• 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.

• 대한기계학회논문집
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• 제7권2호
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• pp.226-232
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• 1983

회전수를 용접변수로 했을 때 이종강봉 및 이종강관의 마찰용접에 있어서 소성변형중에 발생한 AE(acoustic emission)량과 용접후의 냉각중에 발생한 AE량의 총량을 측정해석하고, 용접표면상 에 0.635mmR의 반원 노치를 가공했을 때의 용접부 인장강도를 구하여, AE총량과 용접부강도와 의 상관관계실험식 모델을 만들었고, 이들과 관계계산식과의 비교 조사와 95%신뢰성을 검증하였 고, 이종강의 마찰용접 중에 용접강도와 품질을 검토관리할 수 있는 기본자료가 되게 하였다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 추계학술대회 논문집
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• pp.101-104
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• 1995

A acoustic emission (AE) sensor has been used to monitor tool were during milling process. The relation between tool wear and AE RMS (Root mean Square) signal was investigated experimentally. A avaliable monitoring index for monitoring toolwear was newly extracted form AE RMS. And on-line monitoring program was developed. The proposed monitoring system has verified experimentally by roughing end milling titanium alloy with TIN coated HSS tool.

• 한국안전학회지
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• 제16권4호
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• pp.7-13
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• 2001

Wire electrical discharge machining experiments in conducted to investigate characteristics of acoustic emission (AE) and electrical discharge energy due to current peak (I$_{p}$), pulse on time($\tau$/on/). The AE signals are obtained with a sensor attached to workpiece side. Machining states are identified with scanning electron microscopy and residual stress analyzer. It is demonstrated that the residual stress provide reliable informations about the machining states. Moreover, machining states can be detected successfully using both the residual stress and AE count rate.e.

• 한국생산제조학회지
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• 제5권1호
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• pp.43-50
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• 1996

From a manufacturing standpoint it would be desirable to monitor the degradation of drawing die, that is essential for the maintenance of die quality, the evaluation of product integrity and the reducing scrap. Acoustic emission is powerful method in monitoring fine wire drawing process, especially in detecting the die fracture at early stage. Experiments also suggested that acoustic emission sigals contained valuable information regarding the stage of a drawing process such as the surface appearance of products and the condition of lubrication. These informations are AE monitoring techniques a possible tool in monitoring the drawing process operation. In order to approach this, this paper discusses the nature of acoustic emission signal presented which illustrate the effects of wire and die material, lubricants, and drawing speed on the generation and the mean voltage level of acoustic emission signal. From these experimental, results, we understanded controlling factors of acoustic emission generation.

• Smart Structures and Systems
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• 제16권1호
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• pp.213-222
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• 2015

Early detection and precise location of leakage is of great importance for life-cycle maintenance and management of municipal pipeline system. In the past few years, acoustic emission (AE) techniques have demonstrated to be an excellent tool for on-line leakage detection. Regarding the multi-mode and frequency dispersion characteristics of AE signals propagating along a pipeline, the direct cross-correlation technique that assumes the constant AE propagation velocity does not perform well in practice for acoustic leak location. This paper presents an improved cross-correlation method based on wavelet transform, with due consideration of the frequency dispersion characteristics of AE wave and the contribution of different mode. Laboratory experiments conducted to simulate pipeline gas leakage and investigate the frequency spectrum signatures of AE leak signals. By comparing with the other methods for leak location identification, the feasibility and superiority of the proposed method are verified.

• Smart Structures and Systems
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• 제19권2호
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• pp.127-136
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• 2017

Fiber reinforced polymer (FRP) has received widespread attention in the field of civil engineering because of its superior durability and corrosion resistance. This article presents the damage mechanisms of a novelty composite called carbon nanofiber modified flax fiber polymer (CNF-modified FFRP). The ability of acoustic emission (AE) to detect damage evolution for different configurations of specimens under uniaxial tension was examined, and some useful AE characteristic parameters were obtained. Test results shows that the mechanical properties of modified composites are associated with the CNF content and the evenness of CNF dispersed in the epoxy matrix. Various damage mechanisms was established by means of scanning electron microscope images. The fuzzy c-means clustering were proposed to classify AE events into groups representing different generation mechanisms. The classifiers are constructed using the traditional AE features -- six parameters from each burst. Amplitude and peak-frequency were selected as the best cluster-definition features from these AE parameters. After comprehensive comparison, a correlation between these AE events classes and the damage mechanisms observed was proposed.

