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Contribuição ao estabelecimento de parâmetros para ensaios não-destrutivos em madeira serrada por meio de ondas de ultra-som / Contribution to the study of the nondestructive evaluation of timber using ultrasonic techniqueFabiana Goia Rosa de Oliveira 20 June 2005 (has links)
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
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Non-Linear Optical Characterization of Stressed MaterialsRellaford, Kaylee N. 09 December 2021 (has links)
Interactions between materials, their surfaces, and applied stresses are involved in every man-made construction in the world. Therefore, finding ways to interact without altering inherent properties of materials is of great interest. Surface spectroscopies, including second harmonic generation (SHG) and sum frequency generation (SFG), are inherently noninvasive testing methods. Both SHG and SFG are well-developed techniques that can be used in various applications including the characterization of material state. Both of these techniques allow for a noninvasive analysis of various materials, such as metals and polymers. We have used SHG as a method to characterize the change in signal strength before and after mechanical, chemical, and thermal stress. The results have allowed for comparisons to established methods such as electron backscatter diffraction (EBSD) and indenter testing. SHG shows great potential for a new nondestructive evaluation (NDE) technique to provide more information alongside current destructive and nondestructive methods. SFG has long been used to excite vibrations in the bulk and at interfaces. This allows for a deeper understanding of any molecular change induced by stress such as preferred orientation and new chemical interactions. Overall developments in surface specific methods deepens our understanding of how we interface with the universe.
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Use of Vertical Electrical Impedance for Nondestructive Evaluation of Concrete Bridge DecksBoekweg, Enoch Thomas 27 July 2021 (has links)
Nondestructive evaluation of civil infrastructure is increasingly important in the modern world to assess structures, predict longevity, and prescribe rehabilitation or replacement. For concrete bridge decks, one emerging diagnostic technique is vertical electrical impedance (VEI) testing, which is a nondestructive evaluation technology that quantitatively assesses the cover protection offered to steel reinforcement. Because VEI testing is still a relatively new approach to bridge deck inspection, additional studies are needed to increase the interpretability of VEI data. This thesis increases VEI interpretability with two advances. The first advance, presented in Chapter 2, offers an analytical model for interpreting VEI measurements of cracked bridge decks. The analytical model allows crack depth to be predicted from VEI measurements. The second advance, presented in Chapter 3, offers an interpretation of VEI measurements within the context of other, more typical, nondestructive bridge deck measurements. Surface cracks cause a significant acceleration of chloride ingress towards the steel reinforcement because they provide a direct path for chlorides to penetrate the concrete cover and corrode the steel. Estimating the depth of these cracks enables better prediction of chloride loading and influences predictions of service life. An invertible analytical model for VEI measurements of cracks based on a cylindrical dipole approximation is presented. This model is validated with numerical simulations, laboratory experiments, and destructive field tests performed on concrete parking garage decks. Inversion of the model permits depth estimation of cracks and a quantitative interpretation of VEI measurements for this specific concrete defect. An additional study was performed on a newly constructed bridge deck in Midvale, Utah, that was subject to an unexpected rainstorm during construction. Several forms of nondestructive testing, including VEI testing, were performed on the deck. Statistical analysis of the tests permitted assessment of the bridge deck. Comparing VEI testing with these other NDT methods has not been done before, and the results of this work will assist those who are unfamiliar with VEI with interpretation of VEI data in the context of other, more typical NDT techniques.
