Optical Strain and Crack-Detection Measurements on a Rotating Disk

The development of techniques for the in-situ measurement and structural health monitoring of the rotating components in gas turbine engines is of major interest to NASA. As part of this on-going effort, several experiments have been undertaken to develop methods for detecting cracks and measuring strain on rotating turbine engine like disks. Previous methods investigated have included the use of blade tip clearance sensors to detect the presence of cracks by monitoring the change in measured blade tip clearance and analyzing the combined disk-rotor system's vibration response. More recently, an experiment utilizing a novel optical Moir based concept has been conducted on a subscale turbine engine disk to demonstrate a potential strain measurement and crack detection technique. Moir patterns result from the overlap of two repetitive patterns with slightly different spacing. When this technique is applied to a rotating disk, it has the potential to allow for the detection of very small changes in spacing and radial growth in a rotating disk due to a flaw such as a crack. This investigation was a continuation of previous efforts undertaken in 2011 to 2012 to validate this optical concept. The initial demonstration attempted on a subscale turbine engine disk was inconclusive due to the minimal radial growth experienced by the disk during operation. For the present experiment a new subscale Aluminum disk was fabricated and improvements were made to the experimental setup to better demonstrate the technique. A circular reference pattern was laser etched onto a subscale engine disk and the disk was operated at speeds up to 12 000 rpm as a means of optically monitoring the Moir created by the shift in patterns created by the radial growth due the presence of the simulated crack. Testing was first accomplished on a clean defect free disk as a means of acquiring baseline reference data. A notch was then machined in to the disk to simulate a crack and testing was repeated for the purposes of demonstrating the concept. Displacement data was acquired using external blade tip clearance and shaft displacement sensors as a means of confirming the optical data and for validating other sensor based crack detection techniques

In-situ Grain Scale Strain Measurements using Digital Image Correlation

Materials used in engineering structures fatigue and ultimately fail due to the various applied loads they are subject to, a process which compromises structural performance and potentially poses threats to society. Commonly employed theoretical models capable of describing and predicting deformation and failure are typically validated by relevant experimental results obtained from laboratory testing. However, such models are also often based on simplifying assumptions including for example homogeneous composition and isotropic behavior, since available experimental information relates primarily to bulk behavior.Metals are crystalline in nature and their failure depends on several parameters that span a wide range of time and length scales. Therefore, significant efforts have been made over the past decades to investigate the mechanical behavior of polycrystalline metals by formulating important microstructure-properties relations. In this context, this thesis presents a framework to obtain reliable, non-destructive, non-contact, full field measurements of deformation and strain at the grain-scale of polycrystalline materials to assist the understanding of materials phenomena and contribute in the development of realistic mechanics models. To this aim, the method of Digital Image Correlation is used, adapted and expanded.Digital Image Correlation relies on images of the surface of tested specimens, components or structures and the identification of surface contrast patterns which are tracked as a function of deformation and are subsequently used to define displacements and strains. To quantify stains at the grain-scale, three different approaches based on Digital Image Correlation are described. The first involves the use of a commercial system adapted to make grain-scale measurements at the meso-scale (~4mm). A magnesium AZ31alloy was observed for this purpose and full field strain maps are reported. The second employs the same commercial system augmented with a long distance optical microscope to in-situ quantify strains at the tip of a propagating crack in a Compact Tension specimen of an Al2024 aluminum alloy subjected to Mode I loading and using a field of view of ~870 x 730 μm. Finally, the third approach uses an image series acquired from loading a stainless steel sample inside a scanning electron microscope equipped with a micro-tensile stage. Such information was post processed ex-situ and strains were obtained. The advantages and limitations of the proposed approaches are critically evaluated and future work is described to further enhance the reliability and repeatability of grain scale strain measurements using Digital Image Correlation.M.S., Mechanical Engineering -- Drexel University, 201

Multiplexed optical fibre sensors for civil engineering applications

Fibre-optic sensors have been the focus of a lot of research, but their associated high cost has stifled their transferral from the laboratory to real world applications. This thesis addresses the issue of multiplexing, a technology that would lower the cost per unit sensor of a sensor system dramatically. An overview of the current state of research of, and the principles behind, multiplexed sensor networks is given. A new scheme of multiplexing, designated W*DM, is developed and implemented for a fibre Bragg grating (FBG) optical fibre sensor network. Using harmonic analysis, multiplexing is performed in the domain dual to that of the wavelength domain of a sensor. This scheme for multiplexing is compatible with the most commonly used existing schemes of WDM and TDM and thus offers an expansion over, and a resultant cost decrease from, the sensor systems currently in use. This research covered a theoretical development of the scheme, a proof of principle, simulated and experimental analysis of the performance of the multiplexed system, investigation into sensor design requirements and related issues, fabrication of the sensors according to the requirements of the scheme and the successful multiplexing of eight devices (thus offering an eightfold increase over current network capacities) using this scheme. Extensions of this scheme to other fibre sensors such as Long Period Gratings (LPGs) and blazed gratings were also investigated. Two LPGs having a moiré structure were successfully multiplexed and it was shown that a blazed Fabry Perot grating could be used as a tuneable dual strain/refractive index sensor. In performing these tests, it was discovered that moiré LPGs exhibited a unique thermal switching behaviour, hereto unseen. Finally the application of fibre sensors to the civil engineering field was investigated. The skill of embedding optical fibre in concrete was painstakingly developed and the thermal properties of concrete were investigated using these sensors. Field tests for the structural health monitoring of a road bridge made from a novel concrete material were performed. The phenomenon of shrinkage, creep and cracking in concrete was investigated showing the potential for optical fibre sensors to be used as a viable research tool for the civil engineer

