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.

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Ovako products are in many cases used in high fatigue applications. Currently Ovako use ultrasonic evaluation at 10 MHz as a volumetric method for inclusion control. This study intends to investigate two new methods for quantification of micro inclusions.The aim of this study is to develop a method for large area scanning by creating a polishing method that allows you to polish away a specified amount of material, in this case 60 μm. This method will be used to capture the true distribution of critically sized non-metallic inclusions by creating a 3D image out of several 2D scans from the light optical microscope. These results will be compared to the results of high frequency ultrasonic testing at 125 MHz to get a quantitative idea of what can be captured by the high frequency ultrasonic investigation.Two different steel grades were studied, named Grade A and Grade B, with one sample of each. Both grades have similar composition, except that Grade B contains more sulphur. Both grades are of approximately the same hardness. The two steel samples were scanned with a scanning acoustic microscope at the same time as a method to polish away 60 μm was developed. After this, the method was used to scan several layers with an image recognition program in the light optical microscope. The results from both methods were then compared.After testing, it was concluded that the inclusion distribution pattern was completely different for the two steel grades, however the same pattern could be seen for each grade in the LOM and in the ultrasonic. This indicates that the same types of inclusions could be found. It was also found that the ultrasonic enlarges the indications by a severe amount making it hard to take any measurements directly from the ultrasonic images in this study. What is possible to see in the ultrasonic images are the distribution of inclusions and the inclusion placement in the sample. A result of 10 % matching inclusions between both methods is found, which is to say that the same 50 inclusions out of the 500 largest indications from each method in the steel sample is found. These 10 % is however not sufficient enough to conclude by how much the ultrasonic enlarges the indications compared to the light optical microscope. / Ovako i Hofors tillverkar stål för komponenter som kräver hög utmattningshållfasthet. För närvarande utför Ovako ultraljudsundersökningar på 10 MHz som en volymetrisk testmetod för inneslutningskontroll. Den har studien kommer att undersöka två nya testmetoder för kvantifiering av mikroinneslutningar.Syftet med denna studie är att skapa en slipmetod för att polera bort 60 μm material som sedan kan användas för att bygga en 3D bild från ett flertal 2D scanningar i ett ljusoptiskt mikroskop. Detta resultat kommer att jämföras med resultatet från högfrekvens ultraljud på 125 MHz för att få en kvantitativ uppfattning av vad ett högfrekvens ultraljud kan undersöka.Två stålsorter, ett prov av vardera, används i undersökningen, dessa benämns Prov A och Prov B. Båda stålsorterna har ungefär samma hårdhet och sammansättning. Skillnaden i sammansättningen finns i svavelhalten, där Prov B innehåller mer svavel än Prov A. De två stålproverna skannades med ett akustiskt mikroskop samtidigt som en slipmetod för att polera bort 60 μm skapades. Därefter användes metoden för att skanna flera lager med ett bildigenkänningsprogram i det ljusoptiska mikroskopet. Resultatet från både metoderna jämfördes sedan.Ett resultat av studien är att samma inneslutningsmönster kan ses i ultraljudsresultaten och de ljusoptiska resultaten, detta trots att de två olika stålsorterna uppvisade helt olika mönster i sig. Ultraljudet tenderar att förstora upp inneslutningar vilket gör det svårt att mäta inneslutningens storlek direkt från ultraljudsbilden i den här studien. Däremot går det att se fördelningen och placeringen av inneslutningarna direkt i bilden. Ett resultat av 10 % matchning av inneslutnings-indikationer mellan ultraljud och ljusoptiskt hittades. Med detta resultat så går det i denna undersökning inte att jämföra samma inneslutning på ett bra sätt mellan ultraljud och ljusoptiskt för att hitta en faktor av hur mycket ultraljudet förstorar inneslutningarna.

