Evaluation of the sensitivity of higher order modes cluster (HOMC) guided waves to plate defects

• Published in: Applied acoustics 2022-02, Vol.187, p.108512, Article 108512
• Main Authors: Abbasi, Zahra, Honarvar, Farhang
• Format: Article
• Language: English
• Subjects: Defect detection; Finite element method; Lamb waves; Ultrasonic testing
• ISSN: 0003-682X; 1872-910X
• DOI: 10.1016/j.apacoust.2021.108512

Higher Order Modes Cluster (HOMC) guided waves are non-dispersive wave packets consisting of higher order Lamb wave modes. This paper investigates the effect of frequency and dominant mode(s) of an HOMC guided wave on its sensitivity to plate defects. The propagation of HOMC guided waves in a 10-mm thick mild steel plate is simulated by two-dimensional finite element model. The level of contribution of Lamb wave modes to the wave cluster is analyzed by using a two-dimensional Fast Fourier Transform (2D FFT) at various frequency-thickness products ranging from 15 to 35 MHz-mm. The normal stress profiles of the HOMC guided waves are plotted and used to show the changes in normal stress as a function of frequency-thickness product. The HOMC guided waves interactions with notches of 5%, 10%, 30% and 50% depths relative to the plate thickness are examined at various frequency-thickness products ranging from 15 to 35 MHz-mm. It is observed that the reflected energy from these notches decreases with increase in frequency-thickness product. Experimental measurements are also conducted on a similar plate. The experimental results are in line with simulations and confirm the changes observed in the reflection coefficient of notches at different frequency-thickness products.