| As a renewable green environmental material, wood has attracted more and more research interesting. However, in the long-term use of wood, the stress and strain will directly affect the physical properties of wood. But the traditional testing methods can not monitor the stress change process in time. Acoustic emission technique, abbreviated as AE, as a non-destructive and active monitoring method, can objectively reflect the stress evolution within the measured object. Due to the complex internal structure of wood and the density difference that leads to the anisotropic characters of the signal propagation. For this reason, the existing AE signal process and analysis technology can not be directly used to tackle AE signal of woody materials.Thus, an AE signal acquisition and analysis platform based on LabVIEW is proposed in this paper. The original wood AE signals are acquired through the multi-channel and high speed data acquisition equipment. After that, with wavelet and wavelet packet signal processing technology, a multi-channel wood acoustic emission signal processing software is built in the LabVIEW environment. The designed platform can be used to extract and analyze time-frequency characteristics of wood AE signals. Furthermore, a triangle location approach is designed to locate the site of the AE resource. At last, a series of wood mechanical tests are performed to verify and improve the designed platform. The main contents of the thesis are listed as follows.The first chapter. From the software,hardware, software and hardware combination, this chapter elaborates on the signal acquisition and processing platform of acoustic emission. In hardware selection, it from the perspective of application and actual situation. First,by comparison, it selects to determine the choice of acoustic emission SR 150 N sensor as wood acoustic emission signal acquisition sensor, after IN company’s NI-USB-6366, 8 channel high speed data acquisition card signal through the PAI preamplifier treatment into the computer. Then, in the LabVIEW software platform design the program based on the complete hardware platform. According to the wood acoustic emission signal,design the collection and preservation program, the transfer and separation program, the filer and noise reduction program, the date analysis program. Finally, connected by software and hardware interface, build a complete,software and hardware combination, can use to acquisition and analysis as one of AE signal processing system.The second chapter. In order to test and improve the previous chapter construct the platform.This chapter compares with windowed Fourier, low pass and wavelet signal noise reduction method of the treatment. The experimental results show that wavelet analysis has good filtering effect,and can effectively extract the useful acoustic emission signal.The third chapter. IT use the platform to test the wood damage and fracture acoustic emissionsignal. The damage and fracture test are loaded in the universal mechanical testing machine. The test results show that at the beginning the wood damage test acoustic emission signal has continuous low amplitude characteristics. Then with the increase of the loading force, acoustic emission signal has sudden large amplitude characteristic. This is the same as the wood in the loading process of stress and strain of the development. In order to determine the position of the acoustic emission source of wood, this paper designs a kind of triangle positioning method, and through the wood acoustic emission effect source localization test to find the acoustic emission source. The result shows that the triangle positioning method proposed in this paper can find the acoustic emission source in a high accuracy.The research result of this paper can be directly used for wood acoustic emission signal collection and analysis, at the same time as acoustic emission signal acquisition and analysis platform, it provides a feasible approach and reference architecture based on LabVIEW. |
PDF Full Text Request