The development of high-energy lasers has focused attention on the need to assess the mechanical strength of optical components made of fused silica (Si0₂). The strength of this material is known to be highly dependent on the stressed area and the surface finish, but has not yet been properly characterized in the published literature. Recently, Detrio and collaborators at the University of Dayton Research Institute (UDRI) performed extensive ring-on-ring flexural strength measurements on fused Si0₂ specimens ranging in size from 1 to 9 inches in diameter and of widely differing surface quality. In this contribution, we report on a Weibull statistical analysis of the UDRI data-an analysis based on the procedure outlined in Proc. SPIE 4375, 241 (2001). We demonstrate that: (a) a two-parameter Weibull model, including the area-scaling principle, applies; (b) the shape parameter (m is asymptotically equal to 10) is essentially independent of the stressed area as well as the surface finish; (c) the characteristic strength (1-cm2 uniformly stressed area) obeys a linear law, σ_C(in MPa) is asymptotically equal to 160 - 2.83x PBS®(in ppm/sr), where PBS® measures the surface/subsurface "damage." In this light, we evaluate the cumulative failure probability of optically polished and superpolished fused Si0₂ windows as a function of the biaxial tensile stress, for uniformly stressed areas ranging from 0.3 to 100 cm².

Date Published: 27 April 2009
PDF: 13 pages
Proc. SPIE 7302, Window and Dome Technologies and Materials XI, 730210 (27 April 2009); doi: 10.1117/12.817714

Published in SPIE Proceedings Vol. 7302:
Window and Dome Technologies and Materials XI
Randal W. Tustison, Editor(s)