<p dir="ltr">Ultrasonic testing (UT) is a commonly used inspection method for buildings and bridges, yet variability in inspector performance has brought the validity of the UT process into question. While practical tests and performance testing are required as part of most UT certification processes and some industry standards, the building and bridge industries currently have no standardized testing body to verify the qualification of UT technicians. This research aimed to develop and implement a possible standardized testing protocol based on the American Welding Society (AWS) structural welding codes. Results from performance tests conducted in this research demonstrated high variability and low precision in UT measurements and generally poor performance amongst the 20 technicians that took part in the tests. It is clear from this research that certification from the existing certification programs do not always indicate qualification. Therefore, standardized performance testing would add value and increase the reliability of UT inspections by identifying those technicians that are clearly unqualified.</p>

Machining operations in automated manufacturing centers are under-performing by 20-80%. Optimizing these machining operations requires on-line knowledge about the cutting tool's condition and the process state. Currently, this information is either not reliable or not available in a timely manner. This is due to the lack of suitable sensors, which must measure on-line directly and accurately one or more of the relevant tool and process information sources in the hostile machining environment. A direct, active, ultrasonic method for on-line sensing of the tool condition and process state in turning operations was developed. Sensing is achieved by using an ultrasonic transducer operating at 10 MHz in a pulse-echo mode to send pulses through the tool. The amplitude and propagation time of the reflected pulses are modulated by the tool nose, flank, temperature, and by the material in contact with the tool. The reflected pulses are received and processed by a high speed digital signal processing system. This method has the potential to directly and accurately measure on-line several relevant processes and cutting tool parameters through the use of a single sensor. These parameters are tool-workpiece contact, tool wear, tool chipping, temperature and chatter. / Ph. D.

Research effort was directed towards developing a near real-time, acousto-ultrasonic (AU), nondestructive evaluation (NDE) tool to study the failure mechanisms of ceramic composites. Progression of damage is monitored in real-time by observing the changes in the received AU signal during the actual test. During the real-time AU test, the AU signals are generated and received by the AU transducers attached to the specimen while it is being subjected to increasing quasi-static loads or cyclic loads (10 Hz, R = 0.1). The received AU signals for 64 successive pulses were gated in the time domain (T = 40.96 µsec) and then averaged every second over ten load cycles and stored in a computer file during fatigue tests. These averaged gated signals are representative of the damage state of the specimen at that point of its fatigue life. This is also the first major attempt in the development and application of real-time AU for continuously monitoring damage accumulation during fatigue without interrupting the test. The present work has verified the capability of the AU technique to assess the damage state in silicon carbide/calcium aluminosilicate (SiC/CAS) and silicon carbide/magnesium aluminosilicate (SiC/MAS) ceramic composites. Continuous monitoring of damage initiation and progression under quasi-static ramp loading in tension to failure of unidirectional and cross-ply SiC/CAS and quasi-isotropic SiC/MAS ceramic composite specimens at room temperature was accomplished using near real-time AU parameters. The AU technique was shown to be able to detect the stress levels for the onset and saturation of matrix cracks, respectively. The critical cracking stress level is used as a design stress for brittle matrix composites operating at elevated temperatures. The AU technique has found that the critical cracking stress level is 10-15 % below the level presently obtained for design purposes from analytical models. An acousto-ultrasonic stress-strain response (AUSSR) model for unidirectional and cross-ply ceramic composites was formulated. The AUSSR model predicts the strain response to increasing stress levels using real-time AU data and classical laminated plate theory. The Weibull parameters of the AUSSR model are used to calculate the design stress for thermo-structural applications. Real-time AU together with the AUSSR model was used to study the failure mechanisms of SiC/CAS ceramic composites under static and fatigue loading. An S-N curve was generated for a cross-ply SiC/CAS ceramic composite material. The AU results are corroborated and complemented by other NDE techniques, namely, in-situ optical microscope video recordings and edge replication. / Ph. D.

