No description available.

Gas Metal Arc welding (GMAW) is one of the primary techniques used to join structural components together. The major obstacle precluding full closed-loop control of GMAW has been the lack of robust techniques using non-destructive and non-contact sensors capable of operating in high temperature and harsh environments typical of GMAW processes. This research uses laser generated ultrasound and electromagnetic acoustic transducer (EMAT) to receive ultrasound. Previous research has focused on ultrasonic shear wave time of flight (TOF) techniques to determine weld penetration depth, a key measure of weld quality. The objective of this research was to use a new technique, frequency modulation of a laser phased array (FMLPA), to determine weld penetration depth. Theoretical background of the FMLPA was developed. An analytical model of the FMLPA was derived and validated through experimentation. The FMLPA was experimentally validated. However, both the FMLPA and shear wave TOF techniques have proven to be impractical for real-time control. These techniques are impractical because the required ultrasonic waves are difficult to acquire due to attenuation and interference from other waves. A new type of wave called the RGLS wave was discovered during the course of this research. The RGLS wave was used to create a new RGLS TOF method for measuring weld penetration depth. The RGLS TOF method for measuring weld penetration depth has proven to be highly accurate, precise, and repeatable. The RGLS TOF method for measuring weld penetration depth has been demonstrated to work both off-line after welding and real-time during welding. Although the FMLPA and shear wave TOF technique was proven to be impractical, the RGLS TOF method has met the ultimate goal of this research area. Other new methods such as the RGSL, RGLL, and RGSS TOF methods related to the RGLS TOF method was also developed. The RGLS TOF method is suited for non-destructive and non-contact sensing. It will help future researchers achieve closed-loop control and automation of the GMAW process, which will help to improve quality and efficiency of welding, and also reduce waste and cost of welding parts together.

In the design of cryogenic fuel tanks for the next generation Reusable Launch Vehicles (RLVs), the permeability of liquid hydrogen (LH2) across the thickness of the tank is a critical issue. The rate of permeation of LH2 is largely dependent on the internal damage state of the composite tank wall. Damage in the form of matrix cracks in the composite material of the tank is responsible for the through-the-thickness permeation of LH2. In this context, the detection of matrix cracks takes on an unprecedented significance. In this work, an ultrasonic technique for the ply-by-ply detection of matrix cracks in laminated composites is developed. Experimental results are presented for graphite/epoxy laminates with different lay-ups and laminate thicknesses. Matrix cracks in each of the plies of the laminated composites were detected even when there was a rather high density of cracks in all of the plies. The ultrasonic data were calibrated by comparing them with the corresponding results obtained by using the traditional methods of optical microscopy and penetrant enhanced X-radiography. Excellent quantitative correlation was observed between the results obtained with ultrasonics and the traditional methods.

In the design of cryogenic fuel tanks for the next generation Reusable Launch Vehicles (RLVs), the permeability of liquid hydrogen (LH2) across the thickness of the tank is a critical issue. The rate of permeation of LH2 is largely dependent on the internal damage state of the composite tank wall. Damage in the form of matrix cracks in the composite material of the tank is responsible for the through-the-thickness permeation of LH2. In this context, the detection of matrix cracks takes on an unprecedented significance. In this work, an ultrasonic technique for the ply-by-ply detection of matrix cracks in laminated composites is developed. Experimental results are presented for graphite/epoxy laminates with different lay-ups and laminate thicknesses. Matrix cracks in each of the plies of the laminated composites were detected even when there was a rather high density of cracks in all of the plies. The ultrasonic data were calibrated by comparing them with the corresponding results obtained by using the traditional methods of optical microscopy and penetrant enhanced X-radiography. Excellent quantitative correlation was observed between the results obtained with ultrasonics and the traditional methods.

In this research, through-transmission ultrasonic (TTU) Acoustography was applied to measure and quantify porosity levels in carbon fiber reinforced polymer (CFRP) composite laminates. This study employed several CFRP specimens with wide ranges of porosity prepared by altering the curing pressure during the manufacturing process. The Acoustography method, operating at 5 MHz, was able to show contrast in ultrasonic images obtained for composite laminates with varied porosity levels. Porosity levels in composite laminates were quantified using destructive methods: acid digestion and microscopy. Also, strength analysis tests were conducted to investigate the effect porosity has on the laminate’s structural integrity. From the results obtained, it was demonstrated that the mechanical properties, interlaminar shear strength (ILSS), and flexural strength of CFRP decreased with the increasing void content. In addition, Acoustography absorption coefficient measurements were related to varied porosity levels in the composite laminates. As the porosity content increased within the laminates, the acoustic absorption coefficient increased. These findings are significant because Acoustography is being developed as a faster alternative to traditional ultrasonic inspection of composites and porosity is an important anomaly to quantify utilizing NDE methods.

