• Journal of Mechanical Science and Technology
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• v.14 no.3
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• pp.320-330
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• 2000

It is desirable to perform nondestructive evaluation (NDE) to assess material properties and part homogeneity because the manufacturing of carbon/carbon brake disks requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon brake disks (322mm ad, 135mm id) for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon disk manufactured by chemical vapor infiltration (CYI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CYI process. Low frequency (e.g., 1-5MHz) through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Images based on both the amplitude and the time-of-flight of the transmitted ultrasonic pulse showed significant variation in the radial direction. The radial variations in ultrasonic velocity and attenuation were attributed to a density variation caused by the more efficient densification of pitch impregnation near the id and od and by the less efficient densification away from the exposed edged of the disk. Ultrasonic velocities in the edges of the disk. Ultrasonic velocities in the thickness direction were also measured as a function of location using dry-coupling transducers ; the results were consistent with the densification behavior. However, velocities in the in-plane directions (circumferential and radial) seemed to be affected more by the relative contents of fabric and chopped fiber, and less by the void content.

• Tribology and Lubricants
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• v.23 no.6
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• pp.266-271
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• 2007

The brake performance of sintered friction materials for the high speed train was studied. In this study, newly developed sintered materials based on copper were compared with the commercial products for high speed trains. They were tested on a 1/5 scale dynamometer using low carbon steel disks. Effectiveness, fade, and recovery tests were carried out to examine friction performance and the change of disk thickness variation (DTV) during brake applications and noise propensity were also evaluated. Results showed that the two sintered friction materials exhibit similar friction coefficients and braking performance, whereas the newly developed friction material was superior in terms of DTV generation and noise propensity to the commercial friction material. The improvement of the newly developed friction material was attributed to the high graphite content which reduced the stick-slip phenomena and prevented uneven disk wear by producing friction films on the counter disk.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.5
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• pp.17-22
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• 2005

In this study, a disk-type piezoelectric transformer was fabricated. Its diameter was 50[mm] and thickness was 4.5[mm]. The driving and generating electrode with their gap of 1[mm] were fabricated on the top surface. But the common electrode was fabricated on the whole bottom surface. The electrode surface ratio of driving and generating part on the top surface was the range of 1.4:1 to 3:1. We investigated the electrical characteristics with the variation of its thickness and the electrode surface ratio of driving and generating part in the range of load resistance of 100${[\Omega]}\~70{[k\Omega]}$.. Form the experimental results, their influence on the set-up voltage ratio were investigated quantitively and qualitatively.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.2
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• pp.835-840
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• 2011

In this study, a disk-type piezoelectric transformer was fabricated. Its diameter was 50 mm and thickness was 4.5 mm. The driving and generating electrode with their gap of 1mm were fabricated on the top surface. But the common electrode was fabricated on the whole bottom surface. The electrode surface of driving and generating part on the top surface was divided into 2, 4 and 8 pieces. The electrical characteristics with its electrode variation was measured in the range of load resistance of $100{\Omega}{\sim}10_{K\Omega}$. We investigated quantitively the influence of the set-up voltage ratio.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.195-198
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• 2004

In this paper, the disk-type piezoelectric transformer for the high power was investigated with the variation of road resistance. The diameter and thickness of a disk-type piezoelectric transformer was 50mm and 4.5mm, respectively. The piezoelectric transformer was composed to PZT-PMN-PSN. The ratio of driving electrode and generating electrode ranges from 1.4:1 to 3:1. The poling direction of driving part and generating part are the same. A voltage step-up ratio increased with increasing the load resistance, $R_L$, so it reached 60 times under no road resistance. also, the maximum efficiency of 97% was obtained.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1992.10a
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• pp.81-85
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• 1992

