Photoelastic measurements and evaluation methods for edge stress in architectural tempered glass

Abstract The mechanical and safety-relevant properties of tempered architectural glass are tested using destructive bending strength and fracture pattern tests. The edge stress provides essential information on the quality of the tempering process and can, therefore, be used to ensure quality characteristics. The paper shows that the current valid evaluation method for edge stress, according to ASTM C 1279-09, is unsuitable for architectural glass. The chamfer which is required for tempered glass by the European standards for tempered glass prevents the direct measurement of retardation and edge stress. Therefore, an extrapolation of the retardation curve towards the edge is necessary. The paper compares fitting functions of different polynomial degrees to determine and assess the edge stress. The objective is to develop a proper evaluation method of edge stress for quality control in the latest inline measurement systems which can be applied to replace operator-dependent measuring devices. The study presents appropriate methods and evaluates them through experimental investigations using the phase shift technique and multiple wavelength photoelasticity.