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Improved Method of Visual Instrumentation for Ballistic Experiments, 18-9965 Printer Friendly VersionPrincipal Investigators Inclusive Dates: 07/01/96 - 02/04/99 Background - The major goal of this program is to image and analyze three-dimensional, high-speed deformation, fracturing, and propagation of fracture that leads to the onset of fragmentation of targets during impact. The highly dynamic conditions that occur during impact make acquisition of these data difficult. However, the information is essential for the analysis of armor materials designed to minimize behind-armor debris and for the study of fracture effects of very strong, yet brittle, advanced armor materials. Additionally, the data are required for fundamental verification of computer codes and material models that simulate failure in ballistic experiments. Approach - To accomplish this goal, the principles of Moiré fringe analysis are used to determine the out-of-plane deformation of the rear of the target plate. Images are taken of the fringe patterns at a series of small (on the order of 10 microseconds) time increments using an SwRI-acquired Imacon 468 ultrahigh-speed digital camera. The two key elements in the project include 1) the development of photographic techniques and fiducial systems that provide high-quality, quantitative fringe lines and 2) the automation of the fringe line reading process, which requires development of image enhancement and interpretation software. The basic principles of the software were established through an earlier quick-look internal research program. This program is concerned with advancing those earlier results to develop a system that can be used easily and quickly at the ballistic range. Accomplishments - To date, a number of trial images have been produced and recorded with static deformed plates, and the lighting and camera angle requirements have been studied. Several software methodologies that contribute to an autonomous fringe segmentation system are being investigated, including low-pass filtering, circle finding using decoupled Hough transforms, radial profiling, fringe enhancement using local statistical measures, and local constraint propagation. The two illustrations show the progress made toward locating the fringes and reconstructing a three-dimensional model based on contours automatically computed from a processed image.
Two-dimensional Moiré fringes are obtained from digital camera images and analyzed computationally to isolate the fringe center.
After the fringe centers are identified, the three-dimensional image of the deformed target can be reconstructed. Materials Research and
Structural Mechanics Program |
