The research focuses on measuring body wave by continuous laser scanning along the surface of aluminum plate. The model of aluminum plate was established by finite element method. The temperature near the upper edge rises, and the temperature rise is small. In infinite large aluminum plates, there are transverse and longitudinal wave front, and the wave front velocity is affected by the velocity of the scanning laser source. Finally, the wave front in plate bottom is used to identify the wave front type, which is generated by scanning laser and determined by combining the relationships between wave velocity and scanning velocity and Bscan diagram.
The investigation focuses on analyzed the influence of periodic V-defects on wedge waves by laser ultrasound technique. Usually, wedge tip is almost non-perfect, which may bring in break and enormous economic losses. The wedge waveguide models with different periodic V-defects were established by using finite element method. We have observed multiple mode wedge waves in 20° wedge. The depth of defect is 0.1mm, and the periodic number are 1, 6, 12, and 24, respectively. Both reflected and transmitted waves are observed. And the low order reflected wave and transmitted wave modes separate from high order mode. As periodic number increase, the amplitude of reflected wave and transmitted wave decreased. By integrating the power spectra of the wedge waves, the energy distribution of these wedge waves of different periodic are analyzed. It is found that the energy has a fluctuation, which could be determined the location of defect. The energy has a gradually increase as the propagation before defect, and dramatic decrease after the defect. The results of this study can provide theoretical guidance for the positioning and size estimation of wedge defects.
The investigation focuses on measuring the influence of crack and its width on wedge waves propagating along wedge tip by using laser ultrasound technique. Usually, ideal wedge is almost non-existent, the non-perfect wedge may bring in break and enormous economic losses. Therefore, it is necessary to investigate the characteristic of wedge waves propagating along line wedge with cracks. The wedge waveguide models with different cracks were built by using finite element method. For 20° wedge, multiple mode wedge waves were observed through B-scan. The width of crack of rectangle shape is 0.1mm, and the width are 0.01mm, 0.05mm, 0.1mm, and 0.2mm, respectively. Both reflected and transmitted waves are observed. Due to the dispersion characteristics, we observed the reflected and transmitted A1, A2 mode. Meanwhile, A1 mode separated from the reflected and transmitted A2 mode are also obtained as the wedge wave mode propagating to crack. As the width diverse, it is found that the propagating of wedge waves is almost no change. This study can provide theoretical guidance for the positioning and size estimation of wedge cracks.
Bars or tubes are widely used in all kinds of equipment such as automobile shafts or power plant boilers. Effective detection of internal transverse defects is very important to the security of the equipment. In this paper, the time-delay algorithm for the detection by using the combination of a phased array ultrasonic probe and a wedge was discussed. Firstly, a coordinate system was established and the position of each element was calculated. The focal point position of phased array ultrasonic wave was specified. Secondly, based on the geometric acoustics assumption, the equation of the sound wave incident location of each element and its scope on the interface between wedges and artifacts were deduced by using Fermat's principle. The numerical method was implied to solve the equations. And the delay time of each element of the array was computed. Finally, the computed delay time of each element was imported to the finite element model and the acoustic beam was simulated. The result shows that the detecting waves can be focused to the specified position by using the calculated delay time. This paper provides a method to calculate the delay time of each element of phased array probes for detecting the transverse defects of cylindrical surface artefacts.
In the ultrasonic testing of submarine pipelines by using guided waves, wave energy leakage is a main reason of signal decay. For overcoming the decrease of energy attenuation, the propagation of guided waves of immersion plates is studied in this paper. The dispersion equations of guided waves is numerically solved. Then the appropriated modes of which phase velocity are small or large are selected for optical Schlieren visualization and propagation of leaky waves is discussed. It is shown that selecting some modes of which imaginary part are small can retard guided wave decay and extend length of testing.
The research focuses on measuring the influence of V-defect on wedge waves propagating along line wedge tip by using laser ultrasound technique. Generally, wedge has more or less defect or damage on the tip, which may result in break and bring economic losses. Thus it is necessary to investigate characteristic of wedge waves propagating along line wedge with defect. The wedge waveguide models with different defect depth were built by using finite element method. Multiple mode wedge waves were observed through B-scan. The open of defect is 0.1mm, and the depth is 0.01mm, 0.05mm, 0.1mm, 0.2mm, and 0.3mm, respectively. It was seen that both reflected and transmitted waves were observed. Due to the dispersion characteristics, we observed the reflected and transmitted A1 mode separated from A2 mode, which can be used to determine the width of V-defect. Meanwhile, models of V-defect with different depth are also built. We had found that wedge waves are totally reflected and there is no transmitted wave observed as the depth is bigger than 0.3mm.
The research focuses on study the influence of truncations on the dispersion of wedge waves propagating along cylinder wedge with different truncations by using the laser ultrasound technique. The wedge waveguide models with different truncations were built by using finite element method (FEM). The dispersion curves were obtained by using 2D Fourier transformation method. Multiple mode wedge waves were observed, which was well agreed with the results estimated from Lagasse’s empirical formula. We established cylinder wedge with radius of 3mm, 20° and 60°angle, with 0μm, 5μm, 10μm, 20μm, 30μm, 40μm, and 50μm truncations, respectively. It was found that non-ideal wedge tip caused abnormal dispersion of the mode of cylinder wedge, the modes of 20° cylinder wedge presents the characteristics of guide waves which propagating along hollow cylinder as the truncation increasing. Meanwhile, the modes of 60° cylinder wedge with truncations appears the characteristics of guide waves propagating along hollow cylinder, and its mode are observed clearly. The study can be used to evaluate and detect wedge structure.
The research focuses on measuring the influence of angel on wedge waves propagating along cylinder wedge tip and its characteristic of dispersion by using the laser ultrasound technique. The wedge waveguide models with different angle were built by using finite element method (FEM). The dispersion curves were obtained by using 2D Fourier transformation method. Multiple mode wedge waves were observed, which was well agreed with the results estimated from Lagasse’s empirical formula. We had established cylinder wedge with radius of 3mm and angle of 10°, 20°, 30°, 40‡, 50°, 60°, 70°, and 80°, respectively. It was found that radius caused abnormal dispersion to the mode of cylinder wedge with small angle and normal dispersion to the mode of cylinder wedge with big angle.
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