21 August 2009 Proof load testing of lightweight silicon carbide mirror substrates
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Abstract
An important space application for structural ceramics is the large (~1m diameter) silicon carbide mirrors used in telescopes. However, all ceramics have two drawbacks. First, ceramics are brittle and have a low resistance to catastrophic flaw propagation during service. Second, ceramics have a population of preexisting flaws produced during manufacturing. The most modern and successful theory of fracture control is "defect tolerant design", which recognizes that engineering structures are inherently flawed and which is used to predict the structure's service life. As part of defect tolerant design, the size of the inherent flaws is controlled by combining nondestructive evaluation (which has a threshold for the smallest flaw that can be reliably identified) and proof testing (which provides an independent measurement of the largest preexisting flaw). We are developing a novel proof test that is specialized for a lightweighted ceramic mirror. The most promising loading method is identified and an experimental implementation has been proposed and designed for future development.
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Michael J. O'Brien, Aldrich De La Cruz, Ching-Yao Tang, Iwona A. Palusinski, "Proof load testing of lightweight silicon carbide mirror substrates", Proc. SPIE 7425, Optical Materials and Structures Technologies IV, 74250A (21 August 2009); doi: 10.1117/12.826920; https://doi.org/10.1117/12.826920
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