Structural crack detection system using internet of things (IoT) for structural health monitoring (SHM): a review

Monitoring the state of civil engineering infrastructure is critical for a country’s economic development since structures with long service life and timely maintenance have lower reconstruction costs. Crack occurrence is the most important element that influences the performance and lifespan of civil infrastructures like bridges and pipelines. As a result, several fracture detection and characterization approaches have been explored and developed in the domains of Structural Health Monitoring (SHM) throughout the last few decades. The major goal of implementing the Internet of Things (IoT) paradigm is to enable the Internet-based connectivity extension of various typical SHM devices. As a result, connected devices can communicate and process data, opening new possibilities in the design of acquisition systems in various disciplines of research and engineering. The researchers have extended the application of the IoT paradigm to the SHM crack detection because of the advances, ensuring that the tests done in this framework can produce good results with promising future improvements. Thus, this paper reviews structural crack detection based IoT for SHM as reported by previous research in the literature. The strengths and limitations of current systems are discussed. This paper is aimed to serve as a reference for crack detection and characterisation researchers as well as others who are interested in SHM in general. In addition, several case studies on real structures, as well as laboratory experiments for monitoring structural crack health of civil engineering structures, are also presented

New advances in vehicular technology and automotive engineering

An automobile was seen as a simple accessory of luxury in the early years of the past century. Therefore, it was an expensive asset which none of the common citizen could afford. It was necessary to pass a long period and waiting for Henry Ford to establish the first plants with the series fabrication. This new industrial paradigm makes easy to the common American to acquire an automobile, either for running away or for working purposes. Since that date, the automotive research grown exponentially to the levels observed in the actuality. Now, the automobiles are indispensable goods; saying with other words, the automobile is a first necessity article in a wide number of aspects of living: for workers to allow them to move from their homes into their workplaces, for transportation of students, for allowing the domestic women in their home tasks, for ambulances to carry people with decease to the hospitals, for transportation of materials, and so on, the list don’t ends. The new goal pursued by the automotive industry is to provide electric vehicles at low cost and with high reliability. This commitment is justified by the oil’s peak extraction on 50s of this century and also by the necessity to reduce the emissions of CO2 to the atmosphere, as well as to reduce the needs of this even more valuable natural resource. In order to achieve this task and to improve the regular cars based on oil, the automotive industry is even more concerned on doing applied research on technology and on fundamental research of new materials. The most important idea to retain from the previous introduction is to clarify the minds of the potential readers for the direct and indirect penetration of the vehicles and the vehicular industry in the today’s life. In this sequence of ideas, this book tries not only to fill a gap by presenting fresh subjects related to the vehicular technology and to the automotive engineering but to provide guidelines for future research. This book account with valuable contributions from worldwide experts of automotive’s field. The amount and type of contributions were judiciously selected to cover a broad range of research. The reader can found the most recent and cutting-edge sources of information divided in four major groups: electronics (power, communications, optics, batteries, alternators and sensors), mechanics (suspension control, torque converters, deformation analysis, structural monitoring), materials (nanotechnology, nanocomposites, lubrificants, biodegradable, composites, structural monitoring) and manufacturing (supply chains). We are sure that you will enjoy this book and will profit with the technical and scientific contents. To finish, we are thankful to all of those who contributed to this book and who made it possible.info:eu-repo/semantics/publishedVersio

Assessing wood quality by spatial variability of transverse elastic properties within the stem: Case study on P. pinaster at the meso scale

