Natural Hazards are a risk to buried gas pipeline infrastructure, but these risks are difficult to assess and quantify. This can often lead to the risks not being properly identified by pipeline owners. The risk to pipelines within landslide areas are particularly difficult to assess given the complex nature of landslide movements and the soil-pipeline interaction mechanisms imposing loads on a pipeline. This thesis research examines the relationship between ground movements and strains/stresses in buried pipelines through field measured ground movements and in-situ measured pipe strains/stresses. The pipe stresses and strains are then used to estimate probability of pipeline failure and risk based on RBDA limit states approaches. Within Manitoba Hydro’s pipeline network, three at-risk landslide areas (riverbank and deep river valleys) were selected for detailed studies. A field investigation and monitoring program was undertaken to assess possible sources of load and stresses on pipelines. Soil, ground, and pipe instrumentation were installed at the sites and monitored over a four year period. Monitoring results identified soil near the pipeline does not freeze, and ground movements at valley sites are slow moving (<50 mm/year) landslides. The monitoring results also showed pipe stresses and behaviour were affected by backfilling, changes in river levels, thermal affects, soil-pipe relaxation, and ground movements. Pipe push tests were conducted in conjunction with FEM modelling to examine pipe adhesion and to possible explain the pipe behaviour observed. Several ultimate and serviceability limit states pipe failure modes were assessed using the measured pipe stresses. Statistical analysis was undertaken to calculate the probability of pipeline failure for the various limit states failure modes and compared against limit states targets for several scenarios (backfill loads, initial stress-state of the pipeline, other pipelines within Manitoba Hydro network). Overall, the probability of failure estimates were generally insignificant or low due to a postulated soil-pipe relaxation mechanism which is causing a repeated release in longitudinal pipe stresses as the landslide continues to accumulate ongoing ground movements. Three mechanisms are presented and discussed. The statistical analysis indicate pipelines within Manitoba Hydro’s network may exceed limit states targets for yielding and local buckling depending on the loading scenario and the class of the pipeline within the landslide area. The outcome of the research was used to develop a risk managements system to examine geotechnical hazards within Manitoba Hydro’s pipeline network. Specifically, risks associated with ground movements along natural slopes and at river crossings are examined within the system. / October 2016

This thesis analyzes and solves the problems of monitoring of constructions strains (small resistance changes) in a number of points of the structure. The essence of investigated systems is test of the strain gauges small resistance changes proportional to displacement or strain and reaching only thousandths of parts of percent. The main objects of research is strain detection circuits working under automatic multipoint balanced Wheatstone bridge and the current balancing methods. The introduction reveals the importance of investigated problem, formulates the aim and tasks, introduces publications and presentations of the author’s and the structure of the dissertation. The first chapter is a review of literature. It analyzes practical use of strain measurement methods, their advantages and disadvantages, opportunities to use these methods in automated systems. The chapter ends with formulated conclusions. The second section presents balanced methods of the strain monitoring. Analysis of balanced Wheatstone bridge device is made. New strain monitoring device by balancing currents are proposed and investigated. There are two possible ways: with two current sources and one current source. The third and fourth sections provide results of computer simulation and experimental models. The