Study On The Theory And Application Of FBG Intelligent Materials And Structure

The intellectualizing of materials and structures is the most challenging subject in the 21th century. The study on the health monitoring and safety evaluation within the whole life cycle of the huge engineering structure is a popular subject all over the world and has great social significance and economic benefits. The " health monitoring of structure " has become the symbol of the development and integration of intelligent materials and structures, the development and integration of high-tech., and also the concentrated reflection of the experimental technique of the modern structure. One of the key work to realize the health monitoring of structure fundamentally is to study and develop the sensing components whose durability and stability can meet the engineering needs and to develop the new kinds of fiber optic grating intelligent materials and structures.Financially supported by the National Natural Science Fund, National 863 Program, Key Research Projects of Hubei Province, and under the elaborate guidance of my tutor, in this thesis, the basic theories, fundamental experiments and engineering application of the intelligent materials and structures of fiber optic grating have been studied. The preparation technology for fiber optic grating sensors, the design and system integration technology for fiber optic sensing network, which will be used in huge engineering structures, have been explored in the aspects of materials, components and structures. The purpose is to develop the fiber optic strain, temperature and pressure sensors and their health monitoring system, and to use them in huge engineering construction. The related research work has been undertaken for five years and several achievements were evaluated. They were used in several huge engineering and became parts of the second class of the National Scientific and Technological Prize .The main contents of this thesis include the intelligent sensing mechanism of the fiber optic grating, the manufacturing technology for the stable and reliable fiber optic grating sensing components, the development of fiber optic grating sensors with multiparameter, the study of fiber optic grating intelligent materials and structures, the realization of self-diagnose function, and the application of "health monitoring of structures" in huge engineering.1. The current study situation and development direction of intelligent materials and structures, their sensing technology and fiber optic grating sensing technology were reviewed and forecasted. The basic concepts and forming patterns of the fiber optic grating intelligent materials and structures were explored.2. According to the study of photosensitive mechanism, the transmitting theory and basic intelligent sensing characteristics of fiber optic grating were reasoned and proved theoretically, the sensing mechanism of fiber optic grating was illustrated, and the sensing mechanism of fiber optic grating was analyzed. According to the demands of fiber optic grating used for sensing and through the theoretical and experimental study on the influence of hydrogen loading, structural parameters of fiber optic grating, photoetching strips and annealing process to the characteristics of grating spectra, the rather perfect technics and process conditions for preparing the fiber optic grating sensing components have been summarized.3. Based on the compatibility demand of intelligent materials and structures, and through the theoretical study and analysis on the strain transmitting characteristics of fiber optic grating/sensors/interface to be detected and the structures of the complex elastomer of fiber optic grating, the basic theories and methods for the design of fiber optic grating strain sensor based on the strain transmitting efficiency were formed. The new method based on the study of the coupling of heat and force to detect the long-term stability of fiber optic grating sensors has been summarized.(1) The fiber optic strain, temperature and pressure sensors were developed and used in the safety monitoring of several huge engineering projects.(2) The mechanical states of the complex interface of the detecting structure-optic fiber-elastomer-encapsulation materials were analyzed and the problems of their strain transmitting were studied. Analyzed by finit element method, the basic design principle and method for fiber optic strain sensors which can meet the detection need of concrete structure and metal structure has been proposed.(3) The encapsulation technics and the properties standardization method for fiber optic grating sensors have been formed.(4) It has been found that the main factor to influence the long term stability of fiber optic grating sensors was the change of the stain transmittingcharacteristics caused by the coupling effect of heat and force. The new method for improving the long term stability of fiber optic grating sensors based on the coupling of heat and force was proposed.4. The design theory and method for fiber optic grating intelligent materials andstructures have been studied.(1) The experimental device based on the structure damage recognition of the fiber optic grating sensing array was designed by studying the multi-application sensing technology of fiber optic grating. The damage recognition mechanism of four-side upholded plank structure was studied through BP nerve net and model experiment. And the technology and method for realizing the self-diagnosing of fiber optic grating intelligent materials and structures were explored(2) The basic composition and function of the health monitoring and damage diagnosis system for huge engineering structure have been proposed initially.(3) The rationality of the installation and arrangement technics of fiber optic strain sensors were validated by huge structure tests. The ideal installation technics, organizing and implementing methods for the health monitoring system of huge engineering structure have been proposed.5. The fiber optic grating sensors and their monitoring system for structure safety have been used in many huge engineering structures firstly , including steel structure, concrete bridge and prestress structure, which were compared with the traditional detecting technology. The application results show that fiber optic grating sensors and their monitoring system are suitable for the detection of complex stress and supramaxilmal strain parameters for several object structure with several working condition, and that their stability and durability can meet the practical engineering demand of the construction monitoring and long term health monitoring for huge engineering structure, demonstrating the realization of the application of fiber optic grating sensors in engineering and in large scale.