• Tribology and Lubricants
• /
• 제34권4호
• /
• pp.132-137
• /
• 2018

Ultrasonic waves are used in various applications in multiple devices, sensors, and high-power machinery, such as processing machines, welders, and cleaners, because the acoustic vibration frequencies are above the human audible frequency range. In ultrasonic machining, electrical energy at a high frequency of 20 kHz or more is converted into mechanical vibration by a vibrator and an amplifier. This technique allows instantaneous separation between a tool and a workpiece during machining, machining by pulse impulse force at the time of re-contact and minimizes the minute elastic deformations of the workpiece and machine tools due to the cutting effect. The Al7075 alloy used in this study is a typical aluminum alloy with superior strength that is mainly used in aircrafts, automobiles, and sporting goods. To investigate the optimal conditions for machining aluminum alloy using ultrasonic vibration, the present experiment utilized the Taguchi orthogonal array method, and the coefficient of friction was analyzed using the characteristics of the Taguchi technique. In ultrasonic friction and abrasion tests, the changes in the friction coefficient were measured in the absence of ultrasonic vibrations and at 28 kHz and 40 kHz. As a result, the most considerable influence on the friction coefficient was found to be the normal load, and the frequency of ultrasonic vibrations increases, the coefficient of friction increases. It was thus confirmed that the amount of wear increases when ultrasonic vibration is applied.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.783-788
• /
• 2001

Voids created with concrete construction or deterioration result in serious weakness from the aspects of both structural and durable function. Ultrasonic method using image processing technique was used for detecting pattern of voids in concrete in this study Experimental investigation was carried out for three types(patterns) of void in concrete. The effect of curing period of concrete and ultrasonic measurement method was also investigated. As a result it has been verified that the semi-direct measurement method is more effective than the other methods for detecting pattern of voids in concrete in ultrasonic method using image processing technique. The longer the curing period of concrete is, the better the detection accuracy of void pattern can be obtained.

• 한국항해항만학회:학술대회논문집
• /
• 한국항해항만학회 1995년도 VTS and IBS 95 The Korean Institute of Navigation 1995년도
• /
• pp.184-192
• /
• 1995

Although ship's draught information onboard is substantial for both the safety of navigation and the estimation of loaded cargoes its accuracy depends in traditional surveying method on the skillfulness of observers and the condition of the sea surface round the vessel. To obtain more accurate information accessibly measuring instruments with sophisticated sensors such as mechanical electronic and ultrasonic transducers have been developed. however they have still limitation in accuracy and in making up a system due to the complexity of processing signal. In this paper we propose a he technique for analyzing ultrasonic pulse signal in order to improve the measurement accuracy and simplify a remote sensing system of draught by ultrasonic waves. This technique is useful for measuring draught being considered the influence of sea surface fluctuation and for transferring its data briefly to required equipment in integrated bridge system.

• Journal of Mechanical Science and Technology
• /
• 제20권2호
• /
• pp.185-190
• /
• 2006

An ultrasonic self-calibrating technique for the characterization of a ceramic which was fabricated by change pressing time during the HIP process has been applied by using the ratio of the reflection and transmission coefficients of normal incidence longitudinal waves. The ratio is self-compensated, in that it is independent of the characteristics for transmission and reception of ultrasound by the transducer and the condition of the couplant. The insensitive direction in parameter space is defined as the direction in which the variation of the ratio to changes of two parameters vanishes. For inverse problem the distribution of minima in an error surface is investigated.

• 비파괴검사학회지
• /
• 제34권6호
• /
• pp.435-440
• /
• 2014

Contact-guided-wave tests are impractical for investigating specimens with limited accessibility and rough surfaces or complex geometric features. A non-contact setup with a laser-ultrasonic transmitter and receiver is quite attractive for guided-wave inspection. In the present work, we developed a non-contact guided-wave tomography technique using the laser-ultrasonic technique in a plate. A method for Lamb-wave generation and detection in an aluminum plate with a pulsed laser-ultrasonic transmitter and Michelson-interferometer receiver was developed. The defect shape and area in the images obtained using laser scanning, showed good agreement with the actual defect. The proposed approach can be used as a non-contact online inspection and monitoring technique.

