MATLAB & OTDR BASED DEFECT ANALYSIS

Abstract

Development and propagation of cracks can be detrimental to the operation of an engineering structure and causes the failure of structure due to fatigue or harsh environmental condition. Many techniques has been proposed and implemented for detection of cracks within the structure such as Radio Frequency Identification (RFID) , Piezo-Electric Transducers (PZT) and Multiple Sequential Image Filtering . But there are several disadvantages of these techniques which prohibit the use and application of these techniques as fully distributed sensing system. Fiber optic Sensors have recently gained acceptance in the sensing community for its inherent ability for multiplexing, immunity to EMI and inherent multiplexing abilities. The present work uses standard telecommunications optical fiber (SMF28e) and EXFO 150-TB commercial OTDR to demonstrate a multiple crack detection mechanism. Simulation has been performed to evaluate the response of light flowing through optical fiber in the presence of single / multiple cracks. Response of light and modulation of light propagating within the fiber in the presence of singular or multiple cracks has been practically obtained using OTDR A novel ‘S’ type fiber layout has been developed for the crack localization in real time using the OTDR technique and single mode optical fiber. ‘S’ type layout has shown to have greater sensitivity to cracks and hence proven to be a more effective configuration for detection of cracks. The ‘S’ type configuration allows an increase in the sensitivity to the crack, while improving the spatial resolution of the OTDR. Results have shown an increase in the sensitivity by 1.43 times allowing a greater chance of signal pickup from the OTDR. Therefore such a sensing system would be highly useful in the determination of the position and characterization of cracks in an engineering structure.