• 비파괴검사학회지
• /
• 제9권2호
• /
• pp.25-36
• /
• 1989

This essay is a general review of the application of ultrasonic NDE techniques to the performance assessment and characterization of composite materials. A brief review of ultrasonic input-output characterization of a composite plate by shear waves is presented. A theoretical development of ultrasonic wave propagation in isotropic and anisotropic media excited, respectively, by a circular transducer and an oscillatory point source is summarized. Some experimental results are described in which ultrasonic velocity and attenuation measurements give insight into material degradation of fatigued composite laminates. Ultrasonic determination of the elastic constants of a composite plate and an experimental attempt at ultrasonic testing of an isotropic plate containing a crack are also included. A recent effort for the characterization of viscoelastic materials using the ultrasonic NDE technique is outlined. Finally, the reliability of ultrasonic NDE is briefly touched upon.

• Smart Structures and Systems
• /
• 제3권3호
• /
• pp.357-372
• /
• 2007

Parametric density concept is proposed for a long-range pipeline health monitoring. This concept is designed to obtain the attenuation of ultrasonic guided waves propagating in underwater pipelines without complicated calculation of attenuation dispersion curves. For the study, three different pipe materials such as aluminum, cast iron, and steel are considered, ten different transporting fluids are assumed, and four different geometric pipe dimensions are adopted. It is shown that the attenuation values based on the parametric density concept reasonably match with the attenuation values obtained from dispersion curves; hence, its efficiency is proved. With this concept, field engineers or inspectors associated with long-range pipeline health monitoring would take the advantage of easier capturing wave attenuation value, which is a critical variable to decide sensor location or sensors interval.

• 동력기계공학회지
• /
• 제20권6호
• /
• pp.58-63
• /
• 2016

A stainless steel has high corrosion resistance because of nickel in material, so it is used as materials for transportation and storage of hydrogen. In this study, TIG(tungsten ingot gas) welding was carried out on the stainless steel using the storage vessel of hydrogen. The microscopic structures at each region of TIG welded material such as HAZ, weld and base metals using optical microscope were observed. And the damage behavior of stainless steel that underwent the hydrogen charging using nondestructive evaluation was also studied. Ultrasonic test, which is the most generalized nondestructive technique, was applied to evaluate the relationship between the ultrasonic wave and mechanical properties at each zone of TIG welded stainless steel. The velocity and attenuation coefficients of ultrasonic wave didn't show a remarkable difference at each region of welded stainless steel. However, the attenuation coefficient was the highest at the weld zone when hydrogen charged stainless steel. In addition, acoustic emission test was also used to study the dynamic behavior of stainless steel experienced both hydrogen charging and weld. Lots of AE event at elastic region of stress-strain curve were occurred both the hydrogen charged specimen and the free specimen.

• The Journal of the Acoustical Society of Korea
• /
• 제29권1E호
• /
• pp.38-44
• /
• 2010

This paper is based on our comments and proposed amendments to the documents, Annex A, Phantom for determining Maximum Depth of Penetration, and Annex B, Local Dynamic Range Using Acoustical Test Objects 87/400/CDV. IEC 61391-2 Ed. 1.0 200X, prepared by IEC technical Committee 87; Ultrasonics. The documents are concerned with the influence of microstructure of reference target material on the ultrasonic backscattering. Previous works on the attenuation due to backreflection and backscattering of reference target materials are reviewed. The drawback to the use of ungraded stainless steel and metallic materials without microstructural data such as, crystal structure, basic acoustic data of sound velocity and attenuation, grain size, roughness and elastic constants has been discussed. The analysis suggested that the insightful conclusion can be made by differentiating the influence arising from target size and microstructure on the backscattering measurements. The microstructural parameters are associated with physical, geometrical, acoustical and mechanical origins of variation with frequency. Further clarification of such a diverse source mechanisms for ultrasonic backscattering would make the target material and its application for medical diagnosis and therapy simpler and more reliable.

• 한국안전학회지
• /
• 제33권6호
• /
• pp.58-65
• /
• 2018

The life span of the porcelain insulator was made to be 30 years, but currently many of the 154kV NGK porcelain insulators using in Korea are found to have passed the production life. Accidents caused by aged mechanical breakdown can lead to disruption of power supply in some areas, large economic losses, and casualties. Therefore, ultrasonic method, which is one of the non - destructive test methods, is applied as a method for evaluating the integrity of porcelain insulators. In this study, the experiment on the interface of cap was conducted and the difference between the energy difference and the attenuation coefficient of the reflected wave was derived according to the interface state of the steel - cement. The results of this study are expected to be used as the basic data of the ultrasonic testing to evaluate the interface condition of the porcelain insulator cap.

