• 비파괴검사학회지
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• 제30권6호
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• pp.569-577
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• 2010

Nonplanar surface geometries of components are frequently encountered in real ultrasonic inspection situations. Use of rigid array transducers can lead to beam defocusing and reduction of defect image quality due to the mismatch between the planar array and the changing surface. When a flexible array is used to fit the complex surface profile, the locations of array elements should be known to compute the delay time necessary for adaptive heam focusing. An alternative method is to employ the time reversal focusing technique that does not require a prior knowledge about the properties and structures of the specimen and the transducer. In this paper, a time reversal method is applied to simulate beam focusing of flexible arrays and imaging of point-like defects contained in specimens with nonplanar surface geometry. Quantitative comparisons are made for the performance of a number of array techniques in terms of the ability to focus and image three point-like reflectors positioned at regular intervals. The sinusoidal profile array studied here exhibits almost the same image quality as the flat, reference case.

• 비파괴검사학회지
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• 제35권3호
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• pp.185-192
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• 2015

동적하중에서의 베어링 결함에 대한 실시간 진단기술은 상대적으로 저조하다. 따라서 볼베어링의 이상상태 현상으로 인한 온도 상승 및 진동 증가 등을 사전에 검출하는 기술이 필요하며, 회전체에 대한 운전상태 감시 및 손상 진단을 통해 발전설비의 원활한 운전을 기할 수 있는 검출 기술이 필요하다. 적외선 열화상 실험과 더불어 ANSYS를 이용한 유한요소해석으로부터 실험과 동일한 베어링을 구조 설계 및 해석하여 데이터를 분석함으로써 열화상 기술로 얻은 데이터의 신뢰성을 확보하였다.

• 비파괴검사학회지
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• 제28권3호
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• pp.302-308
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• 2008

Composite materials are widely used as structural materials for aerospace engineering because of its excellent mechanical properties such as light weight, high stiffness, and low thermal expansion. In driving, impact damage is one of the common but dangerous damages, caused by internal failure of the laminas interface which is not detected by in the surface. Many techniques to detect defects or delaminate between laminates have been reported. Shearography is a kind of laser speckle pattern interferometry with the advantages of non-destructive, non-contact, high resolution and displacement slope measurement. In this paper, the shearography is used to evaluate non-destructively impact damaged surface of the composite material and a measuring method using shearography for the thermal deformation of a impact damaged composite material is discussed. The basic principles of the technique are also described briefly.

• Structural Engineering and Mechanics
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• 제28권5호
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• pp.525-548
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• 2008

This article deals the theory for solving an inverse problem of plate structures using the frequency-domain information instead of classical time-domain delays or free vibration eigenmodes or eigenvalues. A reduced set of output parameters characterizing the defect is used as a regularization technique to drastically overcome noise problems that appear in imaging techniques. A deconvolution scheme from an undamaged specimen overrides uncertainties about the input signal and other coherent noises. This approach provides the advantage that it is not necessary to visually identify the portion of the signal that contains the information about the defect. The theoretical model for Quantitative nondestructive evaluation, the relationship between the real and ideal models, the finite element method (FEM) for the forward problem, and inverse procedure for detecting the defects are developed. The theoretical formulation is experimentally verified using dynamic responses of a steel plate under impact loading at several points. The signal synthesized by FEM, the residual, and its components are analyzed for different choices of time window. The noise effects are taken into account in the inversion strategy by designing a filter for the cost functional to be minimized. The technique is focused toward a exible and rapid inspection of large areas, by recovering the position of the defect by means of a single accelerometer, overriding experimental calibration, and using a reduced number of impact events.

• 한국산학기술학회논문지
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• 제8권2호
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• pp.245-249
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• 2007

본 논문은 핵발전소의 초음파 비파괴 평가를 수행하기 위하여 핵발전소 설비의 초음파 비파괴 평가시 발생될 수 있는 스펙클 잡음을 억제하고 디컨벌루션 기법을 이용하여 결함의 정확한 위치 및 크기를 추정할 수 있는 영상 처리 기법을 제안하였다. 제안된 방법은 실제 핵발전소의 증기발생기 파이프라인으로 만들어진 시편을 이용하여 영상의 선명도를 확인 할 수 있었다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2004년도 추계학술발표대회 논문집
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• pp.15-18
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• 2004

