Papers by Keyword: Surface Wave

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Authors: Yang Yang, Meng Yang Zhang, Li Xiao, Wen Zhong Qu
Abstract: Existing non-destructive test methods are usually ineffective in detection of surface breaking cracks with large depths in concrete structure. This paper introduces a method suitable for detection of deep cracks based on surface wave time reversal theory. A numerical simulation based on the finite element model is performed to investigate surface cracks detection. A damage index was defined based on the correlation coefficient between the actuated and the reconstructed wave signals. The results demonstrated that the presence of crack had a significant influence on the propagation characteristics of surface waves along concrete. Cracks in different sizes were introduced and correlated with the damage index. Enlarging the crack depth resulted in an increase in the distortion of reconstructed signals, and a higher damage index was obtained. The results illustrated the effectiveness of the surface wave time-reversal process in identifying cracks in concrete structures.
165
Authors: Yong Sang Cho, Yeon Shik Ahn, Sang Ki Park, Jae Hoon Kim
264
Authors: Taehyung Nam, Sung Ho Choi, Tae Hun Lee, Kyung Young Jhang, Chungseok Kim
Abstract: The bending fatigue of Al6061 alloy has been evaluated by the acoustic nonlinearity of laser-generated surface wave. The surface wave is very attractive for field applications since it enables to pulse and receive signals at the same surface of materials, and has strong acoustic nonlinear effects on the surface. A relative acoustic nonlinear parameter was measured successfully on the surface of fatigue-damaged aluminum 6061 alloy. The results show that the acoustic nonlinear parameter increased with fatigue damage accumulation in relation to dislocation evolution. Consequently, this study suggests that the acoustic nonlinearity technique of a laser-generated surface wave can be potentially used to characterize surface damage resulting from bending fatigue.
19
Authors: Shiuh Chuan Her, Sheng Tung Lin
Abstract: Surface cracks are the most common defects in structures. Ultrasonic has been widely used as a non-destructive evaluation technology in the case of crack characterization. In this investigation, surface waves are applied to a steel block with artificial slots to characterize the crack depth. A series of test specimen with different depths of surface crack ranging from 4mm to 10mm was fabricated. The depth of the surface crack was evaluated using the pitch-catch ultrasonic technology. In this work, 2.25 MHz, 5 MHz and 10 MHz of incident waves were employed to investigate the effect of frequency on the crack depth detection. Experimental test results show that the accuracy of crack depth detection is increasing with the increase of frequency.
1931
Authors: Wei Zhu, Xv Fu Lu, Qiang Gao
Abstract: High-impedance ground plane (HIGP) is applied in the design of rectangular waveguide end-slot phased array. The benefits of using such a HIGP are related to the suppression of surface waves because of its obvious frequency bandgap and, therefore, the scan blindness could be eliminated. Both of the bandgap curve of the HIGP structure and the scan properties of the phased arrays have been calculated. The elimination of scan blindness is obtained.
3200
Authors: A. L'Etang, Zhi Hong Huang
Abstract: This paper describes a study of laser generated ultrasonic waves in an 2-layer elastic, isotropic biomaterial model, in order to establish a modelling technique to simulate the thermoelastic response of high-power short pulse laser beams in human skin. The theory proposed in this paper takes into consideration the fundamental understanding of the laser/material interface. A finite element model using the commercial finite element code ANSYS is used to study the effects of laser pulse duration and energy flux contribution to the surface waves. The simulation comprises a set of boundary conditions that approximate a heat flux point source located on top of the surface of the material. Because of the time scale of interest, the elastic effects do not feed back into the thermal problems, so that a sequential coupled-field analysis was performed where the thermal and elastodynamic fields are uncoupled and treated separately. The initial finite element analysis involves a transient thermal analysis using a heat flux with Gaussian spatial variation to simulate the laser pulse heating. The results from the thermal analysis were read and applied to the structural analysis where the out-of-plane displacements histories are analyzed in the skin model with varying thicknesses
85
Authors: Young Gil Kim, Bong Young Ahn, Young Joo Kim, Young Bae Moon, Sung Hwa Kim
619
Authors: Kazuhiko Iwai, Shigeo Asai
Abstract: Free surface motion of a liquid metal submerged in an alternating magnetic field has been examined. A copper vessel filled with a liquid gallium is set in a coil for the imposition of the alternating magnetic field. The alternating magnetic field penetrates into a liquid gallium only from an upper free surface because thickness of the copper vessel is larger than the electromagnetic skin layer of copper. Time variation of displacement of the standing wave loop excited on the free surface is detected by a laser level sensor. The standing wave was suppressed not only by intensification of the magnetic field magnitude but also increase of the magnetic field frequency.
1071
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