Assessment of Quantitative and Qualitative Characteristics of Ultrasonic Guided Wave Phase Velocity Measurement Technique

Various time-of-flight measurement techniques are widely used in ultrasonic nondestructive testing (NDT) and structural health monitoring (SHM). On the basis of changes in the amplitude or the velocity of propagating guided wave signal, defects and delamination in objects can be detected. However, ultrasonic guided waves possess a dispersion phenomenon therefore an accurate determination of the signal amplitude or velocity is complicated. In this paper, a technique assessing a dispersion phenomenon using one of the time-of-flight measurement methods is proposed. This method deals with measured phase velocity values from different frequency components of the signal based on measurement of multiple zero-crossing time instants. Then, it identifies fundamental Lamb wave modes, allows to express evaluation of presence of dispersion effect, estimates if low or high dispersion is appearing within frequency range of interest and reconstructs a segment of the dispersion curve using only a few different spatial positions of the receiving transducer. The proposed measurement algorithm was tested using Lamb wave signals propagating in aluminium plate. To assess the quantitative and qualitative characteristics of phase velocity measurement technique, simulated and experimental signals were used. Systematic errors for given conditions and the expanded uncertainty of the measurement process have been calculated. The errors and uncertainties depending on Lamb wave phase velocity and for the A\(_{0}\) mode are equal to approximately 1.2% and 3% while for the S\(_{0}\) mode −0.65 and 1.1% respectively.