Advanced Nondestructive Evaluation I

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Authors: Hyun Chul Jung, Koung Suk Kim
Abstract: The stroboscopic phase shifting ESPI (SPS-ESPI), one of the optical vibration amplitude measurement techniques, is presented. Although the general PS-ESPI can be used for quantitative deformation measurement of the object, this technique cannot measure the vibration amplitude with itself only. The phase change due to the vibration of the object cannot be calculated with general PS-ESPI correctly. Therefore, in order to solve this problem, the stroboscopic illumination must be introduced to the general PS-ESPI. This can be done by using a device called as AOM (Acousto-Optic Modulator). In this paper, SPS-ESPI is applied to measure the vibration amplitude of the square plate whose all edges were fixed. The natural frequencies and mode shapes are analyzed by using ANSYS. And the results obtained by using SPS-ESPI technique are compared with that of the ANSYS analysis. The vibration amplitude is measured by using SPS-ESPI quantitatively.
Authors: Jin Tae Kim, Dohyoung Kim, Hyun Su Kim, Jong Rak Park
Abstract: The profile of the mirror surface is measured by using optical phase shift method and Twymann-Green interferometer. Phase map is calculated by applying 4–buckets method and Vikhagen phase shift algorithm is applied to escape convolution errors. From that the obtained roughness of the mirror surface is around 20 nm rms roughness value. Also, the interferometer was stabilized by using fringe locking method. Also, we propose two colors method very precise surface profile and the length can be measured in the harsh environmental conditions.
Authors: Seung Seok Lee, Sang Whoe Dho
Abstract: We present a suppressing technique of the antisymmetric mode by superposition of Lamb waves generated by two laser beams in a thin plate. Two Lamb waves of the same frequency propagating from the opposite direction simultaneously arrive at the point of measurement and are superposed to compose one Lamb wave. The amplitude of the superposed Lamb wave depends on the distance between two laser beams. The suppressing of antisymmetric Lamb wave mode is accomplished by selecting the distance between two beams which simultaneously satisfies the condition of the anti-node(maximum) for the symmetric mode and the minimum for the antisymmetric mode. By this method, the antisymmetric Lamb wave mode is suppressed to the degree of 1.4% of the amplitude measured at zero distance between two beams.
Authors: Seung Seok Lee, Sang Whoe Dho
Abstract: We present a laser-ultrasonic technique to generate the lowest symmetric ( ) Lamb wave in a thin plate. Using this special technique, in which two symmetric laser beams quasi-simultaneously hit at the same point on both sides of the plate, we absolutely suppress anti-symmetric Lamb wave modes. This technique is applicable to any situation that requires symmetric Lamb wave mode operation and does not need additional contacts or special equipments.
Authors: Ki Soo Kang, Koung Suk Kim, Hyun Chul Jung, Heo Sub Jang
Abstract: Shearography, a type of speckle interferometry, is a powerful tool for nondestructive testing (NDT) because it is insensitive to environmental vibration disturbance and easy to detect strain concentration in an internal defect with noncontact and whole field. The shearing amount in Shearography has influence on determining defect size and source location. Thus the shearing amount must be optimally adjusted to get accurate evaluation. This paper investigates the defect size and source location according to the change of shearing amount in artificial slender defects along longitudinal direction of pipeline. Based on the investigation, a new technique is proposed for the quantitative determination of defect size and source location.
Authors: Dong Iel Kim, Yong Hak Huh, Chang Doo Kee
Abstract: To measure the micro-mechanical properties for micro/nano materials, out-of-plane ESPI system and micro-strip bend testing system were developed. For the bending system, PZT actuator was controlled with the stroke resolution of 0.6 nm and out-of-plane ESPI system was developed in compact and portable type. To quantitatively analyze the out-of-plane ESPI fringe patterns, 4-bucket technique was used and unwrapped phase map was obtained. Electrolytic copper foil with the thickness of 18 μm was used for preparation of the strip bend specimen with length of 8 mm and three different widths of 2, 3 and 5 mm. The strip bending tests showed that the out-of-plane deflection in the bend specimen was measured with a maximum of 8 % in error. Furthermore, from the experiment, the variation of the deflection along the supporting span could be determined and significant region was linear.
Authors: Jae Hyun Kim, Hak Joo Lee, Seung Woo Han, Jong Man Kim, Chang Wook Baek
Abstract: In this study, we use the strip-bending test to measure the residual stress of a thin film structure. The principle of the strip bending test and the test procedures are described and the analysis of the strip deformation is presented. The explicit formula for estimating the residual stress is given, which requires the initial stress as an input. As an example, the E-beam evaporated Au thin film is chosen, and the residual stress is measured by the present method. The Au thin film structure has a tensile or compressive residual stress depending on the film thickness. The tensile and the compressive residual stresses of Au thin film are successfully measured by the present method.
Authors: Hyo Sung Cho, Sung Il Choi, Hok Yung Kim, Bong Soo Lee, Sin Kim
Abstract: The gas electron multiplier (GEM), placed in the drift volume of a conventional gas detector, is a conceptually simple device for producing a large gas gain by concentrating the drift electric field over a very short distance to the point that electron avalanching occurs. This device consists of a thin insulating foil of several tens of μm in thickness, covered on each side with a thin metal layer, with tiny holes, usually 100 μm or less in diameter, and with a spacing of 100-200 μm through the entire foil, perforated by using chemical etching or high-powered laser beam technique. In this study, we have investigated its operating properties with various experimental conditions and demonstrated the possibility of using this device as a digital X-ray imaging sensor, by acquiring X-ray images based upon the scintillation lights of the GEM with a standard CCD camera.
Authors: Seung Baek, Sung Kuen Cho, Chang Sung Seok
Abstract: In this study, we investigated indentation behavior by varying the tip radius in a finite element model. We measured the tip radius and shape of the nano-indenter by SPM (scanning probe microscope) and compared them with the simulation results. The tip radius of cube corner indenter was measured to be 39nm, in agreement with the common tip radius of such indenters, which range from 20~50nm.
Authors: Bong Young Ahn, Ki Bok Kim, Hae Won Park, Young Joo Kim, Yong Seok Kwak
Abstract: As cMUTs (capacitive Micromachined Ultrasonic Transducer) offer numerous advantages over traditional transducers in terms of efficiency, bandwidth, and cost, they are expected to replace piezoelectric transducers in many applications. In particular, 2D-array cMUTs have aroused great interest in the medical engineering society because of their ability to materialize a true volumetric ultrasonic image. In this study, single element cMUTs with 32 x 32 and 64 x 64 cells were successfully fabricated. The diameter and thickness of the membrane are 35  and 1000 nm, respectively, with a sacrificial layer thickness of 600 nm. The electric characteristics of the fabricated cMUT were measured. Tests on the efficiencies of the cMUT in terms of wave generation and in terms of detection according to the bias and pulse voltage were performed in an air atmosphere.

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