• Composites Research
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• v.20 no.1
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• pp.15-22
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• 2007

As a fundamental approach to studying elastic wave behaviors in fiber-reinforced composites, this paper introduces the analytical method to predict the modes, directions, and amplitudes of all reflected waves that are generated by free-surface reflection in fiber-reinforced composites. The paper also explores a new phenomenon where a reflected wave that is predicted to exist in accordance with the slowness surface may disappear. This may occur when the angle of incidence of a quasi-shear wave exceeds a newly defined critical angle, named the third critical angle. It is hoped that the analytical approach introduced in this paper will provide an easy-to-follow guideline for researchers in the relevant area such as ultrasonic nondestructive testing.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.2
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• pp.151-157
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• 2004

Ultrasonic testing is a kind of nondestructive test to detect a crack or discontinuity in materials or on material surfaces by sending ultrasound to it. This conventional ultrasonic technique has some limitations in reliably detecting crack or accurately assessing materials in the case of complex-shaped power plant components such as a turbine blade root. An alternative method for such a difficult inspection is highly needed. In this study, application of a phased array ultrasonic testing (UT) system to a turbine blade, one of the critical power plant components, has been considered, and the particular incident angle has been determined so that the greatest track detectability and the most accurate crack length evaluation nay be achieved. The response of ultrasonic phased array was also analyzed to establish a special method to determine the track )ength without moving the transducer. The result showed that the developed method for crack length assessment is a more accurate and effective method, compared with the conventional method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.151-154
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• 1993

지동 및 음향분야의 발달과 더불어 가청주파수 이상의 초음파에대한 연구가 여러분야에 걸쳐 다양하게 많은 학 자들에 의해진전되어 왔다. 이중에서 실용적인 초음파 장치가 처음으로 등장한 것은 1921년경 프랑스의 랑지방 (P. Langevin)에 의해 만들어진 초음파측심기라고 전해지고 있다. 당시 사용된 진동자는 두 장의 금속원판 사이에 수정을 샌드위치 형태로 만든것으로써 랑지방형 진동자라고 한다. 최근 각종기계의 경량화, 고도화, 고성능화가 요구 되면서 고인성, 고내열성, 고경도 등의 특성을 갖는 재료를 가공함에 있어서 저동력 및 고정밀도가 요구되고 있다. 본 연구에서는 선삭가공에서 초음파발생기에서 보낸 초음파신호를 초음파 진동혼의 설계에 의한 진폭을 증가시켜 사각형 단면을 갖는 양단자유지지 굽힘진동 공구홀더의 공진조건을 초음파 진동절삭 가공시스템에 적용시키는데 목표를 두며 또한 초음파 진동절삭을 적용시켰을 때의 절삭 특성을 규명하기 위하여 선정된 절삭조건으로 선삭할 때 발생하는 절삭분 력 및 표면거칠기를 측정하고 분석하여 그 결과로부터 절삭특성을 해석코자 본 연구를 수행하였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.991-996
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• 2013

In this paper, the ultrasonic horn having the natural frequency with 60 [kHz] for the dissimilar material bonding of the glass and solder tried to be designed. The ultrasonic horn was designed through the relational formula including the aspect ratio of the input terminal and output terminal, length of the ultrasonic horn. The modal analysis was performed for the propriety analysis of the designed horn. The parameters and response was set through the basic experiment. The dissimilar material bonding strength analysis using the ultrasonic transducer was done. The optimal process parameters having maximum bonding strength was derived.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.1
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• pp.40-45
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• 2008

Immersion ultrasonic testing (UT) was used to determine elastic moduli of solid materials instead of the widely-used contact UT method. Conventionally, immersion UT is only used for determining the longitudinal wave speed. However, in this research, transverse wave speed was measured through finding transverse wave echoes caused by mode-conversion at material's boundary. Also, even in the cases when wave speeds could not be determined due to unknown thickness, Poisson's ratio was able to be calculated from the ratio of longitudinal and transverse wave speeds. This technique was verified for several materials, and it was found that higher accuracy was obtained by immersion UT method for materials either with relatively high wave speed or with relatively small Poisson's ratio. This technique thus will be suitable fur ceramics or high strength materials.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.4
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• pp.818-829
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• 1990

본 연구에서는 공구의 진동에 사용되는 혼(hone)의 재료로 강성과 초음파진동 이 우수한 티타늄 합금을 사용하였으며, 이의 설계 및 진동절삭 기구의 구성과 공구형 상 및 이송에 의하여 결정되는 선삭의 이론적 표면조도를 근간으로 각종 절삭 조건 등 을 변화시키면서 실험을 행하여 초음파 진동 절삭시 나타나는 특성들 중 절삭저항, 다 듬질면 거칠기, 칩형태, 가공정도 등을 관찰하여 범용절삭과 비교 검토하여 초음파 진 동절삭이 정밀가공 및 생산성 향상에 적합한 가공방법임을 입증코져 한다.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.426-430
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• 2003

본 연구에서는 초음파현미경의 기하학적 원리와 초음파현미경의 특징중 하나인 V(z)곡선의 간섭파형을 시뮬레이션 하였고, 실제 초음파현미경의 V(z)곡선법을 이용하여 미소영역에서의 누설탄성표면파 음속을 측정하였다. 초음파현미경을 이용한 V(z)곡선법의 음속측정결과가 시뮬레이션 음속값과 큰차이를 보이지 않으므로 미소영역에 초음파현미경의 V(z)곡선법을 적용하여 초음파의 음속측정이 가능함을 확인하였다. 이는 향후 초음파현미경을 이용하여 미세한 재료의 물성평가에 적용할 수 있을 것으로 기대된다.

• 기계와재료
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• v.10 no.1 s.35
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• pp.85-92
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• 1998

• 기계와재료
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• v.14 no.3 s.53
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• pp.85-92
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• 2002

• Proceedings of the Materials Research Society of Korea Conference
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• 1995.11a
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• pp.64-64
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• 1995