Future Work

Since DIC is a scale independent technique, the resolution of the results is dependent on the magnification of the images taken during the experiments. When determining the crack closure using the two-point digital extensometers, using higher magnification images would provide results more sensitive to the crack opening. When used in conjunction with a slower measurement cycle frequency to increase the number of loads recorded, these images would provide a method to pinpoint the exact load at which the crack opens.

A higher spatial resolution would also be beneficial when determining the strains at the fatigue crack tip. The highest magnification used during this thesis was 6x, but magnifications up to 50x have been used with digital image correlation for determining strain fields (Carroll, Abuzaid et al. 2010). At higher magnifications, the subset sizes can be on the order of 10 μm.

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With subsets this small, the slip irreversibility inside individual grains in a polycrystalline aggregate could be measured. When used in combination with EBSD results, the changes in slip irreversibility between grains as the fatigue crack propagates will be able to be determined. Greater accuracy in the measurement of crack tip slip irreversibility is beneficial when using one of the fatigue crack growth rate models discussed in Section 2.3.

One of the greatest strengths of the DIC technique is the ability to use it in a variety of settings. The anisotropic regression analysis developed during this research can be utilized to characterize fatigue crack growth at high temperatures or in different environments, such as in vacuum. If experiments were run in both air and vacuum at high temperatures, oxide-induced crack closure is able to be studied and measured using the anisotropic regression algorithm.

The techniques used during this study provided insight into the crack closure and slip irreversibility found during fatigue crack growth experiments in both isotropic and anisotropic materials. By expanding the testing schedule and using some of the aforementioned suggestions, further insights into the effects of different testing conditions on fatigue crack growth can be made. The analytical techniques developed in this thesis are not limited by the environment or testing temperature.

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