• Journal of Mechanical Science and Technology
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• v.18 no.7
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• pp.1055-1061
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• 2004

In this research, a vision system for detecting breakages of small-diameter taps, which are rarely detected by the indirect in-process monitoring methods such as acoustic emission, cutting torque and motor current, was developed. Two HMI (Human Machine Interface) programs to embed the developed vision system into a Siemens open architecture controller, 840D, were developed. They are placed in sub-windows of the main window of the 840D and can be activated or deactivated either by a softkey on the operating panel or the M code in the NC part program. In the event that any type of tool breakage is detected, the HMI program issues a command for an automatic tool change or sends an alarm signal to the NC kernel. An evaluation test in a high-speed tapping machine showed that the developed vision system was successful in detecting breakages of small-diameter taps up to M1.

• Journal of the Korean Society for Railway
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• v.10 no.1 s.38
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• pp.1-6
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• 2007

Railway wheels in service are regularly checked by ultrasonic testing, acoustic emission and eddy current testing method and so on. However, ultrasonic testing is sometimes inadequate for sensitively detecting the cracks in railway wheel which is mainly because of the fact of crack closure. Recently, many researchers have actively fried to improve precision for defect detection of railway wheel. The development of a nondestructive measurement tool for wheel defects and its use for the maintenance of railway wheels would be useful to prevent wheel failure. The induced current focusing potential drop(ICFPD) technique is a new non-destructive tasting technique that can detect defects in railway wheels by applying on electro-magnetic field and potential drops variation. In the present paper, the ICFPD technique is applied to the detection of surface and internal defects for railway wheels. To defect the defects for railway wheels, the sensor for ICFPD is optimized and the tests are carried out with respect to 4 surface defects and 6 internal defects each other. The results show that the surface crack depth of 0.5 mm and internal crack depth of 0.7 mm in wheel tread could be detected by using this method. The ICFPB method is useful to detect the defect that initiated in the tread of railway wheels

• Journal of Power System Engineering
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• v.18 no.6
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• pp.166-173
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• 2014

In this study, a laminated composite material with dispersing aluminum oxide powder between the CFRP laminate plies, and also CFRP composites without aluminium oxide powder were fabricated for Mode I experiments using the DCB specimen and a tensile test. The behavior of the crack and the change of the interfacial fracture toughness were evaluated. Also in order to evaluate the damage mechanism for the crack extension, the AE sensor on the surface of the DCB test specimen was attached. AE amplitude was estimated for CFRP-alumina and CFRP composite. And the fracture toughness was evaluated by the stress intensity factor and energy release rate. The results showed that an unstable crack was propagated rapidly in CFRP composite specimen along with the interface, but crack propagation in CFRP-alumina specimen was relatively stable. From results, we show that aluminium oxide powder spreaded uniformly in the interface of the CFRP laminate carried out the role for preventing the sudden crack growth.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.4
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• pp.403-413
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• 2007

As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these types of structures. The purpose of this study is the evaluation of rock bolt integrity using Fourier and wavelet transforms of the guided ultrasonic waves. After five rock bolt specimens with various defect ratios are embedded into a large scale concrete block, guided waves are generated by a PZT (lead zirconate titanate) element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the frequency domain using the Fourier transform, and in the time-frequency domain using the wavelet transform based on a Gabor wavelet. The spectrum obtained from the Fourier transform shows that a portion of high frequency contents increases with increase in the defect ratio. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with the defect ratio. This study shows that the spectrum ratio and the energy velocity may be indicators fur the evaluation of rock bolt integrity.

• Journal of Dental Rehabilitation and Applied Science
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• v.30 no.2
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• pp.102-111
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• 2014

Purpose: Surface damage and bonding strength difference after micromechanical treatment of zirconia surface are to be studied yet. The aim of this study was to evaluate the difference of fracture resistance and bonding strength between more surface-damaged group from higher air-blasting particle size and pressure, and less damaged group. Materials and Methods: Disk shape zirconia ($LAVA^{TM}$) was sintered and air-blasted with $30{\mu}m$ particle size (Cojet), under 2.8 bar for 15 seconds, $110{\mu}m$ particle size (Rocatec), under 2.8 bar for 15 seconds, and $110{\mu}m$ particle size (Rocatec), under 3.8 bar for 30 seconds respectively. Biaxial flexure test and bonding failure load test were performed serially (n = 10 per group). For bonding test, specimens were bonded on the base material having similar modulus of elasticity of dentin with $200{\mu}m$-thick resin cement for tension of surface damage. Failure load of bonding was detected with acoustic emission (AE) sensor. Results: There were no significant differences both in the biaxial flexure test and bonding failure load test between groups (P > 0.05). Sub-surface cracks were all radial cracks except for two specimens. Conclusion: Within the limitations of no aging under monotonic load test, surface damage from higher air-blasting particle size and pressure was not significant. Evaluations of failure load with bonded zirconia disks was clinically relevant modality for surface damage and bonding strength, simultaneously.

