A refined approach to glass strength forecasting

As aerospace instruments become increasingly more precise and elaborate, the mechanical limits of glass components can become key design constraints. The probabilistic fracture behavior of glass is complex, and dependent on many variables. Typically, to avoid such complexity, overly simplistic strength estimates are employed that fail to take advantage of well understood glass properties. Such a simple approach requires the use of conservative strength values that encompass the weakest possible cases. This results in optic designs that, while robust, are unnecessarily massive and display excess wavefront error and instability, threatening mission viability. This paper presents a complete approach to glass strength analysis, as compiled from existing literature, incorporating both the principles of fracture mechanics and details of the specific design in question. The mathematical formulae needed to accurately predict failure rates of individual glass components using laboratory data are presented. The result is a method of analysis that accurately represents our understanding of fracture and uses known information about the specific mechanical design. By replacing conservative strength values with detailed, application specific survival forecasts, engineers gain greater design freedom. Optic mass and performance can be more effectively optimized, improving instrument performance.