Identifier

etd-07032009-131245

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

An explicit, two-dimensional, Lagrangian finite and discrete element technique is formulated and used to computationally characterize meso-scale fluctuations in thermomechanical fields induced by low pressure deformation waves propagating through particulate energetic solids. Emphasis is placed on characterizing the relative importance of plastic and friction work as meso-scale heating mechanisms which may cause bulk ignition of these materials and their dependence on piston speed (vp ~ 50-500 m/s). The numerical technique combines conservation principles with a plane strain, thermoelastic-viscoplastic constitutive theory to describe deformation within the material meso-structure. An energy consistent, penalty based, distributed potential force method, coupled to a penalty regularized Amontons Coulomb law, is used to enforce kinematic and thermal contact constraints between particles. The technique is shown to be convergent, and its spatial (~ 2.0) and temporal (~ 1.5) convergence rate is established. Predictions show that alhough plastic work far exceeds friction work, considerably higher local temperatures result from friction work. Most mass within the deformation wave (~ 99.9%) is heated to approximately 330, 400, and 500 K, for vp = 50, 250, and 500 m/s, respectively, due to plastic work, whereas only a small fraction of mass (~ .001%) is respectively heated to temperatures in excess of 600, 1100 and 1400 K due to friction work. In addition to low speed impact, and contrary to conventional belief, friction work is shown to also be an important heating mechanism at higher impact speeds. The variation in spatial partitioning of bulk energy within the deformation wave structure with particle morphology and material properties is demonstrated.

Date

2009

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Keith A. Gonthier

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