proposed devices of balancing currents has been modeled and tested in practice. Stability of the devices was tested and their work simulating in real conditions. Conclusions, references and the... [to full text] / Disertacijoje nagrinėjamos ir sprendžiamos konstrukcijų deformacijų (varžų mažų pokyčių) nustatymo daugelyje konstrukcijos taškų problemos. Tiriamų sistemų funkcionavimo esmė yra įtempių jutiklių varžos mažų pokyčių proporcingų poslinkiui ar deformacijai ir siekiančių tik tūkstantąsias procento dalis nustatymas. Pagrindiniai tyrimo objektai yra automatinių daugiataškių balansuojamo Vitstono tiltelio ir srovių balansavimo metodais veikiantys deformacijų nustatymo grandynai. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas ir uždaviniai, pristatomi autoriaus pranešimai ir publikacijos, pateikiama disertacijos struktūra. Pirmajame skyriuje pateikta literatūros apžvalga. Jame analizuojami praktikoje naudojami deformacijų nustatymo metodai, pateikiami jų privalumai ir trūkumai, galimybės naudoti šiuos metodus automatizuotose sistemose. Antrajame skyriuje pateikti konstrukcijų deformacijų balansuojami nustatymo būdai. Yra atlikta balansuojamo Vitstono tiltelio metodo analizė. Pateiktas naujas deformacijų stebėjimo balansuojant sroves metodas ir atlikta jo analizė. Jame išskiriami du galimi būdai: su dviem srovės šaltiniais ir su vienu srovės šaltiniu. Trečiajame ir ketvirtajame skyriuose pateikti kompiuterinio modeliavimo ir eksperimentinių tyrimų rezultatai. Buvo sumodeliuotas ir praktiškai patikrintas pasiūlyto srovės balansavimo metodo praktinis veikimas. Patikrintas įrenginių stabilumas ir jų darbas imituojant realias sąlygas. Disertacijos... [toliau žr. visą tekstą]

Disertacijoje nagrinėjamos ir sprendžiamos konstrukcijų deformacijų (varžų mažų pokyčių) nustatymo daugelyje konstrukcijos taškų problemos. Tiriamų sistemų funkcionavimo esmė yra įtempių jutiklių varžos mažų pokyčių proporcingų poslinkiui ar deformacijai ir siekiančių tik tūkstantąsias procento dalis nustatymas. Pagrindiniai tyrimo objektai yra automatinių daugiataškių balansuojamo Vitstono tiltelio ir srovių balansavimo metodais veikiantys deformacijų nustatymo grandynai. Įvadiniame skyriuje nagrinėjamas problemos aktualumas, formuluojamas darbo tikslas ir uždaviniai, pristatomi autoriaus pranešimai ir publikacijos, pateikiama disertacijos struktūra. Pirmajame skyriuje pateikta literatūros apžvalga. Jame analizuojami praktikoje naudojami deformacijų nustatymo metodai, pateikiami jų privalumai ir trūkumai, galimybės naudoti šiuos metodus automatizuotose sistemose. Antrajame skyriuje pateikti konstrukcijų deformacijų balansuojami nustatymo būdai. Yra atlikta balansuojamo Vitstono tiltelio metodo analizė. Pateiktas naujas deformacijų stebėjimo balansuojant sroves metodas ir atlikta jo analizė. Jame išskiriami du galimi būdai: su dviem srovės šaltiniais ir su vienu srovės šaltiniu. Trečiajame ir ketvirtajame skyriuose pateikti kompiuterinio modeliavimo ir eksperimentinių tyrimų rezultatai. Buvo sumodeliuotas ir praktiškai patikrintas pasiūlyto srovės balansavimo metodo praktinis veikimas. Patikrintas įrenginių stabilumas ir jų darbas imituojant realias sąlygas. Disertacijos... [toliau žr. visą tekstą] / This thesis analyzes and solves the problems of monitoring of constructions strains (small resistance changes) in a number of points of the structure. The essence of investigated systems is test of the strain gauges small resistance changes proportional to displacement or strain and reaching only thousandths of parts of percent. The main objects of research is strain detection circuits working under automatic multipoint balanced Wheatstone bridge and the current balancing methods. The introduction reveals the importance of investigated problem, formulates the aim and tasks, introduces publications and presentations of the author’s and the structure of the dissertation. The first chapter is a review of literature. It analyzes practical use of strain measurement methods, their advantages and disadvantages, opportunities to use these methods in automated systems. The chapter