Application of 3D Digital Image Correlation In Ballistic Testing

Abstract

Digital image correlation has been identified as a promising technique for use in terminal ballistic research; however, the limited resolution of ultra-high-speed cameras requires coarse speckle patterns not consistently achievable by conventional methods like spray painting. Thus, a robust and automated speckling technique that can apply a speckle pattern with appropriate speckle size and density is desired. The current study outlines an efficient, repeatable means of applying a high-quality black-on-white speckle pattern to test specimens. The speckle patterns were designed digitally and reproduced on the samples using a 3-axis mill coupled to a permanent marker with a custom-made, spring-actuated marker holder. By automating the process, the resulting speckle pattern is significantly more consistent compared to traditional specking techniques like spray painting or using a permanent marker manually. It also allows for precise control of the speckle size, density, and speckle pattern randomness. The method outlined in this work is capable of easily achieving 0.2–4 mm speckles and can generate speckles at a rate of 1–2 speckles per second. Example patterns ranging in size from 10 × 10 mm to 200 × 200 mm are shown which required as little as 5–10 min to complete (each containing ~600 speckles). High-velocity impact experiments were then performed on 6.35 mm thick aluminum plates that were speckled using the described technique to demonstrate the high-rate, localized deformation that takes place during an impact event. It emphasizes the extreme spatial and temporal difficulties of using digital image correlation for ballistic research and the need for a tailored speckle pattern.