In this work the radial and longitudinal variations of maritime pine (Pinus pinaster Ait.) transverse elastic properties, within the stem, were investigated. Ring-oriented tensile tests through five radial positions and three height levels were carried out in 750 radial-tangential specimens, at the growth ring scale (meso scale). The strain fields over the gauge section were measured by digital image correlation. A suitable balance between accuracy and spatial resolution was achieved in order to reconstruct the gradient strain fields generated by the material heterogeneity at the growth rings level. A segmentation technique based on image processing and analysis was implemented in order to split each annual ring cross the region of interest, into three main tissue layers: resin channels, earlywood (EW) and latewood (LW). Accordingly, transverse elastic moduli of each EW and LW layers were then estimated by two different identification methods: the Anisotropicbased Method (AbM) and the Virtual Fields Method (VFM). The VFM was applied to directly identify in-situ Q11 and Q66 stiffness components associated to EW and LW. The AbM was applied to the global ER and GRT evaluation. These effective elastic properties were then used to infer the local ones as a function of mean density, combining the application of a micromechanical model (mixture law) and a unit cell model. The Q11 and Q66 LW/EW ratios were found in the order of 1.32 and 2.45, respectively. These ratios suggest a linear relationship between elastic properties and density. Furthermore, the spatial variability of the elastic properties was analysed and related to the meso structure heterogeneity, which was given namely by means of density measurements provided by Xray microdensitometry. The results were found in good agreement, presenting significant correlations with density. Specifically, both effective ER and GRT were most often up to approximately 90% determined by mean density.Neste trabalho investigou-se a variação radial e longitudinal das propriedades elásticas nas direções perpendiculares ao fio da madeira de pinho marítimo (Pinus pinaster Ait.) ao nível do tronco. Foram realizados ensaios de tracção na direcção radial utilizando 750 provetes com faces orientadas no plano radial-tangencial e à escala do anel de crescimento (escala meso). Os campos de deformação ocorridos na região de interesse foram medidos por correlação digital de imagem. Um equilíbrio entre a preçisão e a resolução espacial do método foi estabelecido, a fim de avaliar correctamente os gradientes dos campos de deformação gerados pela estrutura heterogénea do material à escala de observação. Uma técnica de segmentação baseada em processamento e análise de imagem foi implementada, no sentido de separar em cada anel as áreas correspondentes aos três tecidos principais: canais de resina, lenho inicial (LI) e lenho final (LF). Por conseguinte, as constantes elásticas transversais de cada tipo de lenho, dentro do anel, foram então estimadas através da aplicação de duas metodologias de identificação distintas: o método baseado na anisotropia (MbA) e o método dos campos virtuais (MCV). O MCV foi aplicado na identificação directa das componentes da matriz de rigidez Q11 e Q66 associadas ao LI e ao LF e o MbA foi aplicado na identificação do módulo de elasticidade radial (ER) e do módulo de corte (GRT ) globais. Estas propriedades elásticas efetivas foram depois utilizadas para inferir as respetivas propriedades locais do LI e do LF em função da densidade média, combinando a aplicação de um modelo micromecânico (lei de misturas) e um modelo celular unitário. Os rácios LF/LI obtidos para as componentes Q11 e Q66 foram 1.32 e 2.45, respetivamente, sugerindo a existência de uma relação linear entre as propriedades elásticas e a densidade. Por outro lado, foi analisada a variabilidade espacial das propriedades elásticas em função da heterogeneidade da meso estrutura, traduzida nomeadamente pelas medições de densidade que foram realizadas através de microdensitometria de raios-X. Os resultados demonstraram a existência de correlações significativas com a densidade. Concretamente, tanto o ER como o GRT efetivos apresentaram determinações pela densidade muitas vezes na casa dos 90%

Development of temporal phase analysis techniques in optical measurement

Ph.DDOCTOR OF PHILOSOPH

Use of X-ray K-edge Tomography and Interferometry Imaging Techniques for the Studies of Brominated Flame Retardants

The work presented in this dissertation is based on the studies of flame retardancy performance of various formulations consisting of brominated flame retardants (BFRs: Saytex 8010 and Green Armor) and their synergist, antimony trioxide (Sb2O3) in high impact polystyrene (HIPS). Chemical flame retardants are incorporated in polymers to improve their flame inhibition for optimal applications in electrical and electronic devices, furniture, printers and more. These flame retardant polymer blends are studied using the Underwriters Laboratory vertical burn test (UL 94) and X-ray imaging techniques such as X-ray K-edge absorption tomography and X-ray grating interferometry. The UL 94 burn test is initially performed to assess the flammability behavior of flame retardant samples before X-ray imaging methods of burnt and pristine polymer blends. Because the UL 94 test bars are formulated with varying concentrations of a brominated flame retardant (Saytex 8010® or Green Armor®) and a synergist, Sb2O3 into a high impact polystyrene (HIPS), samples pass or fail the UL 94 plastics flammability test based on the burn time and other factors. Then, the X-ray imaging techniques are used to reveal internal features for the flame retardant performance during the burn. The Underwriters Laboratory 94 test bars are imaged with X-ray K-edge absorption tomography between 12 to 32 keV to assess the bromine and antimony concentration gradient across char layers of partially burnt samples. X-ray grating interferometry on partially burnt samples shows gas bubbles and dark-field scattering ascribed to residual blend inhomogeneity. In addition, X-ray single-shot grating interferometry is used to record X-ray movies of test samples during heating intended to mimic the UL 94 plastics flammability test. Key features such as char layer, gas bubble formation, micro-cracks, and dissolution of the flame retardant in the char layer regions are used in understanding the efficiency of the flame retardant and synergist. The samples that pass the UL 94 test have a thick, highly visible char layer, low bromine and antimony concentration in the char layer as well as an interior rich in gas bubbles. Growth of gas bubbles from flame retardant thermal decomposition is noted in the X-ray phase contrast movies