| Description |
This thesis is a discussion of the effects of frequency on corrosion fatigue, with specific application to the aluminum alloy 2224 - T3511 and its use in the commercial aircraft industry. Corrosion fatigue is becoming recognized more and more as a primary contributor to fatal accidents, especially those involving aircraft. It has been recognized that frequency, which has long been neglected with respect to fatigue, plays a significant role in crack growth due to corrosion fatigue, corrosion being a time dependent mechanism. Due to its current popularity with the aircraft industry, the alloy 2224-T3511 has been chosen to exemplify the techniques used to examine these frequency effects. The first part of this paper consists of an introduction into the need to study frequency effects on corrosion fatigue. There follows a partial epistemology of fracture mechanics extending into recent developments concerning the corrosion fatigue of aluminum in particular. The second portion of this thesis is a discussion of experiments conducted by Mr. Michael Blinn, a doctoral candidate at the University of Utah studying these effects. The details of the experimental set up and some of the results are discussed with the permission of Mr. Blinn as the primary investigator of the research. Also discussed are the methods of reducing and examining the data, mainly in the form of log da/dN versus i\K plots. These plots show that frequency has a definite effect on the crack growth rates of this particular specimen. As expected, lower frequency resulted in higher crack growth rates. It was also demonstrated that the dry air used in the experiment, less than 10% relative humidity, acts as a corrosive environment for the alloy. In the discussion, some of the models discussed in the first portion are used to analyze the data. Suggestions are made on how to utilize the data and on what further work would be beneficial are then made. |