Advanced nondestructive inspection techniques like stress wave timing and resistance microdrilling have been used to successfully inspection timber bridges, but it is most effective on girder style bridges. There is a noted need to develop additional inspection techniques for longitudinal deck/slab timber bridges, which comprise about 20% of the national bridge inventory. One technique that holds potential is ground penetrating radar, a recognized nondestructive testing technique that has been used effectively for many different environmental and transportation applications. It has been utilized successfully to identify buried objects, internal defects and material changes. The objective of this research was to assess the potential for using GPR to identify and assess simulated deterioration in longitudinal timber deck timber bridges. GPR scans were completed in the longitudinal and transverse directions of a screwlaminated timber bridge deck before and after a bituminous layer was added to assess embedded defects that simulated voids, decay, insect damage and horizontal shear splitting. Assessment of the GPR wave energy signal was completed using visualization software that was provided with the commercial GPR unit used for the testing. The radar signal was analyzed in both the longitudinal direction (antenna front to back) and the transverse direction (antenna side to side). Interpretation of the radar signals allowed for the identification of various internal defects present in the deck. Based on the results, GPR has the potential to identify internal defects in timber bridge decks before and after a bituminous layer was added. Large, rectangular void defects (at least 6? by 12? by 5 in. (15.2? by 30.4? by 12.7 cm)) that were hollow, filled with foam, or filled with sawdust/adhesive were most easily identified under all scanning conditions. The addition of a bituminous layer, common to slab bridge construction, damped the signal response and made it more difficult to identify defects. Several smaller defects that were found in the deck without a bituminous layer were not identified in scanning completed after the bituminous layer was added.

No description available.

The objective of this thesis is to present analysis techniques that quantify the scattering of angle-beam ultrasonic waves from through-holes in plates. This topic is of interest because increased understanding of the scattering of ultrasonic waves by a defect is important for the development of many nondestructive evaluation (NDE) applications. Angle-beam techniques are commonly used in industry to detect and characterize defects, and many structures of concern have plate-like components. Scattering from through-holes is particularly important because cracks tend to form around fastener holes, which have high stress concentrations. In addition, varying boundary conditions within a fastener hole can change over the course of a structure’s lifetime and may have significant effects on NDE results. In this research, two signal processing techniques are developed to obtain scattering information from through-holes for a variety of fill conditions, including epoxy and complete and partial filling with metal inserts, using experimentally acquired wavefield measurements. Experimental procedures for acquiring wavefields, which measure the out of plane motion of ultrasonic waves on the surface of a specimen and allow for the visualization and characterization of propagating waves, are presented. Methods for obtaining radial and directional energy maps, which quantify scattering as a function of scattered angle and phase velocity, are described. In addition, baseline subtraction is used to obtain scattering patterns for both methods, which quantify scattering as a function of polar angle for each wave mode present in the wavefield. These techniques are applied to wavefield measurements from through-holes with various fill conditions to investigate the effects of boundary conditions on ultrasonic scattering. A comparison of the radial and directional energy mapping techniques, discussing the strengths and weaknesses of each approach, is provided, and recommendations are made for future work.

