Theses and Dissertations at Montana State University (MSU)
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Item Static and dynamic behavior of stress coated membranes(Montana State University - Bozeman, College of Engineering, 2006) Nandurkar, Kuldeep Pandurang; Chairperson, Graduate Committee: Christopher H. M. JenkinsLarge space mirrors need to be made of ultra-lightweight materials (membranes) that have very low densities and high flexibility (compliance) for packaging. A coating application necessary for optical reflectivity may also impart to these ultra-lightweight materials a desired shape and to help maintain that shape in the harsh environment of space. When a coating is applied on the membrane substrate, stresses develop in the coating due to atomistic processes. These stresses are fundamental to the final shape of the substrate. Coatings applied to the substrate in order to maintain a particular shape are known as the 'stress coating prescription'. As there is no way one could directly measure stresses in the coatings experimentally, in this work it will be explained how finite element analysis (FEA) was used in estimating stresses in the coatings. This work mainly comprises static pressuredeflection tests (bulge tests) on the coated and uncoated membranes, and a comparison of the experimental results to FEA findings in order to estimate the stresses in the coatings. Before FEA results are matched with the experimental results, an analytical solution to the problem in hand will be derived. Uncertainties due to variation in coating thicknesses and difficulties in coating process have led to various uncertainties in this work, and these uncertainties are also discussed. The ability to use changes in vibration frequency as a measure of coating stress is also investigated.Item Investigation of membrane tearing characterization and healing(Montana State University - Bozeman, College of Engineering, 2011) Zignego, Donald Lee; Chairperson, Graduate Committee: Christopher H. M. JenkinsAs man's curiosity for deep space exploration increases, so does the demand for long duration space systems. To be able to explore deeper into space, a system is required in which little or no fuel is required for propulsion. Solar sails met this challenge by using solar photon momentum exchange for propulsion. Solar sails are large gossamer structures spanning as long as three football fields in width and length, but only microns in thickness. The main photon catching structure is constructed of thin polymeric membranes, which are quite susceptible to damage. Other applications for these polymeric membranes include flex circuits, and thermal control membranes. The tearing behaviors of these materials are vital in the design of these structures. In this study, the tear behaviors of two popular thin polymeric materials used in the space industry are explored; biaxially-oriented polyethylene terephthalate (Mylar) and Kapton. Tearing properties for the Mylar were experimentally determined using essential work of fracture methodology. Experiments were performed on DENT specimens with varying ligament lengths, and on three different thicknesses of Mylar: 25.4 micron (1 mil), 50.8 micron (2 mil), and 76.2 micron (3 mil). Specific essential work of fracture values were determined to be 37.027 kJ/m ², 36.974 kJ/m ², 36.853 kJ/m ² for the 25.4 micron, 50.8 micron, and 76.2 micron thick Mylar specimens, respectively. The specific essential work of fracture values were nearly identical for the three separate thicknesses, and therefore can be concluded that it is indeed a material property of the Mylar itself. Using biology as inspiration, the possibilities of self-healing in both the Mylar and Kapton are also analyzed. Analysis of the possibilities of self-healing was studied using an ultrasonic transducer. Specimens with an initial crack were created and strain or fracture energy values computed with and without healing. The Mylar's ability to resist tearing increased as much as 1300% in the healed specimens, and likewise as much as 950% increase for the Kapton. Tear tests were also performed at sub-zero temperatures to analyze the effects at space equivalent temperatures.