• 한국안전학회지
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• 제12권2호
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• pp.3-16
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• 1997

In modern high performance engineering applications, the structural integrity of materials and structures are quite often evaluated using fracture mechanics. This evaluation in turn requires information on the flaw geometry (location, type, shape, size, and orientation). The ultrasonic nondestructive evaluation (NDE) method is one technique that is commonly used to provide such information. Flaw classification (determination of the flaw type ) and flaw sizing (prediction of the flaw shape, orientation and sizing parameters) are very important issues for quantitative ultrasonic NDE. In this paper new approaches to both classification and sizing of flaws are described together with extensive review of previous works on both topics. In the area of flaw classification, a methodology is developed which can solve classification problems using probabilistic neural networks, and in the area of flaw sizing, a time-of-flight equivalent (TOFE) sizing method is presented. The techniques proposed here are in a form that can be used directly in many practical applications to quantitative estimates of the flaw's significance.

• Journal of Welding and Joining
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• 제21권5호
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• pp.547-554
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• 2003

Apparent mechanical properties in structural components can be different from the initially designed values due to the formation of the residual stress in metal forming and welding. Therefore, the evaluation of residual stress has great importance in the reliability diagnosis of structural components. A nondestructive instrumented indentation technique has been proposed to evaluate various strength concerning mechanical properties from the analysis of load-depth curve. In this study, quantitative residual stress estimation on API X65 welded joints for natural gas pipeline was performed by analyzing the variation of indentation loading curve by residual stress through a new proposed theoretical model. The residual stress from the indentation method was compared with that from the saw-cutting method.

• Journal of Advanced Marine Engineering and Technology
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• 제17권4호
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• pp.38-48
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• 1993

A study on friction welding of stainless steel bar(SUS431) to chrome molybdenum steel bar(SCM21) was accomplished experimentally through analysis for relations among friction welding conditions, tension test, hardness test, microstructure test and acoustic emission test. The results obtained are summarized as follows ; 1. Through friction welding of SUS431 bar to SCM21 bar, the optimum welding condition by considering on strength and toughness was found to be the range of heating time of 3-5 sec when the number of rotating speed of 2000rpm, heating pressure of 10kg/$mm^2$, and upsetting time of 4 sec. 2. Quantitative ralationship was identified between heating time($T_1$, sec) and tensile strength (${\sigma},\;kgf/mm^2$) of the friction welded joint and the relation equation is $\sigma$=52.62$T_1{^{0.06}}$. 3. Through AE test, quantitative relationship was confirmed between heating time($T_1$, sec) and total AE(N, counts) during welding, and the relation is computed as follows ; N=30413.6$e^{0.06T1}$. 4. It was confirmed that the quantitative ralationship exists between the tensile strength of the welded joints and AE cumulative counts. And the relation is computed as the following ; ${\sigma}$=16.37(ln N)- 116.4. 5. When ONZ=36500-41500 counts by $OT_1Z$=3~5sec, it was identified by experiment that the range of welded joint tensile strength is 55.6-57.7kgf/$mm^2$/ whose joint efficiency is more than 100%, and it was experimentally confirmed that the real-time nondestructive quality(strength) evaluation for the friction welded joints could be possible by acoustic emission technique.

• 비파괴검사학회지
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• 제34권2호
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• pp.176-183
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• 2014

음향방출법은 차량 내부에 장착된 실린더의 경우 분해없이 동작중에 실시간으로 측정이 가능하므로 다른 비파괴평가 방법보다 많은 장점을 가지고 있다. 이러한 장점을 가지고 음향방출법은 미국 교통부(DOT)로부터 수압시험의 대체로 압력용기의 안정성 평가 방법으로 승인되었다. 본 논문은 압력용기 제조사로부터 UT 결함용기 및 결함이 있는 이음매 없는 압력용기인 Type 1과 Type 2에 대한 정량적인 평가기준에 대한 연구를 수행하였다. Type 1의 경우, ASTM E 1419-02를 기준으로 113L 규격의 준비된 용기로 피로반복시험을 통해 크랙의 성장부터 누설까지 경향을 파악하였다. Type 2의 경우, ASTM E 2191-02를 기준으로 119L 건전한 용기와 수압가압으로 불량용기를 용기에 slow-fill 방법으로 검증하였다. 본 연구에서 음향방출법을 이용한 Type 1과 Type 2의 시험은 불량용기와 건전한 용기를 효과적으로 구분할 수 있었다.

