• Geomechanics and Engineering
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• 제14권2호
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• pp.107-113
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• 2018

Coal samples with different joints morphology were subjected to uniaxial compression experiments, cracks evolution was recorded by Nikon D5300 and acoustic emission (AE) energy signals were collected by AEwin Test for Express-8.0. During loading process, coal samples deformed elastically with no obvious cracks changes, then they expanded gradually along the trace of the original cracks, accompanied by the formation of secondary cracks, and eventually produced a large-scale fracture. It was more interesting that the failure mode of samples were all shear shape, whatever the original cracks morphology was. With cracks and damage evolution, AE energy radiated regularly. At the early loading stage, micro damage and small scale fracture events only induced a few AE events with less energy, while large scale fracture leaded to a number of AE events with more energy at the later stage. Based on the multifractal theory, the multifractal spectrum could explain AE energy signals frequency responses and the causes of AE events with load. Multifractal spectrum width (${\Delta}{\alpha}$), could reflect the differences between the large and small AE energy signals. And another parameter (${\Delta}f$) could reflect the relationship between the frequency of the least and greatest signals in the AE energy time series. This research is helpful for us to understand cracks evolution and AE energy signals causes.

• 한국재료학회지
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• 제21권11호
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• pp.623-627
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• 2011

This is a study on the distribution of acoustic emission parameters during a burst test for a type-II CNG vehicle fuel tank. A resonant AE sensor with a central frequency of 150 kHz was attached to the composite materials in the center of the fuel tank. The pressure was increased from 30 to 100% of the expected burst pressure and was maintained for 10 minutes at each level. Damage at 70% of expected burst pressure occurred by various damage mechanisms including fiber breakage and delamination, while that of below 60% only occurred by matrix crack initiation and growth. The count, duration and rise time of the AE signal at 60% of the expected burst pressure are distributed below 500, 5000 ${\mu}s$ and 300 ${\mu}s$, respectively. Then, at above 70% they increased with pressure by superimposing of individual AE signal generated at a nearby place. These results confirmed that the analysis of the distribution of AE parameters is an effective tool for estimating damage of a CNG fuel tank.

• Smart Structures and Systems
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• 제18권3호
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• pp.525-540
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• 2016

The CFRP-confined circular concrete-filled steel tubular column is composed of concrete, steel, and CFRP. Its failure mechanics are complex. The most important difficulties are lack of an available method to establish a relationship between a specific damage mechanism and its acoustic emission (AE) characteristic parameter. In this study, AE technique was used to monitor the evolution of damage in CFRP-confined circular concrete-filled steel tubular columns. A fuzzy c-means method was developed to determine the relationship between the AE signal and failure mechanisms. Cluster analysis results indicate that the main AE sources include five types: matrix cracking, debonding, fiber fracture, steel buckling, and concrete crushing. This technology can not only totally separate five types of damage sources, but also make it easier to judge the damage evolution process. Furthermore, typical damage waveforms were analyzed through wavelet analysis based on the cluster results, and the damage modes were determined according to the frequency distribution of AE signals.

• 한국안전학회지
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• 제38권2호
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• pp.36-43
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• 2023

In this study, a four-point bending test was conducted to assess and detect the damage to reinforced concrete structures using the acoustic emission (AE) technique. Based on the crack investigation results, flexural failure was classified into four stages and compared with the characteristic analysis results of AE parameters. The parametric characterization indicated that the activity of the primary AE signal was high in the early stage, and that of the second signal increased after the flexural cracks stabilized. Because the secondary AE signal included noise generated by friction, parameter-based analysis for damage assessment was performed using the primary signal; the secondary signal was used as complement. The activity analyses of the primary and secondary signals effectively classified crack propagation; however, determining the macrocracks and yielding of reinforcing bars had certain limitations. Nevertheless, applying the damage index with cumulative AE energy is a complementary technique for detecting and assessing structure damage that well detects the occurrence of macrocracks.

• Journal of the Korean Data and Information Science Society
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• 제17권4호
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• pp.1375-1386
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• 2006

In life testing, the lifetimes of test units under the usual conditions are so long that life testing at usual conditions is impractical. Testing units are subjected to conditions of high stress to yield informations quickly. In this paper, the inferences of parameters on the three step-stress accelerated life testing are studied. The two-parameter exponential distribution with a failure rate function that a log-quadratic function of stress and the tempered failure rate model are considered. We obtain the maximum likelihood estimators of the model parameters and their confidence regions. A numerical example will be given to illustrate the proposed inferential procedures.

