<p> The stress relieving mechanisms in two different batches of thermal-shock resistant calcia-PSZ have been investigated. The nature of the stress relief in the two materials appears to result from the transformation of the pure ZrO₂ component of the microstructure at temperatures below, within, and above the normal transformation temperature range. In the batch #1 material, which contains a larger volume fraction of monoclinic phase, the cubic matrix material behaves in a "brittle" fashion resulting in the production of a high density of microcracks in the body. The density of these cracks is such that the level of energy that can be stored in the body is limited and thermal shock resistance results. The batch #2 material contains considerably less monoclinic material and the evidence suggests that the cubic matrix within it can act in a ductile fashion. This ductility together with the twinning of the monoclinic component of the microstructure possibly relieves the stresses developed in the material on thermal shock. </p> <p> In the batch #2 material, large platelets were observed to develop following thermal cycling from temperatures above those of the normal transformation. It has been demonstrated that stress plays a major role in the development of these features. In view of the possible ductility of the cubic matrix in this material it is suggested that the thermal cycling "works" the material, texturing the pure zirconia component in it, so leading to the development of the observed platelets. </p> / Thesis / Master of Engineering (ME)

The propagation of a shock and flame from a detonation wave injected orthogonally into a combustible, supersonic flow was observed. The detonation wave was generated through the use of a miniaturized detonation tube, henceforth referred to as a predetonator. Conditions within the test section, including stagnation pressure and equivalence ratio, were varied between cases. Through the use of high-speed schlieren, shadowgraph, and broadband OH chemiluminescence imaging, the leading shock and reaction were recorded as they moved through the test section. Variation of stagnation pressure affected the propagation of the leading shock. Higher stagnation pressures caused greater deflection of the shock wave and jet issued by the predetonator. It was seen that at sufficiently high equivalence ratios, the shock and reaction were able to travel upstream from the test section into the diverging section of the converging-diverging nozzle. Shortly after the shock entered the nozzle, evidence of the initiation of shock induced combustion was observed. Stagnation pressure variation in the range tested had little effect on the ability to initiate a reaction. Multiple behaviors of the shock-induced-combustion were observed, dependent upon the equivalence ratio of the flow through the test section. Behaviors include sustained reaction on the edges of the flow, sustained reaction in the core of the flow, and periodic, non-sustained reaction.

No description available.

The major goal of this PhD project is to investigate the fundamental properties of energetic materials, including their atomic and electronic structures, as well as mechanical properties, and relate these to the fundamental mechanisms of shock wave and detonation propagation using state-of-the-art simulation methods. The first part of this PhD project was aimed at the investigation of static properties of energetic materials (EMs) with specific focus on 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). The major goal was to calculate the isotropic and anisotropic equations of state for TATB within a range of compressions not accessible to experiment, and to make predictions of anisotropic sensitivity along various crystallographic directions. The second part of this PhD project was devoted to applications of a novel atomic-scale simulation method, referred to as the moving window molecular dynamics (MW-MD) technique, to study the fundamental mechanisms of condensed-phase detonation. Because shock wave is a leading part of the detonation wave, MW-MD was applied to demonstrate its effectiveness in resolving fast non-equilibrium processes taking place behind the shock-wave front during shock-induced solid-liquid phase transitions in crystalline aluminum. Next, MW-MD was used to investigate the fundamental mechanisms of detonation propagation in condensed energetic materials. Due to the chemical complexity of real EMs, a simplified AB model of a prototypical energetic material was used. The AB interatomic potential, which describes chemical bonds, as well as chemical reactions between atoms A and B in an AB solid, was modified to investigate the mechanism of the detonation wave propagation with different reactive activation barriers. The speed of the shock or detonation wave, which is an input parameter of MW-MD, was determined by locating the Chapman-Jouguet point along the reactive Hugoniot, which was simulated using the constant number of particles, volume, and temperature (NVT) ensemble in MD. Finally, the detonation wave structure was investigated as a function of activation barrier for the chemical reaction AB+B ⇒ A+BB. Different regimes of detonation propagation including 1-D laminar, 2-D cellular, and 3-D spinning and turbulent detonation regimes were identified.

