Non-destructive testing of trunks: Studying elastic wave propagation by numerical simulation

作者：Schubert Sandy^*; Gsell Daniel; Motavalli Masoud; Dual Juerg; Niemz Peter

来源：Wood Research, 2006, 51(3): 11-24.

• non-destructive testing
• numerical simulation
• fungal decay
• wave propagation
• FDTD
• Visual Tree Assessment (VTA)

Visual tree assessment (VTA) is carried out to evaluate the stability of urban trunks. For identification of fungal decay non-destructive methods, based on elastic wave propagation, are used to supplement VTA. This study aims at a profound understanding of the wave propagation phenomena in the radial-tangential plane of a trunk with the intention of enhancing those methods for identification of decay.
The simulation model is described in detail. Since no closed form analytical solution of this propagation problem exits, numerical simulation based on the finite-difference-time domain method (FDTD) is used. Thus, a two-dimensional cylindrical FDTD code is developed, which represents the cylindrical cross-section and considers the anisotropy of wood. The characteristics of wave propagation in the anisotropic material are studied by a "healthy" reference model using snapshots of the displacement amplitudes at different propagation times. The influence of fungal decay is investigated for two different sizes of decayed regions (5% and 11% of the total area) and two different degrees of decay: total degradation of the wood (cavity) and reduced wave velocities (75%). Subsequently these results are compared with the influence of a heterogeneous distribution of density and different moisture content.
The anisotropy of the material results in a characteristic wavefront of the P-wave. The influence of size and degree of decay is significant in the synthetic data. However, the uncertainties according to the natural grown material wood and to the measurement system require a robust and overdetermined data processing algorithm to interpret the travel-times.

• 出版日期2006