This work examines the application of different magnetic flux leakage (MFL) inspection concepts to the non destructive evaluation (NDE) of residual (elastic) stresses in CANDU reactor feeder pipes. The stress sensitivity of three MFL inspection techniques was examined with flat plate samples, with stress-induced magnetic anisotropy (SMA) demonstrating the greatest stress sensitivity. A prototype SMA testing system was developed to apply magnetic NDE to feeders. The system consists of a flux controller that incorporates feedback from a wire coil and a Hall sensor (FCV2), and a magnetic anisotropy prototype (MAP) probe. The combination of FCV2 and the MAP probe was shown to provide SMA measurements on feeder pipe samples and predict stresses from SMA measurements with a mean accuracy of ±38MPa. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2010-03-11 15:59:23.978

No description available.

This Thesis describes the design, manufacture and evaluation of a single sided through-air Lamb wave scanner for Non-Destructive Evaluation (NDE). The new scanning system utilises novel wideband piezocomposite transducers and specialised receive electronics to detect and monitor the thickness of faults within the structure under investigation using a frequency agile approach. Based upon the superheterodyne principle, this frequency agility dispenses with the costly requirement for precision manipulation of the transducer alignment, by effectively tuning the system for the thickness of the sample. Several important applications are identified, including defect detection on samples with tapered thicknesses and defect depth characterisation on plates with thickness erosion, in addition to conventional defect evaluation. Through the application of finite element modelling and practical analysis, a new range of wideband composite transducer have been developed which offer a considerable improvement in operational bandwidth in comparison to conventional piezocomposites. Moreover, a specialised ultra low noise heterodyning amplifier was designed and constructed to provide sufficient gain and selectivity to detect the Lamb waves generated in the various structures under examination. Experimental results obtained from the prototype system illustrate a capability to distinguish defects within test specimens of differing materials and determine the thickness of the given defect. The current system is capable of resolving defects down to less than 2mm in diameter or 20% thinning in a 1mm thick aluminium plate for a Lamb wave with a wavelength of 3mm. Moreover, the handheld nature of the scanning head employed within this system has facilitated the examination of practical NDE examples, such as disbonds between vehicle support structures and outer panelling over curved structures.

This work has two parts. The first part of the work (in Chapters II, III, IV and V) presents a method for locating the point of impact using acoustic emission techniques.The second part of the work is modeling the ultrasonic fields generated by one and two spherical cavities placed in front of a point focused acoustic lens using the semi-analytical distributed point source method (DPSM).Acoustic emission (AE) refers to the generation of transient elastic waves during the rapid release of energy from localized sources within a material.In this work the acoustic emission has been used for locating the point of impact on anisotropic and homogeneous or non-homogenous flat plates and cylindrical structures. In these cases the wave speed is a function of the angle of propagation. An optimization function is introduced and minimized to get the location of the impact point.This method has been used on a flat (fiber reinforced polymer) plate. The proposed new objective function reduces the amount of time needed for solving the problem and improves the accuracy of prediction. The method is extended to cylindrical structures for which the objective function is written in cylindrical coordinates and the method is tested on a FRP shell.In Chapter IV an alternative method is introduced called the near-field acoustic emission (AE) beamforming method. It has been used to estimate the source locations by using a small array of sensors closely placed in a local region. To validate the effectiveness of the AE beamforming method a series of experiments on a FRP shell are conducted. The experimental results demonstrate that the proposed method can correctly predict the point of impact.The semi-analytical mesh-free technique DPSM is then used to model the ultrasonic field in front of a point focused acoustic lens; anomalies such as cavities are introduced in the medium in front of the acoustic lens and the effect of those cavities are studied. Solution of this problem is necessary to get an idea about when two cavities placed in close proximity can be distinguished by an acoustic lens and when it is not possible.

Rayleigh scattering, that is the elastic and coherent scattering of photons from bound atomic electrons, has been investigated for use as an active probe for substance identification. An angular dispersive scattering system has been developed for materials identification utilising the 22 keV Kalpha X-ray line from a low power (25 Watt) silver anode X-ray tube. Differential scattering cross-sections have been measured for a wide range of low- to high-Z materials and compared with free atom theoretical predictions. Experimental results compare favourably with theory and evidence has been found to suggest that inter-atomic and inter-molecular interference effects have little or no effect upon the total scattering cross-section. The potential of Rayleigh scattering for detection of inclusions of low-Z media within extended objects of similar atomic constitution has been investigated with particular emphasis on the detection of potential contaminants in food products. The contrasts obtained with scatter techniques are substantially in excess of those achievable with conventional transmission measurements. By exploiting the ratio of the scattering in two regions of momentum space as the scatter parameter the contrast between inclusion and matrix may be increased to over five times that of transmission methods. This technique may be used in many situations where alternative photon interrogation methods such as X-ray transmission or X-ray fluorescence are unsuitable and a wide range of potential applications including quality control, sorting of plastics, security screening and oil/water discrimination have been considered.

