레일리각 근처에서 도색된 거친 표면으로부터 후방 산란된 초음파

권성덕,권용규,윤석수 한국비파괴검사학회 2004 한국비파괴검사학회지 Vol.24 No.1

1-17㎛ 범위의 표면 거칠기를 가진 철 시편에 대해 물속에서 후방산란된 초음파의 입사각 의존성(프로파일)이 측정되었다. 거칠기가 도색에 의해 숨겨졌을 때 수직 프로파일은 거칠기에 대한 분별력이 사라졌으나 레일리 각 근처에서의 후방산란 프로파일은 거칠기 의존성을 여전히 보여주었다. 레일리 각에서 직접 복사된 프로파일 세기는 거칠기와 비례하였고 코너에서 반사되어 되돌아오는 표면파로부터의 후방복사의 세기는 거칠기와 반비례하였다. 도색 처리된 시편에서 0.03 파장 이하의 직접 후방복사에서도 선형성이 관찰되었고 주기적 거칠기에 의해 발생한 비정상 저면 다중반사 현상이 사라졌다. The angular dependence (or Profile) of backscattered ultrasound was measured for steel specimens with a range of surface roughness, 1~71 ㎛. Backscattering profiles at or near the Rayleigh angle still showed roughness dependence while the assessment of surface roughness via normal profile became impossible due to the paint layer masking the roughness. The peak amplitude directly radiated at the Rayleigh angle was proportional to the surface roughness, while the averaged peak amplitude radiated from the backward propagation Rayleigh wave, produced by reflection at a corner, was inversely proportional. In the painted specimens, the linearity of direct backward radiation with the roughness was observed even at the roughness of less than three hundredths of a wavelength, and the abnormal multiple back reflection caused by periodic roughness disappeared.

표면탄성파 분산 섭동이론과 응용

권성덕,김영환,송성진 한국비파괴검사학회 2003 학술대회 논문집 Vol.- No.1

The perturbation theory of Auld [Acoustic fields and waves in solids,(Wiley,NewYork,1973) vol.Ⅱ,p.294], which describes the effect of a subsurface gradient on the velocity dispersion of surface waves has been modified to a simpler form, by an approximation using a newly defined velocity gradient for the case of isotropic materials. The modified theory is applied to the wear-in procedure in AISI 1045 steel with various residual stress distributions. The frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the barkward radiation of the incident ultrasonic wave in the scuffing specimens, and then compared to the perturbation theory. It was concluded that Break-in procedure in order to elongate the safety life reduce 8, fractional change in velocity per unit stress by 20-30%

Mechanism of the Ultrasonic Back-Reflection Peak at the Rayleigh Angle

권성덕 안동대학교 기초과학연구소 1991 基礎科學 硏究論文集 Vol.2 No.1

다결정 알루미늄에 대한 레일리(Rayleigh)임계각에서 나타나는 후방산란 초음파의 Peak크기는 Rayleigh산란지역에서 grain크기와 함께 증가하였고 Diffusive지역에서는 그 의존성이 반전되었다. 또한 그 peak크기의 주파수 의존성은 Norris의 예견(J.Acoust.Soc. Am.,23(2), 427-434(1983))과 질적으로 일치하였다. 이 결과들은 후방산란 Peak현상이 입사지역에서 직접 발생되는 후방진행 leaky표면파의 복사 뿐 아니라 표면 아래지역에서 그 leaky파의 산란에 의해서도 기여를 받음을 보여준다. The peak amplitude of the backscattered wave for aluminum at or near the Rayleigh angle increases with grain size in the Rayleigh scattering region but the situation is reversed in the diffusive region. The frequency dependence of the peak amplitude agrees qualitatively with Norris`s prediction (J.Acoust.Soc.Am., 23(2),427-434(1983)). The analysis indicates that the back reflection peak is caused by the scattering of a leaky surface wave in the subsurface region as well as the radiation of the backward propagation leaky wave generated directly in the incidence region.

