Nondestructive testing (NDT) uses different wave propagation modes to evaluate the internal structure of materials, revealing internal damage such as corrosion and fracturing that cannot be detected by traditional methods. Civil infrastructures are considered high priority assets in Ontario and Canada because of their value, high consequence of failure, and the continual influence of aging effects. Unexpected failure of infrastructure not only costs more than planned replacements but also results in increased safety risks. The in-situ condition assessment of civil infrastructure is critical for the successful implementation of maintenance and safety programs. Therefore, reliable nondestructive methods of inspection are required for the implementation of economical and efficient maintenance and asset management programs. Continuing technological developments in data collection, acquisition equipment, and data processing techniques have provided useful applications of nondestructive methods in many engineering fields. Among the many applications, this research study examines three applications of nondestructive testing in civil engineering: (1) condition assessment of construction joints in asphalt pavements, (2) average thickness evaluation of steel pipes, and (3) void and debonding detection in grouted steel tanks. The study on asphalt focuses on the improvement of the coupling system between the transducers and the asphalt surface, and the development of a new data processing technique to reduce user input and increase the reliability of the condition assessment of longitudinal joints. The current wavelet transmission coefficient (WTC) method requires user input, making the automatic data processing difficult. In the WTC method, the coupling between the transducers and the asphalt surface requires the use of epoxy and aluminum plates. This procedure is not practical for testing in-service roads. A new coupling mechanism using polyurethane foam to provide a spring action on the transducers and calibrated weights to generate a compression force was developed and showed good results, reducing the testing time by up to 50%. A new and robust data analysis methodology, called instantaneous transmission coefficient (ITC), is proposed based on measured instantaneous frequencies and damping ratios. The main advantage of the ITC procedure is that it can be performed automatically, reducing user input. A laboratory scale asphalt slab is used to evaluate the new methodology. Results show good agreement between the WTC and ITC measurements for both jointed and joint-free areas. The second study investigates the feasibility of the multichannel analysis of surface waves (MASW) technique for the evaluation of the average wall thickness of steel pipes. Electromagnetic NDT methods, such as the eddy current and the remote field testing, are common tools for thickness measurement of conductive materials. However, these methods give only localized results where measurements are made, making the process time consuming and inaccurate for assessing the full cross-sectional area of the pipe. Lamb waves have been used previously in the evaluation of steel pipes; however, the existing techniques require prior calibration to a theoretical wave mode, and their accuracy decreases with the length of the pipe evaluated due to wave attenuation effects. Preliminary results show the capability of the MASW test for providing reliable thickness information. The measured dispersion curves include information of fundamental modes and the higher modes, providing an improved characterization of the medium. Thicknesses between 3.2 mm and 12.7 mm are tested with an error of less than 2%. The third study explores the detection of voids in a steel tank filled with lightweight grout. A joint analysis of surface waves and Lamb waves is used for void detection and the identification of debonding conditions in a laboratory scale model of a steel tank filled with grout. Different configurations of the MASW method are conducted using an instrumented hammer (large wavelengths, 10 cm < λ < 25 cm) and a 50 kHz piezoelectric transmitter (small wavelengths, 5 cm < λ < 9 cm) as sources. The attenuation coefficient computed from the Fourier spectra of the measured signals indicates that the presence of a void has an effect on the propagation of the wave. The comparison between experimental and theoretical dispersion curves show that mainly Lamb waves are generated during the testing of the steel tank; thus, detecting the debonding conditions between the steel plate and the grout. Lamb modes are used successfully for detecting the presence of a void beneath the steel wall. The laboratory measurements are effective in the detection of the void, showing amplitudes up to 50% higher, likely because the deformation of the wall is attenuated by the grout.