The sensitization of stainless steel describes the process by which a high-carbon steel alloy is heated above a certain threshold (either naturally or artificially) followed by a cooling period during which chromium (one of the elements most responsible for providing stainless steel with its corrosion-inhibiting properties) forms new compounds with the carbon present in the steel. With the chromium being taken from the parent material to form these compounds, the corrosion-resistant properties are compromised, which can lead to corrosion, cracking, and broader failure. Currently, the accepted techniques used to test for the presence of sensitization are qualitative and/or destructive in nature. Attempts have been made to non-destructively detect and characterize sensitization through various means, but all with mixed results. With the use of these high-carbon alloys in a range of industries, a comprehensive, in-place process is desirable. This thesis will focus specifically on non-destructive evaluation of sensitization seen as a result of welding steel plates using induction infrared thermography (IIRT). This process uses an induction coil to generate heat within a sample whose resulting heat signature can then be detected with an infrared (IR) camera and analyzed. Previous IIRT experimental results have shown higher levels of heating in the HAZ when sensitization is present as it modifies the original microstructure of the material. New IIRT experiments have been conducted on both welded and unwelded 440C alloy samples to establish quantitative data on the heating profiles. These results (in conjunction with the appropriate experimental parameters) were then used to create a numerical model to replicate them. Despite some limitations in populating the model with accurate parameters, the results obtained were in good agreement with the experiments and provide a foundation for future work. Future work will focus on establishing a predictive tool that can detect and quantify the level of sensitization in an arbitrary steel sample in the field. / Master of Science / The sensitization of stainless steel describes the process by which a high-carbon steel alloy is heated above a certain threshold (either naturally or artificially) followed by a cooling period during which chromium (one of the elements most responsible for providing stainless steel with its corrosion-inhibiting properties) forms new compounds with the carbon present in the steel. With the chromium being taken from the parent material to form these compounds, the corrosion-resistant properties are compromised, which can lead to corrosion, cracking, and broader failure. Currently, the accepted techniques used to test for the presence of sensitization are qualitative and/or destructive in nature. Attempts have been made to non-destructively detect and characterize sensitization through various means, but all with mixed results. With the use of these high-carbon alloys in a range of industries, a comprehensive, in-place process is desirable. This thesis will focus specifically on non-destructive evaluation of sensitization seen as a result of welding steel plates using induction infrared thermography (IIRT). This process uses an induction coil to generate heat within a sample whose resulting heat signature can then be detected with an infrared (IR) camera and analyzed. Previous IIRT experimental results have shown higher levels of heating in the HAZ when sensitization is present as it modifies the original microstructure of the material. New IIRT experiments have been conducted on both welded and unwelded 440C alloy samples to establish quantitative data on the heating profiles. These results (in conjunction with the appropriate experimental parameters) were then used to create a numerical model to replicate them. Despite some limitations in populating the model with accurate parameters, the results obtained were in good agreement with the experiments and provide a foundation for future work. Future work will focus on establishing a predictive tool that can detect and quantify the level of sensitization in an arbitrary steel sample in the field.

Birefringence has been used to study transparent materials since 1815, and is based on the decomposition of a polarized ray of light into two distinct rays when passing through an optically anisotropic material. This thesis uses this phenomenon in a study of phase retardation in crystalline materials. Single and multicrystalline silicon was chosen as the model material. Silicon is an interesting and important material in its own right, and the use of photoelasticity to determine stresses at linear and planar defects can have important consequences in the electrical performance of devices such as electronics and photovoltaic cells. This thesis presents the results of an experimental investigation of residual stresses in multicrystalline silicon wafers using near-infrared (NIR) transmission photoelasticity. NIR transmission through multicrystalline silicon is found to vary with crystallographic orientation and relate to planar atomic density, enabling the assignment of appropriate stress-optic coefficients to different grains. Noise in the data is reduced with the Ramji and Ramesh 10-step phase shifting algorithm when compared to the Patterson and Wang process. Normal stresses at points of zero maximum shear stress can be characterized based on isoclinic behavior around the point. Points at which all normal stresses are zero serve as boundary conditions for shear difference integration and allow for stress separation from a point that is not a free boundary. The second part of this work focuses on residual stresses in silicon wafers subjected to known physical damage such as indentations. Residual stress fields around Vickers indentations in silicon are found to be larger in size than predicted by contact mechanics. Placing Vickers indentations in close proximity creates a secondary stress field surrounding the entire indentation array, and a relationship is developed to explain this behavior. High residual stresses measured at grain boundaries are found to be consistent with models of atomic displacement. Placement of Vickers indentations near grain boundaries results in a change in stress state at the grain boundaries. The results of this study demonstrate the capacity of birefringence as a non-destructive evaluation tool and describe the effects of residual stress concentrations in silicon wafers.

