Digital Speckle Radiography in the Penetration of Granular Materials

Abstract

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The significance of grain morphology and moisture content on the response of silica sand to ballistic penetration

“…A random distribution of lead shot (sourced from Sigma Aldrich) ~1.6 mm diameter was scattered across the horizontal impact plane of the sand bed during filling, providing an x-ray opaque speckle pattern to enable DSR analysis. A previous study29 has confirmed that the presence of a small amount of lead shot in a sand cell does not affect penetration response, and additional x-ray images taken from different angles confirmed that the lead does not flow relative to the surrounding sand once the cell has been filled.The sand bed was imaged with a Scanditronix Scandiflash 150kV x-ray unit (about 70 ns flash x-ray pulse) both before and after impact (timing of the latter being controlled by the make-trigger and a delay generator). Agfa Curix ht 1.000 g medical X-ray film was used in Agfa Curix Ortho regular cassettes containing an image intensifier screen.…”

“…Schematic of the experiment, detailing the cylindrical sand cell, axisymmetric impact geometry and impact plane in which a layer of lead shot 'speckle' is deposited.The experiment utilized Digital Speckle Radiography (DSR) to track granular flow within the sand bed during impact27 . DSR employs a Digital Image Cross Correlation (DICC) algorithm written and supplied by Sjödahl of the University of Luleå, Sweden28 to track the displacement of small sub-images between two x-ray images by maximizing correlation.…”