Nondestructive damage sensing and mechanical properties for thermal treated carbon nanotube(CNT) and nanofiber(CNF)/epoxy composites were investigated using electro-micromechanical technique. Carbon black (CB) was used only for the comparison. Electro-micromechanical techniques were applied to obtain the fiber damage and stress transferring effect of carbon nanocomposites with their contents. Thermal treatment and temperature affected on apparent modulus and electrical properties on nanocomposites due to enhanced inherent properties of each CNMs. Coefficient of variation (COV) of volumetric electrical resistance can be used to obtain the dispersion degree indirectly for various CNMs. Dispersion and surface modification are very important parameters to obtain improved mechanical and electrical properties of CNMs for multifunctional applications. Further optimized functionalization and dispersion conditions will be investigated for the following work continuously.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.141-144
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• 2005

Sensing and interfacial evaluation of Ni nanowire strands/polymer composites were investigated using Electro-micromechanical technique. Electro-micromechanical techniques can be used as sensing method for micro damage, loading, temperature of interfacial properties. Using Ni nanowire strands/silicone composites with different content, load sensing response of electrical contact resistivity was investigated under tensile and compression condition. The mechanical properties of Ni nanowire strands with different type/epoxy composites were measured using uniformed cyclic loading and tensile test. Ni nanowire strands/epoxy composites showed humidity and temperature sensing within limited ranges, 20 vol% reinforcement. Some new information on temperature and humidity sensing plus loading sensing of Ni nanowire strands/polymer composites could be obtained from the electrical resistance measurement as a new concept of the nondestructive interfacial evaluation.

• 비파괴검사학회지
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• 제35권5호
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• pp.341-348
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• 2015

능동적 열화상 기법은 재료의 수동적 열적결함에 있어 기존의 적외선 열화상 기법에 비해 우수한 결함 검출능력을 보이는 것으로 알려져 있다. 적외선 비파괴 검사는 지금까지 다양한 검출 기법에 대한 발전이 이루어졌으나 신뢰성에는 다소 의문이 있다. 따라서 본 논문에서는 위상잠금 열화상기법을 적용하여 각각 다른 결함의 크기와 깊이의 인공결함을 갖는 SM45C 시험편을 가지고 제안된 기법을 검증하고, 불확도를 평가하여 위상잠금 열화상 기법을 이용한 결함의 크기측정에 대한 신뢰성을 검토하였다.

• 비파괴검사학회지
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• 제33권3호
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• pp.264-269
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• 2013

Since MFC(macro-fiber composite) transducer has been developed, many researchers have tried to apply this transducer on SHM(structural health monitoring), because it is so flexible and durable that it can be easily embedded to various kinds of structures. The objective of this paper is to figure out the benefits and feasibility of applying MFC transducers to guided wave technique. For this, we have experimentally tested the performance of MFC patches as transmitter and sensors for excitation and reception of guided waves on the thin aluminum alloy plate. In order to enhance the signal accuracy, we applied the FIR filter for noise reduction as well as used STFT(short-time Fourier transform) algorithm to image the guided wave characteristics clearly. From the results, the guided wave generated based on MFC showed good agreement with its theoretical dispersion curves. Moreover, the ultrasonic Lamb wave techniques based on MFC patches in pitch-catch manner was tested for detection of surface notch defects of which depths are 10%, 20%, 30% and 40% of the aluminum plate thickness. Results showed that the notch was detectable well when the notch depth was 10% of the thickness or greater.

• 비파괴검사학회지
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• 제33권3호
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• pp.283-288
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• 2013

This paper describes development of a high speed Doppler OFDI system for non-invasive vascular imaging. Doppler OFDI (optical frequency domain imaging) is one of the phase-resolved second generation OCT (optical coherence tomography) techniques for high resolution imaging of moving elements in biological tissues. To achieve a phase-resolved imaging, two temporally separated measurements are required. In a conventional Doppler OCT, a pair of massively oversampled successive A-lines is used to minimize de-correlation noise at the expense of significant imaging speed reduction. To minimize a de-correlation noise between targeted two measurements without suffering from significant imaging speed reduction, several methods have been developed such as an optimized scanning pattern and polarization multiplexed dual beam scanning. This research represent novel imaging technique using frequency multiplexed dual beam illumination to measure exactly same position with aimed time interval. Developed system has been verified using a tissue phantom and mouse vessel imaging.