Huo Shao-Yong, Chen Jiu-Jiu, Song Guang-Huang, Han Xu «Asymmetric propagation of the first order antisymmetric lamb wave in a tapered plate based on time domain analysis» Акустический журнал, 63, № 4, с. pp. 393-401 (2017)

The asymmetric propagation of the first order antisymmetric (A₁) Lamb wave in a tapered plate respectively carved with sharp bottom corner and round bottom corner is theoretically investigated. Through numerical simulation of A₁ Lamb wave in time domain, we find that when the thickness of the waveguide abruptly decreases to below the cut-off thickness, about half of the A₁ mode is converted into the fundamental symmetrical S₀ and antisymmetrical A₀ modes to pass through the defected region. Furthermore, the transmitted modes A₀ and S₀ are completely apart from each other and can be quantitatively evaluated. Conversely, when the thickness change is very smooth, most of the energy of A₁ Lamb wave is reflected back. It is the unique mode conversion behavior that leads to great transmission difference value of A₁ Lamb wave along the opposite directions. Finally, the influence of geometrical parameters on the transmission coefficient is also studied. The higher efficiency and proper working frequency range can be realized by adjusting the slope angle τ, height h₁ and h₂. The simple asymmetric systems will be potentially significant in applications of ultrasound diagnosis and therapy.

Naserabadi M.J.Ranjbar, Sodagar S. «Ultrasonic high frequency lamb waves for evaluation of plate structures» Акустический журнал, 63, № 4, с. pp. 402-409 (2017)

The potentials of high frequency Lamb wave modes are investigated in the inspection of plate-like structures. The wave propagation characteristics of higher order wave modes and the corresponding sensitivity and detectability are studied. Finite element simulations are carried out using infinite elements to model the ultrasonic wedge transducer and the inspection system. Experimental pulse–echo measurements are conducted to verify the influence of different modes characteristics predicted from the finite element simulations. The experimental measurements show a good agreement with the obtained numerical results for the fundamental modes, S₀ and A₀, and the higher order modes, S₁ and A₁, at 4 MHz mm of frequency–thickness.

Ding S.S., Jin S.J., Luo Z.B., Chen J., Lin L. «Researches on the ultrasonic scattering attenuation of carbon fibre reinforced plastics with 2D real morphology void model» Акустический журнал, 63, № 4, с. pp. 490-495 (2017)

In order to investigate the ultrasonic propagation in carbon fibre reinforced plastics with complex void morphology, the effective mathematical model needs to be established. The current models are oversimplified on void morphology, leading to the significant inconsistency of theoretical calculation with experimental results. In view of the problem, a real morphology void model (RMVM) was established with the idea of image-based modeling. The void morphology was extracted by digital image processing technology, and the material properties were assigned subsequently. As a result of the complex and random void morphology in RMVMs, a non-unique corresponding relationship was verified between porosity P and ultrasonic attenuation coefficient α. In the scatterplot of simulation, about 66 percent of points were plotted within the ±10% error band of fitting line, while almost all the data located at the ±20% error zone. The simulation results showed good consistency with experiments, and it proved the validity of RMVM. The investigation provides a novel model to explore the ultrasonic scattering mechanism for the composite materials containing random voids.