Theses and Dissertations at Montana State University (MSU)
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Item Temperature dependence study of FEP Teflon and Kapton H erosion in a simulated LEO atomic-oxygen environment(Montana State University - Bozeman, College of Letters & Science, 2004) Buczala, Deanna Marie; Chairperson, Graduate Committee: Timothy K. MintonPolymer degradation occurs as a result of exposure to atomic oxygen in low Earth orbit (LEO). The damaging effects of the space environment on materials have prompted the simulation of LEO to study polymer erosion. The laboratory setting provides a method of evaluating material erosion by atomic oxygen attack in an affordable and time-efficient manner: This study investigates the temperature dependence of the erosion of Kapton H and FEP Teflon when exposed to hyperthermal 5 eV atomic oxygen beam. This study extends earlier investigations of the temperature dependence of Kapton H erosion and helps unveil the reaction mechanisms that lead to erosion of Kapton H and FEP Teflon in LEO. The investigations reported in thesis relied on the use of Kapton H to calibrate the atomic oxygen exposures, so an additional study was performed to verify the linear dependence of Kapton H erosion. Surface characterizations of the eroded samples in this study were performed by surface profilometry and atomic force microscopy. The Kapton H erosion yield grew exponentially with temperature in the range 298 K to 573 K. The temperature dependence of Kapton H erosion could be explained by temperature-dependent and -independent mechanisms. The temperature-independent mechanism dominates at lower temperatures and involves the direct reaction of O atoms with the polymer surface, with an activation energy that is easily overcome by the O-atom collision energy with the surface. The temperature-dependent mechanism becomes important at higher temperatures. Apparently, at high surface temperatures, material is removed through reactions that occur in thermal equilibrium with the surface and have an effective activation energy of 0.31 eV. From 298 K to 423 K the erosion yield of FEP Teflon grew exponentially. The nonlinear Arrhenius behavior suggested a two-term mechanism analogous to that used to describe the temperature dependent erosion of Kapton H. At temperatures lower than 373 K the temperature-independent mechanism dominates the material erosion and at higher temperatures, a mechanism becomes important that occurs in thermal equilibrium with the surface and has an activation energy of 0.24 eV.Item Ultrasonic repair of polymers : fundamentals and modeling for self-healing(Montana State University - Bozeman, College of Engineering, 2009) Sarrazin, John Cody; Chairperson, Graduate Committee: Christopher H. M. JenkinsAlthough current research focuses within self-healing materials are advancing, most pursuits are passive systems, unlike the active biological systems they aim to mimic. In this paper an active method utilizing ultrasonic energy is explored. Ultrasonic inspection has served as an effective means toward nondestructive damage detection for decades. Also, a recent method called time-reversed acoustics allows for the redirection of acoustic waves back towards the source. The active healing method utilizes ultrasonic nondestructive damage detection to locate and categorize damage, and then provide coordinates for the redirection of an amplified ultrasonic energy to heal the material. First, the temperature change as a result of ultrasonic treatment was measured, and then a variety of dogbone samples were tensile tested, including virgin samples, damaged samples, and damaged but ultrasonically treated dogbone samples. The ultrasonic treatment increased the ultimate stress of the ultrasonically treated dogbone samples, which was a result of increased crystallinity. The crystallinity was confirmed with differential thermal analyses. The ultrasonic influence of material temperature and effect of ultrasonically treated damaged samples versus just untreated damaged samples were replicated with finite element models as a means to predict future application and use.Item Molecular beam studies of hyperthermal atomic oxygen and argon interactions with polymer surfaces and gas-phase molecules(Montana State University - Bozeman, College of Letters & Science, 2007) Brunsvold, Amy Leigh; Chairperson, Graduate Committee: Timothy K. Minton; Robert Szilagyi (co-chair)O atoms and N2 molecules in the outer atmosphere of the Earth collide with spacecraft surfaces and various gases that are released from space vehicles. The high relative velocity of the collisions promotes high reaction probability and large energy transfers, leading to materials degradation and chemiluminescent reactions, which may interfere with the mission of the vehicle. The work presented in this thesis uses sophisticated molecular beam and surface science techniques to study materials degradation and individual reactive and inelastic collisions in an effort to understand the complex chemistry and physics that are characteristic of space vehicle interactions with Earth's upper atmosphere. A new space-durable polymer, polyhedral oligomeric silsesquioxane polyimide, has been identified. When exposed to atomic oxygen, this polymer forms a protective SiO2 layer on its surface. Beam-surface scattering experiments showed that collision-induced dissociation becomes an important gassurface process when the translational energy of the incident atom or molecule is greater than 8 eV.