Yong-dong Pan

Application of the Surface Wave Survey Method on Multi-Scale Engineering Problems: Laboratory and Field Testing Case Studies

The geometric dispersion of surface waves offers the feature to infer the properties of a medium. The surface wave survey method is under continuous evolution and its applications include the noninvasive characterization of a medium at a small scale and the earthquake geotechnical survey at a large scale. Despite the significant difference in scales, these applications generally utilize the propagation of the surface waves along the boundary of a layered medium. This paper discusses standard steps involved in surface wave surveys. Two application case studies are conducted and presented in detail. In the small scale laboratory application case, a nondestructive testing (NDT) methodology is proposed for the coating investigation using laser interferometric measurements of surface waves. In the large scale field application, an accelerometer-based passive surface wave survey is designed for earthquake geotechnical engineering site characterization. Finally, recommendations for practical application of surface waves in multi-scale engineering problems are presented.

Wave propagation in a functionally graded magnetoelectric coating on a cylinder

In this paper, the wave propagation in a functionally graded magnetoelectric coating on a cylinder is studied. Considering the piezoelectricity and piezomagneticity of the coating with an orthotropic symmetry, the wave equations and system matrices for state vector are obtained for SH and P-SV waves propagating along both the axial and circumferential directions. It is found that the wave propagation of the SH wave along the axial direction and the P-SV wave along the circumferential direction is not coupled to the electric and magnetic field, i.e., their corresponding dispersion patterns are same as that for a functionally graded coating without piezoelectricity and piezomagneticity. However, the wave propagation of the P-SV wave along the axial direction and the SH wave along the circumferential direction is coupled to the electric and magnetic field, i.e., their corresponding dispersion patterns depend on the applied electric and magnetic field, their dispersion curves are different under the open and close electric or magnetic boundary conditions.In this paper, the wave propagation in a functionally graded piezoelectric coating on a cylinder is studied. Considering the piezoelectricity of the coating with an orthotropic symmetry, the wave equations and system matrices for state vector are obtained for SH and P-SV waves propagating along both the axial and circumferential directions. It is found that the wave propagation of the SH wave along the axial direction and the P-SV wave along the circumferential direction is not coupled to the electric field, i.e., their corresponding dispersion patterns are same as that for a functionally graded coating without piezoelectricity. However, the wave propagation of the P-SV wave along the axial direction and the SH wave along the circumferential direction is coupled to the electric field, i.e., their corresponding dispersion patterns depend on the applied electric field, their dispersion curves are different under the open or close electric boundary conditions.

Measurement and Analysis of Laser Generated Rayleigh and Lamb Waves Considering its Pulse Duration

In this article, laser generated Rayleigh and Lamb waves are studied by taking into account its pulse duration. The physical model and theoretical solution are presented to predict the corresponding waveforms for aluminum samples under the ablation generation regime. The waveforms of the excited Rayleigh and Lamb waves by laser with selected pulse duration were measured by laser interferometer and analyzed theoretically, and the agreement between measurement and analysis is demonstrated for the validation of the theoretical model and solution. The broadening of the Rayleigh wave and the disappearing of high order Lamb wave modes can be found with the increase of the pulse duration by the laser ultrasonic technique.

Scattered echoes from surface defect in the far field of Rayleigh wave generated by laser

In order to realize the quantitative detection of surface defects by the laser ultrasonic technique, the finite element method had been employed to simulate the interaction of the laser-generated surface wave to the open rectangular defect. Signals received at the same position were compared for the laser generation in the near-field and far-field of the defect. The mode-converted waves and reflected waves could be separated when the laser was located in the far field of the defect, and it is helpful for the analysis of the complicated interaction between the incident waves and the defect. Then, the wave interaction either to the front or the back of the defect was studied in details, and Huygens principle was further employed to interpret the possible interaction features among the reflected signals. Finally, influences of the depth and width of the defect on the scattered echoes were also studied. It is shown that the arrival time difference of the scattered echoes are linearly related to the depth and ...

Defect detection by ultrasonic guided wave for a steel wire in the anchorage zones

The aim of this paper is to investigate the propagation of ultrasonic waves in a steel wire and to determine whether it is possible to detect and locate the defects by the finite element method. First, the dispersion curves of longitudinal modes were obtained and calculated analytically. Then, the ultrasonic guided waves propagating in a steel wire with or without defects were simulated by the finite element method. To take account of the damage, the V-type groove defects were modeled to have different sizes in the mouth width and the tip depth. It is found that the finite element method can be applied to model the guided-wave propagation in a steel wire with corrosions.

