Internal damages detection for structural timber members using low-frequency anti-symmetric guided wave

Abstract

Structural timber is one of the commonly used construction materials. Timber can contain natural internal defect such as knot or natural decay due to its anatomical complexity. Moreover, internal damages or stiffness reductions can also be induced by environmental and biological factors such as weathering and termite attacks. This hidden internal damage increases the difficulty of damage detection using conventional non-destructive testing (NDT) methods. Ultrasonic guided wave (GW) damage detection technique is one of the promising damage detection techniques, which can be employed to achieve an effective and robust damage inspection in timber. However, limited attention has been paid to the use of GW for damage detection in timber, due to the material anisotropy and inhomogeneity. This paper assesses the capability of GW in detecting different sizes of the internal damages in a structural red oak timber using the fundamental anti-symmetric mode (A₀) of GW. Measured GW signals in forward and backward scattering directions are used to calculate the reflection and transmission ratios for different sizes of internal damages. A series of comprehensive experimental and numerical parametric studies are carried out using three-dimensional (3D) finite element (FE) simulations. Good agreement is obtained between numerical and experimental results. The experimentally verified FE model is utilized to further investigate the wave reflection and transmission phenomena from different characteristics of internal damages, such as different lengths, widths, thicknesses, and through thickness locations. The outcomes of this study demonstrate the robustness of GW technique in detecting conspicuous internal damages in structural timber. It demonstrates the feasibility of quantitative assessments of internal damages in timber using A₀ GW.