• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.21 no.4
• /
• pp.601-607
• /
• 2012

The magnetic abrasive polishing (MAP), for online monitoring with AE sensor attachment, was performed in this study. To predict the surface roughness after the magnetic abrasive polishing of NAK80, the signal data acquired from the AE sensor were analyzed. A dimensionless coefficient, which consisted of average of AErms and standard deviation of AE signal, was defined as a characteristic of the MAP and a prediction model was obtained using least square method. A neural network, which had multiple input parameters from AE signals and polishing conditions, was applied for predicting the surface roughness. As a result of this study, it was seen that there was very close correlation between the AE signal and the surface roughness in the MAP. And then on-line prediction of the surface roughness after the MAP of the NAK80 was possible by the developed prediction model.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.10 no.6
• /
• pp.906-915
• /
• 1986

This study reviewed the theory of acoustic emission applying generation of acoustic emission in metal cutting and proposed a relationship between fundamental cutting parameters and the root mean square (RMS) voltage of the acoustic emission on the basis of the mechanics of the orthogonal cutting operation. Experimental results are presented for 6063-T5 Auminum and the validity of this relationship is evaluated by a series of tests varying cutting speed, feed rate and rake angle in orthogonal cutting. The original formula derived theoretically has been modified in order to utilize independent of fundamental cutting parameters. RMS voltage of acoustic emission depends on cutting speed and strain rate, but it is not much affected by feed rate. Applying lubricant, the drop of RMS level has been observed.

• Korean Journal of Materials Research
• /
• v.21 no.11
• /
• pp.623-627
• /
• 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.

• The Journal of the Acoustical Society of Korea
• /
• v.35 no.3
• /
• pp.208-215
• /
• 2016

To control and improve a combustion behavior of an engine, various studies for the in-cylinder pressure have been consistently carried out. In this paper, the level of the combustion noise for a diesel engine is estimated from the in-cylinder pressure and defined as the combustion noise index. The combustion noise index is calculated from the FFT(Fast Fourier Transform) of the in-cylinder pressure and its validity is verified. The control system based on the combustion noise index is developed and implemented in a vehicle. A number of injection parameters are controlled to meet the desired combustion noise index, and the combustion noise of a vehicle is improved up to 4.0 dB(A) in the specified frequency band.

• The Journal of the Acoustical Society of Korea
• /
• v.40 no.6
• /
• pp.649-659
• /
• 2021

Wall absorption treatment effectively reduces reverberation, but requires a large area for a live room and each wall absorption affects speech intelligibility differently. In this study, we try to find the most effective wall for the absorption treatment using the beamforming array microphone in terms of speech intelligibility. The absorption importance factor is defined by using the collision number of reflected sounds on each wall. It allows estimating how much the speech signal will be enhanced by the absorption treatment. A cuboid room with a size of 107 m³ and a reverberation time of 1.1 s is selected for the simulation. When a Helmholtz-type absorption is treated on the wall with the most significant importance factor, the modified clarity for 500 and 1k Hz is improved by 5.1 dB and 4.8 dB respectively, and the speech transmission index is enhanced by 0.06. The difference in results between the proposed method and commercial simulation code is less than a Just-Noticeable Difference (JND). The absorption treatment on the wall with the most significant importance factor shows improvement greater than the wall with the largest area, and its difference is larger than a JND value.

• The Journal of the Acoustical Society of Korea
• /
• v.24 no.2
• /
• pp.78-86
• /
• 2005

This study considers the magnitude of the harmonic components radiated from the ultrasonic contrast agents (UCA) activated by a typical diagnostic ultrasound. The nonlinear dynamic response of UCA to a 2 MHz diagnostic ultrasound pulse was predicted using Gilmore Model. The elastic property of the shell membrane of the UCA was ignored in the numerical model. Simulation was carried out for the UCA varying from 1 - 9 $\mu$m in its initial radius and the driving diagnostic ultrasound whose mechanical index (MI) ranges from 0.125 to 8. The powers of the sub. ultra and second harmonics of the acoustic signal from the UCA activated were compared with that of the fundamental component. The results show that. if the UCA is bigger than its resonant size (2 $\mu$m in radius for the present case) the sub harmonic power was much bigger than the fundamental. In particular, the 2nd harmonic component currently used as an imaging parameter for the harmonic imaging, was predicted to be lower in power than both the sub and the ultra harmonic component. This study indicates that, for obtaining harmonic imaging with UCA, the sub or ultra harmonics could be taken as imaging parameters better than the 2nd harmonic component.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.21 no.1
• /
• pp.80-90
• /
• 2001

The aim of this study is to develop the methodology which enables to identify the mechanical properties of element such as stress intensity factor by using the AE parameters. Considering the multivariate and nonlinear properties of AE parameters such as ringdown count, rise time, energy, event duration and peak amplitude from fatigue cracks of machine element the principal component regression(PCR) and artificial neural network(ANN) models for the estimation of stress intensity factor were developed and validated. The AE parameters were found to be very significant to estimate the stress intensity factor. Since the statistical values including correlation coefficients, standard mr of calibration, standard error of prediction and bias were stable, the PCR and ANN models for stress intensity factor were very robust. The performance of ANN model for unknown data of stress intensity factor was better than that of PCR model.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.16 no.3
• /
• pp.174-183
• /
• 1996

Acoustic emission(AE) response during stress corrosion cracking(SCC) of Inconel 600 alloy has been monitored to study the AE detectability of crack generation and growth by comparing the crack behavior with AE parameters processed, and to evaluate the applicability as a nondestructive evaluation(AE) by measuring the minimum crack size detectable with AE. Variously heat-treated specimens were tensioned by constant extension rate test(CERT) in various extension rate to give rise to the different SCC behavior of specimens. The AE amplitude level generated from intergranular stress-corrosion cracking(IGSCC) is higher than those from ductile fracture and mechanical deformation, which means the AE amplitude can be a significant parameter for distinguishing the An source. AE can also provide the effective means to identify the transition from the small crack initiation and formation of dominant cracks to the dominant crack growth. Minimum crack size detectable with AE is supposed to be approximately 200 to $400{\mu}m$ in length and below $100{\mu}m$ in depth. The test results show that AE technique has a capability for detecting the early stage of IGSCC growth and the potential for practical application as a NDE.

• Journal of the Korea Concrete Institute
• /
• v.13 no.2
• /
• pp.107-113
• /
• 2001

This study was conducted preliminarily to develop the crack source location technique for plain concrete beam using acoustic emission(AE). Before the main experiment, the test of virtual An source location was achieved in plain concrete block. The sensor layout was mutually compared between triangular layout and rectangular layout. As the results of test, AE source location by triangular layout was evaluated more effective than that by rectangular layout. The specimen to apply he source location technique was man in total nine specimens (each three in 40 %, 50%, 60% of W/C ratio) which the experiment variable was the compressive strength level(W/C ratio). The bending loading method is selected by cyclic loadings to evaluate the degree of concrete damage. It is seen that Kaiser effect and Felicity effect exists through analysis of AE parameters in coming failure experiment. As a result of analyzing the felicity ratio(FR) values, it is shown that this values can be used for evaluating the degree of concerto damage. AE activity is started highly at the 70% of failure load without the compressive strength level. Thus considered by a index in constructing the system of the failure warning at application of the field structure. And the results compared the real cracking location with the source location has perceived by AE monitoring before it is appeared the primary crack by visual observation.