Longitudinal thermoelastic guided waves in functionally graded hollow cylinders with Green–Naghdi thermoelastic theory

At present, functional gradient material (FGM) pipelines are widely used in high-temperature environments, and the need for online inspection of such pipelines is becoming more and more urgent. Ultrasonic guided wave is undoubtedly one of the most promising methods for detection, but research on the propagation characteristics of thermoelastic guided wave in high-temperature FGM pipelines is still limited. In this paper, based on Green–Naghdi thermoelastic theory, a theoretical model of longitudinal thermoelastic guided wave in a hollow cylinder of FGM considering temperature effect is established by using the Voigt model, and the governing equations of thermoelastic guided wave are solved by the Legendre series method. The dispersion, displacement, and temperature distribution curves of guided waves in a hollow cylinder of FGM are plotted. The convergence of the method and the influence of the coupling of thermodynamic equations on the dispersion characteristics of guided waves are discussed. The influence of circumferential order, ratio of radius to thickness, gradient index, and temperature change on the dispersion characteristics of guided waves is analyzed. This study provides a theoretical basis for nondestructive testing and evaluation of high-temperature FGM pipelines.