A combined finite and discrete element method is used to examine the energetics of a two-dimensional microparticle cluster that impacts a rigid planar wall. The method combines conservation principles with an elastic-viscoplastic and friction constitutive theory to predict thermomechanical fields within particles resulting from both particle-wall and particle-particle contact. Emphasis is placed on characterizing the temporal and spatial partitioning of cluster energy with impact angle (0 • ≤ φ ≤ 80 • , where φ = 0 • corresponds to normal impact). Predictions for a close-packed cluster of well-resolved particles having an average initial radius and uniform speed of 50 µm and 300 m/s indicate that particles adjacent to the wall experience the largest plastic and friction work. Friction significantly affects cluster kinetic energy, but minimally affects its elastic strain energy and plastic work. Local temperature rises in excess of 900 K are predicted for φ = 0 • , increasing to 4,400 K for approximately φ > 60 • , with most of the cluster mass (≈98%) experiencing temperature rises less than 200 K due to plastic work. These predictions highlight the importance of friction work as a heating mechanism that may induce combustion of energetic clusters. Sensitivity of the cluster response to its initial packing configuration is demonstrated.
I would like to acknowledge several people who have contributed in several ways to make my graduate experience enjoyable and rewarding. First and foremost, I would like to acknowledge my advisor, Associate Prof. Keith Gonthier, for his technical expertise and guidance. Our countless discussions on technical as well as everyday issues have made me come to think of him as a colleague and a friend rather than a mentor.
A combined finite and discrete element method is used to examine the energetics of a microparticle cluster that impacts a deformable planar wall. The method combines conservation principles with a penalty based, two-dimensional (2-D) distributed potential force algorithm, and an elastic-viscoplastic and friction constitutive theory, to predict thermomechanical fields within the wall and cluster resulting from both particle-wall and particle-particle contact. Emphasis is placed on characterizing the temporal and spatial partitioning of wall and cluster energy for both normal (θ = 0 • , where θ is incidence angle) and oblique (θ = 45 • ) impact. Predictions for an initially close-packed cluster of well-resolved particles, each having an initial radius and speed of 50 µm and 500 m/s, indicate that particles adjacent to the wall experience significant dissipative heating due to plastic and friction work. Frictionally induced temperature rises in excess of 2,000 K are predicted for cluster mass located in the immediate vicinity of sliding contact surfaces, even for normal impact, whereas temperature rises near 200 K are predicted for significantly larger cluster mass due to plastic work. Friction is shown to significantly affect cluster kinetic energy, and to weakly affect its elastic potential energy and plastic work. This analysis highlights the importance of friction as a viable heating mechanism that may trigger combustion of energetic clusters.
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