Inherent stress concentration in patterned glass

Abstract

Patterned glass features textures that generate a non-flat surface and, to some extent, blur its transparency. Patterned glass is roll-casted, and it is when it gets squeezed in the casting rolls that the pattern gets imprinted. There exist a wide variety of commercially available patterns which vary in geometry and depth of imprint. As the patterns involve a surface modification, it is expected that the strength would differ from annealed flat glass. Design standards acknowledge this by proposing a surface profile factor when calculating the design strength from the characteristic value. However, all different patterns are qualified by the same surface factor. There is not enough evidence that one surface profile factor would satisfactorily include all different available patterns. Therefore, in this study, the soundness of this approach is challenged by investigating 4 different patterns. The geometry of each pattern was measured directly. Following, destructive 4-point bending tests were performed to determine the characteristic bending strength. In parallel, a finite element analysis on the actual geometry of the pattern was made in order to identify the pattern’s induced stress concentration. It was found that the current design standards fail to account for the variability in performance of commercially available patterned glass. The main factors affecting patterned glass strength are the geometry of the pattern, inducing stress concentration and the effective thickness resisting the loads. The results of this study confirmed that the characteristic bending strength of patterned glass varies widely from one pattern to another. This suggests that the standards ought to acknowledge the need to expand the surface profile factors linked to patterned glass to more than one.