13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- applied for the evaluation of corrosion of atmospheric environments for long-term performance. By analyzing the magnitude and time variation of the sensor output, I, the occurrence and duration of rain, dew and dry periods, Train, Tdew and Tdry, could be distinguished and determined, respectively. And by referencing to the calibrating curve between output of ACM sensor (I) and relative humidity (RH) - empirical I-RH calibrating curve, the amount of deposited sea salt could also be estimated.[7] However, because ACM sensor was powered by battery, AC power or solar battery and the output data of ACM sensor was recorded by a microcomputer, the setting-up places has been restricted and the data collecting costs time and labor. Thus, it is necessary to develop a wireless monitoring method for ACM sensor which can be used for long-term performance as well as smart patch. In this study, (1) the measurement accuracy of the ion-sputtered metal film on “sputtered smart patch” was improved by changing the shape of the ion-sputtered metal film through FEM; (2) a new wireless device was developed to improve the communication distance between smart patches; (3) fatigue experiments have been executed to figure out whether the existing smart patch is applicable to high-stress low-cycle fatigue environment or not; (4) the wireless monitoring by ACM sensor was realized by using the new wireless device as well as smart patch. 2. Principle 2.1. Estimation of cyclic number and stress amplitude by RFID-based smart patch A schematic image of the sputtered smart patch is shown in Figure 1. This sensor is composed of an ion-sputtered metal film deposited on the smart patch (a thin copper specimen with a pre-crack). Figure 1. Schematic image of the sputtered smart patch. [6] The details of the principle of smart patch is described in the previous paper.[1] The cyclic number ( ) and stress amplitude ( ∆σ) of structures can be estimated from the crack length values detected from the two smart patches with different characteristics using the following equations: ) 1/( /2 1 /2 2 1 1 2 1 2 1 1 2 2 0 2 1 0 1 1 2 ] { ( )} { ( )} ( ) ) ( [ m m m m m m d f d f C C W W W W − − − − − − − ∫ ∫ ⋅ ⋅ ⋅ ⋅ ⋅ ∆ = α α α α α α α α α α π π σ …………………………(1) ) 1/( /2 2 1 2 1 1 2 2 1 1 2 0 2 2 1 0 1 1 2 1 2 2 1 } ] { ( )} } ( / ) { { ( )} [ m m m m m m mm m m m m d f d f C C W W W W − − − − − ∫ ∫ ⋅ ⋅ ⋅ ⋅ = α α α α α α α α α α …………………………(2) where W is the width of specimen, α0 is the normalized initial crack length, α is the normalized
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