Alkali-silica reaction (ASR) and delayed ettringite formation (DEF) are expansive reactions that can lead to the premature deterioration of concrete structures. Both have been implicated in the deterioration of numerous structures around the world, including many transportation structures in Texas. As a result of considerable research advances, ASR and DEF are now avoidable in new construction, but evaluating and managing the existing stock of structures damaged by these mechanisms remains a challenge. While the published guidance for evaluating structures is very effective at diagnosing the presence of ASR and DEF, there remain significant weaknesses with respect to the evaluation of structural safety and serviceability and nondestructive testing (NDT) is a minor component of the evaluation process. The research described in this dissertation involved a wide range of tests on plain and reinforced concrete at multiple scales. This included small cylinders and prisms, larger plain and reinforced concrete specimens in outdoor exposure, full-scale reinforced concrete beams, and core samples from the outdoor exposure specimens and full-scale reinforced concrete beams. Nondestructive test methods were applied at all scales, and the full-scale beams were also tested in four-point flexure to determine the effects of ASR and DEF on flexural strength and serviceability. Severe expansions from ASR and DEF did not reduce the strength of the full-scale beams or result in excessive deflections under live loads, despite significant decreases in the compressive strength and elastic modulus measured from core samples. Most NDT methods were found to be effective at low expansions but had difficulty correlating to larger expansions. Two promising NDT methods have been identified for future research and development, and guidance regarding existing test methods is offered. / text

The purpose of this study is to develop a non-contact air-coupled NDT method to identify and characterize surface-breaking cracks in concrete structures using surface wave transmission measurements. It has been found that the surface wave transmission (SWT) across a surface-breaking crack is related to the crack depth. However, inconsistence was noticed in surface wave transmission measurements. In this dissertation, the author first summarized limitations of the current SWT method for application to concrete structures, which include inconsistent sensor coupling, near-field effect of sensors, effects of crack width, external loading effect on surface wave transmission coefficient, and lack of a repeatable source. In this dissertation, the author attempts to find solutions to the aforementioned problems. First, non-contact air-coupled sensors were applied to the SWT method to reduce experimental errors caused by inconsistent coupling condition of conventional contact sensors. Air-coupled sensing enables reliable and consistent results, and significantly improves test-speed. Results from laboratory and field tests demonstrate effectiveness of air-coupled sensors. Second, appropriate sensor-to-source configurations are proposed to reduce undesirable effects: (i) the near-field effect of sensors around a crack, and (ii) contribution of multiple modes in a plate-like structure with a finite thickness. Near-scattering of surface waves interacting with a surface-breaking crack was investigated using numerical simulations (finite element method) and experimental studies over a wide range of the normalized crack depth (h/λ: crack depth normalized by wavelength of surface waves) and the normalized frequency-thickness ratio (f-H/CR: frequency-thick normalized by Rayleigh wave speed). Third, effects of external loadings on transmission coefficient of surface waves in concrete were investigated through a series of experimental studies. In the research, variation of the transmission coefficient is presented as a function of crack mouth opening displacement (CMOD). This provides a guideline on minimum CMOD to which the SWT method can be reasonably applied. In addition, the author experimentally demonstrates that using low-cost piezoceramic sensors is effective in generating consistent stress waves in concrete. Finally, the author demonstrates that the air-coupled SWT method developed in this study is effective for in-situ estimates of a surface-breaking crack in large concrete structures. / text

In this dissertation different structural materials (aluminum and steel) with different geometrical shapes (plates, pipes and bars) are studied for damage detection with guided waves. Specific guided wave modes (also known as Lamb wave modes for plate type structures) are generated in a laminated aluminum plate for damage detection and quantification using a broad band piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Sensitivity of anti-symmetric and symmetric modes for delamination detection and quantification is investigated. Longitudinal guided waves are excited and recorded after transmission through reinforcing steel bars for monitoring its corrosion level. Instead of investigating the amplitude of the transmitted guided waves, or in other words, monitoring its attenuation, the differential time-of-flight (TOF) is recorded. A reliable guided wave mode is identified for the detection and quantification of corrosion in reinforcing steel bars. Hole type damage, and bonding/de-bonding or lamination/delamination in pipes are studied with Noncontact Electro-Magnetic Acoustic Transducers and PZT transducers. An adaptive method using phase of the recorded signals for detection and quantification of damages in pipes is established using multiple feature extraction techniques (Time-Frequency representations) and differential time-of-flight cross-correlation technique.