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Long Period Grating-Based pH Sensors for Corrosion MonitoringElster, Jennifer L. 27 May 1999 (has links)
Corrosion related deterioration of aging aircraft has proven to cause reduced flight availability, service lifetime, costly repairs, and if undetected, can result in potentially unsafe operating conditions. The purpose of this research is to develop, fabricate and test optical fiber-based chemical sensors for monitoring corrosion from early stages through the entire corrosion event. Although there are several preventative methods under development to address the problem of corrosion degradation, new techniques are still needed that are cost-effective and reliable to ensure an acceptable health status determination of aging aircraft and civil infrastructure. In using optical fiber-based sensors to detect corrosion precursors such as moisture, pH, nitrates, sulfates, chlorates and corrosion related metal-ion by-products the severity of the corrosive environment can be determined allowing predictive health evaluation of the infrastructure. The long period grating (LPG) element is highly sensitive to refractive index changes and with appropriate design geometry a variety of target molecules can be detected. Optical fiber long period gratings are designed to act as spectral loss elements that couple a discrete wavelength out of the optical fiber as a function of the surrounding refractive index. By applying special coating that change refractive index with absorption of target molecules to the LPG surface, it becomes a transducer for chemical measurement. Presented in this research is the incorporation of pH-sensitive hydrogels with long period gratings for the development of a fiber optic-based pH sensor. Optical fiber-based pH sensors offer numerous advantages in wastewater monitoring, blood diagnostics, bioremediation, as well as chemical and food processing. Specifically this research focuses on pH sensors that can be multiplexed with other chemical sensors for a complete chemical analysis of the corrosive environment. / Master of Science
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Investigating Nondestructive Evaluation of Carbon Fiber Reinforced Polymer Beams using Embedded Terfenol-D Particle SensorsRudd, Jonathan D 13 December 2014 (has links)
Reinforced fiber polymer composites are a class of materials that are composed of multiple constituents that work together to create a material specific for applications. By combining different fibers and matricies, laminates can be created that meet demands for high specific stiffness, damping specifications, and electrical resistance. However, their internal complexity subjects them to a number of internal failure modes that have the potential to fail the laminate. Those failure mechanisms are fiber breaking, microcracking in the matrix, debonding of the fibers from matrix, and delamination of ply layers. To assess these failures, nondestructive evaluation methods have been developed to detect internal damage before catastrophic failure occurs. This dissertation investigates an in-situ magnetostrictive based nondestructive method for monitoring delaminations in carbon fiber reinforced polymer laminates by using embedded Terfenol-D particles. The objective is to characterize how laminate ply count and delamination presence affect sensing through the mechanical and magnetic parameters that influence the induced voltage or sensing signal. In addition, the effect of magnetostriction on the formation and propagation of cracks on the sensor boundaries are also investigated. Methods used to characterize this behavior involve experimental testing, analytical, and numerical modeling. From the results, a threedimensional finite element analysis model reveals how the sensor interacts mechanically with the host structure through lower stresses in the delaminated region due to the absence of adhesive forces. The stress variation results in a local magnetic permeability change which influences the induced voltage. The experimental nondestructive testing show that the key parameter influencing the sensing signal for this setup was the particle density, which is controlled by fabrication process. An attempt to analytically model the experimental sensing signal with a first order differential equation using a multi-step process was successful, but there is poor correlation with the experimental results. Finally, analytical mechanics are developed to evaluate the interlaminar failure under a magnetostrictive stress of 55MPa, and was found to not cause interlaminar failure or delamination propagation in Section-A.
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Finite Element Analysis of Rail Base Defect Detection by Line Scan ThermographyCaselato Gandia, Guilherme 01 December 2022 (has links)
Quick, efficient, and reliable methods for in-service inspection of rails to ensure the safety of transportation is an open challenge in the railroad industry. It is well known that fatigue cracks are the leading cause of derailments. Furthermore, new high-speed and heavy-load trains have seen increased use, leading to an increase in the loads and number of cycles experienced by a given section of track. Additionally, most methods for inspecting rails require that sections of the track be shut down for inspection. As a result, much industry attention has been paid to the development of nondestructive methods for inspecting whole sections of the track, although a significant gap in inspection needs and capabilities exists, especially with the inspection of rail base. This studied the feasibility of applying Line Scan Thermography (LST) toward detecting defects in the rail base using Finite Element Analysis (FEA) validated by analytical solutions and experiments and simulated the LST inspection in multiple models at speeds up to 40 mph. In the simulations, subsurface fabricated defects were considered to correlate the necessary thermal contrast, amount of energy, and scan speed. The digital twins, when compared to experimental results, showed the same trend. The rail base section model was simulated with 6000 W of heat, and scanning speeds varying from 0.3 mph up to 40 mph with a 150 mm distance showed an exponential decrease in the thermal contrast. However, when the heat power and camera location are changed proportionally to the speed increase, the thermal contrast remains within a change of 1% and 16% for the detectable reflectors. Moreover, the technique was considered feasible if the previous relationship was respected. Further studies regarding this application account for a deeper investigation of this scanning speed and energy relation, developing a Computational Fluid Dynamics model of this problem, and testing samples with surface defects.