Unsteady shock wave propagation through ducts has many applications, ranging from blast wave shelter design to advanced high-speed propulsion systems. The research objective of this study was improved fundamental understanding of the transient flow structures during unsteady shock wave propagation through rectangular ducts with varying cross-sectional area. This research focused on the fluid dynamics of the unsteady shock-induced flow fields, with an emphasis placed on understanding and characterizing the mechanisms behind flow compression (wave structures), flow induction (via shock waves), and enhanced mixing (via shock-induced viscous shear layers). A theoretical and numerical (CFD) parametric study was performed, in which the effects of these parameters on the unsteady flow fields were examined: incident shock strength, area ratio, and viscous mode (inviscid, laminar, and turbulent). Two geometries were considered: the backward-facing step (BFS) geometry, which provided a benchmark and conceptual framework, and the splitter plate (SP) geometry, which was a canonical representation of the engine flow path. The theoretical analysis was inviscid, quasi-1D and quasi-steady; and the computational analysis was fully 2D, time-accurate, and viscous. The theory provided the wave patterns and primary wave strengths for the BFS geometry, and the simulations verified the wave patterns and quantified the effects of geometry and viscosity. It was shown that the theoretical wave patterns on the BFS geometry can be used to systematically analyze the transient, 2D, viscous flows on the SP geometry. This work also highlighted the importance and the role of oscillating shock and expansion waves in the development of these unsteady flows. The potential for both upstream and downstream flow induction was addressed. Positive upstream flow induction was not found in this study due to the persistent formation of an upstream-moving shock wave. Enhanced mixing was addressed by examining the evolution of the unsteady shear layer, its instability, and their effects on the flow field. The instability always appeared after the reflected shock interaction, and was exacerbated in the laminar cases and damped out in the turbulent cases. This research provided new understanding of the long-term evolution of these confined flows. Lastly, the turbulent work is one of the few turbulent studies on these flows.

Shock waves create a unique environment of high pressure, high temperature and high strain-rates. It has been observed that chemical reactions that occur in this regime are exothermic and can lead to the synthesis of new materials that are not possible under other conditions. The exothermic reaction is used in the development of binary energetic materials. These materials are of significant interest to the energetic materials community because of its capability of releasing high heat content during a chemical reaction and the relative insensitivity of these types of energetic materials. Synthesis of these energetic materials, at nano grain sizes with structural reinforcements, provides an opportunity to develop a dual functional material with both strength and energetic characteristics. Shock-induced chemical reactions pose challenges in experiment and instrumentation. This thesis is addressed to the theoretical development of constitutive models of shock-induced chemical reactions in energetic composites, formulated in the framework of non-equilibrium thermodynamics and mixture theories, in a continuum scale. Transition state-based chemical reaction models are introduced and incorporated with the conservation equations that can be used to calculate and simulate the shock-induced reaction process. The energy that should be supplied to reach the transition state has been theoretically modeled by considering both the pore collapse mechanism and the plastic flow with increasing yield stress behind the shock wave. A non-equilibrium thermodynamics framework and the associated evolution equations are introduced to account for time delays that are observed in the experiments of shock-induced or assisted chemical reactions. An appropriate representation of the particle size effects is introduced by modifying the initial energy state of the reactants. Numerical results are presented for shock-induced reactions of mixtures of Al, Fe2O3 and Ni, Al with epoxy as the binder. The theoretical model, in the continuum scale, requires parameters that should be experimentally determined. The experimental characterization has many challenges in measurement and development of nano instrumentation. An alternate approach to determine these parameters is through ab-initio calculations. Thus, this thesis has initiated ab-initio molecular dynamics studies of shock-induced chemical reactions. Specifically, the case of thermal initiation of chemical reactions in aluminum and nickel is considered.