A nondestructive guided wave propagation method for the characterization of moisture-dependent viscoelastic properties o
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ORIGINAL ARTICLE
A nondestructive guided wave propagation method for the characterization of moisture-dependent viscoelastic properties of wood materials Hamidreza Fathi . Siavash Kazemirad
. Vahid Nasir
Received: 22 July 2020 / Accepted: 2 November 2020 Ó RILEM 2020
Abstract The in-situ monitoring and characterization of the mechanical properties of wood and timber materials is of great importance due to their broad structural applications. The purpose of this study was to propose a nondestructive method to assess the moisture-dependent viscoelastic behavior of structural wood using the guided Lamb wave propagation. Twelve green poplar wood specimens with different moisture content (MC) underwent the Lamb wave propagation tests and the wave characteristics were acquired. The viscoelastic properties of the wood specimens, including the shear storage and shear loss moduli and the loss factor, were then estimated through the solution of the corresponding inverse Lamb wave propagation problem using the experimentally measured Lamb wave characteristics. The structural stiffness and damping of wood specimens were affected by their MC, as the Lamb wave amplitude and velocity significantly decreased with MC. While the shear storage modulus decreased with MC, the shear loss modulus and loss factor increased with MC, resulting in a higher viscoelastic behavior. The loss factor of the wood specimens was estimated H. Fathi S. Kazemirad (&) School of Mechanical Engineering, Iran University of Science and Technology, Tehran 16846-13114, Iran e-mail: [email protected] V. Nasir Centre for Advanced Wood Processing, The University of British Columbia (UBC), Vancouver, Canada
to be between 5.88% and 8.49% for different classes of MC, showing an increase of 44% with MC. The Lamb wave propagation method offers a strong tool for nondestructive characterization of the viscoelastic properties of wood materials and structures over a broad MC range. Wood materials show a significant viscoelastic behavior which is highly impacted by their MC. The loss factor can play an important role in the characterization and classification of structural wood and timber with different MC. Keywords Viscoelastic properties Natural materials Materials characterization Lamb wave Nondestructive evaluation Ultrasound
1 Introduction Wood materials are being extensively used in different structural applications, Therefore, the in-situ nondestructive characterization of the mechanical properties of structural wood is of great importance for health monitoring and quality control purposes. Besides, wood is known to be a viscoelastic natural material. Thus, the viscoelasticity assessment of wood materials is needed to fully comprehend the behavior of loadcarrying wood structuresin different conditions. Destructive methods, including the tensile and bending tests, are mainly used to obtain the mechanical
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properties of balk wood and wood-based composites [1, 2]. Such methods are,
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