Estimation of the Probability Distribution of Wave Velocity in Wood Poles

Ultrasonic testing is a nondestructive technique commonly used for in situ condition assessment of wood poles. A transmitter and a receiver are used in a transillumination configuration to measure the first arrival of compressional waves ($P$-waves). The $P$-wave velocity is computed using the distance between the transducers and the travel time. The condition assessment of wood poles is inferred from the comparison of the measured wave velocity and a reference velocity that depends on the wood species. A wave velocity smaller than the reference value indicates a reduction in the strength of the wood. The elastic and mechanical properties of wood (elastic moduli, mass density, and Poisson’s ratios) are random variables that vary significantly for the same wood species; consequently, the $P$-wave velocity in wood poles is also a random variable. A better understanding of wave propagation in an orthotropic material, including the uncertainty in the mechanical properties of wood poles, is required to improve the reliability of ultrasonic tests. This paper presents a new methodology to evaluate the probability distribution of the $P$-wave velocity in wood poles. This methodology is founded on results from numerical simulations, laboratory tests, a simplified model of $P$-wave propagation in an infinite cylindrical orthotropic medium, and the consideration of the uncertainty in the mechanical properties of wood. The condition assessment of wood poles is improved by comparing the measured wave velocities $V_p$ at different receiver locations and the corresponding probability distributions of the wave velocity $V_p$ for sound wood poles.