The goal of this research is to show the feasibility of detecting density variations in green-state powder metallurgy (P/M) compacts from surface voltage measurements. By monitoring a steady electric current flow through the sample and recording the voltages over the surface, valu-able information is gathered leading to the prediction of the structural health of the compacts. Unlike prior research that concentrated on the detection of surface-breaking and subsurface de-fects, the results presented in this thesis target the density prediction throughout the volume of the sample. The detection of density variations is achieved by establishing a correlation between the conductivity and their respective density. The data obtained from the surface measurements is used as part of an inversion algorithm, calculating the conductivity distribution, and subse-quently the density within the compact. In a first step, the relationship between conductivity and density of green-state P/M com-pacts was investigated. Tests were conducted for a number of parts of various powder mixtures. In all cases a clear correlation between conductivity and density could be established, indicating that measurements of electric conductivity could indeed be exploited in an effort to render valid information about the density of the sample under test. We found a linear correlation for non-lubricated parts and a non-linear behavior for lubricated samples. Specifically, it was found that the conductivity increases with increasing density only up to a maximum value obtained at ap-proximately 6.9g/cm3. Interestingly, any additional density increase leads to a reduction of the conductivity. This behavior was confirmed to be inherent in all powder mixtures with lubricants. The thesis research is able to provide a physical model and a mathematical formulation describ-ing this counter-intuitive phenomenon. A finite element solver in conjunction with an inversion algorithm was then implemented to study arbitrarily shaped part geometries. Based on the principles of electric impedance imag-ing, the developed algorithm faithfully reconstructs the density distribution from surface voltage measurements. The feasibility of the instrumentation approach for both simple and complex parts can be demonstrated using a new sensor concept and measurement arrangement. Measurements were performed on both geometrically simple and complex parts.

Identifying material parameters in composite plates is a necessary first step in a variety of structural applications. For example, understanding the material parameters of carbon fiber composite is important in investigating sensor and actuator placement on micro-air-vehicle wings for control and wing morphing purposes. Knowing the material parameters can also help examine the health of composite structures and detect wear or defects. Traditional testing methods for finding material parameters such as stiffness and damping require multiple types of experiments such as tensile tests and shaker tests. These tests are not without complications. Methods such as tensile testing can be destructive to the test specimens while use of strain gages and accelerometers can be inappropriate due to the lightweight nature of the structures. The proposed inverse problem testing methods using digital image correlation via high speed cameras can potentially eliminate the disadvantages of traditional methods as well as determine the required material parameters including stiffness and damping by conducting only one type of experiment. These material parameters include stiffness and damping for both isotropic and orthotropic materials, and ply angle layup specifically for carbon fiber materials. A finite element model based on the Kirchoff-Love thin plate theory is used to produce theoretical data for comparison with experimental data collected using digital image correlation. Shaker experiments are also carried out using digital image correlation to investigate the modal frequencies as validation of the results of the inverse problem. We apply these techniques first to an aluminum plate for which material parameters are known to test the performance and efficiency of the method. We then apply the method to a composite plates to determine not only these parameters, but also the layup angle. The inverse problem successfully estimates the Young's modulus and damping for the aluminum material. In addition, the vibration analysis produces consistent resonance frequencies for the first two modes for both theoretical and experimental data. However, carbon fiber plates present challenges due to limitations of the Kirchoff-Love plate theory used as the underlining theoretical model for the finite element approximation used in the inverse problem, resulting in a persistent mismatch of resonance frequencies in experimental data. / Graduation date: 2012

