M. S.

Microscopic examination of the tracheal dimensions of normal Florida mice (Peromyscus floridanus) and cotton mice (P. gossypinus) showed no significant differences between the two species, but external examination showed the tracheal length of the Florida mouse to be longer than that of the cotton mouse. Microscopic examination of the intrapulmonary apparatus (bronchioles, alveolar ducts, atria, and alveoli) of normal Florida and cotton mice showed no significant differences in measurements between the two species. Cotton mice were exposed to exhaust gases produced by the burning of solid rocket motor (SRM) fuel. Mice exposed once for a duration of 10 min demonstrated an LD50 of 52 to 56 ppm HCl/g body weight and an LD50 of 169 to 173 mg Al2O3/m3/g body weight. These LD50 values suggested that SRM exhaust components may have a synergistic lethal effect when compared to the effects of individual components of the exhaust. Cotton mice exposed to the exhaust exhibited external signs of respiratory distress and dyspnea. Those mice that received lethal exposures showed internal signs of early inflammatory reactions. However, the most likely cause of death was a sudden shift in blood pH.

Solid propellant research has mainly been directed towards more accurate characterization of the propellant material nature and more reliable structural analysis of the grain. Internal star grain design is among the most popular grain shapes that are used in today's propulsion system. Due to its complex geometry, stress concentrations are inevitably present around the highly curved area. Furthermore, this geometric effect together with various loading conditions throughout the grain's service life actually causes numerous defects inside its body. However, little is known concerning the three-dimensional fracture mechanism of the surface cracks which are the most common defects detected in the real rocket motor grain. After a brief evaluation of the current status of solid propellant research, stress analysis of a star grain model under internal pressure was performed by both photoelastic experiments and finite element calculations. These results illustrated the stress concentration effect around the star finger tip in addition to the global stress distribution across the whole section. Meanwhile, the deformation of the grain's outer surface was also obtained from the finite element results. A series of photoelastic experiments was conducted on cracked specimens with surface flaws emanating both on and off the axis of symmetry starting from the star finger tip. For the symmetric crack problem, cracks with different depths were intensively studied and the three-dimensional stress intensity factor (SIF) distribution was obtained for each test. These experimental data were further used to construct three analytical models, the "equivalent" radius model, the weight function model and the notch-root crack model, to expand the application range of the experimental data base so that a symmetric crack's SIF distribution with an arbitrary depth can be predicted. Moreover, surface cracks initiated off the axis of symmetry were also investigated by considering two off-axis angles. The crack shape and propagation path were achieved through a series of experiments and two methods were developed to effectively predict the possible crack growth path under sufficient pressure. The SIF distribution around the crack border was obtained for different offaxis angles and the factors that might influence the distributions were addressed based on the comparisons between the symmetric and asymmetric cracks, and the asymmetric cracks with different geometries. / Ph. D.

Defects formed in solid rocket propellant during manufacturing, transportation, storage, and assembly can lead to alterations in the thrust time profiles and possibly catastrophic failure of the entire rocket. In order to determine the effects of temperature, loading rate, and thickness on this particulate composite, tests were conducted at three temperatures and two loading rates. Both uncracked and edge cracked "biaxial" specimens were produced from solid rocket propellant. The stress relaxation modulus and stress-strain data were obtained from load curves formed during "biaxial" tension tests. Near crack tip displacements and strains were calculated from photographs taken of a surface grating on the pre-cracked specimens during crack propagation. The effect of thickness, temperature, and loading rate on the stress intensity factor was also studied. Finally, by applying continuum theory the displacement singularity was determined at different stages of crack growth. From the stress strain data, it was found that temperature had a greater influence on behavior than loading rate over the ranges studied. The crack growth in the composite material consists of a series of crack opening, crack blunting, and crack growth/resharpening stages which are highly nonlinear. However, the thick specimen at low temperature did not follow this crack growth mechanism. At -65°F the thick specimen developed transverse constraints which caused a brittle fracture to occur when the specimen was loaded. Determination of the displacement singularity order for the sharp cracks was found to be consistent with the theoretical results predicted by Benthem. / Master of Science

