Numerical analysis of ultrasonic guided waves propagation in highly attenuative viscoelastic material

The propagation of ultrasonic guided waves in viscoelastic isotropic material has been investigated. Based on the plane theory, a numerical model of the guided waves propagating is developed in the frequency domain by employing the SFEM (spectral finite element method). To verify the proposed method, thin bitumen on the steel substrate is examined and compared with the single plate in terms of the dispersion and attenuation. From the dispersion and attenuation of the displacement curves, the propagating properties can be obtained, which depends not only on the viscous parameter, but also on those of the substrate. The guided wave attenuates rapidly at the location near the source, and with the receiver distance increasing, it becomes slowly, compared with single bitumen, the attenuation of amplitude for the guided waves propagating in the viscoelastic is tend to gently. The phenomenon shows propagation distance will increase in bilayer material cause of the substrate influence. Introduction Viscoelastic materials are employed in a number of technical areas. Especially in the oil, gas, and petro-chemical industries highly attenuative materials, such as bitumen, are often used as coatings in order to protect pipe networks from corrosion. As a consequence, the study of wave propagation in highly attenuative materials has been a subject of extensive investigation in the literature1-2. It is of great importance in a variety of applications ranging from nondestructive testing of composite structures to properties evaluating of thin film used in aircraft, spacecraft, or other engineering industries. When guided waves propagating in highly attenuative viscoelastic materials, the multiple propagating modes, the frequency dependent dispersion, and the frequency dependent attenuation will appear due to the interaction of the boundaries and viscosity dissipation. While an accurate knowledge of their dispersive and attenuation properties is indispensable for evaluating such highly attenative materials. There are many methods of wave propagating in isotropic and anisotropic viscoelastic materials, including analysis method and numerical method3-5. Analysis method is accurate but is limited to the complex material structure. Finite element method is flexible as numerical simulation which can be solved in time domain and frequency domain. A common feature of the matrix method 6-7 used in layered linear elastic materials is that a root searching routine is employed to find the real roots in the frequency domain. In viscoelastic material, the search scheme needs to be performed in the complex-valued domain. The search scheme can be time consuming and possibly missing roots. Proceedings of the 8th International Conference on Sensing Technology, Sep. 2-4, 2014, Liverpool, UK