Defects in a plastic floor material produced in Tarketts factory in Ronneby are causing waste of time and material since it is noticed too late in the production line. The objective of this thesis is to investigate if the nondestructive test method NAW®, which is developed by Acoustic Agree in Ronneby, can be a solution to find the defects at an earlier stage. Nondestructive testing mainly means what the name says; quality tests of a material can be made without causing any damage. One simple example of a nondestructive testing tool is the human eye. By looking at a product defects on the surface can be found. The method used in this thesis, NAW®, is a nonlinear acoustical method. By listening to the material, information about disturbances inside the material can be gathered and interpreted to get a picture of the quality status. Although by listening it does not in this case mean by a human ear but with special equipment since the sound used is high frequent ultrasound. For several material samples, experiments were made both for the references and with introduced defects. It was hard to get definitive results since, for example, even the results for the different reference samples were differing a lot. Nevertheless there are some results pointing in the same direction which means that there is still hope for the possibility to use NAW® as a tool in the production at Tarkett. One important problem in this work is the fact that the defect material is not actually a real defect material but an imitated one with defects made by hand in the experiments. This is a possible error and has to be considered in case of further experiments. Either the imitated defects have to be “improved” or, in the ideal case, real defective material from the factory should be used to get as reliable results as possible. / Defekter i golvmaterial i tillverkningen hos Tarkett i Ronneby orsakar slöseri med tid och material eftersom de upptäcks sent i produktionslinjen. Syftet med detta examensarbete är att undersöka om den oförstörande provningsmetoden NAW®, som utvecklats av Acoustic Agree i Ronneby, kan vara en lösning för att hitta defekterna på ett tidigare stadium. Oförstörande provning är helt enkelt materialprovning där föremålet som undersöks inte förstörs. Ett enkelt exempel på verktyg för oförstörande provning är ögat. Genom att undersöka ett föremål med synen kan man enkelt kvalificera ytan. Den metod som används i detta arbete, NAW®, är en olinjär akustisk metod. Genom att lyssna på materialet kan mycket information om störningar inuti materialet samlas ihop och tolkas för att få en bild av kvaliteten. För flera materialbitar har experiment genomförts både för referensmaterial och för material med imiterade defekter. Det var svårt att se entydiga resultat då exempelvis till och med resultaten för referensmaterialet var väldigt olika sinsemellan. Dock pekar vissa av resultaten åt samma håll vilket gör att hoppet lever kvar för att NAW® kan vara ett möjligt verktyg i produktionen hos Tarkett. Ett stort problem i arbetet var frånvaron av trovärdiga defekter. Defekterna tillverkades och introducerades i materialet för hand, och viss tveksamhet finns gällande likheten mellan imiterade och riktiga defekter. Detta ses som en möjlig felkälla och måste tas i beaktan för eventuellt fortsatt arbete. Antingen måste de imiterade defekterna ”förbättras” eller, som vore idealt, så kan riktigt defekt material från tillverkningen användas för att ge så trovärdiga och pålitliga resultat som möjligt.

Techniques for producing X-ray negatives of dendrochronological specimens have been developed at the Geological Survey of Canada and the Nondestructive Testing Laboratory, Mines Branch, The radiographs are produced to provide tree-ring density data to supplement ring-width measurements for dating and climatic studies. New specimen preparation techniques and X-ray methods are discussed. The quality and quantity of tree-ring information is enhanced by the use of X-ray analysis.

Lying between the microwave and far infrared (IR) regions, the "terahertz gap" is a relatively unexplored frequency band in the electromagnetic spectrum that exhibits a unique combination of properties from its neighbors. Like in IR, many materials have characteristic absorption spectra in the terahertz (THz) band, facilitating the spectroscopic "fingerprinting" of compounds such as drugs and explosives. In addition, non-polar dielectric materials such as clothing, paper, and plastic are transparent to THz, just as they are to microwaves and millimeter waves. These factors, combined with sub-millimeter wavelengths and non-ionizing energy levels, makes sensing in the THz band uniquely suited for many NDE applications. In a typical nondestructive test, the objective is to detect a feature of interest within the object and provide an accurate estimate of some geometrical property of the feature. Notable examples include the thickness of a pharmaceutical tablet coating layer or the 3D location, size, and shape of a flaw or defect in an integrated circuit. While the material properties of the object under test are often tightly controlled and are generally known a priori, many objects of interest exhibit irregular surface topographies such as varying degrees of curvature over the extent of their surfaces. Common THz pulsed imaging (TPI) methods originally developed for objects with planar surfaces have been adapted for objects with curved surfaces through use of mechanical scanning procedures in which measurements are taken at normal incidence over the extent of the surface. While effective, these methods often require expensive robotic arm assemblies, the cost and complexity of which would likely be prohibitive should a large volume of tests be needed to be carried out on a production line. This work presents a robust and efficient physics-based image processing approach based on the mature field of parabolic equation methods, common to undersea acoustics, seismology, and other areas of science and engineering. The method allows the generation of accurate 3D THz tomographic images of objects with irregular, non-planar surfaces using a simple planar scan geometry, thereby facilitating the integration of 3D THz imaging into mainstream NDE use.

