A Concept for Measuring and Evaluating Optical Anisotropy Effects in Tempered Architectural Glass (Mechanik, Werkstoffe und Konstruktion im Bauwesen)

Optical anisotropy effects can occur in building envelopes made of tempered glass. The visual effect has been neglected in the evaluation of the building product and increasingly leads to disputes between the parties involved. This thesis extends the state of knowledge on the cause and perception of optical anisotropic effects and presents a concept for measuring and evaluating them in flat monolithic tempered architectural glass. Initially, an overview and description of current photoelastic measurement methods are given, and the accuracy of the used measurement setups is verified for the first time. The experimental basis for the concept is formed by extensive full-field retardation measurements in the laboratory and field studies of the maximum visibility of the anisotropy effects in an outdoor test rig with accompanying polarization measurements of the sky. Various glass types, geometries, and tempering levels are selected based on typically used products, and their influence on the resulting retardation image is investigated. Determining a correlation of the retardation images with the reflection images of selected test specimens in the outdoor test rig complements the experiments. Based on this, digital evaluation methods are presented, further developed, and applied to the measured retardation images. From the critical analysis of these results, limit values for different anisotropy quality classes are derived, and the concept is complemented. With the implementation of the evaluation methods and the limit values in commercial anisotropy scanners, the quality of each glass pane can be determined directly after tempering in the future. By choosing the highest quality class A, it will be possible in the future to significantly reduce anisotropy effects in constructions made of tempered glass panes. Danksagung Abstract Zusammenfassung Contents Glossaries Abbreviations Symbols 1 Introduction 1.1 Motivation 1.2 State of the Art Optical Anisotropy in tempered Architecture Glass Photoelastic Full-Field Methods Evaluation Methods and Quality Assessment 1.3 Structure 1.4 Achievements of this Work 1.5 List of own Publications on this Ph.D. Thesis 2 Theoretical Principles 2.1 Basics of Linear Elasticity 2.2 Nature of Polarized Light 2.2.1 Nature of Light 2.2.2 Types of Polarized Light 2.2.3 Stokes Parameters 2.3 Polarization of Light 2.3.1 General 2.3.2 Polarization by Scattering 2.3.3 Polarization by Reflection 2.4 Brewster’s Angle 2.5 Passage of Light through Media 2.6 Basics of Photoelasticity 2.6.1 General 2.6.2 Artificial Birefringence 2.6.3 Stress-Optical Law 2.6.4 Plane and Circular Polariscope 3 Glass and their Photoelastic Behaviour 3.1 General 3.2 Residual Stresses 3.3 Photoelastic Behaviour 3.4 Visual Perception of Anisotropy Effects 4 Photoelastic Methods for Measuring Anisotropy Effects 4.1 General 4.2 Scattered Light Method 4.3 RGB Photoelasticity 4.4 Half-Wavelength and Multi-Wavelength Photoelasticity 4.5 Phase-Shifting Methods 4.6 PSM for Skylight Observation 5 Photoelastic Measurements on Tempered Flat Glass 5.1 Validation Experiments 5.1.1 Accuracy and Precision 5.1.2 Temperature Dependency 5.2 Specimen 5.3 Influence from Geometry Parameters 5.3.1 Thickness 5.3.2 Size 5.3.3 Holes and Cut Outs 5.4 Influence from Glass-Specific Parameters 5.4.1 Type of Glass 5.4.2 Tempering Level 5.5 Influence from Furnace Parameter 5.5.1 Glass Position 5.5.2 Glass Orientation 6 Experimental Field Studies on Tempered Flat Glass 6.1 Design and Construction the Test Facility 6.2 Setup and Specimen 6.3 Influence from the Building Environment and Use 6.3.1 Background Lighting 6.3.2 Reflection Disturbances 6.4 Influence from Viewing 6.4.1 Viewing Angle 6.4.2 Viewing Position 6.4.3 Viewing Direction and Sun Position 6.5 Influence from Skylight Polarization 6.6 Visual Intensity of Anisotropy Effects 6.7 Correlation between Measurement and Observation 7 Methods for evaluating Anisotropy Effects in Glass 7.1 Evaluation Zone 7.2 Statistical Method Quantile Value 7.3 Threshold Method Isotropy value 7.4 Texture Analysis 7.5 Method and Combined Textural Feature CCP 8 Evaluation and Concept 8.1 Assessment of Evaluation Methods Iso75 x95 CCP 8.2 Anisotropy Quality of Tempered Flat Glass 8.3 Evaluation Concept 8.3.1 General 8.3.2 Definition of the Quality Classes 8.3.3 Requirements for the Measurement 8.3.4 Procedure of the Evaluation Concept 8.4 Discussion 9 Summary and further Research Further Research References Own Publications Standards Bibliography Appendix A Experiments Results Appendix B Field Study Test Results