Although the effectiveness of detecting crack, the reliability and the durability for many sensors /actuators of SHM have been valiated in the lab-scale experimental condition, it should overcome many barriers in the practical applications, for instance, how to integrate the sensors /actuators to an already “overcrowded” aircraft structures effectively, how to connect them by wires to form a SHM net system which do not conflict with current systems in aircraft, how to optimize the number and location of sensors and how to enhance the reliability of the sensors in order to survive in the severe environments. It is no doubt that the gulf may exist between what has been demonstrated in the laboratory and what has been rigorously validated for operational use, since most of sensors are tested by a limited number of components with simple geometric shape such as plates, shells or shafts with possible some notches. But the real aircraft components usually are heavy-loaded and light weight with more complex geometric and shape. Moreover, it is inevitable to increase the costs and complexity when a prototype concept translates into service. It is an indispensable step to carry out validating tests for any type of SHM systems under operational environments before they become the application-ready products. Canada Institute for Aerospace Research (IAR) developed a novel National Research Council (NRC)-developed crack detection system called the “Surface Mountable Crack Sensor (SMCS)” which had shown promising results as a means of detecting cracks proved by lab-experiments. In order to put SMCS into real application, a prototype installation of the SMCS was carried out on an operational aircraft [7] which showed that was a very important step in verifying its operation effectiveness. A new SHM technology called ICM (Intelligent Coating Monitoring) which is mainly based on the intelligent coating sensors has been invented in China [8, 9]. ICM has shown the capability of monitoring crack initiation and propagation verified by a series of coupons with different material and dimensions under fatigue loading. Furthermore various experiments under environmental loading (temperature extremes, thermal shock, high humidity, fluid susceptibility, altitude/pressure) were carried out to test the durability and reliability of ICM system. It should be noted that ICM technology has been applied on several full scale fatigue tests [10]. Besides the achievements mentioned above, the sensors and interrogation units of the ICM system added on an aircraft have very small size and light weigh. Those superiorities make it easier to implant ICM instruments on aircraft structure on the active service as a part of an SHM system than most of other available SHM technologies which usually require heavy instruments. The goal of the present study is to validate the durability, reliability, longevity and crack detecting capability of the ICM system under real flight conditions and improve various properties. An active service fighter aircraft which was in the overhauling was selected for the study. Total 78 sensors monitoring 42 sites were distributed in different areas of the aircraft such as wing, landing gear, horizontal tail and airframe etc, 12 sub-interrogators connecting all sensors and 2 main-interrogators connecting all sub-interrogators were installed on the aircraft. The aircraft returned to service after installing all the instruments of ICM system on the aircraft. So far, the aircraft with ICM system has been on active service more than 2 years, the data recorded by the system during the period were collected and analyzed once per month. ICM system provides more valuable information in the future applications. This paper briefly introduce ICM system including the principle of sensor, the make-up of the system and various lab-experiments as well as full-scale fatigue tests for verification, give information about the installation of ICM system on an operational aircraft structure including the determination of critical locations that needs monitoring, the selection of sensors corresponding to each monitoring point with certain geometry, the method of sensors splicing and main-/sub- interrogation units fixing and the connection of the above hardware through wires laying to form a
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