Sandia Labs FY21 LDRD Annual Report

FY21 ANNUAL REPORT

LDRD IMPACT STORY: Digital Image Correlation: Pushing experimental innovation in data collection and model validation

Digital image correlation (DIC) is a measurement technique that allows us to “see” how materials behave, particularly under circumstances that are typically hard to measure experimentally. For example, DIC has been used at Sandia to understand how explosive devices come apart and how much destruction they cause (so that damage can be mitigated), or how a test-weapon behaves when it slams into a target. Such knowledge can then be used to validate and improve models, ultimately helping gain new insight into complex physical processes. At a high level, DIC is a tracking method that leverages high-speed photography (millions of frames per second) to compare pairs of images.

Typically, an object of interest is coated with a speckled pattern that is tracked over time to ascertain how the object behaves. DIC algorithms analyze the pattern movement to measure displacement, velocity, and strain of the object. It may sound straightforward, but many factors, from the camera setup to the choice of the speckle pattern, can affect the results.

Schematic (top) and experimental x-ray images (bottom) of multiple DIC patterned planes generating a single path-integrated x-ray image. Through novel data algorithms, each plane can be separated to discern independent motion, simultaneously.

Sandia was an early adopter of DIC in 2005, as scientists were looking for better ways to validate and improve models unique to Sandia’s national security missions, particularly in the areas of material deformation and explosive dynamics. Over the next decade, Sandia leveraged and enhanced the technique, including integrating uncertainty quantification into the approach—an important addition to ensure measurements made with DIC at Sandia so they could be considered traceable per the National Institute of Standards and Technology (NIST)—ultimately developing the first NIST traceable measurement for DIC. Sandia became a founding member of the DIC Society in 2015, helping to

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LABORATORY DIRECTED RESEARCH & DEVELOPMENT