A Barkhausen noise (BN) testing system was developed for the non-destructive evaluation (NDE) of residual stresses in CANDU reactor feeder pipes. The system consists of a four-channel arbitrary waveform flux control system (FCS), and the spring-loaded tetrapole prototype (SL4P) BN probe. The combination of the FCS and SL4P was shown to provide repeatable BN measurements on feeder pipe samples, with variations in air gaps between the SL4P poles and the sample from 0.43 mm to 1.29 mm, and typical pickup coil coupling uncertainties for the total BN energy from ±2% to ±7%. Precision for elastic strain estimation in feeder pipes was found to be between ±7 MPa and ±9 MPa in tension, depending on the excitation field configuration, and negligible in compression. Modelling of the BN penetration depth as a function of the excitation field was used to estimate the BN penetration depth between 5 μm at 300 kHz to a maximum of 500 μm at 3 kHz. The modelling, engineering, and procedures developed for this BN testing system provide an improved basis for the future advancement of BN testing, and ferromagnetic NDE in general. / Thesis (Ph.D, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-07-22 15:34:28.967

To evaluate the state of health of the composite, a real-time, in-situ acoustic emission (AE) damage detection system has been developed, where the monitoring of AE activity emitted from within a carbon/epoxy composite material (CFRP) is achieved using an all-fibre Mach-Zehnder interferometric sensor. The basic Mach-Zehnder configuration was modified to achieve the sensitivity needed to detect the low amplitude signals associated with AE. An active homo dyne feedback loop was employed to maintain quadrature, whereas polarisation controllers ensured that the state of polarisation of the guided beams were equal. Two additional components were included in the AE detection system; fibre collimators and a demountable composite test section. The fibre collimators adjusted the optical path length in one of the arms of the interferometer to help maintain system sensitivity from test to test. The demountable test section ensured ease of testing, without the need for continual fusion splicing. The characterisation of the fibre optic sensor was achieved by an analysis of its response to known acoustic disturbances. The fibre optic sensors response to continuous and transient acoustic excitation sources demonstrated the feasibility of using an embedded fibre optic Mach-Zehnder interferometric sensor for the evaluation of composite materials. The sensor's potential for non-destructive evaluation (NDE) was investigated by placing CFRP specimens with the embedded sensors under sufficient tension to cause damage. Signal analysis was performed on the detected AE data, using the time domain parameters and the cumulative event count. The change in the slope of the cumulative count curve coincided with the point where the accumulated damage seriously compromised the structural integrity of the sample. As a damage detection system the fibre optic sensor was adequate, however, the correlation of the time domain parameters with specific damage mechanisms proved inconclusive. Specially designed samples were manufactured to help the fibre optic sensor differentiate between mechanisms. Fibre optic sensor component failure resulted in the testing and analysis using the piezoelectric transducer only. Amplitude and frequency distribution analysis of the piezoelectrically detected signals from these specially designed composite samples was attempted. From the results, it was evident that a correlation could be made between some of the damage mechanisms and the detected AE signals. However, it was apparent that a mixing of distribution occurred in some of the tests. Despite this, the results obtained using the piezoelectric transducer highlighted the benefits of attempting these specially designed tests in future fibre optic sensor work.

This MEng (Master of Engineering) research thesis evaluates the capabilities and limitations of line-scan thermography for the non-destructive evaluation of composite structures containing hidden defects. In simple terms, line-scan thermography is a state-of-the-art technique in which a focused line of thermal energy is transmitted into a material. Line-scan thermography has great potential for the rapid and low cost non-destructive inspection of composite structures for aircraft, automobiles and ships. In this project, theoretical research exploring the heat transfer physics was undertaken in conjunction with experimental studies to develop an optimum inspection regime for line-scan thermography. The capability of line-scan thermography to detect impact damage in carbon/epoxy laminates was experimentally investigated in Chapter 3. From the impact side, in all materials, line-scan thermography overestimated the size of the impact damage whereas flash thermography underestimated the size. There was a close relationship between the ultrasonic profile and the line-scan thermographic thermal response curve. New experimental data has been produced and analysed for the ability of line-scan thermography to determine the defect as well as the defect size. It was found that line-scan thermography was able to distinguish back drilled holes, but it was not possible to determine accurate defect sizing due to the depth of the holes from the inspected surface and the limitations associated with the line-scan thermographic apparatus itself. There was excellent correlation between the C-scan ultrasonics intensity curves and the line-scan thermographs as well as excellent correlation with the theoretical results. The relationship between line-scan thermography and foreign body objects were experimentally investigated for carbon/epoxy composites. A major limitation found with line-scan thermography is its limited depth penetration, which is highlighted in the foreign object study using 6 mm and 13 mm diameter Teflon® discs and 13 mm Teflon® strips embedded in carbon/epoxy laminates. Depth penetration allowed only 2 mm resolution for the 13 mm diameter discs and 1.5 mm resolution for the 6 mm discs in a composite panel. The results of the investigation of stainless steel shim objects in carbon/epoxy laminates reveal that line-scan thermography is capable of determining their presence and size close to the surface. There was also excellent correlation between the ultrasonic response curve and the line-scan thermographic intensity curve. The results of the investigation of thermoplastic film foreign body objects in carbon/epoxy laminates show that at present line-scan thermography does not have the capability to determin e such defects. Experimental results show that line-scan thermography is capable of detecting large voids, back drilled holes, some foreign body objects, and impact damage. However, the ability of line-scan thermography to measure the defect dimensions is dependent on the size and type of damage, the distance from the line source, the depth of the defect, and the type of composite material.

