In-Situ Full-Field Strain Measurement at the Sub-grain Scale Using the Scanning Electron Microscope Grid Method
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In-Situ Full-Field Strain Measurement at the Sub-grain Scale Using the Scanning Electron Microscope Grid Method Hadi Mirmohammad1 · Tristan Gunn1 · Owen T. Kingstedt1 Received: 26 March 2020 / Accepted: 3 September 2020 © The Society for Experimental Mechanics, Inc 2020
Abstract Full-field measurement techniques are invaluable tools for investigating material behavior across length-scales. In the current work, a full-field measurement technique, the Grid Method, is implemented within a scanning electron microscope to demonstrate its ability to capture deformation heterogeneities at sub-grain length-scales. Microgrids, fabricated using focused ion beam platinum deposition are positioned on multiple areas with different underlying microstructure of an aluminum 1100 oligo-crystal. In-situ scanning electron microscope tensile testing is then conducted while capturing micrographs of the deposited grids after individual loading increments. Strain maps are generated through localized spectral analysis of a reference (non-deformed) and deformed micrographs. The strain maps exhibit intragranular and transgranular heterogeneities. The current work demonstrates the successful implementation and promise of the SEM grid method for extracting strain maps at reduced length-scales. Keywords SEM-GM · SEM in-situ testing · FIB platinum deposition · Microscale full-field measurement technique · Aluminum oligo-crystal microstructure characterization
Introduction Digital image correlation (DIC), has seen wide use in experimental solid mechanics studies at the macroscale [1, 2], mesoscale [3–6] and microscale [7–12]. It represents an important tool that has been critical to advancing understanding in multiple areas of engineering. While DIC has had vast impacts, it suffers a noticeable drawback in that its metrological performance can only be determined upon the completion of an experiment. A competing technique, the grid method [13], can be modeled by closedform models which enable metrological performance to be determined during the experiment design stage. Taking advantage of the closed-form model of the grid method, several studies have investigated the metrological
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40799-020-00402-8) contains supplementary material, which is available to authorized users. Owen T. Kingstedt
[email protected] 1
Department of Mechanical Engineering, University of Utah, Salt Lake City, Utah, USA
performance of the grid method in the presence of various noise and image distortion sources at the macroscale. With respect to CCD cameras, investigations have been conducted on aliasing effects in strain maps and how to minimize their presence by rotation of the camera with respect to the imaged grid [14], characterization of noise reductions achieved through automatic time averaging [15], and heteroscedastic CCD noise propagation [16]. The motivation to transition the grid method from the macroscale to the microscale is driven by a
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