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Characterizing the Oblique Incidence Response and Noise Reduction Techniques for Luminescent Photoelastic Coatings

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Characterizing the Oblique Incidence Response and Noise Reduction Techniques for Luminescent Photoelastic Coatings CHARACTERIZING THE OBLIQUE INCIDENCE RESPONSE AND NOISE REDUCTION TECHNIQUES FOR LUMINESCENT PHOTOELASTIC COATINGS By JOHN C. NICOLOSI JR. A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2004 Copyright 2004 by John C. Nicolosi Jr. ACKNOWLEDGMENTS I would like to thank my advisors, Dr. Peter Ifju and Dr. Paul Hubner, for all of their support and guidance. I would also like to thank Dr. Leishan Chen for all of the assistance he provided me, and Dr. Bhavani Sankar for his valuable advice. I would also like to thank my family members for all of the support they have given me over the years. iii TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................................................................................. iii LIST OF FIGURES .......................................................................................................... vii ABSTRACT....................................................................................................................... ix CHAPTER 1 INTRODUCTION ........................................................................................................1 1.1 Historical Background of Photoelasticity..............................................................1 1.2 Research History at the University of Florida .......................................................3 1.3 Research Objectives...............................................................................................4 2 ELEMENTARY PHOTOELASTICITY......................................................................6 2.1 Behavior of Light...................................................................................................6 2.2 Polarized Light and Linear Polarizers ...................................................................7 2.3 Retardation Plates ..................................................................................................7 2.4 Polariscopes ...........................................................................................................9 2.4.1 Plane Polariscope.........................................................................................9 2.4.2 Circular Polariscope ..................................................................................11 2.4.3 Reflection Polariscope...............................................................................12 2.5 Stress Optic Law..................................................................................................13 3 LUMINESCENT PHOTOELASTIC COATINGS ....................................................17 3.1 Introduction..........................................................................................................17 3.2 Excitation and Imaging Equipment .....................................................................18 3.3 Coating Formulation............................................................................................19 3.3.1 Dual-Layer Coating Formulation ..............................................................19 3.3.2 Single-Layer Coating Formulation............................................................21 3.4 Theory of Operation ............................................................................................22 3.4.1 Dual-Layer Coating...................................................................................23 3.4.2 Single-Layer Coating.................................................................................29 3.5 Image Acquisition and Data Processing..............................................................31 iv 4 OBLIQUE INCIDENCE RESPONSE OF PHOTOELASTIC COATINGS .............33 4.1 Introduction..........................................................................................................33 4.2 Principle of Operation..........................................................................................34 4.3 Experiments .........................................................................................................41 4.4 Results and Discussion ........................................................................................43 4.4.1 Optical Fresnel Response ..........................................................................43 4.4.2 Emission Strength......................................................................................45 5 NOISE REDUCTION TECHNIQUES FOR THE LPC METHOD ..........................47 5.1 Introduction..........................................................................................................47 5.2 Experimental Technique and Noise Determination.............................................48 5.3 Testing Conditions...............................................................................................50 5.4 Preliminary Results and Discussion ....................................................................51 5.5 Results and Discussion ........................................................................................57 5.6 Conclusions..........................................................................................................60 6 FINAL RESEARCH CONCLUSIONS......................................................................61 6.1 Oblique Incidence Response of Photoelastic Coatings .......................................61 6.1.1 Optical Fresnel Response ..........................................................................61 6.1.2 Emission Strength on Oblique Surfaces....................................................61 6.2 Noise Reduction Techniques ...............................................................................62 APPENDIX: NOMENCLATURE...................................................................................63 LIST OF REFERENCES...................................................................................................68 BIOGRAPHICAL SKETCH .............................................................................................70 v LIST OF TABLES Table page 2-1 Different circular polariscope arrangements ............................................................12 5-1 Testing conditions ....................................................................................................50 5-2 Percent noise reduction ............................................................................................59 5-3 Noise reduction for each intensity count level .........................................................60 vi LIST OF FIGURES Figure page 2-1 Plane polariscope......................................................................................................10 2-2 Circular polariscope .................................................................................................11 2-3 Reflection polariscope..............................................................................................13 3-1 Strain measurement system......................................................................................19 3-2 Excitation and emission for a luminescent coating..................................................23 3-3 Plane polarized light entering the quarter wave plate ..............................................24 3-4 Circularly polarized light entering the stressed coating...........................................25 3-5 Elliptically polarized emission entering the analyzer ..............................................26 3-6 Intensity response as a function of analyzer angle...................................................29 4-1 Apparent strain observed on an unloaded cylindrical specimen ..............................34 4-2 Light vector obliquely striking the coating ..............................................................35 4-3 Fresnel coefficients as a function of surface inclination..........................................37 4-4 Excitation striking the coating at an arbitrary polarization plane ............................38 4-5 Plane of incidence ....................................................................................................39 4-6 Oblique excitation and emission of a coating ..........................................................39 4-7 Emission traveling through the analyzer..................................................................40 4-8 Experimental setup for measuring OFR...................................................................42 4-9 Experimental setup for measuring emission strength ..............................................43 4-10 OFR with respect to surface inclination...................................................................44 4-11 Normalized intensity with respect to surface inclination.........................................46 vii 5-1 Four-point bending apparatus...................................................................................49 5-2 Plot of OSR for experiments with different imaging conditions .............................50 5-3 OSR standard deviation as a function of the number of images ..............................52 5-4 OSR standard deviation as a function of the intensity count ...................................52 5-5 Intensity drift of the coating emission over a 90 minute time period ......................54 5-6 Intensity drift measurement system..........................................................................55 5-7 Intensity drift for the LEDs over a 90 minute time period.......................................56
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