There is an increasing need of automation for routine tasks like sorting agricultural produce in large scale post-harvest processing. Among different kinds of sensors used for such automation tasks, near-infrared (NIR) technology provides a rapid and effective solution for quantitative analysis of quality indices in food products. As industries and farms are adopting modern data-driven technologies, there is a need for evaluation of the modelling tools to find the optimal solutions for problem solving. This study aims to understand the process of evaluation of the modelling tools, in view of near-infrared data obtained from green leafy vegetables. The first part of this study deals with prediction of the type of leafy green vegetable from the near-infrared reflectance spectra non-destructively taken from the leaf surface. Supervised classification methods used for the classification task were k-nearest neighbors (KNN), support vector machines (SVM), linear discriminant analysis (LDA) classifier, regularized discriminant analysis (RDA) classifier, naïve Bayes classifier, bagged trees, random forests, and ensemble discriminant subspace classifier. The second part of this study deals with prediction of total glucosinolate and total polyphenol contents in leaves using Partial Least Squares Regression (PLSR) and Principal Component Regression (PCR). Optimal combination of predictors were chosen by using recursive feature elimination. NIR spectra taken from 283 different samples were used for classification task. Accuracy rates of tuned classifiers were compared for a standard test set. The ensemble discriminant subspace classifier was found to yield the highest accuracy rates (89.41%) for the standard test set. Classifiers were also compared in terms of accuracy rates and F1 scores. Learning rates of classifiers were compared with cross-validation accuracy rates for different proportions of dataset. Ensemble subspace discriminants, SVM, LDA and KNN were found to be similar in their cross-validation accuracy rates for different proportions of data. NIR spectra as well as reference values for total polyphenol content and total glucosinolate contents were taken from 40 samples for each analyses. PLSR model for total glucosinolate prediction built with spectra treated with Savitzky-Golay second derivative yielded a RMSECV of 0.67 μmol/g of fresh weight and cross-validation R2 value of 0.63. Similarly, PLSR model built with spectra treated with Savitzky-Golay first derivative yielded a RMSECV of 6.56 Gallic Acid Equivalent (GAE) mg/100g of fresh weight and cross-validation R-squared value of 0.74. Feature selection for total polyphenol prediction suggested that the region of NIR between 1300 - 1600 nm might contain important information about total polyphenol content in the green leaves.

No description available.

Free vibrations of a thin elastic circular cylindrical panel localized near the rectilinear edge, propagating along the edge and decaying in its circumferential direction, are investigated in the framework of the two-dimensional equations in the Kircho↵-Love theory of shells. At first the panel is assumed to be infinite longitudinally and semi-infinite along its length of curvature (of course not realistically possible), followed by the assumption that the panel is then finite along its length of curvature and fixed and free conditions are imposed on the second resulting boundary. Using the comprehensive asymptotic analysis detailed in Kaplunov et al. (1998) “Dynamics of Thin Walled Elastic Bodies”, leading order asymptotic solutions are derived for three types of localized vibration, they are bending, extensional, and super-low frequency. Explicit representation of the exact solutions cannot be obtained due to the degree of complexity of the solving equations and relevant boundary conditions, however, computational methods are used to find exact numerical solutions and graphs. Parameters, particularly panel thickness, wavelength, poisson’s ratio, and circumferential panel length, are varied, and their e↵ects on vibration analyzed. This analysis is further extended to investigate localized vibration on the interface (perfect bond) of two cylindrical panels joined at their respective rectilinear edges, propagating along the interface and decaying in the circumferential direction away from the interface. An earlier, similar, localized vibration problem presented in Kaplunov et al. (1999) “Free Localized Vibrations of a Semi-Infinite Cylindrical Shell” and Kaplunov and Wilde (2002) “Free Interfacial Vibrations in Cylindrical Shells” is replicated for comparison with all cases. The asymptotics are similar, however in this problem the numerics highlight the stronger e↵ect of curvature on the decay of the super-low frequency vibrations, and to some extent on the leading order bending vibration.