Dynamic Micro-Strain Analysis of Ultrafine-Grained Aluminum Magnesium Alloy Using Digital Image Correlation
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Tensile tests were performed in situ on an ultrafine-grained (UFG) Al-Mg alloy using a micro-tensile module in a scanning electron microscope. The micro-strain evolution was tracked and measured using digital image correlation (DIC). A fine random speckle pattern was required to achieve high resolution and accuracy of strain measurement using DIC. To produce the speckle pattern, a patterning method was developed using electron beam lithography to deposit a gold speckle pattern. The nanoscale feature size of this gold pattern (45 nm) was useful for identifying the micro-strain among individual grains of the UFG Al-Mg alloy. Microstructural aspects of the UFG Al-Mg alloy were revealed by analysis of electron backscattered diffraction (EBSD) patterns. Finally, the effect of the UFG Al-Mg alloy microstructure on the nanoscale deformation mechanism was investigated by combining EBSD and DIC data in a contour map. This combined technique provides a method for direct measurement of micro-strain and is potentially useful for deformation studies of a wide range of nanostructured materials.
KeywordsPMMA Digital Image Correlation Speckle Pattern Image Distortion Confidence Index
The authors gratefully acknowledge B. Ahn, J. Ma, and Y. Zhao for their advice. The images and data used in this article were generated at The Center for Electron Microscopy and Microanalysis, the University of Southern California. Dr. T.D. Topping and Dr. E.J. Lavernia extend thanks and appreciation to the Materials Design Institute, funded by the LANL/UC Davis Education Research Collaboration, Los Alamos National Laboratory (LANS Subcontract No. 75782-001-09). Gratitude is also extended to Mr. Rodney Peterson and Dr. William Golumbfskie of the Office of Naval Research for support of this work (ONR Contract N00014-12-C-0241).
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