13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Development of a Wireless Sensor for Simultaneous Measurement of Fatigue and Corrosion Fang Yuan1,*, Takayuki Shiraiwa1, Manabu Enoki1 and Tadashi Shinohara2 1 Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan 2 Environment and Energy Materials Division, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan * Corresponding author’s e-mail address: yuanfang@rme.mm.t.u-tokyo.ac.jp Abstract In previous study, it was demonstrated that smart stress-memory patch and ACM (Atmospheric Corrosion Monitor) sensor are suitable and effective for fatigue and corrosion monitoring, respectively. However, some problems still exist on the smart patch and ACM sensor. First, although “sputtered smart patch”, which can estimate crack length wirelessly, has been developed, the crack length could not be estimated accurately sometimes because the resistance of the metal film on it was unstable. Second, it has not been figured out whether the existing patch is applicable to some fatigue condition such as the landing gears of the airplanes. Third, until now the wireless monitoring by ACM sensor has not been developed, and the communication distance of smart stress-memory patch via RFID tag (30 mm) is not sufficient. Therefore, in this research, 1) the measurement accuracy of the ion-sputtered metal film was improved through FEM; 2) whether the existing smart patch is applicable to high-stress low-cycle fatigue environment or not has been figured out; 3) a new wireless device equipped with ZigBee has been developed. By using this device, the wireless monitoring by ACM sensor was realized and the communication distance has been improved to more than 30 m. Keywords Structural health monitoring, Fatigue, Corrosion, Wireless, Smart stress-memory patch 1. Introduction Many construction accidents, which are due to the degradation progress, occur to structures, such as bridges, ships, trains, aircraft, power plants and buildings every year. Since these failure accidents brought much risk to our daily lives and industry production, it is important to prevent them in advance. Moreover, it has been well known that fatigue and corrosion are fate factors of such failure. Thus, a sensor which is able to monitor fatigue and corrosion effectively at the same time for a long-term performance is desired. In previous study, it was demonstrated that smart stress-memory patch and ACM (Atmospheric Corrosion Monitor) sensor are suitable and effective for fatigue and corrosion monitoring respectively. Smart stress-memory patch (hereinafter called “smart patch”) is consists of a thin copper specimen with a pre-crack can estimate fatigue damage parameters such as number of cycles, stress amplitude of structures[1-5], which can be estimated from the fatigue crack growth of smart patch fixed on the structure by using two smart patches with different characteristics. Moreover, “sputtered smart patch”, which has ion-sputtered metal film and insulating layer on smart patch as a thin crack gage, can estimate crack length by measuring electrical resistance change of the ion-sputtered metal film wirelessly via RFID tag.[6] However, some problems still exist for this application. First, the crack length could not be estimated accurately because sometimes the resistance of the ion-sputtered metal film was unstable and did not increase monotonically as the crack length increased. Second, the communication distance of smart patches via RFID tags only (30 mm) is not sufficient for wireless network system. Third, to prevent the fatigue failure of the landing gears of the airplanes, a sensor which is applicable for high-stress low-cycle fatigue environment is also necessary. It has not been figured out whether the existing smart patch is applicable to such fatigue condition or not. For corrosion monitoring, ACM sensor consisting of a Fe-Ag galvanic couple was developed and
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