Session: 12-26-01: Data-Driven Modeling and Simulation for Computational Biomedicine

Paper Number: 69041

Start Time: Friday, 04:05 PM

69041 - The Use of the Discrete Element Method to Study the Response of Packed Particles to a Pressure Wave 

When particles are packed together in a confined container, though each particle is an individual component, they form a structure-like system with both bulk and local behaviors that respond to external mechanical loads in a different manner than do the individual particle components.  These behaviors in the packed particle system depend not only on the materials from which the particles are comprised, but also on their shapes, interface behaviors, surface properties, and the density of the packing. The relative influence of each of these factors on the local or bulk behavior may vary depending on the intensity or duration of the external load applied to the system. The relative influence of system and load parameters can be readily studied using computational modeling methods. To model a system of a large number of particles where the contact between these particles can quickly change with time may be difficult for traditional finite element methods. Discrete element methods (DEM), where the basic units involved are representations of individual particles that interact with each other directly, offer a more direct computational corollary to the particle systems of interest.  The intent of this study is to explore the use of DEM to model the propagation of a pressure wave of varying duration, from quasi-static to a near impulse, through a system of packed particles.  The methods will then be used to understand the relative influence of interface behavior and packing density on the bulk and local behavior of the system.  Of interest is an understanding of the local interactions of individual particles and the forces that result as the pressure wave passes through the system.

Discrete element methods have been successfully used to study a wide range of system and loading conditions.  These methods have been employed to study the packing of particles under quasi-static loads and to assess the effects of particle compression on the bulk material properties of confined and unconfined particle beds. Through DEM, the load paths through a packed bed of unbonded particles have been traced under quasi-static loads. DEM have also been used to study the response of materials and structures under more highly dynamic loads, for example the breakup of otherwise continuous materials, like metal or glass plates, upon impact or the breakup of bonded particle agglomerates, such as rocks, under impulse loads.  However, the use of these discrete element methods to simulate the packing of a set of particles and then the response of the packed particle system to a pressure wave, especially of extreme magnitude or short duration, has not been well explored.  This is the focus of the current work.

A system of a fixed number of particles of a single material type at a given initial density will be arranged within a cylindrical container.  The packing of the particles under a quasi-static load will first be modeled.  The effect of initial packing density, interface conditions, and specific numerical modeling parameters will be explored. The effects of these parameters on the final packing density and resulting particle contact forces will be identified.  Next, a transient pressure wave of a given peak magnitude and varying over 3 order of magnitude in duration, from 0.1 ms to 0.01 ms will be applied to the free surface of the packed particle system.  The same physical system and numerical model parameters will be varied as in the first study of the quasi-static packing, and the mechanical response of the particle system to the initial passage of the pressure wave through the particle pack will be evaluated.  The work will result in a better understanding of the mechanical response of a packed particle system to a dynamic pressure pulse and will help to guide the selection of appropriate model parameters as well as the influential physical properties of the particles which may be used to tailor the behavior of the system.

Presenting Author: Catherine S. Florio US Army DEVCOM AC

Authors:

Catherine S. Florio US Army DEVCOM Armaments Center