• Journal of the Korean Society for Aviation and Aeronautics
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• v.18 no.4
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• pp.59-66
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• 2010

Aerospace structures need high stability and long life because many personal injuries can result from an accident and securing structural integrity for various external environments is more important than any other thing. So first of all we must prove the destruction properties for operating environment, have prediction technology about damage evolution and life, and develop an economical non-destructive technology capable of detecting structure damage. Acoustic emission (AE) have no need of artificial environment like ultrasonic inspection or radio fluoroscopy to emit a certain energy, is a testing technique using seismic signal resulting from interior changes of solids, and enables to observe if any fault is appeared and it grows seriously or not while running. In this study we suggest the method of structural integrity evaluation for aerospace structures through the acoustic emission technique, for which a model plane was manufactured and an actual operation test was conducted.

• Journal of Ocean Engineering and Technology
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• v.7 no.2
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• pp.121-130
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• 1993

A study off riction welding of high speed steel(SKH 51) bar for blade side to carbon steel(STC 3)bar for shank side was carried out experimentally through tensile test, hardness test, microstructure, and acoustic emission (AE) test. So, this paper deals with optimizing the welding conditions and the real-time quality (strength) evaluation of friction weleded joints by acoustic emission technique. The results obtained are summarized as follows: (1) For friction welded joints of SKH 51to STC 3 steel bars, the total upset (U) increases linearly with an increase of heating time (t sub(1)). (2) The determined optimum welding conditions are heating time (t sub(1)) 7-9 sec, upsetting time (t sub(2)) 5 sec, heating pressure(P sub(1)) 12 kg sub(f)mm supper(2), upsetting pressure (P sub(2)) 15 kg sub(f) mm supper(2) and rotating speed (n) 2, 000 rpm, resulting in a computed relationship between the tensile strength of the joint .sigma. (kg sub(f) mm supper(2)) and the heating time t sub(1) (sec) as the following. sigma.=2.39t sub(1)

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.43-48
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• 2008

Gear system has been widely used in industrial applications and unexpected failures of gears are not only extremely damaging but also lead to economic losses. So, early detection of fault is important for diagnosis machine condition. And acoustic emission is an efficient non destructive testing technique for the diagnosis of machine health and is useful technique for early detection of fault because it can find low-amplitude and high-frequency signal on account of high sensibility. Therefore, in this paper, the AE signal was measured and preprocessed using envelop analysis for gearbox with misalignment between pinion and gear. And then the vibration characteristic of gear misalignment was analyzed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.4
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• pp.95-99
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• 2004

In this study, the leak detection technique of pressure vessel by using acoustic emission(AE) signal is suggested experimentally. The leak of pressure vessel is located at the welding line due to welding defects. we measured the AE signal using Rl5I sensor, and examined the AE parameters in leak condition. It is investigated that the mean value of AE signal is dependent on leak source location. So the absolute mean value of AE signal is adopted as dominant AE parameter. We proposed leak detection algorithm using AE signal mean value for monitoring the leak source location.

• Progress in Superconductivity and Cryogenics
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• v.1 no.2
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• pp.8-14
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• 1999

In this study, acoustic emission(AE) technique has been applied to detecting quench which is one of the serious peoblems to assure the integrity of superconducting coil at cryogenic temperature. The characteristics of AE parameters have been analyzed by correlating with the number of quenches, whinding tension of superconducting coil and charge rate of transport current. The quench localization was also performed using AE signals and there was also good correlation between quench current and AE parameters such as AE energy and AE events. In this study, it was confirmed that AE signals were mainly due to the conductor motion which caused by premature quenching. It was also found that optimized winding tension at superconducting coil was needed to prevent quench caused by conductor motion.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.67-75
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• 2000

It was well recognized that the damages associated mainly with the aging of civil infrastructures were one of very serious problems for assurance of safety and reliability. Recently carbon fiber sheet(CFS) has been widely used for reinforcement and rehabilitation of damaged concrete beam. However, the fundamental mechanism of load transfer and its load-resistant for carbon fiber sheet reinforced concrete are not fully understood. In this study, three point bending test has been carried out to understand the damage progress and the micro-failure mechanism of CFS reinforced mortars. For this purpose, four different types of specimens are used, that is, mortar, steel bar reinforced mortar, CFS reinforced mortar, and steel bar and CFS reinforced morter. Acoustic Emission(AE) technique was used to evaluate the characteristics of damage progress and the failure mechanism of specimens. in addition, two-dimensional AE source location was also performed to monitor crack initiation and propagation processes for these specimens.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.560-565
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• 2001

Recently, machining process monitoring technique based on AE(acoustic emission) signal is used widely and becomes very important technique in machining process for improving the efficiency and the confidence of the systems. In this study, we fabricated a cheap acoustic emission sensor and monitoring system and estimated the properties of them through comparing with commercial AE sensor systems. In addition, we evaluated the performance of the fabricated sensor in polishing process. Futhermore, we are scheduled to develop the multi-point polishing process monitoring system through fabrication of the more AE sensors and complement of the monitoring system.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.12
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• pp.1243-1249
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• 2008

Gear system has been widely used in industrial applications and unexpected failures of gears are not only extremely damaging but also leading to economic losses. So, early detection of fault is important for diagnosis machine condition. And acoustic emission is an efficient non-destructive testing technique fur the diagnosis of machine health and is useful technique far early detection of fault because it can find low-amplitude and high-frequency signal on account of high sensibility. Therefore, in this paper, the AE signal was measured and preprocessed using envelope analysis for gearbox with misalignment between pinion and gear. And then the gear misalignment's vibration characteristic were analyzed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.263-267
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• 2001

The changes of interfacial properties and microfailure degradation mechanisms of bioabsorbable composites with hydrolysis were investigated using micromechanical test and acoustic emission (AE). As hydrolysis time increased, the tensile strength, the modulus and the elongation of PEA and bioactive glass fibers decreased, whereas those of chitosan fiber changed little. Interfacial shear strength (IFSS) of bioactive glass fiber/poly-L-lactide (PLLA) composite was significantly higher than that two other systems. The decreasing rate of IFSS was the fastest in bioactive glass fiber/PLLA composite, whereas that of chitosan fiber/PLLA composite was the slowest. With increasing hydrolysis time, distribution of AE amplitude was narrow, and AE energy decreased gradually.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.4
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• pp.46-53
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• 1997

This paper presents a method of detection localized defects on tapered roller bearing in main spindle of machine tool system. The feature vectors, i.e. statistical parameters, in time-domain analysis technique have been calculated to extract useful features from acoustic emission signals. These feature vectors are used as the input feature of an neural network to classify and detect bearing defects. As a results, the detection of bearing defect conditions could be sucessfully performed by using an neural network with statistical parameters of acoustic emission signals.