Stress Rupture Considerations in the Design of Large Aperture, Low Mass Composite Vacuum Windows

Large vacuum vessels are often employed in High Energy and Nuclear Physics experiments to provide a volume for particle traverse in the absence of air molecules. The ends of these vessels generally have a large aperture which is closed with a thin membrane known as a vacuum window. To minimize the vacuum window mass, composites of Kevlar and Mylar have been used in window construction. Historically, these windows have been designed based on the ultimate tensile strength of the materials, however, following the costly failure of a 193 cm x 86 cm window, other design methods emerged. This paper reviews the history of window design and describes the window failure and possible causes. It further presents the phenomenon of stress rupture and describes the analytical and experimental work carried out to improve composite window design methods.