Research On Acoustic Emission Characteristics Of Wood And Source Location Of Failure For Mortise-Tenon Joint

Acoustic emission technology has some research on the evaluation of wood material quality and wood strength,but there is not much research on the health status of solid wood furniture in use.In the aspect of structural damage detection,the location of damage sources and the assessment of damage extent are the ultimate goals pursued by various non-destructive testing technologies,which has attracted widespread attention from scholars at home and abroad.The existing acoustic emission localization methods mainly include time difference localization method and regional localization method.Since these two methods are susceptible to factors such as wave velocity,attenuation,waveform and component shape,the error of damage location detection is big.Recently,the related research on the characteristic parameters of acoustic emission signals shows that:Energy is an important characteristic parameter of acoustic emission signals,and the energy release law in the process of damage can be used to predict the damage of material structure damage.Since the tenon joint of the wood structure is a hidden part,when it is damaged,it cannot be observed by the naked eye.In order to accurately predict the health of the tenon structure,the position of the information source can be identified according to the acoustic emission energy propagation characteristics released by the tenon structure before the destruction.Therefore,in this paper we take the wood commonly used in China's furniture industry as the research object,and use acoustic emission technology to explore its acoustic emission characteristics.The relevant contents and main innovations are as follows:1.The propagation modes of acoustic emission signals and the main factors affecting acoustic emission signals were discussed.According to the characteristics of wood acoustic emission,we designed and constructed a signal acquisition system.Based on wavelet theory and artificial neural network technology,the real-time acquisition of low-frequency acoustic emission signals of wood and its structure was realized.The sound emission signal processing platform was constructed by LabVIEW/Matlab software.The function of processing the collected acoustic emission signal,the system mainly includes three modules of signal playback,feature extraction and pattern recognition.2.Based on the wood acoustic emission signal acquisition and processing system developed in this paper,the effects of main factors such as holes,knots and water content on the propagation characteristics of wood acoustic emission signals were studied.The results show that the effect of holes and knots on energy attenuation is obvious.The larger the hole or knot is,the more obvious the attenuation effect is.The water content has a great influence on the velocity,amplitude and energy in the acoustic emission signal.The larger the water content is,the faster the attenuation rate is.3.The lead-emission simulated acoustic emission experiment was carried out with the self-processed wood specimens.The distance-attenuation curve was measured by the wave velocity measurement and attenuation experiment of the acoustic emission wave.The distance and signal amplitude were obtained.The relationship between the values and the energy attenuation coefficient a is in the range of 1.0 to 2.4.The results show that when the AE signal propagates in the eucalyptus(Juglans mandshurica),its energy shows a decreasing trend with the increase of the distance.The energy attenuation formula is applicable to the eucalyptus,and the wood energy attenuation model is theoretically established.4.Two-point and three-point positioning experiments were carried out on the L-shaped and T-shaped square eucalyptus components without gluing.The pre-crack experiment method was used to verify the correctness of the energy attenuation model.The wood energy attenuation model is used to calculate the location of the damage source under different conditions.The results show that the energy attenuation model can be used to determine the location of the damage source of the L-shaped and T-shaped square uncoated wood components.The three-point positioning method can obtain a more accurate location of the damage source than the two-point positioning.As the main connection structure in the building and furniture structure,the concrete structure of the concrete structure directly affects the safety,reliability and service life of the whole structure.This paper provides a reference for the on-site health monitoring of mortise structure,and also provides a new method for the location of wood structure damage sources.