Propagation behavior of guided waves in timber utility poles : towards application in non-destructive evaluation

Abstract

Long standing in-service utility timber poles require careful health monitoring to prevent them from failure and extend their lifecycle. In this work, we are proposing the application of ultrasonic guided waves (GWs) for the assessment of the embedded length and the health state of western white pine timber pole. The work combined both experimental and numerical modeling using COMSOL Multiphysics. Macro Fiber Composites (MFCs), due to their flexibility and convenience to install on curved profiles, were used to actuate and sense guided waves along the tested structures. Based on the wave propagation characteristics in these types of structures, an MFC ring was designed and developed. The ring is to ensure the excitation of the wave modes of interest, i.e. with high sensitivity to the presence of defects, at an enhanced amplitude and to reduce the complexity of the captured signals. We have studied the effect of external boundary conditions, such as soil embedment, on GW propagation, as well as the assessment of the health state of the structure under study. According to our investigation, the soil had minimum impact on the wave propagation characteristics, given that the waves were confined in the timber pole with minimal leakage to the surrounding. The embedded length of the pole was determined accurately, using both experimental and numerical data, with an error less than 3 percent. The deterioration in the timber, within the embedded region, was also evaluated and high accuracy was obtained in localizing the damage with a maximum error of 7 percent. Based on the obtained results, guided waves have high potential to be used as a non-destructive tool for assessment and evaluation of timber utility poles.