Frequency Response Characteristic Of The Composite Deposited Confining NiTi SMA Thin Films On The PZT Substrate

The composite deposited confining NiTi SMA thin films on the PZT substrate was prepared by magnetron sputtering method with the specially designed mask. The microstructure, mechanical and electric properties of the prepared composite was studied with SEM, XRD, microhardness tester and impedance analyzer.It is found that the NiTiSMA thin films with the width of no more than 2mm and the mutual distance of 1mm exhibit the best equiaxed crystal structure after crystallization. With the increasing of the width of the NiTiSMA thin film, the microstructure of the NiTiSMA thin films gradually changes to columnar crystal structure under mutual distance of 1mm between the NiTiSMA thin films.The results of mechanical testing show that the binding force between the NiTiSMA thin film and PZT substrate decreases with increasing of the cavity width, and the fracture toughness of the prepared composite is greater twice than that of the composite deposited continuous NiTi SMA thin film on the PZT substrate. Compared with the pure PZT, the damping values of the prepared composite decrease slightly.The results of the dielectric measurement show that the prepared composite has similar dielectric loss to the pure PZT, but its dielectric coefficient is higher than pure PZT. So the deposited NiTi SMA thin films have no damage to electrical properties of the PZT.The structural health monitoring system based on the prepared NiTiSMA/PZT composite was constructed as following: the sensors of the system were made of the prepared composite; the sensors were stick on the building structure; the dates were collected and disposed through the electrical system composed of acquisition card, charge amplifier and filter; the system software was finished using VB language, and finally the function of the system was realized. The monitoring results indicate that response radius of the system is 800mm, reaction speed of the system is in millisecond, and response frequency of the system is in range of 0-1000 Hz. So the system is suitable for monitoring architectural engineering structure crack damage status.In the paper, the crack damage statuses of the construction were tested by the exciting means, and the evaluation mechanism of the crack damage statuses for the constructed structural health monitoring system was discussed by the spectral analysis method. The experiment results show that,in the fixed exciting frequency, the location state's changes of the responses peaks directly reflect the changes of the crack state in the structure, and the peak height at the frequency of 9.5Hz reduces with the increasing of the distance between the exciting position and the geometrical center of the structure. Under the excitation of the vehicle load, it is found that the monitoring speed is close to the actual speed, and the values of the signal energy density is advanced nonlinearly in nonexistence of crack with the increasing the loaded weight, but that is opposite in existence of crack.