Electrically controllable propellants (ECPs) provide a new method to increase the control and functionality of rocket motors in particular solid rockets. Traditional solid rockets do not have the capability to modify the burning rate on demand during operation, which greatly limits operational capabilities. The research outlined in this dissertation explores the fundamentals in the creation of ECPs to enable increased control in the burning rate of solid rockets. The research is organized into four studies which step through the fundamentals of ECPs, starting with a focus on the solid oxidizers, then moving into the creation of electrically controllable gel propellants (ECGPs). Next, electrically controllable solid propellants (ECSPs) were explored under atmospheric conditions, and then finally under elevated pressures. The first study explores the ability to electrically control the decomposition characteristics of various solid oxidizers. Typical composite solid propellants are composed of solid fuels and oxidizers and isolating the oxidizer in this study enables the ability to characterize critical components of ECSPs individually. This study discovered that certain solid oxidizers respond differently to applied voltages, but generally the decomposition rate of the solid oxidizers is greatly increased when voltage is applied using metal electrodes. The melt layer formed in the decomposition of the solid oxidizers was observed to be critical in the ability to manipulate the decomposition rate of the oxidizers. The second study built upon the knowledge that the melt layer was critical in the functionality of ECPs and explored the utilization of ECGPs which combined a viscous liquid polymer fuel in which solid oxidizers were dissolved. The ECGPs used in this study readily decomposed and ignited when a voltage potential was applied. The composition of the ECGPs along with the magnitude of the voltage being applied greatly impacted the ignition delay and overall burning characteristics of the propellants. This study illustrated the potential to create ECPs that enable increased control over the burning characteristics compared to conventional propellants. The third study utilized a solid polymer binder along with the solid oxidizers to create ECSPs that would readily decompose and ignite when a voltage potential was applied. Compositional changes in the propellant along with the magnitude of the applied voltage potential were observed to impact the regression rate of the ECSPs utilized in this study. The electrochemical decomposition characteristics of the ECSPs were explored to better characterize the contribution of the electrochemical reactions and how they differ from the more conventional thermochemical decomposition. The fourth and final study builds upon the prior ECSP study, but now experiments utilize compositions with electrically conductive additives to increase the responsiveness of the ECSPs to the applied voltage. This enabled the creation of ECSPs which ignite much more readily and with a higher degree of consistency. Experiments were also conducted at elevated pressures to analyze the combined impact that voltage and pressure play on the regression rate of the ECSPs. / Doctor of Philosophy / Solid rockets have many applications in both the civilian and defense industries due to their relatively low costs and long-term storage capabilities. However, traditional solid rockets have a limited degree of control as a result of the fuel and oxidizer being combined in the propellant and the combustion of the propellant being self-sustaining. The ability to change the thrust of the solid rocket motor on demand is something not currently possible without greatly increasing the complexity of the rocket motor, and even then the thrust control is limited. The addition of a simple method to vary the thrust of the rocket motor would drastically improve the functional capabilities and safety of the rocket. The method explored in this study to enable the creation of controllable solid rockets is through the use of electrically controllable propellants. These are propellants whose burning characteristics can be modified when subjected to an electric field. The work outlined in this dissertation develops a fundamental understanding of the methods to create electrically controllable solid and gel propellants. The electrically controllable propellants in this study demonstrated the capability to have their burning rate greatly increase or decrease by increasing or decreasing the voltage being applied to them. In addition to changing the burning rate, several compositions developed in this study were able to have their burning extinguished by removing the voltage and reignited by reapplying the voltage. These capabilities and the fundamentals behind their development enable the creation of much more functional rocket motors that overcome the limitations of current systems.

need OCR / Master of Science

Thesis (M.S.)--Auburn University, 2006. / Abstract. Vita. Includes bibliographical references.

Thesis (M.S.)--Florida State University, 2004. / Advisor: Dr. Steven Van Sciver, Florida State University, College of Engineering, Department of Mechanical Engineering. Title and description from dissertation home page (viewed Sept. 23, 2004). Includes bibliographical references.

M.S.

Electrically controllable solid propellants are an area of interest as a viable solution to the lack of throttle-ability in solid propellant rocket motors. Existing studies have focused on propellants compositions using hydroxyl-ammonium nitrate, ammonium nitrate, or lithium perchlorate as oxidizers. Additionally, the thermochemical and electrochemical reaction mechanisms have not yet been fully defined. The research in this thesis explores the nitrate and perchlorate oxidizer families to compare their cation-anion relationships. Using these oxidizers, pseudo electrically controllable solid propellant compositions were created with the addition of multi-wall carbon nanotubes to enhance ohmic heating capabilities. These additives were selected based on theory that with a non-complexing polymer, an oxidizer melt layer is required for ions to dissociate and electrically controlled ignition to occur. Using an applied voltage, ignition delay and current draw experiments were performed to expand on prior findings that ignition delay follows oxidizer melt temperature while mobility is associated with the size of the ionic radii. Additionally, neat oxidizer pellets were electrically decomposed to determine their linear regression rate. These results help to characterize the mechanism of reaction. This advances the knowledge of oxidizers in electrically controllable applications. / Master of Science / Solid propellant rocket motors have been extensively studied and used in both space and military applications because they do not use air as the source of oxygen. Their main limitation is the lack of throttle-ability, or inability to control propellant burning. This is because solid propellants, which are generally composed of an ionic oxidizer salt, a polymer fuel, and additives, are pre-combined and stored within the rocket motor. An emerging viable solution to this limitation is electrically controllable solid propellants. With an applied voltage, the oxidizer is heated and melts, allowing ions to dissociate and current to flow between electrodes. This reaction can then be controlled by turning the power supply on and off. Cations, or ions which have a net positive charge, move to the negatively charged cathode while anions, which have a net negative charge, move to the negatively charged anode. The research in this thesis explores different cation-anion oxidizer pairings using both a propellant composition and as a pure oxidizer under an applied voltage. The results help to characterize the mechanism of reaction of each oxidizer in an electrically controllable context and determine their effectiveness in these propellant applications.