In order to assess the damage and fracture behavior of wood under continuous loading, an energy entropy and b-value associated with the acoustic emission (AE) signal were defined to quantitatively describe the release of strain energy during loading. Firstly, the acoustic emission signals of the wood in the three-point bending test were collected. This paper presents the concept of energy entropy according to the definition of information entropy. In order to further evaluate the strain energy intensity released by the damage behavior of the wood specimen, the acoustic emission b-value was defined. Finally, by jointly analysing the dynamics of these two parameters, the test process can be divided into three phases. The results show that even in the elastic phase, micro-destructive behavior occur inside the wood specimen; in the plastic phase, the wood specimen is not only subjected to macroscopic damage, but also often accompanied by fine cracks inside.

The difference in density and wave velocity causes distinct wave impedance between air and wood, resulting in complex acoustic emission (AE) signals due to reflection on the wood's surface. This study explores the suppression of AE signal reflection by modifying the structure of thin wood panels, utilizing the theory of acoustic black holes (ABH). Initially, aone-dimensional ABH structure was created by forming a wedge structure on one side of thespecimen. Pencil-lead break (PLB) tests simulated sudden AE sources on the specimen's surface. AE signals were collected using three equidistant sensors on the upper surface, with asampling frequency of 2MHz. The AE signal was then segmented into frequency bands using the differential method and analyzed in both time and frequency domains. Comparisons were made to understand the impact of the one-dimensional ABH on AE signal propagation. Results demonstrated that the one-dimensional ABH effectively suppressed AE signal reflection on thewood's surface, reducing the high-frequency components by 18.31%, 20.83%, and 12.09% for each sensor, respectively. Furthermore, the experimental cut-off frequency of 0.98 kHz surpassed the theoretically calculated value of 0.39 kHz due to the disparity between the ABH structure's thickness and the theoretical prediction.

Although anisotropic propagation behavior of acoustic emission (AE) in the sawn timber (ST) has been revealed, that in finger-jointed timber (FJT) is still less known.Therefore, a series of velocity and energy models of AE signalswere built as it propagates along different directions on the surface and inside of specimens (ST and FJT). At first, using polar coordinate system, velocity model in 36 directions was built in FJT, which was compared to ST.Furthermore, a continuous sine wave with a frequency of 165 kHz was selected as AE source to explore the energy attenuation law in FJT and ST respectively.The results showed that there are significant differences in velocity models between FJT and ST.The wavefront in STwas regular elliptical, while that in FJT has a clear depression in perpendicular to grain direction.This feature becomes more obvious with the increase of distance when AE signal propagates inside the FJT.Inside the FJT,energy magnitude in STwas 3.00-7.37 times of that in FJT.