• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.923-928
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• 2015

In this paper, we propose an ultrasonic magnetic abrasive polishing (US-MAP) technique to effectively machine a high-strength material, and we prove the efficiency of hybrid finishing. We use Taguchi's experimental method to determine the influence of each parameter. Based on the results, US-MAP exhibited a higher polishing efficiency than traditional MAP, and a suitable frequency for hybrid finishing was 28 kHz. When investigating the effect of the parameters on the surface roughness, the ultrasonic amplitude had the greatest effect. However, when machining with $55-{\mu}m$ amplitude, the machining efficiency decreased as the magnetic flux density varied.

• Applied Chemistry for Engineering
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• v.21 no.4
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• pp.385-390
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• 2010

Transesterifications of vegetable oils (soybean oil, grapeseed oil, corn oil, canola oil) by ultrasonic energy were examined on various catalysts for biodiesel production. Reaction activities of the transesterifications were evaluated to the ultrasonic energy and thermal energy. The physicochemical properties and product distribution were also investigated to the biodiesels produced from the oils in the reaction using ultrasonic energy. The yields of fatty acid methyl ester (FAME) on the alkali catalysts were higher than those on the acid catalysts. The highest FAME yield was obtained as 83% on potassium hydroxide catalyst in the transesterification. The effective reaction conditions by ultrasonic energy were 1 wt% catalyst loading and 6:1 molar ratio of methanol to vegetable oils. The reaction rate of the transesterification by ultrasonic energy was faster than that by thermal energy. The acid values of the biodiesel products were improved above 30% compared to those of the feedstocks.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.3
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• pp.163-171
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• 1998

Near/far field length and directivity of transducers were investigated for the improvement and evaluation of the detectability of flaws in a disc. The reference block is fabricated for the disc of stage 6 in Yonggwang unit 1. The near/far field and directivity of an ultrasonic transducer with the center frequency of 5MHz were calculated for the inspection of the disc. These values showed good agreements with the experimental results. In the system composed of a wedge and a disc, those are evaluated theoretically and experimentally for the specimen with the artificial flaws of the size 2mm and 4mm and an ultrasonic transducer with the center frequency 5MHz and diameter 0.5inch. The detectability of keyway-flaw and detectable region for inspection were evaluated by using both tangential $45^{\circ}$ and $90^{\circ}$ transducers located at the distance of 53mm and 75mm from the disc hub, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.101-106
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• 1999

Pb$(Zr_{0.5},Ti_{0.5})O_3$ thin films were prepared on $Pt/Ti/SiO_2/Si$substrates by spin-coating. The sol was sonicated in an ultrasonic bath to promoto homogenization and the results were compared with untreated case. In the case of PZT thin films prepared from sonicated sol, only perovskite phase was obtained at $550^{\circ}C$ and "rosette" structures in the films disappeared. Dieletric constants (10kHz), remnant polarization, and coercive field of the films prepared from untreated and sonicated sol were 335 and 443, 12.3 and17.7$\mu$C/$\textrm{cm}^2$, 168.4 and 153.5 kV/cm. Electrical properties were improved by introduction of the sonication processon process

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.591-597
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• 2001

Ti alloy is used for essential parts of aircraft for high temperature environment. Although Ti alloy has excellent performance in regard to mechanical properties, it is difficult ot find fatigue cracks by nondestructive ultrasonic inspection due to its two-phase microstructure, which consists of hard alpha and beta phases. Sound energy reflected from microstructural features in the component produces a background inspection noise which is seen even when no defects are present. This noise can inhibit the detection of critical internal defects such as pores cracks or inclusions. To obtain fundamental data on ultrasonic inspection of Ti alloy, ultrasonic testing was performed using a specimen with small drill holes and ultrasonic wave propagation velocites were measured.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.4
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• pp.386-392
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• 2002

Ultrasonic has been proposed as an attractive means of detecting bone loss. There have been several commercial ultrasound devices developed for measuring the heel to predict fracture at other bones. However, these devices select only single point of heel bone as measurement site. It causes poor assessment of bone quality due to the error of transducer positioning. In an effort to improve current ultrasound systems, we evaluated the linear scanning method which provides better prediction of bone quality and an accurate image of bone shape. The system used in this study biaxially scans a heel bone using automated linear scanning technique. The results demonstrated that the values of ultrasound parameters varied with different positions within bone specimen. It has been also found that the linear scanning method could better pre야ct bone quality, eliminating the error of transducer positioning.