Ultrasound generated by laser in a coated cylinder

An alternative theoretical solution is proposed to predict ultrasound excited by a laser line source in a homogeneous, isotropic cylinder coated with a homogeneous and isotropic material. The spectrum and transient displacement are in agreement to authors previous model for the cylinder without coating. Numerical results are obtained for copper on aluminium and vice versa. It is found for the surface waves that the high frequency component travels faster for hard coatings with velocities faster than that of the substrate, and vice versa for soft coatings.

Continuous monitoring of tightening condition of single-lap bolted composite joints using intrinsic mode functions of acoustic emission signals: a proof-of-concept study

Intrinsic mode functions of acoustic emission signals, extracted from signals using empirical mode decomposition, were used to characterize the contact conditions of asperities (e.g. sliding friction or collision) in the mating parts of bolted composite joints undergone flexural vibration, whereby to evaluate the tightening condition of the joints quantitatively. Specifically, the sliding friction–related intrinsic mode functions, generated in the mating parts of the two joining composite components (termed as C-C contact), were ascertained from those generated from the contacts between the joining components and metallic fasteners (termed as M-C contact), via a Hilbert–Huang transform. Subsequently, the C-C contact–related intrinsic mode functions were linked to the contact behaviors of asperities at the joining interfaces, reflecting quantitatively the degree of the residual torque of the bolted joints. The fatigue performance of the joints was further evaluated according to the changes in the energy ratios of the C-C contact–related intrinsic mode functions. Experimental results have revealed that the gross energy of acoustic emission signals is capable of evaluating the residual torque of the joints within a limited range. Vibration loosening of composite joints was found to result in an increase in the energy ratios of C-C contact–related high-frequency intrinsic mode functions, on which basis the detectability of the acoustic emission–based structural health monitoring is further improved, making it possible to evaluate the tightening condition of a bolted joint when the joint undergoes vibration fatigue. This proof-of-concept study provides a promising solution to evaluate the contact conditions of bolted composite joints during assembly and to continuously monitor the tightening condition throughout the service life of the joints using the acoustic emission technique.

Damage detection using high order longitudinal guided waves (HOLGW) in the anchorage zone of stayed cable

High order longitudinal guided waves (HOLGW) are studied for the damage detection in the anchorage zone of stayed cable through the theoretical analysis, numerical simulation and experimental validation. First, based on the theory of elastic wave propagation in cylinder, the dispersion curves of longitudinal modes were obtained and calculated analytically and the high-frequency such as 5MHz corresponding to the higher order longitudinal guided wave modes are identified for the damage detection. Then, the ultrasonic guided waves propagating in a steel wire with or without defects were simulated by using the finite element method and the effects of defect depth and length on the reflection coefficient are studied. Finally, the free wires and a tested cable were studied experimentally. The results show that the finite element method is able to model the high-order guided wave propagation in the steel wire. The agreement between the experiment and theory has demonstrated that the HOLGW is a potential candidat...

The study of P-SV wave propagation in the periodic piezoelectric layered material

The piezoelectric material is playing a more and more important role in the active control of the wave propagation, and is introduced into the one-dimensional phononic crystal for the actively wave control. In this paper, the P-SV wave propagation in the periodic piezoelectric layered material is studied, a model of the problem is established, and the wave propagation is simulated by the COMSOL multi-physics software. The relationship between the transmission coefficients and the incident angle under the different electrical boundary conditions are obtained numerically; meanwhile the results are compared to those obtained by the softness matrix method. And the analytical and numerical results agree quite well for the electric circuit open or closed piezoelectric material and the piezoelectricity ignored material. The influence of the electric boundary condition on the P-SV wave propagation in the periodic piezoelectric layered material is obtained, The acoustic field and electric field distribution are also obtained by the numerical simulation.

Numerical analysis of the interaction of Rayleigh wave to the sub-surface cracks

The interaction of ultrasonic waves with cracks is analyzed numerically in this paper. The nonlinear effect due to the asymmetric stiffness called contact acoustic nonlinearity (CAN) is focused. Longitudinal wave and Raleigh wave are excited separately to investigate their nonlinear interaction with cracks. Numerical results demonstrate that super-harmonics and sub-harmonics can be generated, and frequency of Rayleigh wave only in certain range can excite the harmonics when has some relations with depth of crack.