ends with formulated conclusions. The second section presents balanced methods of the strain monitoring. Analysis of balanced Wheatstone bridge device is made. New strain monitoring device by balancing currents are proposed and investigated. There are two possible ways: with two current sources and one current source. The third and fourth sections provide results of computer simulation and experimental models. The proposed devices of balancing currents has been modeled and tested in practice. Stability of the devices was tested and their work simulating in real conditions. Conclusions, references and the... [to full text]

A fatigue test has been performed on 7075-T651 aluminum specimens which were bonded with polyimide coated optical fibers with discrete Bragg gratings. These fibers were bonded with AE-10 strain gage adhesive. The results indicate that lower strain amplitudes do not produce cause for concern, but that larger strain amplitudes (on the order of 3500 μ) may cause some sensors to become unreliable. The strain response of acrylate coated optical fiber strain sensors bonded to aluminum specimens with AE-10 and M-Bond 200 strain gage adhesives was investigated with both axial and cantilever beam tests. These results were compared to both the strain response of conventional strain gages and to model predictions. The results indicate that only about 82.6% of the strain in the specimen was transferred through the glue line and fiber coating into the fiber. Thus, multiplying by a strain transfer factor of approximately 1.21 was sufficient to correct the optical fiber strain output. This effect was found to be independent of the adhesive used and independent of the three-dimensional profile of the glue line used to attach the fiber. Finally, this effect did not depend on whether the fiber had a polyimide or an acrylate coating. Further investigation was conducted on the feasibility of using optical fiber strain sensors for monitoring subcritical damage (such as matrix cracks) in fiber reinforced composite materials. These results indicate that an array of optical fibers which monitor the strain profile on both sides of a composite panel may be sufficient for these purposes / Master of Science

In recent years, additive manufacturing (AM) has been one of the essential production techniques in the engineering community. Rapid integration of this technique drew a bead on the reliability of the microstructural and mechanical properties of engineering components. However, due to the nature of the layer-by-layer approach of AM, complex thermal gradients can cause inhomogeneous microstructure and significant residual stresses (RS). These, expectedly, can lead to a dramatic reduction in material performance. Therefore, especially for alloys like Ni-based Inconel 718 (IN718) used in critical applications, the characterization and later optimization of the DED process on material properties become essential. Nevertheless, empirical and conventional approaches are needed to improve, or new techniques should be introduced. In this regard, this study aims to understand better the evolution of the mechanical and microstructural properties of IN718 during and post-DED processes. For this purpose, an in-situ 2D neutron diffraction strain monitoring was carried out during the DED of IN718. The strain contributions originated from microstructural, thermal, and stress-based events during deposition and cooling periods at different positions concerning melt pool were investigated. Stabilization of different positions and processing regions on the sample as a function of the temperature profile, build height, and microstructural events are examined. Laboratory-scale microstructural studies were performed on wire-DED parts to observe the process parameter dependency of precipitation, composition, and morphology of microstructural constituents. Moreover, these findings were benchmarked with neutron powder diffraction measurements to relate the crystallographic behavior with macroscopic ones. Solidification under different cooling rates and heat treatments was carried