• 비파괴검사학회지
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• 제20권1호
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• pp.10-17
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• 2000

화력발전소 보일러의 주증기관, 헤더, 스팀드럼 등과 같은 주요 고온배관설비에서 발생하는 크리프 손상을 측정하는 비파괴적 측정방법에는 레프리카, 전기저항법 및 경도법 둥이 적용되고 있으나, 이들 방법들은 측정절차 및 준비가 복잡할 뿐만 아니라 접근이 가능한 설비표면에만 적용되는 제한점을 가지고 있다. 따라서 본 논문은 이들 종래의 방법을 신뢰성 있고 정량적인 초음파 비파괴평가법으로 보완 및 적용을 위하여, 실제 고온배관의 운전조건을 모의하여 수행한 크리프 인공열화실험 및 이들 크리프손상재에 대한 초음파실험을 통한 주파수분석 연구로서, 크리프손상 상태별 초음파 신호 분류를 위해 초음파신호의 각종 주파수특성을 평가하였다.

• 비파괴검사학회지
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• 제30권5호
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• pp.437-443
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• 2010

최근 재료, 생물의학(biomedicine), 음향, 전자 등 다양한 분야에서 나노 구조를 갖는 박막 기술이 도입되면서 박막 계면의 수명과 내구성 확보를 위한 초고주파수의 초음파현미경을 이용한 정량적인 비파괴적 접합평가에 관한 연구가 큰 이슈가 되고 있다. 본 연구에서는 초음파의 집속, 누설탄성표면파의 발생과 V(z) 곡선의 시뮬레이션 그리고 초고주파수 음향 이미징 기법을 이용하여 나노 스케일 구조를 갖는 박막 시험편의 접합계면을 평가하였다. V(z) 곡선의 컴퓨터 시뮬레이션을 통하여 접합계면에 존재하는 미세 결함(디라미네이션 등)의 검출 감도를 추정할 수 있었으며, 1 GHz의 초고주파수 디포커싱 모드로 박막 시험편의 접합계면에 존재하는 나노 스케일의 미세 결함을 음향 이미지로 가시화 할 수 있어 나노 구조를 갖는 박막의 접합계면의 비파괴평가에 초음파현미경이 매우 유용함을 알 수 있었다.

• 비파괴검사학회지
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• 제25권2호
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• pp.81-86
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• 2005

본 논문에서는 반도체 패키지 내부결함의 비파괴 정량평가를 위한 ESPI 기법을 이용한 시스템 및 검사기 법을 제안하고 있으며, 검사시스템은 ESPI 검사장치, 열변형유도장치, 단열챔버로 구성되어있다. 기존 초음파, X-ray 기반의 검사기법에 비하여 측정시간 및 검사방법이 용이하며, 결함의 정량검출이 가능하다는 장점이 있다. 검사결과에서 대부분의 결함이 열 방출이 많은 칩 주위에서 박리결함으로 나타났으며, 원인은 층간 접착강도의 약화와 열분배 설계에서 문제점인 것으로 사료된다.

• 비파괴검사학회지
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• 제29권3호
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• pp.235-241
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• 2009

Composite wood materials are very sensitive to water and inspection without any coupling medium of a liquid is really needed to wood materials due to the permeation of coupling medium such as water. However, air-coupled ultrasound has obvious advantages over water-coupled experimentation compared with conventional C-scanner. In this work, it is desirable to perform contact-less nondestructive evaluation to assess wood material homogeneity. A wood material was nondestructively characterized with non-contact and contact modes to measure ultrasonic velocity using automated data acquisition software. We have utilized a proposed peak-delay measurement method. Also through transmission mode was performed because of the main limitation for air-coupled transducers, which is the acoustic impedance mismatch between most materials and air. The variation of ultrasonic velocity was found to be somewhat difference due to air-coupled limitations over conventional scan images. However, conventional C-scan images are well agreed with increasing the resin-infiltrated time as expected. Finally, we have developed a measurement system of an ultrasonic velocity based on data acquisition software for obtaining ultrasonic quantitative data for correlation with C-scan images.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.726-730
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• 1997

One approach to testing the suitability of an adhesive joint for a particular application is to build and test to destruction a representativc, sample of the joini. The noncdestructive test will not measure strength directly but will measure a parameter which can be correlated to strength. It is thercforc, essential that a suitable nondestructive rest is chosen and that its results are correctly intcrpreted. In this paper, typical Ultrasonic Signal Analysis in adhesive joints are cvaluatcci together with Interface Stress from the result of Finite Elenlent Method.

• 대한기계학회논문집A
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• 제26권12호
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• pp.2535-2540
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• 2002

ESPI is a noncontact, nondestructive and relatively fast inspection method. For these reasons ESPI is being applied as a valuable tool in the nondestructive evaluation of structural components. Phase shifting ESPI is used more effectively than the traditional ESPI because spatial resolution of small object displacements are improved and numerical phase values are obtained for all pixels in the image. Consequently the quantitative measurement of deformation is possible. ESPI fringe patterns are contaminated with high levels of speckle noise. Therefore the phase image is to be smoothed to remove the noise and obtain a better signal-to-noise ratio. In this study, smoothing is done by phase shifting convolution to avoid smoothing errors close to the 2$\pi$ phase ambiguities in the deformation phase image, and median filter is used as a smoothing filter.