• 비파괴검사학회지
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• 제16권3호
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• pp.174-183
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• 1996

본 연구에서는 인코넬600 합금을 열처리 상태 및 변형속도 등이 서로 다른 SCC 발생 조건하에서 정변형 속도 시험법으로 인장시켜 그때 발생되는 AE신호와 균열 거동을 비교하므로서 SCC 발생 및 진전을 AE로서 적절히 탐지할 수 있는가를 연구하였고, AE로 탐지 가능한 초기의 최소 균열 크기를 측정하므로서 비파괴시험법으로서의 적용성을 평가하고자 하였다 실험 결과, IGSCC에서 발생되는 AE amplitude 준위는 연성파괴 및 기계적인 변형에서 발생되는 것들보다 큰 것으로 나타났으며, 이것은 AE amplitude준위가 AE발생원을 식별할 수 있는 중요한 변수가 될 수 있음을 의미한다. IGSCC 미소균열의 성장 및 주균열의 형성으로부터 주균열의 성장으로 전환되는 시점을 AE로 적절히 감시할 수 있음을 보였으며, AE로 탐지 가능한 최소 균열 크기는 길이 $200{\sim}400{\mu}m$, 깊이 $100{\mu}m$ 이하의 균열인 것으로 나타났다. 결론적으로 AE기술은 입계 응력 부식 균열의 진전을 조기 탐지할 수 있는 유용한 방법으로 평가되며 비파괴시험법으로서의 실제 적용 가능성도 높을 것으로 판단된다.

• 한국안전학회지
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• 제17권1호
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• pp.1-5
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• 2002

An approach for the damage of delamination which is the major concern during mechanical working for composite laminate material is proposed based on linear elastic fracture mechanics. This paper presents method evaluating of damage crack length using by average thrust force with AE characteristics. Also, the relations of AE characteristics are obtained from delamination damages. We found the onset ply of the delamination and a critical energy release rate and expressed a stress intensity factor by AEcount equation.

• Geomechanics and Engineering
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• 제12권4호
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• pp.627-637
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• 2017

The high positive correlation between plastic strain of loaded coal-rock and AE (acoustic emission) characteristic parameter was studied and proved through AE experiment during coal-rock uniaxial compression process. The results show that plastic strain in the whole process of uniaxial compression can be gained through the experiment. Moreover, coal-rock loaded process can be divided into four phases through analyzing the change of the plastic strain curve : pressure consolidation phase, apparent linear elastic phase, accelerated deformation phase, rupture and development phase, which corresponds to conventional elastic-plastic change law of loaded coal-rock. The theoretical curve of damage constitutive model is in high agreement with the experimental curve. So the damage evolution law of coal rock damage can be indicated by both acoustic emission and plastic strain. The results have great academic and realistic significance for further study of both AE signal characteristics during loaded coal-rock damaged process and the forecasting of coal-rock dynamic disasters.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.975-979
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• 2002

This paper studies the indirect parameters when the new and worn end mill working in the machining center. The parameter output methods are cutting force, current values and AE signals. In the result, when the worn end mill operating, cutting forces increase the 14.71〔N〕, current values increase the 2.917〔A〕 and 1.168〔A〕 according to the spindle mote. and feed motor, and AE signals increase the 0.588$\times$10$^{-5}$ 〔A〕. We can use these parameters in the detection of end mill wear.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.229-232
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• 2006

The HPFRCCs show that the multiple crack propagation, high tensile strength and ductility due to the interfacial bonding of the fibers to the cement matrix. Moreover, performance of cement composites varies according to type and weight contents of reinforcing fiber. and HPFRCCs with hybrid fiber have better performance than HPFRCCs with single fiber in damage tolerance. Total four cylindrical specimens were tested, and the main variables were the type and weight contents of fiber, which was polyvinylalchol (PVA), polyethylene (PE). In order to clarify effect of hybrid types on the characteristics of fracture and damage process in cement composites, AE method was performed to detect micro-cracking in HPFRCCs under cyclic compression. Loading conditions of the uniaxial compression test were monotonic and cyclic loading. And from AE parameter value, it is found that the second and third compressive load cycles resulted in successive decrease of the amplitude as compared with the first compressive load cvcle.