• Nuclear Engineering and Technology
• /
• 제54권4호
• /
• pp.1167-1174
• /
• 2022

Cast austenitic stainless steels (CASSs) are widely used as structural materials in the nuclear industry. The main drawback of CASSs is the reduction in fracture toughness due to long-term exposure to operating environment. Even though ultrasonic non-destructive testing has been conducted in major nuclear components and pipes, the detection of cracks is difficult due to the scattering and attenuation of ultrasonic waves by the coarse grains and the inhomogeneity of CASS materials. In this study, the ultrasonic signals measured in thermally aged CASS were discriminated for the first time with the simple ultrasonic technique (UT) and machine learning (ML) models. Several different ML models, specifically the K-nearest neighbors (KNN), Support Vector Machine (SVM), and Multi-Layer Perceptron (MLP) models, were used to classify the ultrasonic signals as thermal aging condition of CASS specimens. We identified that the ML models can predict the category of ultrasonic signals effectively according to the aging condition.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 1995년도 추계 학술발표 강연 및 논문개요집
• /
• pp.130-130
• /
• 1995

• 비파괴검사학회지
• /
• 제20권5호
• /
• pp.373-380
• /
• 2000

파괴적인 방법으로 재료나 설비의 기계적 성질을 평가하기 위해서는 많은 경비와 시간이 소요되므로 비파괴적인 방법을 이용한 재료의 기계적 성질 평가가 주목을 받고 있다. 본 논문에서는 초음파 특성을 이용하여 열처리 온도와 조건에 따른 기계적 성질 변화를 평가하였다. 초음파의 감쇠계수는 열처리 온도가 높을수록 결정립의 크기가 커지므로 증가하였다. 초음파의 감쇠계수는 열처리(담금질, 템퍼링, 용접후열처리)가 진행됨에 따라 감소하였다. 초음파 속도는 담금질과 템퍼링/PWHT한 시편에서 40 m/s의 차이를 보이고 있었다. 감쇠계수와 인성과의 상관성은 매우 좋으며 이러한 상관관계는 단조한 압력용기의 비파괴 평가에 이용할 수 있으며, 더욱이 현장 적용에 효율적으로 응용할 수 있을 것이다.

• 비파괴검사학회지
• /
• 제19권2호
• /
• pp.118-128
• /
• 1999

초음파 비파괴검사와 관련하여 많은 측정 방법들이 사용되고 있으며, 전형적인 예로서 재료성질 결정, 미시구조 특성 평가, 결함의 탐상 등을 들 수 있다. 이러한 응용에서 속도와 감쇠계수는 가장 흔히 요구되는 초음파 측정 파라미터이다. 본 연구에서는 수침식 펄스 에코방법으로 속도 및 감쇠 측정을 위한 5가지 해석 알고리즘 (펄스 겹침법, 상호 상관법, Fourier 변환, Hilbert 변환, Wavelet 변환)을 소개하였다. 먼저 연속한 두 저면 반사파 사이의 시간지연 측정을 위하여 펄스 겹침법, 상호 상관법, Fourier 변환에 의한 위상 기울기법 및 Hilbert 변환법을 사용하였다. 주파수 의존위상/군속도와 감쇠계수는 Fourier 변환에 의한 위상 및 진폭 스펙트럼이 사용되었으며, 이와 더불어 시간-주파수 해석법인 wavelet 변환이 이용되었다. 사용된 시편은 분산을 무시할 수 있는 강판과 약한 분산성을 지닌 기공을 함유한 복합판재이다. 각 측정 알고리즘의 특성에 대해 논의하였으며 측정된 결과들을 서로 비교하였다.

• 비파괴검사학회지
• /
• 제32권5호
• /
• pp.509-517
• /
• 2012

본 연구에서는 상용화된 monomer-cast nylon (MC nylon)계 고분자 재료로 만든 6종류의 시편에 대하여 감쇠계수 및 위상속도와 같은 초음파 특성의 온도 및 주파수 의존성을 조사하였다. 시편의 초음파 특성은 수중에서 2 MHz부터 8 MHz까지의 광대역 주파수 범위에 대하여 펄스투과법을 이용하여 측정하였다. 수온은 $10^{\circ}C$부터 $60^{\circ}C$까지 $10^{\circ}C$ 간격으로 변화시켰다. 측정에 사용된 모든 시편에서 감쇠계수는 주파수가 증가함에 따라 증가하였으며, 주파수의 지수 의존성 n이 선형 (n=1)에서 약간 벗어난 1.16부터 1.44이내의 값을 가졌다. 위상속도는 $60^{\circ}C$에서 ivory 시편을 제외한 모든 경우에 대하여 주파수가 증가함에 따라 감소하는 음의 분산 특성을 나타냈다. 주파수에 의존하는 위상속도는 모든 시편에서 온도가 증가함에 따라 감소하는 특성을 나타내었다.