Research On Self-diagnose And Self-repair In Smart Structures By Hollow-center Optical Fiber

The detection of damage in composite materials is one of significant problems because such damage can reduce the load-bearing ability. Many factors can influence the nature and extent of damage development in composite materials. From a structural health monitoring point of view, it is necessaiy to monitor the strain of damage of the whole composite materials. Optical fiber was one of the sense components used in structure inspection early. Now, Optical fiber sensors have been widely applied to measure strain, temperature and chemical change, etc. This paper is reported on self- diagnose and self-repair with hollo~v-center optical fiber in smart structures. A new system of self-diagnose and self-repair with 5 X 5 hollow-center optical fiber strain sense network for in-situ strain measurements, rupture location and automatic repair in composite materials. In this system, SMA wire is embedded to reinforce the material strength. A sensor design was used along with hollow-center optical fiber. This system may have a number of applications in navigation, architecture, civil engineering and aerospace in the future. The manufacture and performance of hollow-center optical fiber are explained firstly. Based on the optic theory, hollow-center optical fibers possess the similar performance to common optical fibers. Secondly, the theory of hollow-center optical fiber is discussed in detail. The analysis of theory and the testing result of performance show that hollow-center optical fiber not only acts as a sense component, but also has a lot of applications. Thirdly, experimental research of composite materials with or without embedded optical fiber is made to compare the performance of each other and the results show that there is little change in performance of composite materials. The theory of light transmission attenuation is used to determine rupture locations in composite materials embedded hollow-center optical fiber. Finally, the feasibility of detecting the strain in the composite materials is demonstrated successfully at the 5 X 5 hollow-center optical fiber strain sense network within a 16-ply fiber glass/epoxy composite panel. Preliminary results indicate that the sense network is also capable of detecting the residual strain and forecasting the degree of damage future. Self-repair of composite materials using hollow-center optical fiber is reported too. Samples of paper honeycomb and glass/epoxy composite materials are made to study material performances with or without self-repair. Preliminary results indicate that the performance of repair is up to that of original for paper honeycomb material and about 1/3 in tension, over 2/3 in compression for glass/epoxy composite material. The whole system was made for self-diagnose and self-repair with hollow-center optical fiber. The creative results of this paper are as following: I) Hollow-center optical fibers are manufactured, their application and performance are researched. 2) The geometsy optical and electromagnetism theory of hollow-center optical fiber are preliminary studies. So as the transmission attenuation of hollow-center optical fiber and the function between fiber optic parameters and its transmission luminous intensity. 3) The theory of light transmission attenuation by snipping optical fiber is used to determine rupture location of composite materials. 4) Self-repair using hollow-center optical fiber is reported and the repair performances are tested in two composite materials.