The effect of rod nose shape on the internal flow fields during the ballistic penetration of sand

This paper discusses the technique of Digital Speckle Radiography (DSR) and its application to the measurement of the internal flow fields in penetration of sand by long-rod projectiles at velocities up to 200 m/s. Three different rod nose shapes were studied: flat-ended, ogive-2, and hemispherical. Impacts performed on gelatine and concrete gave significantly different displacement fields to sand. Sand, therefore, cannot either be modelled as a fluid or as a conventional solid. Simulations performed using a code written by two of the authors (Bobaru and Promratana) showed that the velocity distribution has a very different appearance to the force distribution. This suggests that processes such as reorganisation, sliding and void filling take place, allowing the grains to move in directions other than the applied force. The resulting velocity distribution bears a strong resemblance to the experimentally measured displacement fields.

► Digital Speckle Radiography was used to experimentally measure internal flow fields in sand.
► Three different rod nose shapes were studied: flat-ended, ogive-2, and hemispherical.
► The rod velocities ranged from quasistatic up to 200 m/s.
► Simulations showed the velocity distribution is different to the force distribution.
► Both experiments and modelling showed that the grains move in directions different to the applied force.