• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1993년도 추계학술대회 논문집
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• pp.650-655
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• 1993

Carbon/epoxy composite(CFRP) coupons previously damaged by low velocity impact were tested under static tensile loading and microscope progress of damage was characterized by ultrasonic C-scan, Scanning Acoustic Microscopy (SAM) and Acoustic Emission(AE) techniques which were based on the application of elastic waves. The degress of impact damage has been correlated with the AE activity during monotonic or loading/unloading tensile testing as well as the result of ultrasonic test. The coupons were subjected to impact velocities ranged from 0.71 to 2.17 m/sec, which introduced the amount of damage rated as 0%, 10%, 30%, and 50% with reference to the total absorbed energy at fracture. Special attention was paid to determine optimal AE parameters to characterize the microscopic fracture process and to predict the residual strength of composite laminates. AE RMS voltage during the early stage of tensile loading was found an effective parameter to quantify the degree of impact damage. It was also found that the Felicity ratio is closely related to the stacking sequence and the residual strength of the CFRP laminates.

• 한국공작기계학회논문집
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• 제13권4호
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• pp.113-120
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• 2004

The object of this study is to investigate the effect of compounded welding through the AE(Acoustic Emission) characteristics for weld HAZ(Heat Affected Zone) under the static tensile test. This study was carried out an SWS 490A, high tension steel for electric shield metal arc welding(SMAW), $CO_2$ gas arc welding and TIG welding. Data displays are based on the measured parameters of the AE signals, along with environmental variables such as time and load. The accumulated AE event curve of HAZ definitely have the point of inflection subject to tensile test. The results of the tensile test of HAZ come out electric shield arc welding ＞$CO_2$ gas arc welding＞TIG welding in case of single welding, but generally the tensile test of HAZ come out electric shield arc welding＞ TIG welding ＞ $CO_2$ gas arc welding. These history plots give us useful and powerful information to analyze the results of material evaluation testing.

• 한국항공운항학회지
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• 제18권4호
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• pp.51-58
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• 2010

Recently, aerospace structures have lightweight trend in order to reduce the cost of fuel and system, Carbon Fiber Reinforced Plastic (CFRP) can give the ability to reduce weight at 20~50% as the substitution of metal alloy, and there are advantages such as high Non-rigid, specific strength and anti-corrosion, but it is difficult to prove its destruction properties due to heterogeneous structure and anisotropy. In this study we designed specimen, inducing distinguishing destructions of material (for example, matrix crack, fiber breakage, and delamination) by using the Carbon Fiber Reinforced Plastic (CFRP) which is used in a real aircraft, to apply acoustic emission technique to aerospace structures. And we gained data via tensile testing and acoustic emission technique, from which each fault signal was classified respectively by using AE parameters and waveform.

• 한국암반공학회:학술대회논문집
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• 한국암반공학회 2006년도 춘계학술발표회 논문집
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• pp.79-93
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• 2006

It is well known that acoustic emission (AE) is indicator of rock fracturing or damage as rock is brought to failure under the uniaxial compressive loads. In this paper, an experimental study on the source location of acoustic emission on the cylindrical specimens of granite under uniaxial compression test was made. The AE source location was made by measuring the six channel AE data. Comparing to this experiment, the numerical method is applied to model the initiation and propagation of fracture by AE using a numerical code, RFPA (Realistic Failure Process Analysis). This code incorporates the mesoscopic heterogeneity in Young's modulus and rock strength characteristic of rock masses. In the numerical models, values of Young's modulus and rock strength are realized according to a Weibull distribution in which the distribution parameters represent the level of heterogeneity of the medium. The results of the simulations show that RFPA can be used not only to produce acoustic emission similar to those measurements in our experiments, but also to predict fracturing patterns under uniaxial loading condition.

• Annals of Clinical Neurophysiology
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• 제23권1호
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• pp.7-16
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• 2021

Transcranial magnetic stimulation (TMS) is a safe and noninvasive tool for investigating the cortical excitability of the human brain and the neurophysiological functions of GABAergic, glutamatergic, and cholinergic neural circuits. Neurophysiological biomarkers based on TMS parameters can provide information on the pathophysiology of dementia, and be used to diagnose Alzheimer's disease and differentiate different types of dementia. This review introduces the basic principles of TMS, TMS devices and stimulating paradigms, several neurophysiological measurements, and the clinical implications of TMS for Alzheimer's disease.

