Mechanical degradation of wood under ultraviolet radiation characterized by Lamb wave propagation

Abstract

Nondestructive characterization of wood exposed to ultraviolet (UV) radiation is a critical task for health monitoring purposes since photodegradation affects the mechanical properties of materials. The main purpose of this study was to assess the effect of UV radiation on the elastic and viscoelastic properties of fir, poplar, oak, and alder wood using the Lamb wave propagation method. The Lamb wave propagation and mechanical three-point bending tests were performed on the wood specimens exposed to UV radiation for different time periods. The modulus of elasticity (MOE) and the viscoelastic properties of the specimens including the storage and loss moduli and the loss factor were estimated using the experimentally measured wave characteristics. The difference between the MOE estimated from the Lamb wave propagation and three-point bending tests was less than 4%, proving the capability of the Lamb wave propagation method for accurate nondestructive and in situ assessment of wood. It was revealed that the UV radiation led to a decrease in the MOE and storage modulus of wood specimens and an increase in their loss factor, resulting in lower stiffness and higher viscoelasticity of wood. It was also shown that the sensitivity of the loss factor to UV radiation was higher than that of the MOE and storage modulus, emphasizing the importance of the viscoelasticity assessment of wood products under photodegradation, weathering, and extreme radiation.