STUDY ON THE TIME-FREQUENCY CHARACTERISTICS AND PROPAGATION LAW OF ACOUSTIC EMISSION LONGITUDINAL WAVES IN WOOD GRAIN DIRECTION

To study the propagation law of acoustic emission (AE) longitudinal waves in wood, the relationship among wave velocity, standing wave fundamental frequency and Young's modulus of elasticity was studied, and the energy decay model of AE longitudinal waves along the grain direction was established. Firstly, the propagation velocity of the longitudinal wave was calculated using the time-difference method. Then, the relationship between the wave velocity and Young's modulus of elasticity was analyzed and the method of calculating the longitudinal wave velocity using the fundamental frequency was proposed. Finally, using different levels' pulse strings as AE sources, the attenuation law of AE signal energy with distance was studied. The results show that the longitudinal wave velocity can be estimated more accurately by using the standing wave fundamental frequency. The influence of Poisson's ratio needs to be considered when calculating the Young's modulus of elasticity by using the longitudinal wave velocity.