The aim of this research is to assess the material properties of concrete like modulus of elasticity, compressive strength, and Poisson’s ratio using various nondestructive Testing (NDT) methods like Ultrasonic Pulse Velocity (UPV) and Rebound Hammer (RH). Assessment of material properties of concrete is very important as they are used for structural design process. Various NDT methods are applied to ensure the quality of concrete specimens but they can also be used to find material properties. UPV is a NDT method which is used to test the internal condition of the concrete specimen. RH is a surface hardness testing method and can be used to test the homogeneity of the specimen. For this study, several batches of concrete samples with three different design strengths of 6000 psi, 8000 psi, and 12000 psi were casted. Modulus of elasticity and Poisson’s ratio were calculated from UPV P-wave and S-wave velocities. A Nomogram was developed by combining the longitudinal ultrasonic pulse velocities, rebound numbers, and compressive strengths measured from UPV, RH, and compressive strength tests respectively. This combined NDT correlation curve (Nomogram) can be used to estimate compressive strength of concrete if UPV and rebound values are known. The accuracy of these NDT methods were determined by comparing estimated strength to the actual strength. Furthermore, the effect of moisture content on UPV and rebound values was reviewed and also studied dynamic modulus of elasticity and its relation with static modulus of elasticity of the concrete was investigated for better understanding.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / Includes bibliographical references. / by Tomas A. Gonzalez. / Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980.

Em formação de imagens por ultrassom de objetos com superfícies curvas, em imersão, se as velocidades de propagação no ruído e no objeto forem muito diferentes os efeitos de refração precisam ser compensados. Nesse caso a posição e a forma da superfície precisam ser conhecidas. Neste trabalho a superfície é detectada pelo mesmo array linear que captura os sinais para a formação de imagem.Dois métodos rápidos de detecção de superfície foram propostos, um baseado em técnicas de formação de imagem e outro que utiliza informações de tempo de percurso de ecos extraídas diretamente dos sinais de ultrassom.Os dois métodos foram comparados,e o método baseado em imagem apresentou uma maior tolerância a erros nos sinais, enquanto o método baseado em tempo de percurso mostrou-se mais rápido.Com a superfície detectada, a imagem foi formada por combinação de imagens por abertura sintética, que apresentou uma boa resolução. O uso conjunto dos métodos de detecção de superfície propostos e da formação de imagem resultou em uma taxa de imagens que permite ensaios interativos,com processamento em uma CPU de uso geral. / In ultrasound imaging ofobjects with curved surface, in immersion, the refraction eects must be compensated for if the propagation speed in the uid is very dierent from the speed in the object. In this case the surface position and shape must be known. In this work the surface is detected by the same linear array that captures the signals for the image formation. Two fast methods for surface detection were proposed,one is based on image formation techniques and another utilizes the echotime-of-ight information directly from the ultra\\sound signals.The two methods were compared,and the image-based method was more tolerant of signal errors, while the time-of-ight-based method was faster. After the surface detection, the image was formed by combination of synthetic aperture images,with a good resulting resolution. The utilization of the proposed surface detection methods together with the image formation resulted in an image rate that allows interactive testing, with processing on a general-purpose CPU.

In recent decades techniques related to the measurement of elastic waves have advanced significantly. It is now possible with relatively inexpensive equipment to record amplitudes and frequency bands that were unthinkable two decades ago. This has led to the development of theoretical topics which application was questionable until not long ago, to profit from new technological potential in obtaining more and better experimental information. In this context the study of the propagation of guided waves in solids is presented as a knowledge that allows to detect damage with efficiency and economy in a number of structures in which at least one dimension is much larger than the other two. This is the case for rails, tubulations and pressure vessels among others. In this work, guided waves propagation characteristics are studied, first in a prismatic bar and then within the geometry of a rail. In both cases, dispersion curves were computed according two different work methodologies, first using an axisymmetric model and then corroborated with a model of periodic conditions. Finally propagation of a Tone-Burst waves were simulated on the analyzed geometries, leading to the discussion of how the waves scatter along its propagation. The results obtained were the dispersion curves of both sections. / En las últimas décadas técnicas relacionadas con la medición de ondas elásticas han avanzado sensiblemente. Actualmente, con equipamientos relativamente económicos es posible registrar amplitudes y franjas de frecuencia que eran impensables dos décadas atrás. Este hecho ha motivado que tópicos teóricos que hasta hace un tiempo tenían una aplicación cuestionable tengan que ser desarrollados para poder aprovechar las nuevas potencialidades tecnológicas en la obtención de mayor y mejor información experimental. En este contexto, el estudio de la propagación de ondas guiadas en sólidos se presenta como un conocimiento que posibilita detectar daño con eficiencia y economía en una serie de estructuras en las cuales por lo menos una dimensión es mucho mayor que las otras dos. Es el caso de estructuras tubulares, rieles o recipientes sometidos a presión entre otras. En el presente trabajo se estudian las características de propagación de ondas guiadas primeramente una barra rectangular y posteriormente en la geometría de un riel. En ambos casos, fueron calculadas las curvas de dispersión obtenidas con por dos metodologías de trabajo por elementos finitos, la primer metodología fue emplear un cálculo aplicando un modelo axisimétrico, y luego corroborado con un modelo de condiciones periódicas y posteriormente fue simulada la propagación de una onda tipo Toneburst sobre las geometrías analizadas discutiendo cómo dicha onda se dispersa durante su propagación. Los resultados obtenidos fueron las curvas de dispersión de ambas secciones.

