accurate and reliable predictions. The Palmgren – Miner damage accumulation hypothesis is widely used in determining the fatigue life of components exposed to variable loading conditions. Modifications have been made to this hypothesis trying to achieve a greater degree of accuracy, of these the Liu – Zenner modification has been the most successful. In this report the systematic process of fatigue life prediction using the Liu – Zenner modification to achieve reliable results is calculated. A representative stress time history measured in service on the component forms the basis for defining a flight cycle which is the chosen unit in which to express the fatigue life. Rainflow cycle counting performed on the stress time history allowed the formulation of a load spectrum to which the component is exposed in one cycle. Combining the load spectrum with the developed SN curve of the component and using the Liu – Zenner modification to the Palmgren – Miner rule a reliable fatigue life in cycles is predicted.

Uni-directional stresses have been applied, to copper wires, and the potential difference between such wires and unstressed wires determined in various electrolytes. The potential differences have been determined both by a galvanometer method and potentiometrically. The latter method gave more consistent results and is thought to eliminate some of the possibilities of polarization. Some correlation has been found between the amount of applied stress and the potential difference observed, and thermodynamic arguments have been advanced to explain such results, at least qualitatively. A correlation of these same results with time has led to the conclusion that the potential difference is essentially due to a surface effect. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

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This thesis experimentally investigates the statistics (mean and variance) of the fatigue-cycle-dependent evolutions of both the crack tip front penetration's distribution function and the microscopic growth rate's distribution function, as a fatigue crack propagates to final fracture. A novel technique which facilitates striation counting and striation spacing measurements, is developed and used for extracting and analyzing the relevant statistical data for characterizing the stochastic fatigue crack propagation in polycrystalline metals. Two types of pure copper materials are investigated. / The investigation confirms the existence of the mean and variance of both the crack front penetration and its growth rate. Details of the variations of the mean crack penetration with respect to the dispersion of the crack front distribution and the mean growth rate, respectively, are established. Other contributions include the evaluation of the material characteristic associated with the transition intensity of the growth process. / These results are correlated with the predictions of the "Provan-Ghonem" theory in order to ascertain the validity of the linear Markov birth stochastic process, as a viable description of the fatigue crack propagation process in polycrystalline metals. The trend of the experimental results suggest a spatially correlated Markov process which accounts for both the strong nearest-neighbour-interactions between "points" along the crack front, and the boundary effects as a more viable representation of the fatigue crack propagation process.

This paper describes an investigation carried out to study the fatigue failures of a "keyed tapered-shaft assembly" as affected by the keyway. Two fatigue testing machines were built and used: one tested a keyed assembly in reversed bending, and the other tested a keyed assembly in reversed torsion or a combination of reversed bending and reversed torsion. Both sled-runner and round-ended keyways were tested and the failures were compared with a view to establishing a law of failure. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate