Identifier

etd-06282006-132639

Degree

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Document Type

Thesis

Abstract

Conventional granular explosives are widely used in aerospace and defense-related industries. Powdered metals are often mixed with high explosives to enhance detonation. The effectiveness of these mixtures is limited by the slow burning of the metal relative to the explosive and their sensitivity to mechanical loading. Granular energetic composites, composed of an aluminum core coated with a layer of the high explosive RDX (C3H6N6O6), may be a high-performance alternative to conventional explosives because of a higher metal combustion rate and lower impact sensitivity. Though the technology required to manufacture granular energetic composites exists, it is difficult to experimentally characterize the mesoscale response due to the small length and time scales involved. In this thesis finite-element analyses were conducted for mesoscale simulations that represent accidental impact scenarios. A 2-D plane strain analysis was performed on systems containing cylindrical grains having an outer diameter of 50 microns, arrayed in symmetric and random configurations, and enclosed within rigid planar walls. Dynamic compaction was simulated using a rigid piston moving at constant speeds of 50, 100, and 200 m/s, and the RDX layer thickness was also varied. Although mechanical features of each system response are sufficiently resolved on the finite-element meshes used in this work, finer grids are required to resolve the effects of thermal conduction. The absence of a monotonic relationship between the RDX thickness and pressure at the low piston speed suggests that simple mixing rules cannot be used to predict the response of composite systems. Hot spots were present near the piston surface in each case, with peak temperatures of 490 K and 596 K for the symmetric and random simulations, respectively. Thus, ignition may occur in asymmetric systems, though symmetric systems remain insensitive to weak impact. However, temperatures within the domain interior did not exceed 350 K. Cases involving intergranular friction showed negligible temperature increases compared to heating caused by plastic deformation. In the random configuration, wall friction significantly raised hot-spot temperatures in grains adjacent to the lateral walls, resulting in peak temperatures of 1480 K.

Date

2006

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Keith A. Gonthier

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