Numerical Simulation And Experimental Study On The Evaluation Of Creep Damage In Metal Materials By Ultrasonic Lamb Wave

Selection of appropriate frequency and mode has an important significance to the prac-tical application of ultrasonic Lamb wave for the nondestructive testing and evaluation. In this paper, we performed a deep analysis on the propagation characteristics and modes vatiations of Lamb waves propagating in the Ti60 thin plates (titanium alloy) with different levels of creep damage based on the theoretical calculations, numerical simulations and experimental measurements. The main contents and conclusions are summarized as following.(1) Theoretical analysis of the effect of creep damage-induced material parameters variation on the propagation characteristics of ultrasonic Lamb wave in Ti60 thin plates. According to Rayleigh-Lamb dispersion equation, the displacement formula of Lamb wave propagating in the thin plate can be derived. Then, the influence of the changes in the elastic modulus and density of the materials on the phase velocity and the vertical displacement on the plate sur-face of Lamb wave has been analyzed. The results have shown that the elastic modulus and the phase velocity has a same variation trend, while the density and the phase velocity has an opposite variation trend, and also that the changes of both the elastic modulus and density have an obvious effect on the vertical displacement on the surface of thin plate.(2) Numerical simulation of the Lamb mode variations induced by creep damage in Ti60 thin plates. The propagation properties of different Lamb wave modes propagating in the Ti60 plates with different creep damage levels are simulated by using the finite differential method (FDM), where the creep damage levels are characterized by the elastic modulus variation and the porosity variation in materials, respectively. Simulation results showed that the SO mode is not easy to be dispersive even though in the material with a very serious damage, and that the Al modes and the S1 modes are also not easy to be dispersive when their group velocities near the minimum values, in which these modes have good detection ability.(3) Experimental measurement of the Lamb wave propagarion in the different damages Ti60 plates. The frequency-scan and single mode of Lamb wave measurements were carried out in the different Ti60 plates which undergoing various high-temperature creep loadings. The ex-perimental results showed that the Lamb modes with phase velocity between the (0.67-1.02)C1 are more sensitive to the damage state in materials, which are in accordance with the results acquired by theoretical analysis, numerical simulation and experimental mea-surements.