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Dynamic Fatigue of ULE GlassUltra Low Expansion (ULE) glass is used in a number of applications which require a low thermal expansion coefficient. One such application is telescope mirror elements. An allowable stress can be calculated for this material based upon modulus of rupture data; however, this does not take into account the problem of delayed failure. Delayed failure, due to stress corrosion can significantly shorten the lifetime of a glass article. Knowledge of the factors governing the rate of subcritical flaw growth in a given environment enables the development of relations between lifetime, applied stress and failure probability for the material under study. Dynamic fatigue is one method of obtaining the necessary information to develop these relationships. In this study, the dynamic fatigue method was used to construct time-to-failure diagrams for both 230/270 ground and optically polished samples. The grinding and polishing process reduces the surface flaw size and subsurface damage, and relieves residual stress by removing materials with successively smaller grinding media. This resulted in an increase in the strength of the optic during the grinding and polishing sequence. There was also an increase in the lifetime due to grinding and polishing. It was found that using the fatigue parameters determined from the 230/270 grit surface are not significantly different from the optically polished values. Although the lower bound of the polished samples is more conservative, neither time-to-failure curves lie beyond the upper or lower bound of the confidence limits. Therefore, designers preferring conservative limits could use samples without residual stress present (polished samples) to determine the fatigue parameters and inert Weibull parameters from samples with the service condition surface, to determine time-to-failure of the optical element.
Document ID
20010020947
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Tucker, Dennis S.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Nettles, Alan T.
(NASA Marshall Space Flight Center Huntsville, AL United States)
Brantley, Lott W.
Date Acquired
August 20, 2013
Publication Date
January 1, 2001
Subject Category
Nonmetallic Materials
Meeting Information
Meeting: International Congress on Glass
Location: Edinburgh
Country: United Kingdom
Start Date: July 2, 2001
End Date: July 6, 2001
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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