• Title/Summary/Keyword: AE Signals

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Nondestructive Evaluation of Damage Modes in a Bending Piezoelectric Composite Actuator Based on Waveform and Frequency Analyses (파형 및 주파수해석에 근거한 굽힘 압전 복합재료 작동기 손상모드의 비파괴적 평가)

  • Woo, Sung-Choong;Goo, Nam-Seo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.8
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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.

Damage Behavior of Singly Oriented Ply Fiber Metal Laminate under Concentrated Loading Conditions (집중하중을 받는 일방향 섬유 금속 적층판의 손상 거동)

  • Nam, H.W.;Kim, Y.H.;Jung, S.W.;Jung, C.K.;Han, K.S.
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.407-412
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    • 2001
  • In this research, damage behavior of singly oriented ply (SOP) fiber metal laminate (FML) subject to concentrated load was studied. The static indentation tests were conducted to study fiber orientation effect on damage behavior of FML. During the static indentation tests, Acoustic Emission technique (AE) was adopted to study damage characteristics of FML. AE signals were obtained by using AE sensor with 150kHz resonance frequency and the signals were compared with indentation curves of FML. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. Cumulative AE counts were well predicted crack initiation and crack propagation and AE amplitude were useful for prediction of damage failure mode. During the matrix cracking, fiber debonding and fiber breakage, AE amplitude has $45{\sim}60dB,\;60{\sim}80dB\;and\;90{\sim}100dB$, respectively.

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Deformation Behaviors and Acoustic Emissions of Rock Joints in Direct Shear (직접전단시험을 통한 암석 절리의 변형거동 및 미소파괴음 발생에 관한 연구)

  • 김태혁;이상돈;이정인
    • Tunnel and Underground Space
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    • v.4 no.3
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    • pp.274-286
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    • 1994
  • Direct shear tests were on ducted in a laboratory setting in order to investigate the shear strength and deformation behavior of rock joints. Also, the characteristics of acoustic emissions (AE) during shearing of rock joints were studied. The artificial rock joints were created by splitting the intact blocks of Hwangdeung granites and Iksan marbles. Joint roughness profiles were measured by a profile gage and then digitized by Image analyzer. Roughness profile indices(Rp) of the joints were calculated with these digitized data. Peak shear strength, residual shear strength, shear stiffness and maximum acoustic emission(AE) rate were investigated with joint roughness. The peak shear strenght, the residual shear strength and the shear stiffness were increased as roughness popfile index or normal stress increased in the shear tests of granites. In the tests of marble samples, the shear deformation characteristics were not directly affected by joint roughness. As the result of two directional shear tests, the shear characteristics were varied with shear direction. AE count rates were measured during the shear deformation and the AE signals in several stages of the deformation were analyzed in a frequency domain. The AE rate peaks coincided with the stress drops during the shear deformation of joint. The dominant frequencies of the AE signals were in the vicinity of 100 kHz fo rgranite sample and 900 kHz for marble samples. The distribution of amplitude was dispersed with increasing normal stress.

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Fatigue Crack Growth Behavior of and Recognition of AE Signals from Composite Patch-Repaired Aluminum Panel (복합재 패치로 보수된 알루미늄 패널의 피로균열 성장거동과 AE신호의 유형인식)

  • Kim, Sung-Jin;Kwon, Oh-Yang;Jang, Yong-Joon
    • Journal of the Korean Society for Nondestructive Testing
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    • v.27 no.1
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    • pp.48-57
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    • 2007
  • The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by usiag the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location.

A Perceptual Study on the Temporal Cues of English Intervocalic Plosives for Various Groups Depending on Background Language, English Listening Ability, and Age (언어별, 연령별, 수준별 집단에 의한 모음간 영어 파열음 유/무성 인지 연구)

  • Kang, Seok-Han
    • Speech Sciences
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    • v.13 no.2
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    • pp.133-145
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    • 2006
  • In order to understand the various groups' perceptual pattern in both VCV trochee and iambus, this study examined the identification correctness and cue robustness for the unit intervals in light of background language, age, and English listening ability. The 4 groups of Native Speakers of English, Korean College Students of High Listening Achievement, Korean College Students of Low Listening Achievement, and Korean Elementary Students took part in the experiments. Tokens of $/d{\ae}per,\;d{\ae}per,\;d{\ae}per,\;d{\ae}per,\;d{\ae}per,\;d{\ae}per$ in trochee and of $/{\eth}{\partial}\;p{\ae}d,\;{\eth}{\partial}\;b{\ae}d,\;{\eth}{\partial}\;t{\ae}d,\;{\eth}{\partial}\;d{\ae}d,\;{\eth}{\partial}\;k{\ae}d,\;{\eth}{\partial}\;g{\ae}d/$ in iambus were extracted and modified into experimental signals composed of two digits(voiced-1, voiceless-0) by following the temporal intervals, in which the signals consisted of preceding vowel, closure, VOT, and post-vowel. In the first experiment of identification correctness in VCV iambus environment, all groups showed almost 100% correctness rate, while in trochee environment all groups were different(native speaker 87%, college high 74%, college low 70%, elementary 65%). In the second experiment of cue robustness, all groups showed the similar perceptual pattern in both environments. There was the order of robustness cues in VCV trochee: pre-vowel ${\gg}$ closure ${\gg}$ VOT ${\gg}$ post-vowel, while the order in VCV iambus: VOT ${\gg}$ post-vowel ${\gg}$ closure ${\gg}$ pre-vowel. In some condition, however, we found moderately different perceptual pattern depending on language, age and listening level.