• Parasites, Hosts and Diseases
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• v.33 no.2
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• pp.117-124
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• 1995

This study was performed to evaluate diagnostic sensitivity and specificity of sonography on clonorchiasis. During the 9 months from March to November 1994, sonography skin test, stool examination, and medical examination were performed to 609 volunteers of Pohang which is located along the Hyongsan-gang (Rivers and is one of well-known endemic areas of clonorchiasis. The sensitivity of sonography was either 21% if the intrahepatic ducts dilatation was assumed to be the only positive anding or 52% if the periductal echogenicity was also included as one of positive findings. The sensitivity of skin test was 62%. The sensitivity was 46% if the diagnostic criteria were arbitrarily assumed as being positive in skin test and having either sonographic findings. The sonographic finding of fusiform, non-shadowing, weakly echogenic foci in gallbladder or in billiaiy tree indicating the flukes or aggregates of flukes was not obvious in this study. The specificity of sonography was either 95% if the intrahepatic ducts dilatation was assumed to be the only positive finding or 82% if the periductal echogenicity was also included as one of positive findings. The specificity of skin test was 52%. The specificity was 90% if the diagnostic criteria was arbitrarily assumed as being positive in skin test and having either sonographic findings.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.367-373
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• 2011

Guided waves inspection techniques that are different with inspection technique by bulk waves are widely used in pipe line evaluation due to advantages of long distance inspection. However, most of pipe lines at industrial fields are buried and/or coated. In this case, due to the attenuation effect from soil and/or coating material, there are a lot of difficulty on inspection by conventional ultrasonic technique. In this paper, guided waves propagating patterns are calculated with respect to excitation mode by Normal Mode Expansion(NME). Guided waves patterns based on excited by single transducer and guided wave focusing technique have employed to analyze focusing pattern on a pipe. A longitudinal mode and high order flexural modes are used with various number of transducers to determine sensitivity. Guided waves energy excited by multi transducer with focusing algorithm was successfully focused at a desired point.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.536-542
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• 2011

Dissimilar metal welds in nuclear power plant are known as very susceptible to PWSCC flaws, and periodically inspected by the qualified inspector and qualified procedure during in-service inspection period. According to field survey data, the majority of their DMWs are located on tapered nozzle or adjacent to a tapered component. These types of configurations restrict examination access and also limit examination volume coverage. Additionally, circumferential scan for axially oriented flaw is very difficult to detect located on tapered surface because the transducer can't receive flaw response from reflector for miss-orientation. To overcome this miss-orientation, it is necessary adapt skewed ultrasonic transducer accomodate tapered surface. The skewed refracted longitudinal ultrasonic transducer designed by modeling and manufactured from the modelling result for axial flaw detection. Experimental results showed that the skewed refracted longitudinal ultrasonic transducer get higher flaw response than non-skewed refracted longitudinal ultrasonic transducer.

• Journal of Energy Engineering
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• v.20 no.2
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• pp.84-89
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• 2011

In this study, individual(alkaline, ultrasonic) and combined(alkaline+ultrasonic) pretreatment effect on sewage sludge solubilization was investigated. COD solubilization rates increased with the dose of NaOH added: solubilization reached 27.6%. Additional alkaline agents did not increase solubilization further. Ultrasonic pretreatment achieved 33~39% solubilization when 140 W/L amplitude. In(alkaline(pre-treatment)+ultrasonic (after-treatment)) treatment, solubilization increased as the combined intensity in creased($70.4{\pm}9.4%$). SCOD rising rate(0.076) was achieved.