Circular air-coupled ultrasonic testing (ACUT) setup for the inspection of commercial carbon-carbon composite aircraft brake disks was developed in Intelligent Measurement and Evaluation Laboratory (IMEL) at Southern Illinois University Carbondale (SIUC). The developed test setup utilizes Airstar single channel air-coupled equipment and has only manual A-scan and B-scan capability. The developed ACUT technique is unique compared to the commercial C-scan ultrasonic systems and is proficient, fast, economically feasible, and easy to implement method particularly for the inspection of carbon-carbon (C/C) composites aircraft brake disks. Prior to conducting air-coupled measurements, wobble analysis was carried out. This was important because significant wobbling in the test setup can lead to the interference of the reflected and the incident beam which would result to inaccurate ultrasonic measurements. The measured deviation due to wobbling, surface profile of the disk, design, and experimental error were relatively small. Therefore, these errors were neglected while performing ACUT measurements. For ACUT measurements, several through-transmitted amplitude signals were recorded within the C/C brake disks manually. The images were then reconstructed using Matlab based on the through-transmitted amplitude signals. Finally, a comparison was drawn between the reconstructed images and the C-scan images of the C/C brake disks obtained from the commercial Airstar C-scan ACUT system. Like commercial C-scan ACUT image results, reconstructed images were also able to detect all defects in the commercial C/C brake disks which served for the system verification and validation. In addition, defect, non-defect, and suspected areas within the C/C brake disks were quantified with air-coupled measurement. For this, light microscopy was conducted for every sample made from each C/C brake disks at lower magnification of 10X. It was concluded that it is very difficult to assess the crack or delamination situation based on a 2D micrograph of one depth. Also, it was concluded that an internal porosity and micro-cracks may not be only factors that can be related to defects. Finally, an intelligent systems approach, specifically, fuzzy logic and artificial neural network (ANN) methodologies were implemented for the automatic defect detection in commercial C/C aircraft brake disks by using air-coupled ultrasonic results. For this, a multi-layer perceptron (MLP) with two hidden layers and a scaled conjugate gradient back-propagation (BP) learning algorithm was used for the ANN training. The network training process was performed in an off-line mode using the ANN toolbox in Matlab. The network training was repeated until a steady state was reached, where there was no further change in the synaptic weights. The ANN provided plausible results in detecting the defect areas for different C/C brake disks. It was also demonstrated that the system was able to learn the rules without knowing any algorithm for automatic defect detection.

Increasing use of composite materials in industry brings the need for newer and more practical methods to evaluate them. Widespread use of composite materials heavily depends on the manufacturer’s ability to unquestionably ensure its safety, given how much the user trusts them. Non-Destructive Evaluation (NDE) can be used to evaluate adhesive bondline health. This thesis employs Digital Image Correlation (DIC) method, one of the known methods in NDE, and combines it with an embedded speckle pattern in order to obtain valuable information from within the adhesive bondline. By recording the movement of the speckles and analyzing their behavior according to DIC algorithms, a strain map of the adhesive is drawn. An adhesive strain map helps find defects that might be out of sight using conventional NDE methods. This thesis discusses different possible materials to be used as the speckle pattern and chooses the one shows better results based on different criteria. Then employing the material, it records the speckle pattern using optical and ultrasonic methods to draw a strain map. By analyzing the obtained strain maps, defects within the bondline are revealed.

