Clay, Stephen B.2014-03-142014-03-141995-08-05etd-06302009-040551http://hdl.handle.net/10919/43520Polycarbonate is commonly used in windshield-canopy structures for military aircraft since it is transparent and possesses excellent toughness characteristics at temperatures well below its glass transition region. It is believed that ultraviolet radiation present in sunlight causes polycarbonate to degrade. This is a serious problem since the majority of the military aircraft in the United States spend their entire service lives outdoors. This study was conducted in connection with the United States Air Force to analyze the photodegradation of polycarbonate caused by ultraviolet radiation. First, aircraft-grade polycarbonate plates were exposed to continuous ultraviolet light in a QUV laboratory weathering chamber for durations of three, seven, ten, and twenty weeks. The material changes were then characterized by several mechanical, viscoelastic, and chemical experiments. The feasibility and sensitivity of each test method was determined, and the amount of polymer degradation was measured. The results from uniaxial tension and dynamic mechanical (DMA) tests indicated a significant reduction in strength and ductility and an increase in stiffness. Polycarbonate also experienced a decrease in impact resistance of approximately 42% at intermediate exposure levels followed by a slight increase for the longest exposure durations. Micro-indentation experiments showed about a 27% increase in hardness for surfaces directly exposed to ultraviolet light while the hardness of the surfaces indirectly exposed was insensitive to ultraviolet exposure. A 30% weight loss was also seen after only seven weeks of exposure. A few conclusions were made about the causes of photodegradation along with recommendations for future work in the area of ultraviolet exposure of thermoplastic materials.xiii, 118 leavesBTDapplication/pdfenIn Copyrightmilitary aircraftLD5655.V855 1995.C539Thesishttp://scholar.lib.vt.edu/theses/available/etd-06302009-040551/