Application of Generalized Lamb Wave for Evaluation of Coating Layers

권성덕,김학준,송성진 한국비파괴검사학회 2007 한국비파괴검사학회지 Vol.27 No.3

This work is aimed to explore a possibility of using the generalized Lamb waves for nondestructive evaluation of the bonding quality of layered substrates. For this purpose, we prepared two sets of specimens with imperfect bonding at their interfaces; 1) TiN-coated specimens with various wear conditions, and 2) CVD diamond specimens with various cleaning conditions. A dispersion simulation performed for layered substrates with imperfect interfaces are carried out to get the characteristics of dispersion curves that can be used for bonding quality evaluation. Then the characteristics of dispersion curves of the fabricated specimens are experimentally determined by use of an ultrasonic backward radiation measurement technique. The results obtained in the present study show that the lowest velocity mode (Rayleigh-like) of the generalized Lamb waves are sensitively affected by the bonding quality. Therefore, the generalized Lamb waves can be applied for nondestructive evaluation of imperfect bonding quality in various layered substrates.

표면탄성파를 이용한 마모 표면부의 평가

권성덕,윤석수,송성진,이영제 한국비파괴검사학회 2002 한국비파괴검사학회지 Vol.22 No.2

레일리(Rayleigh) 표면탄성파의 속도와 산란의 주파수 의존성을 이용하여 마모로 인해 열화된 AISI 1045강 시편의 깊이방향 잔류응력 분포(열화 기울기)의 비파괴적인 평가가 시도되었다. 액체/고체 경계면에 초음파가 특정각도로 입사할 때 발생한 표면탄성파의 산란과 복사로 인해 나타나는 후방복사 프로파일의 오른쪽 반치폭과 크기 그리고 발생각으로 잔류응력 분포의 해석도 가능하였으며 평균법에 의한 복사파의 세기 및 스펙트럼의 변화는 잔류응력 분포의 열화로 인해 발생한 미세 결함 밀도와의 연관성을 보여주었다. The frequency dependency of the Rayleigh surface wave was investgated indirectly by measuring the angular dependency of the backward radistion of the incident ultrasonic wave in the abrasion specimens, which was explained in view of the residual stress distribution. The peak intensity of the backward radiation profile decreased and the right halt width of the profile increased with an increase of the variational rate of residual stress for the scuffing specimen. The peak intency was also affected by the surface wave scattering during the propagation around the micro damages. The peak angle might depend on not only the amount of residual stress but also the micro-structure. The result observed in this study demonstrates the high potential od the backwatd radiated ultrasound as a tool for the nondestructive evaluation of the subsurface gradients of materials.

후방복사된 초음파를 이용한 12Cr강 부식 피로특성 평가

권성덕,윤석수,송성진,배동호 한국비파괴검사학회 2000 한국비파괴검사학회지 Vol.20 No.5

화력발전 플랜트의 터빈 블레이드(blade) 재료인 12Cr 합금강의 고속 열화 시편에 대한 레일리(Rayleigh) 표면탄성파의 산란과 속도의 주파수 의존특성을 액체/고체 경계 면에서 표면파의 발생기구에 의해 나타나는 후방복사 초음파 세기의 입사각 의존성으로 간접 평가하고 부식피로 특성과 비교 분석하였다. 후방복사 현상이 발생하는 입사각 폭은 부식온도와 반비례하였으며 이는 효과적 부식층의 두께 증가로 설명되었다. 이 프로파일의 폭은 피로시험에서 균열성장 관계식인 파리스(Paris) 법칙의 지수 m과 선형적으로 반비례하여 열화시편의 부식 피로 특성의 비파괴적 평가에 있어 후방복사된 초음파를 이용한 기술이 매우 유용함을 보여주었다. The corrosion-fatigue characteristics of the 12Cr steel, which is widely used in fossil power plants as a turbine blade material, are evaluated nondestructively by use of the Rayleigh surface wave. In this study, the frequency dependency of the Rayleigh surface wave is investigated indirectly by measuring the angular dependency of the backward radiation of the incident ultrasonic wave in the aged specimens, and then compared to the corrosion-fatigue characteristics. The width of the backward radiation profile decreases as the increase of the aging temperature, which seems to result from the increase of the effective degrading layer thickness. This parameter also shows an inversely proportionality to the exponent, m, in the Paris law which predicts the crack size increasement due to fatigue. The result observed in this study demonstrates high potential of the backward radiated ultrasound as a tool for the nondestructive evaluation of the corrosion-fatigue characteristics of the aged materials.