Cette étude s'intègre dans le cadre d'un développement accru de nouvelles techniques de contrôle non destructif des matériaux magnétiques basées sur les phénomènes de couplage magnéto-mécanique. L'objectif est de promouvoir des méthodes originales de mesure des propriétésmagnétiques permettant d'évaluer quantitativement l'état thermo-métallurgico-mécanique d'un matériau par une simple identification inverse.Nous proposons dans ce document un modèle magnéto-mécanique couplé dit modèle multidomaine compatible avec la procédure de contrôle magnétique. Ce modèle analytique permet de simuler le comportement magnétique et magnétostrictif d'un matériau magnétique soumis à un chargement mécanique unidirectionnel. Il a montré une bonne adaptabilité à des états de contraintes et structures magnétiques variées. Le modèle multidomaine a pu être validé dans le cas d'un chargement élastique uniaxial et multixial par un simple recours à une contrainte équivalente magnéto-mécanique. Il a pu également intégrer les éléments nécessaires à la modélisation de l'influence de la plasticité sur l'état magnétique. La plasticité est introduite via un état de contrainteinterne caractérisant une structure hétérogène biphasée. Des corrélations intéressantes entre variables d'écrouissage macroscopiques et propriétés magnétiques ont été élaborées et l'approche a été validée sur un acier dual phases.Nous nous sommes enfin intéressées à a mise en place d'un protocole expérimental novateur assurant un suivi continuel du comportement piézomagnétique du matériau au cours d'un essai de fatigue. Cette technique permet d'estimer la limite d'endurance des matériaux magnétiques. / This study is within a recent research largely motivated by the possibility of development of new non-destructive techniques based on the magneto-mechanical coupling. Thus, the issue is to propose original magnetic methods allowing a quantitative evaluation of the thermo-metallurgicomechnical state of ferromagnetic materials by a simple inverse identification.We propose in this document a coupled magneto-mechanical modeling called multidomain modeling suitable for the non-destructive process. This model is able to simulate magnetic and magnetostrictive behaviors of materials submitted to an uniaxial mechanical loading. It exhibits an adaptability to various mechanical states and magnetic structures. Multidomain modeling provides good results in the case of elastic loading either uniaxial or multiaxial by the use of an equivalent stress. It can also integrate the key elements for modeling the effect of plasticity on the magneticbehavior. Plasticity is introduced through internal stress characterizing heterogenous biphasic structure. Interesting correlations between macroscopic hardening parameters and magnetic properties are shown and the plasticity approach is confirmed by experiments carried out on a dual phase steel.Finally, we propose an experimental protocol allowing in situ continuous investigation of the piezomagnetic behavior during fatigue test. This experimental technique permits the estimation of fatigue limit of ferromagnetic materials.

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Image-based techniques are a promising non-destructive approach for road pavement condition evaluation. The main objective of this study is to extract, quantify and evaluate important surface defects, such as cracks, using an automated computer vision-based system to provide a better understanding of the pavement deterioration process. To achieve this objective, an automated crack-recognition software was developed, employing a series of image processing algorithms of crack extraction, crack grouping, and crack detection. Bottom-hat morphological technique was used to remove the random background of pavement images and extract cracks, selectively based on their shapes, sizes, and intensities using a relatively small number of user-defined parameters. A technical challenge with crack extraction algorithms, including the Bottom-hat transform, is that extracted crack pixels are usually fragmented along crack paths. For de-fragmenting those crack pixels, a novel crack-grouping algorithm is proposed as an image segmentation method, so called MorphLink-C. Statistical validation of this method using flexible pavement images indicated that MorphLink-C not only improves crack-detection accuracy but also reduces crack detection time. Crack characterization was performed by analysing imagerial features of the extracted crack image components. A comprehensive statistical analysis was conducted using filter feature subset selection (FSS) methods, including Fischer score, Gini index, information gain, ReliefF, mRmR, and FCBF to understand the statistical characteristics of cracks in different deterioration stages. Statistical significance of crack features was ranked based on their relevancy and redundancy. The statistical method used in this study can be employed to avoid subjective crack rating based on human visual inspection. Moreover, the statistical information can be used as fundamental data to justify rehabilitation policies in pavement maintenance. Finally, the application of four classification algorithms, including Artificial Neural Network (ANN), Decision Tree (DT), k-Nearest Neighbours (kNN) and Adaptive Neuro-Fuzzy Inference System (ANFIS) is investigated for the crack detection framework. The classifiers were evaluated in the following five criteria: 1) prediction performance, 2) computation time, 3) stability of results for highly imbalanced datasets in which, the number of crack objects are significantly smaller than the number of non-crack objects, 4) stability of the classifiers performance for pavements in different deterioration stages, and 5) interpretability of results and clarity of the procedure. Comparison results indicate the advantages of white-box classification methods for computer vision based pavement evaluation. Although black-box methods, such as ANN provide superior classification performance, white-box methods, such as ANFIS, provide useful information about the logic of classification and the effect of feature values on detection results. Such information can provide further insight for the image-based pavement crack detection application.

Additive manufacturing (AM) is a novel fabrication technique capable of producing highly complex parts. Nevertheless, a major challenge is improving the quality of the fabricated parts. While there are several ways of approaching this problem, developing data-driven methods that use AM process signatures to identify these part anomalies can be rapidly applied to improve the overall part quality during the build. The objective of this dissertation is to model multiple processes within the AM to quantify the quality of the parts and reduced the uncertainty due to variation in input process parameters. The objective of first study is to build a new layer-wise process signature model to characterize the thermal-defect relationship. Based on melt pool images, we propose novel layer-wise key process signatures, which are calculated using multilinear principal component analysis (MPCA) and are directly correlated with layer-wise quality of the part. Second study broadens the spectrum of the dissertation to include mechanical properties, where a novel two-phase modeling methodology is proposed for fatigue life prediction based on in-situ monitoring of thermal history. In final study, our objective is to pave the way toward a better understanding of the uncertainty in the process-defect-structures relationship using an inverse robust design exploration method. The method involves two steps. In the first step, mathematical models are developed to characterize and model the forward flow of information in the intended additive manufacturing process. In the second step, inverse robust design exploration is carried out to investigate satisfying design solutions that meet multiple AM goals.

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