The mechanism by which a spherical shell of granular matter is accelerated by an internal explosion together with its subsequent loading of a high ductility, edge clamped steel plate are investigated by a combination of instrumented experimentation and particle-based simulation. By using a large spherical explosive charge to drive the expansion of a water saturated synthetic sand shell, it has been possible to create sand front impact speeds with a test plate that exceeded 1200 m/s. Direct observations of the evolution of the sand front were made using a pair of high speed video cameras, and revealed rapid initial acceleration of the sand followed by deceleration, and the formation of locally faster sand spikes. The pressure evolution and specific impulse during sand particle impact were measured using a Kolsky bar. A discrete particle-based numerical simulation method implemented in the IMPETUS Afea code was then used to simulate the impulse applied to the Kolsky bar and to model deformation of the plate. The simulation analyzed the interactions between the explosively accelerated high explosive, air, and sand particles and the shock fronts that propagated across each interface after detonation. The impulse applied to the test plate and its support structure were well reproduced by the simulation. The simulations also revealed significant dispersion of the sand, with some sand particles attaining radial velocities that were almost 50% higher than that of the main front, and identified the presence of (an experimentally unobservable) instability at the energetic material-wet sand interface. The deceleration of the sand with distance of propagation was found to be the result of momentum transferring collisions with the background air, resulting in the formation of a strong air shock ahead of the sand front. This processes resulted in the eventual transfer of all the sand momentum to the air and significantly influenced the dynamically changing topology of the sand-air interface. While the differential acceleration of the sand particles to form a dispersed front, and their deceleration by air drag were well modelled, the development of "sand spikes" at the main sand front-air interface were not resolved by the simulations.

The deformation of ductile square stainless steel plates during central impact by high velocity, spherically symmetric granular particle shells has been investigated using an approach that combined large-scale experiments with numerical simulation. The study used suspended spherical explosive charges to accelerate 25 to 150 kg concentric shells of water saturated glass or higher density zirconia particles to velocities of 500-1200 m/s. The test charges were positioned above the center of 2.54 cm thick, 1.32 m x 1.32 m wide edge clamped panels made of 304 stainless steel, and their permanent deflection fields measured after testing. A novel edge restraint approach was utilized to avoid disruption of reflected particle flow over the impacted surface of the sample and so avoid plate failure near the gripped regions. The end of a Kolsky bar was positioned at a location symmetrically equivalent to the plate center, and was used to measure both the pressure and the specific impulse applied to the plate center. The evolution of the granular shell topology following charge detonation was characterized by analysis of high-speed video images. The radial expansion of the granular shells, the pressure and impulse that they transferred to the Kolsky bar, and the test plates out of plane displacement field were all well predicted by a discrete particlebased simulation approach. The study confirms earlier simplified model estimates of an approximately linear dependence of the plates out of plane displacement upon incident impulse, and validates the use of the edge restraint concept. It also experimentally identifies the existence of a granular shell velocity dependent instability at the leading edge of the fastest expanding granular shells.

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights  The out of plane displacement of edge restrained, grade 304 stainless steel sandwich panels has been measured after impact by rapidly expanding spherical shells of water saturated granular media at various velocities.  The radial expansion of the spherical shells was imaged using high-speed video techniques and the radial velocity shown to vary from 500 to1200 m/s. The impact pressure and transmitted impulse were also measured using a Kolsky bar positioned at a symmetric location to the panel center.  Discrete particle-based simulations successfully predicted particle front positions, velocities, impact pressures and plate deformations.  The study has confirmed recent predictions that the panels out of plane displacement would be less than that of an equivalent solid plate provided the deflection did not exceed the panel thickness.

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Increasing the inclination of a rigid surface that is impacted by a collimated granular flow reduces the fraction of granular matter momentum transferred. Recent studies have shown that the momentum reduction depends upon the frictional interaction between the granular flow and the impacted surface with high coefficient of friction surfaces suffering significantly more momentum transfer than predicted by resolution of the incident momentum onto the inclined plane. This discovery has raised the possibility that inclined surfaces with very low friction coefficients might reduce the impulsive transferred by the impact of ejecta from buried explosions. Here the use of a lubricated sliding plate is investigated as a means for reducing interfacial friction and impulse transfer. The study uses a combination of experimental testing and particle-based simulations to investigate impulse transfer to rigid aluminum surfaces inclined either perpendicular or at 53 o degrees to synthetic sand that had been impulsively accelerated to a velocity of 350-550 m/s. The study shows that impact of this sand with lubricated plates attached to an inclined surface, rapidly accelerates them to a velocity of about 55-70 m/s, and reduces the impulse transferred to the inclined surface. The reduction of impulse by this approach is shown to be comparable to that achieved by changing the inclination of the impact.