Quality of cut is strongly dependent on the cutting pressure, so this relationship can be identified by pressure measuring system. In this paper, the experiments presented were performed with the devised pressure measuring system and the laser cutting of STS 304. Convergent type and convergent-divergent type nozzle were used for pressure variation of the distance between nozzle and workpiece. In laser cutting of STS 304, 1.0 kW CO $\_$2/ laser used. The convergent type nozzle(1.0 mm diameter) pressured above 3 kgf/cm $\^$2/, the MSD(Mach Shock Disk) created, which caused the the pressure variations of the distance between nozzle and workpiece. The maximum cutting pressure exists in accordance with the variation of distance. In spite of far distance the maximum cutting pressure is achieved by using the pressure measuring system. The higher cutting pressure beneath the workpiece the less quantity of dross and the kerf width. Since the higher cutting pressure helps to remove the quantity of dross and to stop the exothermic energy into the material. The optimum laser cutting parameter of STS 304(2.0 mm thickness) with the convergent type nozzle(1.0 mm diameter)is 0.75 mm and 2.5 mm distance between nozzle and workpiece, 4 kgf/cm $\^$2/ cutting pressure. In 3.0 mm thickness case, 1.5 mm and 2.25 mm distance is achieved for good quality.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 1996.04a
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• pp.122-127
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• 1996

In this paper, the effects of the film tinckness, pre-treatment and testing load on. the tribological characteristics have been studied. During the "Ring on-Disk" testing period silica-gel was used to remove the effect of humidity. As a result, increasing the film thickness revealed prolonged wear life, in the case or reasl the testing loads the dynamic friction coefficient was decreased gradually but in regarding the wear life, an intermideate contact pressure (4kgf/mm${2}$) revealed the maximum value. In regarding the surface protuberance friction an intermediate value of area fraction (60%) revealed maximum wear life. In this paper, the qualitative model in regarding the variation of the friction coefficient andworn depth was presented.presented.

• Journal of radiological science and technology
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• v.23 no.1
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• pp.97-101
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• 2000

In this study, the highly sensitive $CaSO_4:Tm$-PTFE TLDs has been fabricated for the purpose of measurement of high energy electron. $CaSO_4:Tm$ phosphor powder was mixed with polytetrafluoroethylene(PTFE) powder and moulded in a disk type(diameter 8.5 mm. thickness $90\;mg/cm^2$) by cold pressing. The absorbed dose distribution and ranges for high energy electron were measured by using the $CaSO_4:Tm$-PTFE TLDs. The ranges determined were $R_{100}=14.5mm$, $R_{50}=24.1mm$ and $R_P=31.8mm$, respectively and the beam flatness, the variation of relative dose in 80% of the field size, was 4.5%. The fabricated $CaSO_4:Tm$-PTFE TLDs nay be utilized in radiation dosimetry for personal, absorbed dose and environmental monitoring.

• The Journal of the Acoustical Society of Korea
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• v.14 no.2E
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• pp.12-18
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• 1995

Capactive miro pressure sensor is simulated with finite element methods to analyze the effect of geometrical variation on its performace. Sensor material is th silicon single crystal. The sensor consists of a disk type diaphragm and several bridges connected to a rigid frame. Structural variables in consideration are the thickness of the diaphragm and the bridges, radius of the circular plate, and the number of bridges. Results of static, dynamic and sensitivity analyses reveal the best structure of the sensor among the fifteen cases under investigation.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.6
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• pp.432-439
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• 2020

Brake judder has been identified in some operating military units of Korean Light Tactical Vehicles(KLTV) with In-board brake systems to improve braking performance. Severe vibration generated while driving the vehicle may reduce the KLTV's driving stability and further lead to accidents. For the prevention of this, this study analyzes the root cause through the failure analysis on the vehicles with the brake judder identified. Furthermore, the improvement factor was derived by identifying a vibration transmission path by analyzing the vibration transmission mechanism. The study analysis confirmed that the vibration of the frame during braking in the tactical vehicle is a cold judder phenomenon, which is caused by an increase in disk thickness variation due to rust and foreign substances under excessive brake disc's run-out. In addition, it was confirmed that such vibration can be reduced by improving the mounting structure. So, an improvement method for each factor was suggested and its effectiveness was verified by comparison test. Finally, it is expected that the improvement plans derived through this study can be used in the development of a next military vehicle.