Fiber waveguide sensors for intelligent materials

This report, an addendum to the six month report submitted to NASA Langley Research Center in December 1987, covers research performed by the Fiber and Electro-Optics Research Center (FEORC) at Virginia Tech for the NASA Langley Research Center, Grant NAG1-780, for the period from December 1987 to June 1988. This final report discusses the research performed in the following four areas as described in the proposal: Fabrication of Sensor Fibers Optimized for Embedding in Advanced Composites; Fabrication of Sensor Fiber with In-Line Splices and Evaluation via OTR methods; Modal Domain Optical Fiber Sensor Analysis; and Acoustic Fiber Waveguide Implementation

Air coupled ultrasonic inspection of fiber reinforced composite materials

The increase in the use of composite materials in recent years has led the industry into the development of new composite manufacturing processes, like the 3D ultraviolet pultrusion. These new manufacturing processes usually reduce manufacturing costs, cycle time or both. Ensuring the quality of the parts manufactured with these new processes is critical. Therefore, it is necessary to gain knowledge on these manufacturing processes, especially on the behavior of the material during the cure. To monitor these processes, the development of new non-destructive inspection techniques is required. For the 3D ultraviolet pultrusion, the use of non-contact non-destructive testing is necessary. Moreover, for structural parts, ensuring the required mechanical properties gives added value to the part. In this thesis, the viability of air-coupled ultrasonics for plate-like fiber reinforced parts manufacturing is evaluated. At first, isotropic materials are evaluated, considering the ultraviolet cure of a vinyl ester resin. Air-coupled ultrasonics has proved to be fast enough to follow the ultraviolet cure, with quasi-normal ultrasonic spectroscopy. Then, the mechanical properties in fiber reinforced polymers with air-coupled ultrasonics are evaluated. The optimal set-up to generate leaky Lamb waves in plates with different properties is defined. Air-coupled ultrasonics showed that is what difficult to generate Lamb modes with different velocities, although it was possible with a mixed air-coupled laser ultrasonics set-up. Last, leaky Lamb waves where used with air-coupled ultrasonics to evaluate the properties of a fiber reinforced polymer during the thermal cure. The stiffness tensor of the composite was measured during the cure observing the largest variation at the last stages of the cure. The main conclusion of this thesis is that the potential of air-coupled ultrasonics to monitor the fiber reinforced manufacturing processes is elevated. It can presents both the speed required to monitor fast curing processes like ultraviolet cure, with single measurements in less than a second; and the ability to characterize the full matrix of an orthotropic fiber reinforced polymer, through the use of micromechanical models. Air-coupled ultrasonics can be used to characterize the properties of materials with different geometries, like curves or hollow.Material konposatuen erabileraren hazkundeak azken urteetan, material konposatuetarako fabrikazio prozesu berriak garatzera bultzatu du industria, esaterako, 3D pultrusio ultramorea. Fabrikazio prozesu berri hauek, oro har, kostuak, zikloaren denbora edota biak murrizten dituzte. Prozesu berri hauekin fabrikatutako piezen kalitatea bermatzea ezinbestekoa da. Hori dela eta, beharrezkoa da fabrikazio prozesu horien inguruko ezagutza lortzea, batez ere materialak ontzeko garaian. Prozesu horien jarraipena egiteko, suntsitzaileak ez diren ikuskapen teknika berriak garatzea beharrezkoa da. 3D pultrusio ultramorearentzako, beharrezkoa da kontaktu gabeko teknika ez suntsitzaileak erabiltzea. Gainera,pieza estrukturalen kasuan, beharrezkoak diren propietate mekanikoak bermatzeak balio erantsia ematen dio piezei. Tesi honetan zuntzekin indartutako polimerozko plaka motako piezak, airez akoplaturiko ultrasoinuarekin erabiltzeko bideragarritasuna ebaluatu da. Hasieran, material isotropoak ebaluatu dira, binilester erretxina baten ontze ultramorea kontuan hartuta. Airearen akoplamenduarekin egindako ultrasoinuek ultravioleta ontzea jarraitu ahal izateko nahikoa azkarra dela frogatu da, ultrasoinuen espektroskopia bidez, angelu ia normala dela medio. Ondoren, airezko ultrasoinuekin zuntzekin indartutako polimerozko plaken propietate mekanikoak ebaluatzen dira. Airez akoplaturiko ultrasoinuekin Lamb uhinak sortzeko konfigurazio hoberena ebaluatzen da, propietate desberdinak dituzten plakekin. Airearen akoplamenduaerabiltzen duten ultrasoinuek agerian uzten dute zaila dela abiadura ezberdineko Lamb moduak sortzea, baina laser eta airezko ultrasoinuen konfigurazio mistoarekin posible izan zen. Azkenik, airez sorturiko Lamb uhinak erabili dira ontze termikoan zuntzez indartutako polimero baten propietateak zehazteko. Material konposatuko zurruntasuna ontze garaian neurtu zen, ontzearen amaieran aldakuntza handienak ikusiz. Tesi honen ondorio nagusia hauxe da: airez akoplaturiko ultrasoinuekin zuntzekin indartutako polimerozko fabrikazio prozesuak kontrolatzeko duen potentziala handia dela. Bai ultramore ontze prozesu azkarra bezalako prozesuetan, behar den abiadura izan dezake, segundo bat baino gutxiagoko neurketekin; eta zuntz indartutako polimero baten zurruntasunaren matrize neurtzeko gaitasuna, eredu mikromekanikoak erabiliz. airez akoplaturiko ultrasoinuekin geometria ezberdinekin materialen propietateak neurtzeko erabil daitezke, kurbatuak eta hutsak adibidez.El aumento en el uso de materiales compuestos en los últimos años ha llevado a la industria al desarrollo de nuevos procesos de fabricación de maetriales compuestos, como la pultrusión ultravioleta 3D. Estos nuevos procesos de fabricación, generalmente reducen los costes, el tiempo de ciclo o ambos. Garantizar la calidad de las piezas fabricadas con estos nuevos procesos es fundamental. Por lo tanto, es necesario obtener conocimiento sobre estos procesos de fabricación, especialmente sobre el comportamiento del material durante el curado. Para monitorizar estos procesos, se requiere el desarrollo de nuevas técnicas de inspección no destructivas. Para la pultrusión ultravioleta 3D, es necesario el uso de pruebas no destructivas sin contacto. Además, para las partes estructurales, garantizar las propiedades mecánicas requeridas da un valor añadido a la parte. En esta tesis, se evalúa la viabilidad de los ultrasonidos con acoplamiento por aire para la fabricación de piezas reforzadas con fibra de tipo placa. Al principio, se evalúan los materiales isotrópicos, considerando el curado ultravioleta de una resina viniléster. Los ultrasonidos con acoplamiento por aire han demostrado ser lo suficientemente rápidos como para seguir el curado ultravioleta, por medio de espectroscopía ultrasónica en angulo quasi-normal. Después, se evalúan las propiedades mecánicas en los polímeros reforzados con fibra con ultrasonidos con acoplamiento por aire. Se define la configuración óptima para generar ondas de Lamb por aire, en placas con diferentes propiedades. Los ultrasonidos con acoplamiento por aire demostraron que es lo difícil generar modos de Lamb con diferentes velocidades, aunque fue posible con una configuración mixta de ultrasonidos láser y con acomplamiento por aire. Por último, las ondas de Lamb por aire se han utilizado con los ultrasonidos con acoplamiento por aire para evaluar las propiedades de un polímero reforzado con fibra durante el curado térmico. El tensor de rigidez del material compuesto se midió durante el curado observando las mayores variaciones al final del curado. La principal conclusión de esta tesis es que el potencial de los ultrasonidos con acoplamiento por aire para monitorear los procesos de fabricación reforzados con fibra es elevado. Puede presentar tanto la velocidad requerida para monitorizar procesos de curado rápido como el curado ultravioleta, con mediciones en menos de un segundo; y la capacidad de caracterizar la matriz de rigidez ortotrópica de un polímero reforzado con fibra, mediante el uso de modelos micromecánicos. Los ultrasonidos con acoplamiento por aire se pueden usar para caracterizar las propiedades de materiales con diferentes geometrías, tanto curvas como huecas