out using the neutron powder diffraction technique to comprehend the precipitation dynamics and explain the microstructural events during and after the DED process. Laboratory scale and neutron diffraction tensile characterization tests were performed to observe and relate the mechanical response of wire- DED IN718 at different temperatures and microstructural conditions.:Keywords i Abstract iii Table of Contents v List of Figures ix List of Tables xvii List of Abbreviations xix Acknowledgments xxi Chapter 1: Introduction 1 1.1 Residual Stress in Polycrystalline Materials 1 1.1.1 Residual Stress Determination 3 1.2 Neutron Scattering 5 1.2.1 Neutron-Matter Interaction 6 1.2.2 Strain Measurement by Neutron Diffraction 7 1.2.3 SALSA Neutron Strain Diffractometer 14 1.2.4 Neutron Powder Diffraction 16 1.2.5 D20 Neutron Powder Diffractometer 17 1.2.6 Peak Analysis in Diffraction Measurements 18 1.3 Nickel Superalloys 22 1.3.1 Physical Metallurgy of IN718 23 1.4 Metal Additive Manufacturing 33 1.4.1 Direct Energy Deposition (DED) 34 1.4.2 Process Monitoring in Metal AM 36 1.5 Context and Aim of the Study 40 Chapter 2: Materials and Experimental Methods 43 2.1 IN718 Feedstock Material 43 2.2 Fabrication Process by wire-DED Method 43 2.2.1 Post Processing of IN718 via Solution Treatment and Aging 47 2.2.2 Preparation of Tensile Specimens 48 2.3 Microstructural Characterization 49 2.3.1 Electron Microscopy Studies 49 2.3.2 Differential Scanning Calorimetry Analysis 50 2.3.3 Lattice Parameter Evolution of IN718 with Temperature 52 2.3.3.1 Data Reduction for Phase Analysis 54 2.4 Mechanical Characterization 57 2.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 57 2.4.1.1 Temperature Data Treatment and Processing Regions 61 2.4.1.2 Neutron Data Acquisition and Analysis 64 2.4.2 Residual Stress Mapping of Samples for Mechanical Characterization 69 2.4.3 Macro-scale Tensile Characterization at Room and High Temperatures 71 2.4.4 Neutron Diffraction Tensile Characterization Testing 72 2.4.4.1 Neutron Data Processing Procedure 77 Chapter 3: Results and Discussion 79 3.1 Microstructural Characterization of Feedstock Wire 79 3.1.1 Metallography of IN718 Feedstock Wire 79 3.1.2 Simulation of Phase Precipitations in IN718 80 3.1.3 Thermal Stability of IN718 Feedstock Wire 82 3.1.3.1 Differential Scanning Calorimetry 82 3.1.3.2 Lattice Parameter Evolution during Melting & Solidification 83 3.1.4 Discussion 91 3.2 Microstructure of IN718 wire-DED Parts 94 3.2.1 IN718-DED Cylindrical Walls 94 3.2.2 IN718 -DED Prisms 103 3.2.3 Discussion 108 3.3 Heat Treatments of IN718 Wire-DED Parts 112 3.3.1 Time and Temperature Impact into Laves Phase Dissolution 112 3.3.2 Lattice Parameter Evolution of IN718 during Solution and Aging Treatments 115 3.3.3 Discussion 118 3.4 Mechanical Characterization of IN718 wire-DED 122 3.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 122 3.4.1.1 Bragg Angle Evolution 122 3.4.1.2 Evolution of Bragg Angle Position in MP Processing Region 123 3.4.1.3 Evolution of Bragg Angle Position in the NMP Processing Region 126 3.4.1.4 Evolution of Bragg Angle Position in FF Processing Region 129 3.4.2 Discussion 131 3.4.2.1 Comparison of Equilibrium State of IN718 through In-situ and Ex-situ Investigations 135 3.4.3 Reference (d0) Approaches for Strain Calculations 136 3.4.3.1 Stable processing regime reference 136 3.4.3.2 Neutron powder diffraction reference 137 3.4.4 Evolution of Strain Contributions during IN718 wire-DED by Using Stable Reference (d0) Approach 140 3.4.4.1 Strain Evolution in MP Processing Region 141 3.4.4.2 Strain Evolution in NMP Processing Region 143 3.4.4.3 Strain Evolution in FF Processing Region 145 3.4.5 Evolution of Strain Contributions during IN718 wire-DED by Using Neutron Powder Diffraction Reference d0 Approach 148 3.4.6 Discussion 151 3.4.7 Tensile Characterization 153 3.4.7.1 Macro-scale Tensile Behavior 153 3.4.7.2 Residual Stress State in In-situ Tensile Test Specimens 155 3.4.7.3 Lattice-scale Tensile Behavior 158 3.4.8 Discussion 169 3.4.8.1 Residual Stress State prior to Tensile Test Characterization 169 3.4.8.2 