Onset of dynamic jamming in granular medium subject to explosion

The dynamic jamming of granular media consisting of glass spheres subjected to explosion is investigated experimentally via a radial hele-shaw cell connected with a vertical shock tube. The evolution of velocity fields as well as the resulting strain rate fields are attained via the imaging technique, namely Particle Image Velocimetry (PIV). As the expanding internal surface accelerates outwards, a highly localized and exponentially decayed flow field is induced and becomes increasingly diffusional with an increased decay length. The end of the acceleration phase of the advancing internal surface corresponds to the transition of exponentially decayed flows to a jammed band with largely constant velocity in the wake of a circular dynamic jamming front across the thickness of which a large velocity gradient is discerned. The onset of a steady dynamic jamming commences from the transition of flow fields. Afterwards, most compression and shear deformations occur throughout the thickness of the jamming front in a highly heterogeneous manner in contrast with the deformation mode in the prior transient period. The statistical analysis of strain fields reveals a characteristic length scale which may well arise from the grain-scale heterogeneity of granular materials.