13th International Conference on Fracture June 16–21, 2013, Beijing, China -6- 802.15.4) was developed. The schematic of new wireless system for measuring crack length using ZigBee is shown in Figure 7. The transmitter contains sputtered smart patch and microprocessor (PIC12F675, Microchip Technology Inc.) as the same as the method. Moreover, several wireless devices need to transmit with one receiver at the same time, to build the wireless system. The wireless communication among 1 receiver and 4 wireless transmitters has been tested as shown in Figure 8. The distance from transmitters to receiver are 20 m, 30 m, 30 m, 20m, respectively. Moreover, two transmitters were put at about 1 m above the ground, and two were on the ground. Figure 8. The wireless communication among 1 receiver and 4 new wireless devices and the composition of the new wireless device. 3.3. Fatigue experiment To figure out whether the existing smart patch is applicable to high-stress low-cycle fatigue environment or not, fatigue experiments have been executed. Smart patch was clamped at both ends on fatigue testing machine with an electro-magnetic actuator (MMT-500N, Shimadzu), and fatigue pre-crack was introduced under maximum strain of 0.002 and strain ratio of 0.5 until total crack length reached about 2.7 mm. Afterwards, fatigue experiments were carried out under constant amplitude strain with maximum strain of 0.004 twice and 0.006 once respectively, strain ratio of 0.5 and frequency of 19 Hz. During fatigue experiments, the crack length of the sputtered smart patch was observed by optical microscope from the ion-sputtered side. 3.4. Wireless monitoring of ACM sensor Figure 9. The schematic of the wireless system for ACM sensor The wireless monitoring by ACM sensor was tested by using new wireless device. Because the output I from ACM sensor is galvanic electric current, and is so small that it is easy to be affected by noises while wireless communication, a wireless device which combines the new wireless device
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