Macro-scale Tensile Behavior of IN718 at Room and High Temperatures 169 3.4.8.3 Lattice-dependent Behavior As-built and Direct-aged Condition as a function of Applied Stresses 175 Chapter 4: Summary Discussion 182 4.1 Microstructural Considerations 182 4.1.1 Comparison of Materials and Extrapolation of Properties 182 4.2 Thermal Stability of IN718 Feedstock Wire and DED Parts 183 4.2.1 Matrix, Phase Precipitation, and CTE Evolution as a Function of Temperature 183 4.2.2 Heat Treatments of IN718 DED materials 184 4.3 Fabrication and Neutron Strain Monitoring Considerations 185 4.3.1 Temperature Gradients and Regions of Interest 185 4.3.2 In-situ Neutron Monitoring of Bragg Angle Evolution of γ-matrix 185 4.3.3 2D Strain Evolution 186 4.4 Tensile Mechanical Behaviour at Room and High-Temperature Considerations 189 4.4.1 Macro-scale Characterization 189 4.4.2 Lattice-scale Neutron Diffraction Characterization 189 Chapter 5: Conclusions 191 Bibliography 196 / In den letzten Jahren hat sich die additive Fertigung (AM) zu einer der wichtigsten Produktionstechniken in der Ingenieurwelt entwickelt. Die schnelle Integration dieser Technik hat die Zuverlässigkeit der mikrostrukturellen und mechanischen Eigenschaften von technischen Komponenten deutlich verbessert. Aufgrund des schichtweisen Ansatzes der AM können jedoch komplexe thermische Gradienten eine inhomogene Mikrostruktur und erhebliche Eigenspannungen (RS) verursachen. Diese können erwartungsgemäß zu einer dramatischen Verringerung der Materialleistung führen. Daher sind insbesondere bei Legierungen wie Inconel 718 (IN718) auf Ni-Basis, die in kritischen Anwendungen eingesetzt werden, die Charakterisierung und spätere Optimierung des DED-Prozesses auf die Materialeigenschaften von entscheidender Bedeutung. Dennoch müssen empirische und konventionelle Ansätze verbessert werden, oder es sollten neue Techniken eingeführt werden. In diesem Zusammenhang zielt diese Studie darauf ab, die Entwicklung der mechanischen und mikrostrukturellen Eigenschaften von IN718 während und nach dem DED-Prozess besser zu verstehen. Zu diesem Zweck wurde während des DED-Prozesses von IN718 eine in-situ 2D-Neutronenbeugungsmessung der Dehnung durchgeführt. Die Dehnungsbeiträge, die von mikrostrukturellen, thermischen und spannungsbasierten Ereignissen während der Abscheidungs- und Abkühlungsperioden an verschiedenen Positionen des Schmelzbades herrühren, wurden untersucht. Die Stabilisierung verschiedener Positionen und Verarbeitungsbereiche auf der Probe als Funktion des Temperaturprofils, der Aufschmelzhöhe und der mikrostrukturellen Ereignisse wurde untersucht. Im Labormaßstab wurden mikrostrukturelle Studien an Draht-DED-Teilen durchgeführt, um die Abhängigkeit der Prozessparameter von der Ausscheidung, Zusammensetzung und Morphologie der mikrostrukturellen Bestandteile zu beobachten. Darüber hinaus wurden diese Ergebnisse mit Neutronenpulverbeugungsmessungen verglichen, um das kristallographische Verhalten mit dem makroskopischen Verhalten in Beziehung zu setzen. Die Erstarrung unter verschiedenen Abkühlungsraten und Wärmebehandlungen wurde mit Hilfe der Neutronenpulverbeugungstechnik durchgeführt, um die Ausscheidungsdynamik zu verstehen und die mikrostrukturellen Ereignisse während und nach dem DED-Prozess zu erklären. Es wurden Zugversuche im Labormaßstab und mit Neutronenbeugung durchgeführt, um die mechanische Reaktion von IN718 bei verschiedenen Temperaturen und Mikrostrukturbedingungen zu beobachten und in Beziehung zu setzen.:Keywords i Abstract iii Table of Contents v List of Figures ix List of Tables xvii List of Abbreviations xix Acknowledgments xxi Chapter 1: Introduction 1 1.1 Residual Stress in Polycrystalline Materials 1 1.1.1 Residual Stress Determination 3 1.2 Neutron Scattering 5 1.2.1 Neutron-Matter Interaction 6 1.2.2 Strain Measurement by Neutron Diffraction 7 1.2.3 SALSA Neutron Strain Diffractometer 14 1.2.4 Neutron Powder Diffraction 16 1.2.5 D20 Neutron Powder Diffractometer 17 1.2.6 Peak Analysis in Diffraction Measurements 18 1.3 Nickel Superalloys 22 1.3.1 Physical Metallurgy of IN718 23 1.4 Metal