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Discipline: Technology and Engineering
Subcategory: Civil/Mechanical/Manufacturing Engineering
Taylor Spencer - Howard University
Digital Image Correlation is a method of measurement that uses images to analyze the deformation of an object. Patterns of dots on a specimen are used to measure this deformation. One large flaw in this way of testing is that attempting to measure through air turbulence such as heat waves will distort the data collected. The waves create spatially varying index of refraction changes that make the dots appear as if they are moving. This makes it difficult to use DIC outdoors, over long distances, or looking into a furnace since the heat waves will distort the collected images. It is especially hard to remove the heat turbulence because the movements of the waves are unpredictable and simultaneously overlaid on the displacement data being measured. DIC experiments were conducted with four cameras in an attempt to spatially average out the influence of the air turbulence. The four cameras focused on a speckle pattern with a heated burner in between to create the heat waves. The burner was placed in three different locations between the speckle pattern and the cameras to see how different locations of turbulence affected the images. We deformed the speckle pattern toward the cameras using a screw pushing on the back and measured the deflection with a caliper. Thermocouples monitored the temperature at a number of points in the experiment; this included on the burner, at the sample, in the ambient air over the table, and on the cameras. Our hypothesis is that we can spatially average the systems of cameras together to achieve an accurate measurement of the outward deformation. In other words, when we average the systems together the average should appear to be more like the calculated displacement without the heat. The setup of four cameras all pointing at different angles can help fulfill this purpose. Since they are all collecting different data they can average together to form one heat wave. To average the systems together, Correlated Solutions software Vic-3D, Excel, and LabVIEW are used. Before averaging can occur on the collected images, however, they need to be in the same plane. Each of the systems is at different angles when the images are taken, therefore if we try averaging we will have sets of points that don’t fit with the other systems. The W, or outward, displacements are collected after the images are translated onto the same plane. We export the data to Vic-3D or LabVIEW and then average it. It is clear after the averaging that the closer the heat to the cameras, the better the averaging turns out. It still doesn’t turn out similar enough to the displacement with no heat, however. Currently, better ways to average the systems together are being looked at as well as different experiments with higher heats and different camera setups.
Funder Acknowledgement(s): Funding was provided by Sandia National Labs. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under contract No. DE-AC04-94AL85000.
Faculty Advisor: Phillip Reu, plreu@sandia.gov
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