• Asian Pacific Journal of Cancer Prevention
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• 제14권7호
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• pp.4223-4228
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• 2013

Background: The purpose of this study was to determine the clinical and dosimetric factors associated with acute esophagitis (AE) in lung cancer patients treated with conformal radiotherapy (RT) in Turkey. Materials and Methods: In this retrospective review 104 lung cancer patients were examined. Esophagitis grades were verified weekly during treatment, and at 1 week, and 1 and 2 months afterwards. The clinical parameters included patient age, gender, tumor pathology, number of chemotherapy treatments before RT, concurrent chemotherapy, radiation dose, tumor response to RT, tumor localization, interruption of RT, weight loss, tumor and nodal stage and tumor volume. The following dosimetric parameters were analyzed for correlation of AE: The maximum ($D_{max}$) and mean ($D_{mean}$) doses delivered to the esophagus, the percentage of esophagus volume receiving ${\geq}10$ Gy ($V_{10}$), ${\geq}20$ Gy ($V_{20}$), ${\geq}30$ Gy ($V_{30}$), ${\geq}35$ Gy ($V_{35}$), ${\geq}40$ Gy ($V_{40}$), ${\geq}45$ Gy ($V_{45}$), ${\geq}50$ Gy ($V_{50}$) and ${\geq}60$ Gy ($V_{60}$). Results: Fifty-five patients (52.9%) developed AE. Maximum grades of AE were recorded: Grade 1 in 51 patients (49%), and Grade 2 in 4 patients (3.8%). Clinical factors had no statistically significant influence on the incidence of AE. In terms of dosimetric findings, correlation analyses demonstrated a significant association between AE and $D_{max}$ (>5117 cGy), $D_{mean}$ (>1487 cGy) and $V_{10-60}$ (percentage of volume receiving >10 to 60 Gy). The most significant relationship between RT and esophagitis were in $D_{max}$ (>5117 cGy) (p=0.002) and percentage of esophageal volume receiving >30 Gy ($V_{30}$ >31%) (p=0.008) in the logistic regression analysis. Conclusions: The maximum dose esophagus greater than 5117 cGy and approximately one third (31%) of the esophageal volume receiving >30 Gy was the most statistically significant predictive factor associated with esophagitis due to RT.

• Composites Research
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• 제14권4호
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• pp.15-26
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• 2001

Implant용 bioabsorbable 복합재료의 계면물성과 미세파괴분해 메카니즘을 micromechanical 시험법과 음향방출을 이용하여 평가하였다. Poly(ester-amide)와 bioactive 유리섬유의 인장 강도와 탄성률 그리고 연신율은 분해시간에 따라 점차적으로 감소하는 경향을 보인 반면, chitosan 섬유는 분해시간 내에서 거의 변화가 없었다. Dual matrix composite 시험법을 이용하여 측정된 bioactive 유리섬유와 poly(L-lactide) 사이의 계면전단강도는 chitosan이나 poly(ester-amide) 섬유의 경우 보다 큰 값을 보였다. 그리고 계면전단강도 감소는 bioactive 유리섬유 강화 poly(L-lactide) 복합재료에서 가장 빨랐으며, chitosan 섬유의 경우가 상대적으로 가장 느린 경향을 보였다. Poly(ester-amide) 섬유의 분해시간에 따른 음향방출 진폭과 에너지는 점차로 감소하였고, 음향방출 진폭의 분포 역시 점차 좁아짐을 보여주었다. Bioactive 유리섬유에서 인장파단에 의한 음향방출 진폭과 에너지는 압축파단의 경우 보다 크게 나타났으며, 또한, 인장 및 압축시험 모두에서 초기상태가 분해 후 보다 더 큰 값을 보였다. 본 연구에서 평가한 계면물성과 미세파괴분해 메카니즘은 생흡수성 복합재료의 성능을 조절할 수 있는 중요한 요소가 될 것이다.