Electro-optic architecture for servicing sensors and actuators in advanced aircraft propulsion systems

A detailed design of a fiber optic propulsion control system, integrating favored sensors and electro-optics architecture is presented. Layouts, schematics, and sensor lists describe an advanced fighter engine system model. Components and attributes of candidate fiber optic sensors are identified, and evaluation criteria are used in a trade study resulting in favored sensors for each measurand. System architectural ground rules were applied to accomplish an electro-optics architecture for the favored sensors. A key result was a considerable reduction in signal conductors. Drawings, schematics, specifications, and printed circuit board layouts describe the detailed system design, including application of a planar optical waveguide interface

Ultrafast optical pulse manipulation in three dimensional-resolved microscope imaging and microfabrication

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references.The availability of lasers with femtosecond, ultrafast light pulses provides new opportunities and challenges in instrument design. This thesis addresses three aspects of utilizing ultrafast light pulses in two-photon excitation microscopy. First, optical fibers are routinely used in many optical instruments but their use in two-photon microscopy is very limited. As ultrafast light pulses propagate through conventional fiber optics, light pulses are dispersed and broadened, as a result of nonlinear interactions between light and material. Two-photon excitation efficiency is reduced with pulse broadening. The recent development of photonic crystal fibers allows unprecedented control of light properties through them. This thesis provides a thorough quantitative characterization of different conventional optical fibers and photonic crystal fibers enabling better utilization of these fibers for two-photon microscopic imaging. Second, two-photon microscopic imaging is relatively slow due to the sequential nature of raster scanning. Several groups have recently sought to overcome this limitation by developing a 3D-resolved wide-field two-photon microscope using the concept of temporal focusing that is based on manipulating the dispersion of ultrafast light pulses spatially. However, the existing temporal focusing systems have poor optical sectioning capability and, due to a shortage of illumination power, low actual frame rate. In this thesis, a comprehensive mathematical model is derived for temporal focusing two-photon microscope taking key instrument design parameters into account.(cont.) By optimizing instrument design and the use of high two-photon cross section quantum dots, we demonstrate single quantum dot imaging at micron level resolution at video rate. Lastly, we realize that the temporal focus concept may also be used for microfabrication. A prototype three-dimensional lithographic microfabrication system is developed and micro patterning capability based on photobleaching process is demonstrated.by Daekeun Kim.Ph.D

Optical fiber sensors embedded in concrete structures : feasibility and durability studies

Thesis (Civ. E.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1996.Includes bibliographical references (leaves 292-295).by Darmadi Darmawangsa.Civ.E