Longitudinal joints are one of the critical factors that cause premature pavement failure. Poor-quality joints are characterized by a low density and high permeability; which generates surface distresses such as ravelling or longitudinal cracking. Density has been traditionally considered as the primary performance indicator of joint construction. Density measurements consist of taking cores in the field and determining their density in the laboratory. Although this technique provides the most accurate measure of joint density, it is destructive and time consuming. Nuclear and non-nuclear gauges have been used to evaluate the condition of longitudinal joint non-destructively, but did not show good correlation with core density tests. Consequently, agencies are searching for other non-destructive testing (NDT) options for longitudinal joints evaluation. NDT methods have significantly advanced for the evaluation of pavement structural capacity during the past decade. These methods are based either on deflection or wave velocity measurements. The light weight deflectometer (LWD) is increasingly being used in quality control/quality assurance to provide a rapid determination of the surface modulus. Corresponding backcalculation programs are able to determine the moduli of the different pavement layers; these moduli are input parameters for mechanistic-empirical pavement design. In addition, ultrasonic wave-based methods have been studied for pavement condition evaluation but not developed to the point of practical implementation. The multi-channel analysis of surface waves (MASW) consists of using ultrasonic transducers to measure surface wave velocities in pavements and invert for the moduli of the different layers. In this study, both LWD and MASW were used in the laboratory and in the field to assess the condition of longitudinal joints. LWD tests were performed in the field at different distances from the centreline in order to identify variations of the surface modulus. MASW measurements were conducted across the joint to evaluate its effect on wave velocities, frequency content and attenuation parameters. Improved signal processing techniques were used to analyze the data, such as Fourier Transform, windowing, or discrete wavelet transform. Dispersion curves were computed to determine surface wave velocities and identify the nature of the wave modes propagating through the asphalt pavement. Parameters such as peak-to-peak amplitude or the area of the frequency spectrum were used to compute attenuation curves. A self calibrating technique, called Fourier transmission coefficient (FTC), was used to assess the condition of longitudinal joints while eliminating the variability introduced by the source, receivers and coupling system. A critical component of this project consisted of preparing an asphalt slab with a joint in the middle that would be used for testing in the laboratory. The compaction method was calibrated by preparing fourteen asphalt samples. An exponential correlation was determined between the air void content and the compaction effort applied to the mixture. Using this relationship, an asphalt slab was prepared in two stages to create a joint of medium quality. Nuclear density measurements were performed at different locations on the slab and showed a good agreement with the predicted density gradient across the joint. MASW tests were performed on the asphalt slabs using different coupling systems and receivers. The FTC coefficients showed good consistency from one configuration to another. This result indicates that the undesired variability due to the receivers and the coupling system was reduced by the FTC technique. Therefore, the coefficients were representative of the hot mix asphalt (HMA) condition. A comparison of theoretical and experimental dispersion curves indicated that mainly Lamb waves were generated in the asphalt layer. This new result is in contradiction with the common assumption that the response is governed by surface waves. This result is of critical importance for the analysis of the data since MASW tests have been focusing on the analysis of Rayleigh waves. Deflection measurements in the field with the LWD showed that the surface modulus was mostly affected by the base and subgrade moduli, and could not be used to evaluate the condition of the surface course that contains the longitudinal joints. The LWDmod software should be used to differentiate the pavement layers and backcalculate the modulus of the asphalt layer. Testing should be performed using different plate sizes and dropping heights in order to generate different stress levels at the pavement surface and optimize the accuracy of the backcalculation. Finally, master curves were computed using a predictive equation based on mix design specifications. Moduli measured at different frequencies of excitation with the two NDT techniques were shifted to a design frequency of 25 Hz. Design moduli measured in the field and in the laboratory with the seismic method were in good agreement (less than 0.2% difference). Moreover, a relatively good agreement was found between the moduli measured with the LWD and the MASW method after shifting to the design frequency. In conclusion, LWD and MASW measurements were representative of HMA condition. However, the condition assessment of medium to good quality joints requires better control of the critical parameters, such as the measurement depth for the LWD, or the frequency content generated by the ultrasonic source and the coupling between the receivers and the asphalt surface for the MASW method.

