Structural Strength of Heat-Strengthened Glass

Abstract

The paper considers the determining factors in the structural strength of heat-strengthened glass. The values of residual stress were obtained experimentally at different points on the surface of specimens of heat-strengthened, HS-glass and fully tempered, FT-glass using a SCALP-4 laser scanning polarimeter. The distribution of residual stresses is determined over the area of specimens. It is found that the standard methods of in-process control of the degree of strengthening that involve the determination of compressive stresses only at several points, give a fairly rough estimate of the average level of induced residual stresses in glass structural elements and do not determine their real significance near the fracture origins. The necessity of using the methods of more comprehensive in-process control of residual stresses is justified in order to obtain data on their statistical distribution and optimize the heat strengthening modes according to special requirements to building glazing and new engineering products. As shown by the analysis of the investigations dealing with determination of "the strengthening effect" during heat treatment of glass, it does not exceed the level of residual stresses. Due to the statistical nature of glass strength and residual stresses, the determination of the empirical coefficient, which traditionally considers the increasing contribution of residual stresses to the strength value of heat-strengthened glass, presents great difficulties. Based on the sampling of the bending strength values for glass in the initial, as-received state and after heat strengthening using the mathematical statistics methods, the calculated distribution of stress values that characterize the strengthening effect is determined. The influence of the combination of heat strengthening and etching on the strength characteristics of glass is investigated. It is found that the enhancement of the strength of glass and glass products strengthened using combined techniques is accompanied by a significant increase in the scatter of the tensile strength values, and the influence of the combined treatment on the tensile strength of glass is not additive.

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