• 임산에너지
• /
• 제22권2호
• /
• pp.60-68
• /
• 2003

목재의 기계적 특성을 평가하기 위하여 여러 가지 비파괴 측정 기술이 도입되고 있다. 본 실험은 낙엽송(Larix kaempferi Carr.) 소경재 원목을 초음파의 통과 속도와 종진동의 고유진동수를 이용한 비파괴 측정 기술로 영계수를 측정하여 휨강도 실험을 통해 얻은 실측 영계수와 휨파괴계수의 상관관계를 검토하였다. 실험에는 50본의 소경재 원목이 사용되었다. 종진동의 고유진동수를 이용한 영계수와 실측 영계수는 비교적 높은 상관관계를 나타내었다. 초음파를 이용한 비파괴 영계수 측정은 옹이의 출현빈도가 높은 원목의 선별에 효과적이었으며 종진동의 고유진동수를 이용한 측정은 할렬의 출현빈도가 높은 원목의 선별에 효과적임을 확인하였다.

• 비파괴검사학회지
• /
• 제28권1호
• /
• pp.46-53
• /
• 2008

복합재료의 내부 결함 평가를 위해 일반적으로 적용되어온 초음파 C-스캔 기법은 섬유자동 배열을 통한 정밀 성형 공정에 적용하기에는 많은 어려움이 있다. 따라서 본 연구는 복합재료의 정밀 성형 공정 중에 발생되는 각종 내부 결함들을 비파괴적, 비접촉으로 평가하기 위한 새로운 하이브리드 초음파 평가 기법을 확립하는데 목적이 있다. 이를 위하여 본 연구에서는 초음파 산란 반사(scattering reflection) 방식을 토대로 한 새로운 이중 피치-캐치(dual pitch-catch) 기법을 확립하여 기존의 결함평가를 위해 시험편의 스캔에 소요되는 시간을 줄이면서 우수한 결함 영상을 얻을 수 있는 새로운 하이브리드 기법을 개발하였다. 즉 두 가지 종류의 열경화성 및 열가소성 복합재료(carbon/epoxy, carbon/PPS) 적층판의 내부 박리(delamination) 결함의 영상화를 위하여 레이저를 이용한 유도 초음파의 발생 및 이중 피치-캐치(pitch-catch)방식을 토대로 한 비접촉식 공기 정합 트랜스듀서(air-coupled transducer)를 이용하여 결함 영상을 얻기 위한 핵심 알고리즘을 확립하였다.

• Journal of Biosystems Engineering
• /
• 제37권5호
• /
• pp.319-326
• /
• 2012

Purpose: Cheese texture is an important sensory attribute mainly considered for consumers' acceptance. The feasibility of nondestructive measurements of cheese texture was explored using non-contact ultrasonic sensors. Methods: A novel non-contact air instability compensation ultrasonic technique was used for five varieties of hard cheeses to measure ultrasonic parameters, such as velocity and attenuation coefficient. Five texture properties, such as fracturability, hardness, springiness, cohesiveness, and chewiness were assessed by a texture profile analysis (TPA) and correlated with the ultrasonic parameters. Results: Texture properties of five varieties of hard cheese were estimated using ultrasonic parameters with regression analysis models. The most effective model predicted the fracturability, hardness, springiness, and chewiness, with the determination coefficients of 0.946 (RMSE = 21.82 N), 0.944 (RMSE = 63.46 N), 0.797 (RMSE = 0.06 ratio), and 0.833 (RMSE = 17.49 N), respectively. Conclusions: This study demonstrated that the non-contact air instability compensation ultrasonic sensing technique can be an effective tool for rapid and non-destructive determination of cheese texture.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 추계학술대회
• /
• pp.1727-1732
• /
• 2004

For the purpose of monitoring by ultrasonic test of the ball bearing conditions in rotating machinery, a system for their diagnosis was developed. ultrasonic technique is used to detect abnormal conditions in the bearing system. And various data such as frequency spectrum, energy and amplitude of ultrasonic signals, and ultrasonic parameters were acquired during experiments with the simulated ball bearing system. Based on the above results and practical application for power plant, algorithms and judgement criteria for diagnosis system was established.

• 제어로봇시스템학회논문지
• /
• 제21권4호
• /
• pp.315-320
• /
• 2015

This paper describes the implemenation of localization and visualization scheme to find out an ultrasonic source caused by defects of a power distribution line equipment. To increase the fault detection performance, $2{\times}4$ sensor array is configured with MEMS ultrasonic sensors, and from the sensor signals aquired, the azimuth and elevation angles of the ultrasonic source is estimated based on the delay-sum beam forming method. Also, to visualize the estimated location, it is marked on the background image. Experimental results show applicability of the present technique.