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Study on the Damage Characteristics Under the High-Velocity Impact of Composite Laminates Using Various Sensor Signals (다양한 센서 신호를 이용한 복합적층판의 고속충격 손상 특성 연구)

  • Cho, Sang-Gyu;Kim, In-Gul;Lee, Seok-Je;You, Won-Young
    • Composites Research
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    • v.24 no.6
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    • pp.49-55
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    • 2011
  • The use of advanced composite materials in main structures of military and civil aircraft has been increased rapidly because of their considerable metals in high specific strength and stiffness. However, the mechanical properties of composite materials may severely degrade in the presence of damage. Especially, the high-velocity impact such as a hailstorm, and a small piece of tire or stone during high taxing, can cause considerable damage to the structures and sub-system in spite of a very small mass. However, it is not easy to detect the damage in composite plates using a single sensor or any conventional methods. In this paper, the PVDF sensors and AE sensors were used for monitoring high-velocity impact damage initiation and propagation in composite laminates. The WT(wavelet transform) is used to decompose the sensor signals. In the PVDF sensor and AE sensor signal analysis, amounts of high-frequency signals are increased when the impact energy is increased. PVDF sensor and AE sensor signal appeared similar results. This study shows how various sensing techniques can be used to characterize high-velocity impact damage of advanced composite laminates.

A Study on the Stress Corrosion Cracking Propagation Behaviors of high Strength Steel by Means of Emission Test (음향방출시험에 의한 고장력강의 응력부식 균열전파 거동에 관한 연구)

  • Yu, Hyo-Seon;Jeong, Se-Hui
    • Korean Journal of Materials Research
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    • v.3 no.4
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    • pp.361-371
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    • 1993
  • Among the various test methods for stress corrusiun cracking(SCC) susceptibility evaluatiun, the slow stram rate test(SSHT) method is a rapid and effective nwthod to evaluate the SCC susceptibility of metal in relatively short time. But it is very difficult to analyze the microfracture behaviors in SCC process by using the test(SSRT) method only. Up to now, it has been well known that the acoustic emission(AE) test is the effective technique to monitor the microcrack initiation and propagation in material fracture pmcess. Therefore. in this paper, we analyzed the correlation between the see process and the characteristics of AE signal by using the SSHT and the AE test. According to the test results. the AE signals produced from the material microfracture were clearly depended on the test environment. The AE signal characteristics generated during see process in synthetic sea water were comparatively greater than those. in air. In addition, the SCC behaviors could be definitely evaluated by the amplitude parameter of AE signals.

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Nondestructive Evaluation and Microfailure Modes of Single Fibers/Cement Composites using Electro-Micromechanical Technique and Acoustic Emission (Electro-Micromechanical 시험법과 음향방출을 이용한 단섬유시멘트복합재료의 미세파괴구조와 비파괴적 평가)

  • Lee, Sang-Il;Kim, Jin-Won;Park, Joung-Man;Yoon, Dong-Jin
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2001.05a
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    • pp.258-262
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    • 2001
  • The contact resistivity was correlated with IFSS and microfailure modes in conductive fiber/cement composites electro-pullout and AE. As IFSS increased, the number of AE signals increased and the contact resistivity increased latter to the infinity. In dual matrix composite (DMC) test and AE, the number of signals with high amplitude and energy in g]ass fiber composite is significantly larger than that of no-fiber composite. Many vertical and diagonal cracks were observed in glass fiber and no-fiber composite under tensile test, respectively. Electro-micromechanical technique and AE can be used efficiently for sensitive nondestructive (NDT) evaluation and to detect microfailure mechanisms in various conductive fibers reinforced brittle and nontransparent cement composites.

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A Study on the Damage Estimation of Uni-directionally Oriented Carbon Fiber Reinforced Plastics using Acoustic Emission (음향방출을 이용한 일방향 탄소섬유강화 플라스틱의 손상평가에 관한 연구)

  • Rhee Zhang-Kyu;Park Sung-Oan;Kim Bong-Gag;Woo Chang-Ki
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.14 no.1
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    • pp.30-36
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    • 2005
  • This study is to investigate a damage estimation of single edge notched tensile specimens as a function of acoustic emission(AE) according to the uni-directionally oriented carbon fiber/epoxy composites, CFRP In fiber reinforced composite materials, AE signals due to several types of failure mechanisms are typically observed. These are due to fiber breakage, fiber pull-out matrix cracking, delamination, and splitting or fiber bundle breaking. And these are usually discriminated on the basis of amplitude distribution, event counts, and energy related parameters. In this case, AE signals were analyzed and classified 3 regions by AE event counts, energy and amplitude for corresponding applied load. Bath-tub curve shows 3 distinct periods during the lifetime of a single-edge-notch(SEN) specimen. The characterization of AE generated from CFRP during SEN tensile test is becoming an useful tool f3r the prediction of damage failure or/and failure mode analysis.

Identification of failure mechanisms for CFRP-confined circular concrete-filled steel tubular columns through acoustic emission signals

  • Li, Dongsheng;Du, Fangzhu;Chen, Zhi;Wang, Yanlei
    • Smart Structures and Systems
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    • v.18 no.3
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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.