• Journal of the Korean Geotechnical Society
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• v.25 no.12
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• pp.5-12
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• 2009

As rock bolts become one of the main support systems in tunnels and underground structures, the integrity of the rock bolts affects the safety of these structures. The purpose of this study is the evaluation of rock bolt integrity using wavelet transforms of the guided ultrasonic waves by using transmission test in the field. After several rock bolts with various defect ratios are embedded into a large scale concrete block and rock mass, guided waves are generated by a piezo disk element and measured by an acoustic emission (AE) sensor. The captured signals are analyzed in the time-frequency domain using the wavelet transform based on a Gabor wavelet. Peak values in the time-frequency domain represent the interval of travel time of each echo. The energy velocities of the guided waves increase with an increase in the defect ratio. The suitable curing time for the evergy velocity analysis is proposed by the laboratory test, and in-situ tests are performed in two tunnelling sites to verify the applicability of rock bolt integrity tests performed after proposed curing time. This study proves that time-frequency domain analysis is an effective tool for the evaluation of the rock bolt integrity.

• Journal of Korean Society for Atmospheric Environment
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• v.30 no.4
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• pp.327-338
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• 2014

The objective of this study is to enhance the effectiveness of Korean Inspection and Maintenance (I/M) program. Three main tasks are: to measure pollutant emissions of in-use light-duty diesel vehicles (LDVs); to evaluate the validity of existing smoke control scheme for low-smoke-emitting vehicles, which have diesel particulate filters, DPF, to meet stringent Euro-5 emission limits; and to assess the necessity and the benefit of $NO_x$ inspection, which is not involved in current I/M program. We measured second-by-second smoke, particulate and gaseous emissions of 27 LDVs using opacity smoke meter, photo-acoustic soot sensor, and portable emissions measurement system, respectively, under the Korean I/M test driving cycle, KD-147. We find that the DPF plays a key role in controlling soot, which can be considered as black carbon contained in particulate matter. Thus, from an I/M perspective, we believe smoke inspection strategies for Euro-5 diesel vehicles should be more focused on the capability of detecting DPF malfunctions or failures, in order to keep DPF properly functional. Fleet averaged distance-specific $NO_x$ emissions are consistently higher than corresponding emission limits, and the values are similar among pre-Euro-3, Euro-3, and Euro-4 vehicle fleets. These findings indicate that the $NO_x$ inspection should be incorporated into current I/M program in order to manage urban $NO_x$ emissions. This research allows the Korean I/M program keep pace with developments in vehicle technologies, as well as the increased emphasis on $NO_x$ with respect to air quality and human health.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.1
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• pp.17-21
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• 2011

Copper (Cu) had been attractive material due to its superior properties comparing to other metals such as aluminum or tungsten and considered as the best metal which can replace them as an interconnect metal in integrated circuits. CMP (Chemical Mechanical Polishing) technology enabled the production of excellent local and global planarization of microelectronic materials, which allow high resolution of photolithography process. Cu CMP is a complex removal process performed by chemical reaction and mechanical abrasion, which can make defects of its own such as a scratch, particle and dishing. The abrasive particles remain on the Cu surface, and become contaminations to make device yield and performance deteriorate. To remove the particle, buffing cleaning method used in post-CMP cleaning and buffing is the one of the most effective physical cleaning process. AE(Acoustic Emission) sensor was used to detect dynamic friction during the buffing process. When polishing is started, the sensor starts to be loaded and produces an electrical charge that is directly proportional to the applied force. Cleaning efficiency of Cu surface were measured by FE-SEM and AFM during the buffing process. The experimental result showed that particles removed with buffing process, it is possible to detect the particle removal efficiency through obtained signal by the AE sensor.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.1
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• pp.25-30
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• 2007

In this paper, lead-free [$Li_{0.04}(Na_{y}K_{1-y})_{0.96}](Nb_{0.86}Ta_{0.1}Sb_{0.04})O_{3}$ (y=0.4 - 0.58) ceramics were manufactured using conventional miked oxide method for acoustic emission(AE) sensor application and their dielectric and piezoelectric properties were investigated with the variations of Na/K ratio. The samples in the composition Na/K=54/46 exhibited excellent electrical properties of $d_{33}=300$ PC/N and kp=0.49. Taking into consideration above piezoelectric properties, it can be concluded that the [$Li_{0.04}(Na_{y}K_{1-y})_{0.96}](Nb_{0.86}Ta_{0.1}Sb_{0.04})O_{3}$ system ceramics are the promising lead-free materials capable of substituting PZT system ceramics.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.2
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• pp.75-80
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• 2006

In this paper, to detect and observation the void discharges pulse signal, AE signals and tree growth characteristics in case the high voltage is applied to a XLPE sample for a power cable. We also examined the partial discharge current pulse and AE signals with the increase of the applied voltage in XLPE insulation. The experimental results show that a branch-type tree grows in the presence of the voids, and a bush-type tree grows in the absence of the voids in both samples. A rate of tree growth increases abruptly in proportional to the deterioration time in the presence of the of the voids, but in the absence of the voids, a rate of tree growth decreases as time goes by and finally a breakdown occurs. The frequency band of AE signals that are generated from the partial discharges in a XLPE sample, one of solid dielectric materials, is about 1.0[MHz].