Real-Time Full-field Deformation Analysis on the Ballistic Impact of Polymeric Materials Using High-speed Photogrammetry

Report No. ARL-RP-0290
Authors: Jian H. Yu, Alex J. Hsieh, Peter G. Dehmer, and James M. Sands
Date/Pages: April 2010; 16 pages
Abstract: The dynamic deformation of transparent polymeric materials during the ballistic impact is investigated using a unique high-speed imaging technique. This technique involves the use of two high-speed cameras to record stereo images of a speckle patterned impact area and subsequent photogrammetric analysis. Photogrammetry is an image correlation technique that determines geometric properties, such as the displacement and strain history of a deformation event, by tracking the minute changes in the speckle pattern on the area of interest. These minute changes are then translated into three-dimensional displacement vectors as a function of time. Important mechanical behavior, such as strain or shear angle, can be calculated from the displacement vectors. By combining high-speed photography with photogrammetry, a full-field view on the strain as a function of time is made possible, and the strain can be resolved into components, such as the principle strain and shear strain. To demonstrate the capability of the high-speed photogrammetric technique, impact measurements on two different polymers were performed. A steel spherical projectile with a diameter of 5.54 mm and a weight of 0.692 g was used to impact a rigid polycarbonate (PC) and a flexible poly(urethane urea) (PUU) elastomer. The measurements were carried out at striking velocities between 100 m/s and 200 m/s, below the ballistic limits of both materials. At low impact speeds, the strain histories revealed that PC had a smaller deformation zone than PUU. At high impact speeds, it was observed that PC suffered a permanent strain deformation, whereas the strain in PUU relaxed over time. From these impact experiments, it is demonstrated that high-speed photogrammetry is able to capture the different strain behavior of these two polymers. These real-time strain histories cannot be easily observed quantitatively by other methods.
Distribution: Approved for public release
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Last Update / Reviewed: April 1, 2010