Nenhuma / Uma das principais etapas na fabricação de combustíveis nucleares tipo placa, para a utilização em reatores de pesquisa e de propulsão naval, consiste no desenvolvimento de métodos e técnicas de ensaios não destrutivos para a avaliação do combustível nuclear durante a fabricação, assim como para análises do combustível pós-irradiação. Os ensaios não destrutivos podem contribuir para a detecção de descontinuidades durante as etapas de fabricação do combustível, como trincas e falhas na união entre o cerrne e o revestimento, que podem provocar a falha do combustível durante o seu uso em reatores nucleares. Métodos de ensaio como visual, radiográfico, correntes parasitas e ultra-som podem ser utilizados para essa finalidade. Neste trabalho foi abordado o uso do ensaio não destrutivo por ultra-som para a avaliação de combustíveis nucleares tipo placa. Devido às pequenas espessuras dos combustíveis tipo placa, assim como aos diferentes materiais presentes nos mesmos, foram utilizados, nos experimentos, transdutores ultra-sônicos de contato com sapatas de atraso e transdutores de imersão. Os ensaios foram realizados em um protótipo de combustível tipo placa constituído por um núcleo de UO2 disperso em uma matriz metálica de aço inoxidável, com revestimento em aço inoxidável. Neste protótipo foram usinados diferentes tipos de refletores artificiais, simulando a presença de descontinuidades naturais. Para os testes com os transdutores de imersão foi desenvolvido um dispositivo para a obtenção do perfil do feixe sônico emitido pelos mesmos, de forma a identificar a região de maior sensibilidade do feixe para o ensaio. Foram ainda fabricadas algumas lentes acústicas para a focalização do feixe, neste caso, sem sucesso. O uso dos diferentes tipos de transdutores ultra-sônicos possibilitou o estabelecimento de uma metodologia para a detecção de descontinuidades com diferentes geometrias e dimensões. O protótipo de combustível desenvolvido para os experimentos demonstrou ser adequado para estudos de sensibilidade do sistema de ensaio. / One of the most important steps in the fabrication processes of plate type nuclear fuels, intended to be used in research reactors or naval propulsion, is the development of nondestructive testing (NDT) methods and techniques for their quality assessment during fabrication and post-irradiation analysis. Those tests can contribute to detect discontinuities such as cracks and fails in meat-cladding junctions, that can lead to failures when installed and used in reactors. Examples of NDT methods that may be used for this purpose are visual inspection, radiography, eddy current and ultrasound. The objective of this study is to present the utilization of ultrasound methods to evaluate plate type nuclear fuels. Due to the small thicknesses of such kind of fuels, as well as the presence of different materials, the ultrasonic transducers used to perform the experiments were immersion type or contact with delay shims. Furthermore, a dummy plate fuel, constituted by a dispersion of UO2 in stainless steel matrix, with stainless steel cladding, was specially constructed. In the surface of such plate, several kinds of artificial reflectors, simulating the presence of natural flaws were machined. For immersion type ultrasonic transducers, a mechanical scanning system was developed to allow the determination of their sonic beam profiles and identification of the highest sensitivity beam region. Additionally, some acoustic lenses, useful to help on beam focalization, were fabricated and used, but the expected performance was not achieved. The use of different kinds of ultrasonic transducers allowed the establishing of a methodology to detect discontinuities of different geometry and sizes. The developed dummy fuel demonstrated to be adequate for the studies of sensitivity of the test system.

Conventional contact ultrasonic methods suffer from large variability, which is known to originate from a number of sources such as coupling variability, and the surface roughness at the transducer/specimen interface. The inherently small higherharmonic signals can be significantly influenced by the changes in contact conditions, especially in nonlinear ultrasonic measurements. For this reason, the noncontact generation and detection techniques are very attractive. This research first focuses on the optical generation of tone-burst surface acoustic waves in a metallic specimen. Two methods that use laser light as an optical source are compared for generating surface acoustics waves in the 5 MHz range. Both the shadow mask and diffraction grating are used to convert a laser pulse to a tone-burst signal pattern on the specimen. The generated signals are detected by a wedge transducer at a fixed location and then the harmonic contents in the generated signals and the repeatability of the methods are evaluated. Finally, the developed method is used to characterize the material nonlinearity of aluminum (Al 6061) and steel (A36). The results showed repeatable measurements for ablative signal excitation on aluminum.

Corrosion often occurs in the inner aluminum lining of the HB-53 helicopter external fuel tank, resulting in fuel leaks. This project centers on developing an in-situ ultrasonic inspection technique to detect corroded areas inside the fuel tank. Due to the complexity of the composite structure of the tank, the ultrasonic inspection is carried out from inside the tank using a monostatic backscattering technique. The backscattered field contains information related to the insonified surface properties (surface roughness scales). Numerical predictions are implemented with a simplified model of backscattered intensity (Ogilvy, 1991). Experimental results are obtained on artificially corroded plates, and on the actual fuel tank of the HB-53 helicopter. Signal processing techniques (Envelope Correlation and Inverse Technique) are used to detect corroded surfaces with data obtained with a focused 10 MHz pulsed transducer.