• Nuclear Engineering and Technology
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• 제47권4호
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• pp.454-460
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• 2015

Acoustic emission (AE) is one of the promising methods for detecting the formation of stress corrosion cracks (SCCs) in laboratory tests. This method has the advantage of online inspection. Some studies have been conducted to investigate the characteristics of AE parameters during SCC propagation. However, it is difficult to classify the distinct features of SCC behavior. Because the previous studies were performed on slow strain rate test or compact tension specimens, it is difficult to make certain correlations between AE signals and actual SCC behavior in real tube-type specimens. In this study, the specimen was a AISI 304 stainless steel tube widely applied in the nuclear industry, and an accelerated test was conducted at high temperature and pressure with a corrosive environmental condition. The study result indicated that intense AE signals were mainly detected in the elastic deformation region, and a good correlation was observed between AE activity and crack growth. By contrast, the behavior of accumulated counts was divided into four regions. According to the waveform analysis, a specific waveform pattern was observed during SCC development. It is suggested that AE can be used to detect and monitor SCC initiation and propagation in actual tubes.

• Structural Monitoring and Maintenance
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• 제1권1호
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• pp.111-130
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• 2014

The increased use of carbon fiber reinforced polymer (CFRP) in retrofitting reinforced concrete (RC) members has led to the need to develop non-destructive techniques that can monitor and characterize the unique damage mechanisms exhibited by such structural systems. This paper presented the damage characterization results of six CFRP retrofitted RC beam specimens tested in the laboratory and monitored using acoustic emission (AE). The focus of this study was to continuously monitor the change in AE parameters and analyze them both qualitatively and quantitatively, when brittle failure modes such as debonding occur in these beams. Although deterioration of structural integrity was traceable and can be quantified by monitoring the AE data, individual failure mode characteristics could not be identified due to the complexity of the system failure modes. In all, AE was an effective non-destructive monitoring tool that can trace the failure progression in RC beams retrofitted with CFRP. It would be advantageous to isolate signals originating from the CFRP and concrete, leading to a more clear understanding of the progression of the brittle damage mechanism involved in such a structural system. For practical applications, future studies should focus on spectral analysis of AE data from broadband sensors and automated pattern recognition tools to classify and better correlate AE parameters to failure modes observed.

• 대한기계학회논문집A
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• 제31권8호
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• pp.870-879
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• 2007

In this study, various damage modes in bending unimorph piezoelectric composite actuators with a thin sandwiched PZT plate during bending fracture tests have been evaluated by monitoring acoustic emission (AE) signals in terms of waveform and peak frequency as well as AE parameters. Three kinds of actuator specimens consisting of woven fabric fiber skin layers and a PZT ceramic core layer are loaded with a roller and an AE activity from the specimen is monitored during the entire loading using an AE transducer mounted on the specimen. AE characteristics from a monolithic PZT ceramic with a thickness of $250{\mu}m$ are examined first in order to distinguish different AE signals from various possible damage modes in piezoelectric composite actuators. Post-failure observations and stress analyses in the respective layers of the specimens are conducted to identify particular features in the acoustic emission signal that correspond to specific types of damage modes. As a result, the signal classification based on waveform and peak frequency analyses successfully describes the failure process of the bending piezoelectric composite actuator exhibiting diverse failure mechanisms. Furthermore, it is elucidated that when the PZT ceramic embedded actuators are loaded mechanical bending loads, the failure process of actuator specimens with different lay-up configurations is almost same irrespective of their lay-up configurations.