Simulation of Shock Wave Mitigation in Granular Materials by Pressure and Impulse Characterization

The detonation of an explosive charge has two major effects, blast wave generation and fragmentation. New technologies of energy dissipation, based on granular materials, seem to have good shock attenuation capabilities. Plastic deformation, brittle fracture and comminution are different mechanisms of dissipation which can take place in granular media, allowing blast energy absorption and reduction of dynamic solicitation applied on structures. Dynamic solicitation of structures is determined by the reflected pressure in a quasi-static loading case or by the reflected impulse in an impulsive loading case. Blast pressure and impulse damping represent in a macroscopic way the effects of energy dissipation mechanisms appearing in granular materials. Material efficiency can be determined by the study of the attenuation of these two parameters. Vermiculite, a porous crushable material and CRUSHMAT®, a ceramic granular material made of alumina have been tested. Blast impulse amplification has been observed with thin layers of vermiculite while with CRUSHMAT® only attenuation has been observed. Efficiency stagnation has also been noticed for thick layers of CRUSHMAT® in which pressure and impulse, after being passed through the sample’s upper part, seem to be too low for further attenuation in the lower part of the layer. LS-DYNA has been used to simulate the experimental setup in which reflected pressure and impulse measurements have been realized on the different samples. The simulation model has been developed for a better understanding of pressure and impulse decrease, dissipation mechanisms and macroscopic behaviour of granular materials when they are subjected to blast. The CRUSHMAT® stress-strain curve has been optimized with LS-OPT trying to allow a better correlation between simulations and experimental observations.