Frequency Domain Identification of Acoustic Emission Events of Wood Fracture and Variable Moisture Content

The effect of moisture content on acoustic emission (AE) during wood damage was studied and the degree of damage was evaluated accordingly. In this article, the Pinus massoniana test-pieces of three different moisture content states, which are ovendried, air-dried, and water-saturated, were used to study the AE frequency characteristics of wood during bending failure. The original AE signal was subjected to wavelet denoising, and the denoised AE signal was classified into DAE (deformation AE) and FAE (fracture AE) according to the frequency distribution characteristics. Then, the instantaneous frequency of the AE signal was obtained by Hilbert transform, and the density of the two types of AE events was separately counted to evaluate the damage degree of the wood. The test results show that the AE signal in the process of wood damage and fracture was composed of two frequency components. The DAE signal frequency was concentrated at 30 to 60 kHz, the FAE signal was concentrated at 160 to 170 kHz, and the moisture content had no significant effect on the frequency distribution of AE events. In addition, the moisture content caused a change in the fracture toughness of the wood, so that the AE event density characteristics of the three damage processes were different. In particular, the ovendried test-piece showed obvious brittle fracture, and the AE event density level was slightly changed. Studies have shown that the change of AE event density based on instantaneous frequency can objectively evaluate and predict the degree of wood damage and fracture.