Mechanical Reliability Of 8M Class Ule Glass Telescope Blanks During Manufacturing

The manufacture of 8m class ULE glass telescope mirror blanks involves multiple steps, each of which can induce both stresses and flaws. To ensure the mechanical reliability of such large mirror blanks, both during and post-manufacturing, extreme care is required in the various process steps (including handling, grinding, finishing and transportation) so as to limit the stress and flaw severity to below the threshold level for the specific surface finish. This paper examines the critical stress/time histories the blanks experience during manufacturing and their ability to initiate slow crack growth from grinding flaws. Two different surface finishes are characterized with respect to strength, flaw and fatigue behaviour.