Novel Patterning Techniques to Improve Digital Image Correlation in Challenging Environments

A camera-based measurement technique called digital image correlation (DIC) is beneficial to measure displacement and strain in challenging environments (such as post-irradiation evaluation and high temperature environments) due to its non-contacting nature and ability to obtain measurements over multiple length scales. This technique requires a surface pattern which influences the measurement resolution and accuracy of the measurements. This thesis explores two novel patterning techniques to allow the use of DIC in more challenging environments: The first is to determine if a pattern created from printed text can be used as a pattern in DIC. Native patterns are patterns already present on an object which have properties which allow them to be used as a DIC pattern, such as contrast. Rigid body translation, rotation, and bending deformation tests are performed on text speckle patterns. The results are compared to a traditional DIC speckle pattern, and it is determined text patterns can serve as DIC speckle patterns when present as a native speckle pattern. The influence of properties of the text speckle patterns such as font and line spacing on the effectiveness of the text speckle pattern are explored. Line spacing has the most significant influence on the effectiveness of using text as a native speckle pattern. Text patterns have low enough uncertainty to obtain accurate measurements, but do not perform as well as traditional DIC speckle patterns. The second details the creation of a multi-colored, multi-scale speckle pattern created for multi-scale DIC measurements. A method is presented for using color cameras to capture images of the multi-scale multi-colored pattern and then splitting the images by color channels of the image in post-processing to obtain multi-scale measurements simultaneously. The images are analyzed using different DIC settings and it is determined the small scale and large-scale measurements have strong agreement. This method has the advantage of the large and small scale full-field data being inherently mapped onto one another as opposed to other multi-scale DIC measurement methods