Experimental verification of an orthotropic finite element model for numerical simulations of ultrasonic testing of wood poles

Ultrasonic testing is a non-destructive and non-invasive method which has been used for internal condition assessment of wood poles in electric transmission and distribution lines. The reliability of this method of evaluation relies on a good understanding of propagation of ultrasonic waves in wood. However, a full-waveform analysis in ultrasonic testing is rarely performed in practice because of difficulties in establishing realistic values for the elastic parameters, modeling the material damping and characterizing the dynamic response of an ultrasonic transmitter. In this paper, a calibrated orthotropic finite element model for numerical simulations of ultrasonic testing of a sound red pine pole is presented. In the calibrated model, the dynamic modulus of elasticity in the radial and tangential directions, Poisson’s ratio and damping ratios are estimated from ultrasonic testing; whereas the dynamic modulus of elasticity in the longitudinal direction is estimated from transverse-vibration testing. The measured response of an ultrasonic transmitter to a one-cycle sinusoidal pulse of 50 kHz is used as dynamic excitation and introduced in the numerical model as displacement-time history. Results of the first arrival of compression waves and the frequency response magnitude computed at three receiver locations are in good agreement with the obtained ones from ultrasonic testing. The calibrated orthotropic finite element model will be used for a better understanding of propagation of surface and compression waves in ultrasonic testing for the detection of early stages of decay in wood poles.