초음파를 이용한 콘크리트 구조물의 비파괴적 검사

권성덕 安東大學 1988 安東大學 論文集 Vol.10 No.1

The application of ultrasonic wave to nondestructive testing of concrete structure was studied. It was shown that the induced frequency adeguate to concrete is about 50KHz and the influence of test condition must be considered. The propaigation characteristics of ultrasonc wave in concrete make possible to estimate strength, damage and depth of cracks, etc. The specification of standard reqiurements for acoustic properties of concrete and many laboratory investigations are required for effective application to industrial practice.

CVD 다이아몬드 코팅층 평가를 위한 후방복사 신호해석 기법 연구

권성덕,김학준,송성진 한국물리학회 2005 새물리 Vol.51 No.5

A Rayleigh surface wave from an automatic ultrasonic backward radiation system was used to evaluate chemical-vapor deposited (CVD) diamond-coated specimens which were expected to extend the lifetime of mechanical parts that are used in severely abrasive conditions. The bonding quality of the interface between the CVD diamond coating layer and the silicon substrate was severely influenced by the roughness and the cleaning conditions. The quantitative evaluation showed that an important requirements was to improve the bonding quality of the CVD diamond coating layer. For this purpose, signal processing methods, time trace angular scan and frequency spectrum angular scan, were applied. The initial experimental result obtained in this present study demonstrates the high potential of backward radiated ultrasound as a tool for nondestructive evaluation of very thin CVD diamond coating layers. 자동화된 후방복사 초음파 측정 시스템에 의한 레일리 (Rayleigh) 표면파가 심각한 마모환경에서 수명연장의 목적으로 코팅된 CVD (chemical vapor deposit) 다이아몬드 층의 평가를 위해 사용되었다. 두 재질 사이 접합의 질을 개선하기 위해서는 정량적인 평가가 매우 중요하며 이를 위해 후방산란 신호를 효율적으로 분석할 수 있는 TTAS (Time Trace Angular Scan)와 FSAS (Frequency Spectrum Angular Scan)이라는 신호처리 기법이 도입되었다. 신호처리를 통해 획득된 후방복사 프로파일들로부터 CVD 층과 실리콘 기지사이 경계면의 접합의 질은 코팅전 표면 거칠기나 세척조건에 크게 영향을 받음을 확인하였다. 실험의 결과들은 레일리 표면파의 누설 현상인 후방복사와 도입된 신호처리 기법이 매우 얇은 CVD 다이아몬드 층의 비파괴적 평가에 매우 유용함을 보여주었다.

Phase Behaviors of Colloids in Polymer Solutions

권성덕,김석환,신기량,윤석수,김순철 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.4

A density functional theory (DFT) based on the weighted density has been developed for studying the polymer-induced depletion interaction and phase behaviors of colloids in polymer solutions. The depletion potentials between two colloids induced by the polymer fluids and the colloid-colloid second virial coefficients have been calculated. The calculated depletion potentials are compared with the simulation results. The phase diagram shows that short chains can give a more stable dispersion for colloids than long chains. The large colloid/polymer size ratio develops strong attractive interactions. This leads to a broadening of the coexistence region between the solid and the fluid phases of the colloids in a polymer solution.oca

모서리 반사를 이용한 주기적으로 거친 표면에서 숄티파의 관측

권성덕,김영환 한국물리학회 2005 New Physics: Sae Mulli Vol.51 No.1

Surface waves were generated on mild steel specimens with smooth surfaces and with periodic roughness of 515 m, immersed in water by using oblique incidence at the Rayleigh angle. Leaky wave signals of the surface wave reected at the edges of the specimens were obtained. Three peaks were observed in the frequency spectrum of the acquired signal obtained from the specimen with a periodic roughness. In order to analyze the origin of those peaks, we obtained the reected signals at normal incidence. By considering the frequency dependence of the leakage and the scattering,the missing components in the frequency spectrum of the normal incident signal, grating diraction,and the Wood anormaly, we identied the peaks at 0.92 and 2.54 MHz as a Rayleigh surface wave and a Scholte wave corresponding to the periodicity of the roughness, respectively. In addition,the peak at 5.24 MHz was presumed to be a Rayleigh-like wave whose wavelength and wave speed corresponded to the periodicity of the surface roughness and to the wave velocity of the Rayleigh wave, respectively.