Nondestructive testing (NDT) uses different wave propagation modes to evaluate the internal structure of materials, revealing internal damage such as corrosion and fracturing that cannot be detected by traditional methods. Civil infrastructures are considered high priority assets in Ontario and Canada because of their value, high consequence of failure, and the continual influence of aging effects. Unexpected failure of infrastructure not only costs more than planned replacements but also results in increased safety risks. The in-situ condition assessment of civil infrastructure is critical for the successful implementation of maintenance and safety programs. Therefore, reliable nondestructive methods of inspection are required for the implementation of economical and efficient maintenance and asset management programs. Continuing technological developments in data collection, acquisition equipment, and data processing techniques have provided useful applications of nondestructive methods in many engineering fields. Among the many applications, this research study examines three applications of nondestructive testing in civil engineering: (1) condition assessment of construction joints in asphalt pavements, (2) average thickness evaluation of steel pipes, and (3) void and debonding detection in grouted steel tanks. The study on asphalt focuses on the improvement of the coupling system between the transducers and the asphalt surface, and the development of a new data processing technique to reduce user input and increase the reliability of the condition assessment of longitudinal joints. The current wavelet transmission coefficient (WTC) method requires user input, making the automatic data processing difficult. In the WTC method, the coupling between the transducers and the asphalt surface requires the use of epoxy and aluminum plates. This procedure is not practical for testing in-service roads. A new coupling mechanism using polyurethane foam to provide a spring action on the transducers and calibrated weights to generate a compression force was developed and showed good results, reducing the testing time by up to 50%. A new and robust data analysis methodology, called instantaneous transmission coefficient (ITC), is proposed based on measured instantaneous frequencies and damping ratios. The main advantage of the ITC procedure is that it can be performed automatically, reducing user input. A laboratory scale asphalt slab is used to evaluate the new methodology. Results show good agreement between the WTC and ITC measurements for both jointed and joint-free areas. The second study investigates the feasibility of the multichannel analysis of surface waves (MASW) technique for the evaluation of the average wall thickness of steel pipes. Electromagnetic NDT methods, such as the eddy current and the remote field testing, are common tools for thickness measurement of conductive materials. However, these methods give only localized results where measurements are made, making the process time consuming and inaccurate for assessing the full cross-sectional area of the pipe. Lamb waves have been used previously in the evaluation of steel pipes; however, the existing techniques require prior calibration to a theoretical wave mode, and their accuracy decreases with the length of the pipe evaluated due to wave attenuation effects. Preliminary results show the capability of the MASW test for providing reliable thickness information. The measured dispersion curves include information of fundamental modes and the higher modes, providing an improved characterization of the medium. Thicknesses between 3.2 mm and 12.7 mm are tested with an error of less than 2%. The third study explores the detection of voids in a steel tank filled with lightweight grout. A joint analysis of surface waves and Lamb waves is used for void detection and the identification of debonding conditions in a laboratory scale model of a steel tank filled with grout. Different configurations of the MASW method are conducted using an instrumented hammer (large wavelengths, 10 cm < λ < 25 cm) and a 50 kHz piezoelectric transmitter (small wavelengths, 5 cm < λ < 9 cm) as sources. The attenuation coefficient computed from the Fourier spectra of the measured signals indicates that the presence of a void has an effect on the propagation of the wave. The comparison between experimental and theoretical dispersion curves show that mainly Lamb waves are generated during the testing of the steel tank; thus, detecting the debonding conditions between the steel plate and the grout. Lamb modes are used successfully for detecting the presence of a void beneath the steel wall. The laboratory measurements are effective in the detection of the void, showing amplitudes up to 50% higher, likely because the deformation of the wall is attenuated by the grout.

