Study On Acoustic Emission And Propagation Characteristics Of Glulam

As a renewable resource,wood has always been a very important building material.In recent years,thanks to its high hardness and stable physical properties,Glulam has gradually become the main raw material for the construction of stadiums,playgrounds and other large-scale structural buildings.Due to the fact that wood structural materials are all anisotropic materials,traditional non-destructive testing methods are not suitable for internal damage monitoring of wood.At the same time,real-time detection of large-scale wooden structures cannot be achieved.Therefore,a real-time and effective non-destructive testing method is urgently needed.Acoustic emission(AE)is a new and active nondestructive testing technology,which can monitor the internal stress changes of the tested parts online.By artificially simulating the acoustic emission source,the AE signal of the glulam during loading is collected.And the wavelet analysis is used to analyze and process the acquired signals to obtain the range of internal stress concentration.Meanwhile,the principle of signal correlation is used to estimate the location of the AE source,and the locations where cracks may occur in the glued wood structure are preliminarily recorded so as to be reinforced in advance.In view of the propagation characteristics of AE signals in glulam,the following researches have mainly been done:1.A set of AE signal acquisition platform is set up by the high speed data acquisition card,piezoelectric sensor and preamplifier of NI company.And a wavelet analysis platform for AE signals is set up with Matlab software,which realizes the multi channel acquisition of AE signals and the extraction from the noise.In this paper,firstly,the Pseudotsuga menziesii Glulam were used as the research object,and the AE source was artificially simulated by the lead core breaking and two consecutive slides.The original AE signals of the upper and lower surfaces of Pseudotsuga menziesii were collected by the two-channel acquisition system.Moreover,the db wavelet was used to decompose and reconstruct the acquired signal,so as to obtain the frequency and propagation characteristics of the Douglas-son AE signal.Research shows that signals of Pseudotsuga menziesii are stationary and concentrated in the 70 KHz,and the signal’s propagation speed is 514.29 m/s on the surface,and the internal propagation speed is 422.45 m/s.And wavelet analysis can be used to extract the signal that is submerged in the noise.2.The AE technology was used to collect and compare AE signals of Yunnan pine surface with different water content.The results show that with the increase of water content,the amplitude of time domain waveforms of AE signals tends to decrease.The average rate of AE signal propagation on the surface of the specimen is inversely proportional to the moisture content.In the dry state,the average propagation rate reaches a maximum of 4208.77 m/s,while the average rate in the saturated state is only 1414.07m/s.And from the frequency domain distribution of the reconstructed signal,it can be found that the frequency domain waveforms of the test specimens in the four water-containing states are mainly concentrated in the range of 40 to 150 kHz.3.The cross-correlation analysis method was used to locate the sound source of the glulam board surface.At the same time,the spatial localization of AE sources of the Pinus massoniana Lamb Glulam was achieved by using the least squares method.Firstly,the wavelet transform is used to decompose the collected signal and extract the signal of the meaningful frequency band to reconstruct the waveform.Then,the cross-correlation analysis is performed on the reconstructed signal,and the time delay of the signal reaching the two sensors is obtained.Finally,the position of the sound source is obtained according to the measured propagation speed of the signal in the test piece.The results show that cross-correlation is a suitable method for the localization of AE sources for glulam.It provides a reference for the study of internal damage and fracture location of different materials.