Static and dynamic behavior of stress coated membranes

Abstract

Large 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.