Additive Manufacturing 33 1.4.1 Direct Energy Deposition (DED) 34 1.4.2 Process Monitoring in Metal AM 36 1.5 Context and Aim of the Study 40 Chapter 2: Materials and Experimental Methods 43 2.1 IN718 Feedstock Material 43 2.2 Fabrication Process by wire-DED Method 43 2.2.1 Post Processing of IN718 via Solution Treatment and Aging 47 2.2.2 Preparation of Tensile Specimens 48 2.3 Microstructural Characterization 49 2.3.1 Electron Microscopy Studies 49 2.3.2 Differential Scanning Calorimetry Analysis 50 2.3.3 Lattice Parameter Evolution of IN718 with Temperature 52 2.3.3.1 Data Reduction for Phase Analysis 54 2.4 Mechanical Characterization 57 2.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 57 2.4.1.1 Temperature Data Treatment and Processing Regions 61 2.4.1.2 Neutron Data Acquisition and Analysis 64 2.4.2 Residual Stress Mapping of Samples for Mechanical Characterization 69 2.4.3 Macro-scale Tensile Characterization at Room and High Temperatures 71 2.4.4 Neutron Diffraction Tensile Characterization Testing 72 2.4.4.1 Neutron Data Processing Procedure 77 Chapter 3: Results and Discussion 79 3.1 Microstructural Characterization of Feedstock Wire 79 3.1.1 Metallography of IN718 Feedstock Wire 79 3.1.2 Simulation of Phase Precipitations in IN718 80 3.1.3 Thermal Stability of IN718 Feedstock Wire 82 3.1.3.1 Differential Scanning Calorimetry 82 3.1.3.2 Lattice Parameter Evolution during Melting & Solidification 83 3.1.4 Discussion 91 3.2 Microstructure of IN718 wire-DED Parts 94 3.2.1 IN718-DED Cylindrical Walls 94 3.2.2 IN718 -DED Prisms 103 3.2.3 Discussion 108 3.3 Heat Treatments of IN718 Wire-DED Parts 112 3.3.1 Time and Temperature Impact into Laves Phase Dissolution 112 3.3.2 Lattice Parameter Evolution of IN718 during Solution and Aging Treatments 115 3.3.3 Discussion 118 3.4 Mechanical Characterization of IN718 wire-DED 122 3.4.1 Neutron Diffraction 2D Strain Monitoring during IN718 wire-DED 122 3.4.1.1 Bragg Angle Evolution 122 3.4.1.2 Evolution of Bragg Angle Position in MP Processing Region 123 3.4.1.3 Evolution of Bragg Angle Position in the NMP Processing Region 126 3.4.1.4 Evolution of Bragg Angle Position in FF Processing Region 129 3.4.2 Discussion 131 3.4.2.1 Comparison of Equilibrium State of IN718 through In-situ and Ex-situ Investigations 135 3.4.3 Reference (d0) Approaches for Strain Calculations 136 3.4.3.1 Stable processing regime reference 136 3.4.3.2 Neutron powder diffraction reference 137 3.4.4 Evolution of Strain Contributions during IN718 wire-DED by Using Stable Reference (d0) Approach 140 3.4.4.1 Strain Evolution in MP Processing Region 141 3.4.4.2 Strain Evolution in NMP Processing Region 143 3.4.4.3 Strain Evolution in FF Processing Region 145 3.4.5 Evolution of Strain Contributions during IN718 wire-DED by Using Neutron Powder Diffraction Reference d0 Approach 148 3.4.6 Discussion 151 3.4.7 Tensile Characterization 153 3.4.7.1 Macro-scale Tensile Behavior 153 3.4.7.2 Residual Stress State in In-situ Tensile Test Specimens 155 3.4.7.3 Lattice-scale Tensile Behavior 158 3.4.8 Discussion 169 3.4.8.1 Residual Stress State prior to Tensile Test Characterization 169 3.4.8.2 Macro-scale Tensile Behavior of IN718 at Room and High Temperatures 169 3.4.8.3 Lattice-dependent Behavior As-built and Direct-aged Condition as a function of Applied Stresses 175 Chapter 4: Summary Discussion 182 4.1 Microstructural Considerations 182 4.1.1 Comparison of Materials and Extrapolation of Properties 182 4.2 Thermal Stability of IN718 Feedstock Wire and DED Parts 183 4.2.1 Matrix, Phase Precipitation, and CTE Evolution as a Function of Temperature 183 4.2.2 Heat Treatments of IN718 DED materials 184 4.3 Fabrication and Neutron Strain Monitoring Considerations 185 4.3.1 Temperature Gradients and Regions of Interest 185 4.3.2 In-situ Neutron Monitoring of Bragg Angle Evolution of γ-matrix 185 4.3.3 2D Strain Evolution 186 4.4 Tensile Mechanical Behaviour at Room and High-Temperature Considerations 189 4.4.1 Macro-scale Characterization 189 4.4.2 Lattice-scale Neutron Diffraction Characterization 189 Chapter 5: Conclusions 191 Bibliography 196