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Modern Statistical Methods and Uncertainty Quantification for Evaluating Reliability of Nondestructive Evaluation SystemsKnopp, Jeremy Scott 13 May 2014 (has links)
No description available.
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Rapidly Solving Physics-Based Models for Uncertainty Propagation in Nondestructive EvaluationCherry, Matthew Ryan 20 December 2017 (has links)
No description available.
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Development of Ground Penetrating Radar Signal Modeling and Implementation for Transportation InfrastructureLoulizi, Amara 08 February 2001 (has links)
Ground penetrating radar (GPR) technology has been used for the past 20 years for a variety of applications to assess transportation infrastructure. However, the main issue after all these years remains: "How well does GPR work and under what conditions?" Results show that GPR works well for some situations, but is not an appropriate tool for other situations. It is not used currently on a routine basis by the US Departments of Transportation (DOTs) due mainly to difficulties encountered with data interpretation. Data interpretation difficulties are mainly attributed to the fact that images obtained from the reflected signals are not photographs of the features that are beneath the surface being investigated. The images show the amplitude of the radar-reflected signals from the interfaces with different dielectric properties. Therefore, a considerable amount of experience and operator skill may be required to correctly interpret sub-surface radar results. To better understand reflected GPR signals, this research was conducted with the following objectives: to determine the dielectric properties of concrete over the used GPR frequency range; to synthesize the reflected air-coupled radar signals and compare them with measured waveforms; to model and study the effects of simulated defects in concrete on the reflected air-coupled and ground-coupled radar signals; and to validate the research results in the field by predicting layer thicknesses of flexible pavements and detecting moisture in flexible pavement systems. Several concrete slabs, 1.5x1.5 m, were constructed with known thicknesses, simulated defects, and different reinforcement configurations. The concrete mixes included four different bridge deck mixes and one concrete pavement mix used in the State of Virginia. Results have shown that the dielectric constant of concrete is frequency and mix dependent. However, modeling the reflected signals using an average complex dielectric constant over the entire radar frequency range led to modeled waveforms comparable to the measured waveforms. Although air- and water-filled voids did distort the reflected waveforms, a model was developed to predict the reflected waveforms from the simulated defects. Reinforcement was found to affect the reflected waveforms only when it was oriented in a direction perpendicular to the GPR antennas. A model was also developed to predict the GPR waveforms obtained from flexible pavements. This model could be used in a procedure to measure layer thicknesses more accurately by including losses that occur inside the pavement materials. Two different case studies, where a ground-coupled GPR system was used to locate moisture at different layers, have led to the conclusion that the ground-coupled GPR is a feasible tool to detect moisture inside pavements. / Ph. D.
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SYNTHETIC APERTURE GROUND PENETRATING RADAR IMAGING FOR NONDESTRUCTIVE EVALUATION OF CIVIL AND GEOPHYSICAL STRUCTURESBrown, Andrew, Lee, Hua 10 1900 (has links)
International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Synthetic-aperture microwave imaging with ground penetrating radar systems has become a research topic of great importance for the potential applications in sensing and profiling of civil and geophysical structures. It allows us to visualize subsurface structures for nondestructive evaluation with microwave tomographic images. This paper provides an overview of the research program, ranging from the formation of the concepts, physical and mathematical modeling, formulation and development of the image reconstruction algorithms, laboratory experiments, and full-scale field tests.
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