As the capabilities of autonomous vehicles increase, their use in situations that are dangerous or dull for humans is becoming more popular. Autonomous systems are currently being used in several military and civilian domains, including search and rescue operations, disaster relief coordination, infrastructure inspection and surveillance missions. In order to perform high level mission autonomy tasks, a method is required for the vehicle to localize itself, as well as generate a map of the environment. Algorithms which allow the vehicle to concurrently localize and create a map of its surroundings are known as solutions to the Simultaneous Localization and Mapping (SLAM) problem. Certain high level tasks, such as drivability analysis and obstacle avoidance, benefit from the use of a dense map of the environment, and are typically generated with the use of point cloud data. The point cloud data is incorporated into SLAM algorithms with scan registration techniques, which determine the relative transformation between two sufficiently overlapping point clouds. The Normal Distributions Transform (NDT) algorithm is a promising method for scan registration, however many issues with the NDT approach exist, including a poor convergence basin, discontinuities in the NDT cost function, and unreliable pose estimation in sparse, outdoor environments. This thesis presents methods to overcome the shortcomings of the NDT algorithm, in both 2D and 3D scenarios. To improve the convergence basin of NDT for 2D scan registration, the Multi-Scale k-Means NDT (MSKM-NDT) algorithm is presented, which divides a 2D point cloud using k-means clustering and performs the scan registration optimization over multiple scales of clustering. The k-means clustering approach generates fewer Gaussian distributions when compared to the standard NDT algorithm, allowing for evaluation of the cost function across all Gaussian clusters. Cost evaluation across all the clusters guarantees that the optimization will converge, as it resolves the issue of discontinuities in the cost function found in the standard NDT algorithm. Experiments demonstrate that the MSKM-NDT approach can be used to register partially overlapping scans with large initial transformation error, and that the convergence basin of MSKM-NDT is superior to NDT for the same test data. As k-means clustering does not scale well to 3D, the Segmented Greedy Cluster NDT (SGC-NDT) method is proposed as an alternative approach to improve and guarantee convergence using 3D point clouds that contain points corresponding to the ground of the environment. The SGC-NDT algorithm segments the ground points using a Gaussian Process (GP) regression model and performs clustering of the non ground points using a greedy method. The greedy clustering extracts natural features in the environment and generates Gaussian clusters to be used within the NDT framework for scan registration. Segmentation of the ground plane and generation of the Gaussian distributions using natural features results in fewer Gaussian distributions when compared to the standard NDT algorithm. Similar to MSKM-NDT, the cost function can be evaluated across all the clusters in the scan, resulting in a smooth and continuous cost function that guarantees convergence of the optimization. Experiments demonstrate that the SGC-NDT algorithm results in scan registrations with higher accuracy and better convergence properties than other state-of-the-art methods for both urban and forested environments.

This research investigates possible monitoring methods to non-invasively detect blockages in the cyclone of milk powder spray driers to avoid costly production shutdowns. Two possible solutions have been identified. These are guided wave and vibration analysis. This research focuses on vibration analysis method, based on variation in the natural frequencies and/or damping ratios caused by blockages. Experimental simulation studies the performance to assess the viability of the vibration analysis method in identifying blockage in the cyclone. To test this method, a 1.87m long vertical cylindrical steel tube with both ends simply supported was setup as a prototype and flour was used as the powder conveyed by the tube. Analytical, numerical and experimental methods were implemented on the prototype using vibration analysis techniques. Experimental resonant frequencies of the empty shell from the impact hammer excitation were compared with analytical and numerical solutions to analyse the modal shapes. The first bending mode was determined as 79 Hz, which decreased with the amount of added mass and location closer to the middle point. This was validated by the simulated mass experiment, which also matched with the beam-mass theory. Flour induced experiment further validated the variation of the first bending mode. Experimental 270Hz, 380Hz and 398Hz resonant frequencies increased with the amount of added mass, which was validated by the simulated mass and flour induced experiment. Besides the variation of the natural frequencies, the damping ratio was also studied and quantified using the Hilbert transform envelope curve method. Onsite monitoring of the vibration of the cyclone in a spray dryer was done at Fonterra Te Rapa and clear resonant frequencies were obtained. The research results from the prototype demonstrate that vibration analysis as a non-destructive method to detect the milk powder deposition or blockage in the cyclone is possible and promising. However, more work is required before industry application.

