G.F. Bomarito

MicroStamping for Improved Speckle Patterns to Enable Digital Image Correlation

Surface strain measurements using image correlation require a pattern to be applied to the surface of the object being measured. Lithography, the most widely used method for repeatable patterning is expensive, requiring dedicated technical staff and significant infrastructure. Lithography is time consuming, often requiring several days for each patterning application, which limits throughput. An innovative method has been developed and tested whereby repeatable patterns for image correlation are applied without dedicated technical staff or special infrastructure and can be completed in a few minutes rather than days. This new method is more amenable to application of patterns to complex surface geometries and larger surface areas. The new micro stamping method allows for higher contrast patterning materials, which improves the accuracy of strain measurements using image correlation.

Selectively Electron-Transparent Microstamping Toward Concurrent Digital Image Correlation and High-Angular Resolution Electron Backscatter Diffraction (EBSD) Analysis

Digital image correlation (DIC) in a scanning electron microscope and high-angular resolution electron backscatter diffraction (HREBSD) provide valuable and complementary data concerning local deformation at the microscale. However, standard surface preparation techniques are mutually exclusive, which makes combining these techniques in situ impossible. This paper introduces a new method of applying surface patterning for DIC, namely a urethane microstamp, that provides a pattern with enough contrast for DIC at low accelerating voltages, but is virtually transparent at the higher voltages necessary for HREBSD and conventional EBSD analysis. Furthermore, microstamping is inexpensive and repeatable, and is more suitable to the analysis of patterns from complex surface geometries and larger surface areas than other patterning techniques.

Micro Speckle Stamping: High Contrast, No Basecoat, Repeatable, Well-Adhered

Micro Speckle Stamping has been developed and tested whereby repeatable micro speckle patterns for DIC are applied with no basecoat. The speckle patterns are created on a stamp, and ink is applied to the stamp. The user then transfers the speckle pattern from the stamp to the specimen. Micro Speckle Stamping uses high optical contrast and high electrical contrast speckle materials and leaves no residue between speckles. This new method is more amenable to applying patterns to complex surface geometries and large surface areas and also allows investigations of the virgin surface with EDS and EBSD.

Investigation of Optimal Digital Image Correlation Patterns for Deformation Measurement

Digital image correlation (DIC) relies on the visible surface features of a specimen to measure deformation. When the specimen itself has little to no visible features, a pattern is applied to the surface which deforms with the specimen and acts as artificial surface features. Since recent pattern application methods, e.g., micro-stamping [1] and lithography [2] allow for the application of highly customized patterns and because the accuracy and precision of DIC is dependent upon the applied pattern [3, 4, 5, 6], an ideal pattern is sought for which the error introduced into DIC measurements is minimal. It is the goal of the present work to develop and refine an optimization technique to produce this type of DIC pattern.