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Session 15

Influence of HE shape on blast profile
This paper is concerned by the effect of HE geometry on the shape of the blast wave. The aim of this work is to increase the knowledge on pressure profile generated by blast wave so as to optimize the design of explosion chambers. These facilities are commonly designed for spherical HE but most of the customer charges have other geometry (line, plate, cylinder ...). Numerical simulations performed with Multi Materials Arbitrary Eulerian solver in LSDYNA were used to simulate hemispherical and rectangular shape HE events detonated on the ground. Pressure records in front of the charge (reflected pressure) and on lateral positions at different locations (incident pressure) are compared to experiments performed at CEA / Gramat. High speed video has also been used to visualize the shape of the fireball and the shock wave in air. It is confirmed numerically that the shape of explosive generates different shape of blast wave and so will change the way of designing new chambers.
Using LS-DYNA MM-ALE capabilities to help design a wall mitigating accidental blast effects
A solution had to be found in order to protect buildings neighboring an industrial site from the blast effects of possible accidental explosions on the site. One of the main issues was that the point of detonation would occur relatively close to the endangered buildings. A possible answer was to build a blast-mitigating wall between the buildings and possible blasts. The MM-ALE features of LS-DYNA provided a way to evaluate the effects of the wall on the pressure waves around the building. As the amount of explosive was rather small when compared to the distances involved, the new 2D to 3D and 3D to 3D re-mapping methods came in handy to avoid the use of an impractically large numerical model. After a first series of computation showed that the proposed solution was indeed promising, a series of simulation runs enabled the design of a wall tall enough to achieve the desired mitigation effect on the pressure waves experienced by the building’s walls and roof.
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.
Shock Wave Effect on Aluminium Foam
The behaviour of aluminium foam under impact loading conditions and especially the shock wave propagation are still not well understood. The shock wave propagation through the cellular material structure under impact loading conditions has a significant effect on its deformation mechanism and therefore it is imperative to understand its effects thoroughly. The goal of this research was to investigate and examine the effects of shock wave propagation on aluminium foam. Additionally, the material and structural properties of pore- filled aluminium foam under impact loading conditions with particular interest in shock wave propagation and its effects on cellular material deformation have been studied. For this purpose experimental tests and explicit computational simulations of aluminium foam specimens inside a water tank subjected to explosive charge have been performed. Comparison of the results shows a good correlation between the experimental and simulation results.