Os ensaios não destrutivos servem como uma importante ferramenta para a análise de estruturas de concreto armado. A utilização de ensaios de velocidade de propagação do pulso ultra-sônico (VPU) permite realizar um acompanhamento das características do material ao longo de sua vida útil. Através da análise dos dados obtidos, pode-se averiguar a uniformidade do concreto, controlar a sua qualidade, acompanhar sua deterioração e, através de comparação com corpos de prova de referência e, até mesmo, estimar a resistência do mesmo. No entanto, as técnicas atuais para análise dos resultados coletados são, em grande parte, baseadas na sensibilidade dos profissionais que as aplicam. Para facilitar o controle e inspeção de estruturas de concreto armado é fundamental desenvolver estratégias para tornar esta análise mais simples e precisa. Este trabalho se baseia na hipótese de que a aplicação de Redes Neurais Artificiais (RNAs) pode gerar modelos de relacionamento úteis e acurados entre as características do concreto, sua compacidade e sua resistência à compressão. O intuito é determinar se com o uso de RNAs é possível estabelecer relações não-lineares que permitam estimar a resistência do concreto a partir do conhecimento de algumas propriedades básicas e da verificação da sua compacidade por meio de ensaios de VPU. Os resultados indicam que as RNAs podem ser usadas para gerar métodos numéricos robustos e flexíveis para estimativa da resistência à compressão a partir de dados de VPU. O estudo evidencia uma considerável melhora nos resultados de estimação da resistência quando se empregam modelos neurais, em comparação a modelos estatísticos tradicionais. Para os dados coletados, provenientes de diversas pesquisas, os modelos tradicionais geram estimativas com coeficientes de determinação que não ultrapassam um valor de R² de 0,40. Já as redes neurais conseguem ajustes com R² da ordem de 0,90. Além de contribuir para uma melhor análise de situações em que haja dúvidas sobre a resistência ou homogeneidade de elementos de concreto, o trabalho demonstra que modelos neurais são uma forma eficiente de ordenar e transferir conhecimento não estruturado. Constatou-se, ainda, que, dada sua capacidade de aprendizagem e de generalização do conhecimento adquirido, as RNAs se constituem em um meio rápido e preciso para modelagem de fenômenos complexos. / Nondestructive Testing (NDT) techniques are useful tools for analyzing reinforced concrete (RC) structures. The use of Ultrassonic Pulse Velocity (UPV) measurements enables the monitoring of changes in some critical characteristics of concrete over the service life of a structure. The interpretation of the data collected allows an assessment of concrete uniformity, and can be used to perform quality control, to monitor deterioration and even, by means of comparison against reference samples, to estimate compressive strength. Nonetheless, the current techniques for UPV data analysis are, on a large degree, based on the sensitivity of the professionals who apply these tests. For accurate diagnosis it is necessary to consider the various factors and conditions that can affect the results. To proper control and inspect RC facilities it is essential to develop appropriate strategies to make the task of data interpretation easier and more accurate. This work is based on the notion that using Artificial Neural Networks (ANNs) is a feasible way to generate workable estimation models correlating concrete characteristics, compacity and compressive strength. The goal is to determine if it is possible to establish models based on non-linear relationships that are capable of estimating with good accuracy the concrete strength based on previous knowledge of some basic material characteristics and UPV measurements. The study shows that this goal is achievable and indicates that neural models perform better than traditional statistical models. For the data collected in this work, provided by various researchers, traditional regression models cannot exceed R² = 0.40, while the use of ANNs allows the creation of models that can reach a determination coefficient R² = 0.90. The results make clear that, besides contributing to better the analysis of situations where there is doubts regarding concrete strength or uniformity, neural models are an efficient way to order and transfer unstructured knowledge. It was shown that, given the learning capacity and its ability to generalize acquired information into mathematical patterns, ANNs are a quick and adequate way to model complex phenomena.