Thesis (M.A.)--University of North Carolina at Chapel Hill, 2004. / Includes bibliographical references (leaves 82-85). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Also published as Thesis (Ph. D.)--Columbia University, 1912. / Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains vi, 92 p. : ill. (some col.). Includes abstract. Includes bibliographical references.

Thesis (M.A.)--University of North Carolina at Chapel Hill, 2004. / Includes bibliographical references (leaves 82-85).

Diss.--Psychology--University of Stockholm, 1998. / Bibliogr. en fin de chap.

M.Tech.

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

A large number of axially loaded specimens of 2024-T3 aluminum sheet alloy were fatigued to failure in alternating tension. The stress ratio was kept constant at .05 and maximum stresses were chosen to cause failure in the upper part of the S-logN curve where failure is by progressive hardening. The specimens were prepared in three ways, unpolished in which the rough edges were rounded, chemically polished in which the central section was polished chemically, and mechanically and chemically polished in which the central section was rubbed with emery paper then polished chemically. Macroscopic and microscopic examinations of chemically polished specimens tested at a maximum stress of 47.5 ksi were also made. Statistical analysis was used to fit experimental frequency distributions to the life values at each stress level, to determine the effect of the different polishing methods and to determine the effect of a light oil coating. Of the two tried, the Lognormal and the Weibull, the Weibull distribution provided a better fit and was easier to use than the Lognormal. For the three different polishing groups, the mechanically and chemically polished specimens gave the longest lives at all stress levels followed by the chemically polished then the unpolished specimens. Also both groups which received a final chemical polish showed S-logN curves with a much rounder knee than did the unpolished group. Coating the specimens with a light non-corroding oil resulted in all cases in an increase in life and in more scatter in the life values. The increases ranged from 20% to 62%, At the knee of the S-logN curve, all groups showed a bimodal. distribution in the life values. This was felt to be the result of a change in the failure mechanism such as the one postulated by Wood. Examination of the fracture surface and of small cracks which formed near the edges indicated that the failure occurred in two stages; nucleation and growth of a small non-distorting fatigue crack followed by transition to a rapidly propagating ductile crack. Observations of the failures showed that it took approximately 1000 cycles from the appearance of the first small crack to when the ductile crack had propagated through the section. Microscopic examination showed that the fatigue cracks were intercrystalline and grew on the surface along slip marking which formed ahead of the tip of the crack. The only effect the crystal structure had was in the direction of the slip band formation. There was no indication that the mechanism by which the cracks initiated was different than the one by which they propagated. The cracks initiated at the surface and grew through to the other side. Once they reached the other side a ductile crack formed and final failure soon followed. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The Effects of Fatigue on Vigilance in Sailing. Twelve male subjects were tested to determine if increasing amounts of physical fatigue are related to the attention paid to sail trim during sailing. A sailing simulator was used to determine if fatigue, either mental or physical, caused vigilance to vary while the subject was sitting on the side deck, hiking or hiking with weight. Each subject responded to 45 windshifts by adjusting the main sheet to provide proper sail trim for three separate sessions, each one being fifteen minutes long. Telltale deflection was videotaped to provide a vigilance score with deflection time starting when the telltales lifted and ending when adjustment of the sail stopped. Five fitness tests, number of sit-ups in one minute, percent body fat, isometric strength in the hiking position, isometric endurance in the hiking position and maximum oxygen uptake were administered on a separate day to determine if fitness scores were related to vigilance capacity. It was found that neither mental nor physical fatigue caused a decrease in vigilance over the fifteen minute test session. There was a learning effect associated with the apparatus as mean vigilance score for each successive sailing simulator session decreased regardless of the treatment used. Only one of the physical fitness tests was related to vigilance capacity as maximum oxygen uptake values were inversely correlated with mean vigilance scores. Subjects with high aerobic capacity were faster at responding to windshifts, thus supporting the use of a large aerobic component in dry land fitness programs. / Education, Faculty of / Kinesiology, School of / Graduate