L’objectif de ce projet est de développer des méthodes d’analyse et de caractérisation des défauts structurels des matériaux s’appuyant sur la thermographie infrarouge stimulée. Nous pouvons à l’aide d’une excitation photothermique distante et d’un outil d’analyse que nous avons développé en laboratoire, déterminer la structure sous jacente d’un matériau, repérer précisément ses défauts et les mesurer. L’application qui nous intéresse ici porte sur la prévention, le diagnostique et la restauration des oeuvres d’art, nous avons démontré par de précédents travaux, la pertinence de cette approche et son potentiel important dans de nombreux domaines, qu’ils soient industriels, culturels, médicales ou autres. Nous avons fait la démonstration qu’il était possible d’analyse des matériaux fragiles de façon fiable et sans contact et nous comptons généraliser cette approche en l’étendant dans ses domaines d’intervention et dans sa précision. / The objective of this project is to develop analysis and characterization of structural defects in material methods based on photothermal radiometry,We can by means of a remote photothermal excitation and an analysis tool that we have developed in the laboratory to determine the underlying structure of a material, precisely locate its flaws and measure. The application of interest here focuses on the prevention, diagnosis and restoration of works of art, we have demonstrated by previous work, the relevance of this approach and its significant potential in many areas, such as industrial cultural, medical or other. We have demonstrated that it was possible to analyze fragile materials reliably and without contact and we intend to generalize this approach by extending its focal areas and its accuracy.

Delamination and cracks within the multilayer structure are typical failure modes observed in microelectronic and micro electro mechanical system (MEMS) devices and packages. As destructive detection methods consume large numbers of devices during reliability tests, non-destructive techniques (NDT) are critical for measuring the size and position of internal defects throughout such tests. There are several established NDT methods; however, some of them have significant disadvantages for detecting defects within multilayer structures such as those found in MEMS devices. This thesis presents research into the application of transient infrared thermography as a non-destructive method for detecting and measuring internal defects, such as delamination and cracks, in the multilayer structure of MEMS devices. This technique works through the use of an infrared imaging system to map the changing temperature distribution over the surface of a target object following a sudden change in the boundary conditions, such as the application of a heat source to an external surface. It has previously been utilised in various applications, such as damage assessment in aerospace composites and verification of printed circuit board solder joint manufacture, but little research of its applicability to MEMS structures has previously been reported. In this work, the thermal behaviour of a multilayer structure containing defects was first numerically analysed. A multilayer structure was then successfully modelled using COMSOL finite element analysis (FEA) software with pulse heating on the bottom surface and observing the resulting time varying temperature distribution on the top. The optimum detecting conditions such as the pulse heating energy, pulse duration and heating method were determined and applied in the simulation. The influences of thermal properties of materials, physical dimensions of film, substrate and defect and other factors that will influence the surface temperature gradients were analytically evaluated. Furthermore, a functional relationship between the defect size and the resulting surface temperature was obtained to improve the accuracy of estimating the physical dimensions and location of the internal defect in detection. Corresponding experiments on specimens containing artificially created defects in macro-scale revealed the ability of the thermographic method to detect the internal defect. The precision of the established model was confirmed by contrasting the experimental results and numerical simulations.