O objetivo deste trabalho foi avaliar a influência do teor de umidade e da dimensão do corpo−de−prova na velocidade de propagação ultra−sônica em madeira serrada. As espécies utilizadas no procedimento experimental foram: cupiúba {Goupia glabra), eucalipto grandis (Eucalyptus grandis), jatobá (Hymenaea spp), eucalipto citriodora (Eucalyptus citriodora), pinus caribea (Pinus caribea var. caribea) e pinus elliottii (Pinus elliottii var. elliottii). Utilizou−se o equipamento de ultra−som Sylvatest, com transdutores exponenciais de 22 kHz. A experimentação para avaliar a influência da dimensão do corpo−de−prova foi feita em duas etapas: variando a seção transversal e mantendo o comprimento da peça constante e a seguir mantendo a seção e variando o comprimento. Na primeira etapa, foram utilizados doze corpos−de−prova com dimensões variando desde 6 cm x 12 cm x 50 cm até 1 cm x 12 cm x 50 cm. Para a análise da influência do comprimento, foram utilizadas doze vigas por espécie com dimensão inicial de 6 cm x 12 cm x 300 cm, avaliadas até o comprimento final de 10 cm. A aplicação da onda ultra−sônica foi feita na direção longitudinal. Foram feitos ensaios destrutivos em vigas e corpos−de−prova para a comparação entre os módulos de elasticidade obtidos nos ensaios estáticos e no ensaio com ultra−som. Na experimentação para avaliar a influência do teor de umidade na velocidade de propagação, foram avaliadas doze peças por espécie com dimensões 2,5 cm x 30 cm x 75 cm, desde saturadas até o teor de umidade em torno de 6%. Os resultados demonstraram que a influência da seção transversal do corpo−de−prova ocorre em função da relação entre as dimensões da seção e o comprimento de onda utilizado. Quando o comprimento de onda (λ) se aproxima de uma das dimensões da peça, ocorre uma diminuição na velocidade causada pelo efeito fronteira. O estudo sobre a influência do comprimento do corpo−de−prova (L) evidenciou que existe um ponto crítico na relação entre L e comprimento de onda (L/λ)a partir do qual a velocidade não é mais afetada. Os resultados sobre a influência do teor de umidade indicaram uma tendência de diminuição da velocidade com o aumento do teor de umidade, em ambas as direções de propagação da onda ultra−sônica (paralela e perpendicular às fibras), para todas as espécies estudadas. A influência do teor de umidade ocorreu de modo diferente, acima e abaixo do ponto de saturação, sendo mais significativa no segundo caso. Os resultados obtidos permitiram desenvolver uma expressão matemática para a correção da velocidade de propagação em função do teor de umidade e da densidade da madeira / The aim of this research was to evaluate the influence of moisture content and dimensions of specimens on the ultrasonic velocity in wood. The species used were: cupiúba (Goupia glabra),eucalipto grandis (Eucalyptus grandis), jatobá (Hymenaea spp), eucalipto citriodora (Eucalyptus citriodora), pinus caribea (Pinus caribea var. caribea) and pinus elliottii (pinus elliottii var. elliottii). Ultrasonic measurements were taken with the experimental equipment Sylvatest with 22 kHz transducers. Experimental procedure about dimensions were carried out in two steps: specimens of constant length and variable cross−section and of constant cross−section and variable length. In the first case, were taken twelve specimens with initial cross−section of 6 cm x 12 cm, planed until 1 cm x 12 cm and constant length (50 cm). In the second case, were taken twelve specimens with length from 300 cm to 10 cm and constant cross−section (6 cm x 12 cm). Ultrasonic measurements were made in the longitudinal direction. They were also made destructive tests in beams and specimens with the purpose of comparison between static and ultrasonic methods. In the study of the influence of moisture content, twelve specimens (2.5 cm x 30 cm x 75 cm) were dried from green until about 6% moisture content The results showed that the influence of cross−section depends on the relation between dimensions and wavelength, when λ is next to one of the dimensions, the ultrasonic velocity decreases because edge’ s effect. The study about the length showed that there is a critical point in the relation between sample length and wavelength (L/λ), and above it the velocity is not affected. The results about moisture content demonstrated that ultrasonic velocity, parallel and perpendicular to the grain, decreased when moisture content increased, and this influence was more significant below the fiber saturation point. It was developed an expression to correct the ultrasonic velocity as a function of moisture content and density of wood

Monitoring the integrity of civil engineering structures is an imperative aspect of public safety, since structural failures can pose serious threats to life and property. Periodic inspection performed throughout the life span of these structures is also vital for a nation’s economy. Substantial sums of money may be saved upon detecting structural deterioration in a timely manner. Nondestructive damage evaluation (NDE) offers effective and economically feasible solutions to perform such tasks. Better predictions can be made regarding the current state of structures, and structurally deficient regions that need immediate attention may successfully be narrowed down by utilizing NDE. For these reasons, a considerable amount of research has been conducted in the field of NDE over the past few decades. As a result, many different methodologies are now available, and many new ones continue to emerge as the need for better evaluation techniques prevails. Upon reviewing the NDE methodologies proposed to date, it may be concluded that theories based on the fundamental equations of mechanics and mathematics in conjunction with justifiable assumptions provided the best results compared to the algorithms developed pragmatically. The goal of this study is to provide NDE methodologies that simultaneously identify the location, the extent, and the severity of damage in general beams. By general beams, we mean beyond Euler-Bernoulli beams (i.e. slender beams) to deep beams and stubby beams whose response may be based on the Timoshenko beam theory, and the Theory of Elasticity. After presenting the governing equations of equilibrium and stress-displacement relations of the fundamental beam theories including the Euler-Bernoulli Beam theory, the Timoshenko beam theory, and the beam theory based on linear Elasticity Theory, mathematical expressions which relate physical properties (e.g. stiffness) of the undamaged and damaged structure to measurable response quantities (e.g. displacement, strains, etc.) are developed. We believe that these algorithms will lead to earlier and more accurate prediction of damage in critical structures. The findings of this work will also lead to a better understanding of the limitations of the currently proposed NDE techniques. In addition, it is anticipated that by incorporating the methodologies proposed in this study to the continuous health monitoring of structural systems could reduce the cost of maintenance and offer safer infrastructure networks.