WOOD RESEARCH Volume 69, Number 2, 2024
XIN ZHANG, MING LI, SAIYIN FANG, FEILONG MAO, LONGFEI YANG, YUE ZHAO, and GEZHOU QIN

EVALUATION OF WOOD DAMAGE AND FRACTURE BEHAVIOR BASED ON ENERGY ENTROPY OF ACOUSTIC EMISSION SIGNALS

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

WOOD RESEARCH Volume 68, Number 4, 2023
FEILONG MAO, SAIYIN FANG, MING LI, GEZHOU QIN, YUE ZHAO, and Ning Xu

Study on Acoustic Black Hole Effect of Acoustic Emission Signals in Pinus sylvestris var. mongolica litv

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, a one-dimensional ABH structure was created by forming a wedge structure on one side of the specimen. 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 a sampling frequency of 2 MHz. 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 the wood’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.

WOOD RESEARCH Volume 67, Number 6, 2022
GEZHOU QIN, MING LI, SAIYIN FANG, TINGTING DENG, Changlin Huang, Zhouling Yang, FEILONG MAO, and YUE ZHAO

Study on the dispersion characteristics of wood acoustic emission signal based on wavelet decomposition

Artificial AE sources were generated on the surfaces of Ulmus pumila, Zelkova schneideriana, Cunninghamia lanceolata, and Pinus sylvestris var. mongolica Litv. specimens. The AE transverse wave signal was decomposed into 3-layers detail signals by wavelet decomposition and reconstructed, and it was calculated based on correlation analysis. Then the longitudinal wave speed was calculated according to the time-difference-of-arrival (TDOA) method, and the wood dispersion phenomenon was studied. The results showed that the dispersion phenomenon of Ulmus pumila was obvious. The propagation speed of high-frequency signal was 2.38 times that of low-frequency signal. The ratio of high and low frequency propagation speed of soft wood was 1.72 and 1.73. The dispersion degree of Zelkova schneideriana was the weakest, and the propagation speed of the high frequency was 1.25 times of the low one. The ratios of longitudinal and transverse wave speeds of the four specimens were 4.59, 4.07, 4.24 and 4.2, respectively.

WOOD RESEARCH Volume 67, Number 5, 2022
Changlin Huang, MING LI, SAIYIN FANG, YUE ZHAO, and FEILONG MAO

Research on the effect of wood surface cracks on propagation characteristics and energy attenuation of longitudinal acoustic emission

To investigate the effect of Zelkova schneideriana surface cracks on the longitudinal wave propagation characteristics of acoustic emission (AE). Different sizes and numbers of cracks were made on the surface of the specimen, the propagation characteristics of AE longitudinal waves along wood texture direction were studied. Firstly, five regular cracks with the same length, different width, depth and equidistant distribution were fabricated on the surface of the specimen. The burst and continuous AE sources were generated by lead core breakage and signal generator, and the AE signals were acquired by 5 sensors with sampling frequency was set to 500 kHz. Then, the propagation speed of AE longitudinal wave was calculated by Time Difference of Arrival (TDOA) based on lead core breakage. Finally, the 150 kHz pulse signals of different voltage levels generated by the signal generator were used as AE sources to study the influence of cracks on the attenuation of AE longitudinal wave energy. The results showed that the AE longitudinal wave propagation speed under the crack-free specimen was 4838.7 m.s-1. However, after the regular crack was artificially made, the longitudinal wave speed reduced to a certain extent, and the relative error of the change was not more than 9%. Compared with the energy decay rate of 1.29 in the crack-free specimen, the decay rate gradually increased to 2.08 with the increase of the crack cross-sectional area.