• Geomechanics and Engineering
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• 제36권5호
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• pp.511-525
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• 2024

Underground openings significantly affect the mechanical stability of underground spaces and create damaged zones. This study investigated the acoustic emission (AE) characteristics associated with the formation of damaged zones around circular openings. Uniaxial compression experiments were conducted on three types of rock specimens, namely, granite (GN-1 and GN-2), gabbro (GB), and slate (SL), containing a circular opening. AE and digital image correlation (DIC) techniques were used to monitor and evaluate the damaged zones near the circular openings. The AE characteristics were evaluated using AE parameters, including count, energy, amplitude, average frequency, and RA value. The DIC results revealed that the estimated diameters of the damaged zones of GN-1, GN-2, GB, and SL were 1.66D, 1.53D, 1.49D, and 1.9D, respectively. The average displacements at the surface of the damaged zones for these specimens were 0.814, 0.786, 0.661, and 0.673 mm, respectively, thus demonstrating a strong correlation with Young's modulus. The AE analysis with DIC revealed that tensile failure occurred in the direction parallel to the maximum compression axis as the load increased. Thus, this study provides fundamental data for a comprehensive analysis of damaged zones in underground openings and will facilitate the optimization of rock engineering projects and safety assessments thereof.

• 콘크리트학회논문집
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• 제13권2호
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• pp.107-113
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• 2001

본 연구는 AE기법을 이용하여 콘크리트구조물의 균열발생원 탐사방법을 개발하기 위한 기초적인 연구이다. 본 실험에 앞서 무근 콘크리트 블록에 모의 AE 발생원 실험을 실시하였다. 센서배치에서는 삼각형 결함원 탐사기법과 사각형 결함원 탐사기 법을 적용하여 비교 .분석하였다. 실험 결과 콘크리트 보에서는 삼각형 결함원 탐사기법이 사각형 결함원 탐사기법보다 효과적인 것으로 분석되었다. 콘크리트 보에 균열원 탐사기법을 적용하기 위한 시험체는 콘크리트의 압축강도 수준비(물-시멘트비)를 실험변수로 즉, 물-시멘트비를 40%, 50%, 50%로 하여 각각 3개씩 총 9개를 제작하였다. 콘크리트의 손상정도를 평가하기 위해 하중재하방식은 반복 휭재하방식을 채택하였고, 파괴실험시 발생하는 AE 파라미터를 분석하여, 카이저효과와 펠리시티효과를 실험실적으로 확인하였다. 또한, FR값을 분석한 결과 구조물의 열화도지수로서 사용 가능함을 확인하였다. 콘크리트 강도수준에 관계없이 최대하중의 70%대에서 AE의 활동성이 높아지기 시작함을 알 수 있었으며, 실구조물에 적용시 파괴경보시스템구축에 적용 가능한 하나의 인자로 사료된다. 한편, 실제 균열 발생위치와 결함원탐사방법을 비교한 결과 육안조사에 의해 주균열이 발생하기 전에 AE 모니터링으로 사전 감지가 가능하였다.

• 한국터널지하공간학회 논문집
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• 제21권5호
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• pp.657-673
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• 2019

최근 음향방출(Acoustic Emission, AE) 센서를 이용하여 지하 암반 내 구조물의 손상을 평가하는 기법이 활발하게 사용되고 있다. 암반 손상 시 발생되는 미소파괴음은 시간 및 주파수 영역에서 다양한 음향방출 특성인자로 분석된다. 암반 내 초기 균열 발생부터 최종 파괴까지의 특징을 파악하기 위해서는 외부응력 수준과 암반 강도에 따른 음향방출 특성인자 발생 양상을 이해하는 것이 중요하다. 본 연구에서는 경암과 연암 강도를 가진 화강암 시편을 이용하여 일축 압축시험을 수행하여, 암석 시편 파괴 시 발생하는 음향방출 특성인자를 분석하였다. 실험결과, 응력 비율이 증가할수록 이벤트 횟수, 실효값, 최대 진폭, 절대 에너지가 경암 시편에서 연암 시편 보다 높은 경향을 보였다. 또한, 주파수 관련 특성인자는 응력 비율 증가나 시편의 물성특성에 대해 민감도가 낮은 것으로 분석되었다. 본 연구에서 암석 시편 파괴에 따른 음향방출 특성인자 분석 결과, 실효값(RMS)이 가장 민감한 인자로 평가되었다. 본 연구의 결과는 음향방출 기반 모니터링 수행 시 암반 손상 정도 평가를 위하여 유용하게 활용될 수 있을 것으로 기대된다.