• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.06a
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• pp.122-126
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• 2001

Magnetic hard disk drive is continually being pushed to reduce head-disk spacing for higher recording densities. The current minimum spacing between the air-bearing slider and disk has been reduced to under 15 nm. In this work, it was investigated if flying height could be lowered under the height of laser bumps. With the reduction of the spinning speed, the flying height was decreased under the height of laser bumps. When a head swept between landing zone and data zone, the head-disk impact was monitored using AE and friction signals. It is demonstrated that magnetic hard disk drive could be operated without tribological failures under the height of laser bumps.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.664-667
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• 1995

The purpose of this paper is to consider the disk failure phenomenon based on the second kind Fredholm integral equation and numerical inversion of Laplace transform when the head hit disk asperities at HDI under antiplane impact loading. The model for analysis is a two layeered half-space with a circumferential surface edge crack. The optimum design parameters to reduce the disk failure due to impact are presented

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.10b
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• pp.273-274
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• 2002

In order to evaluate the flying characteristics of slider, the acoustic emission (AE) as well as friction signals are typically utilized. In this work the frequency spectrum analysis is performed using the AE signal obtained during the head/disk interaction such as load/unload mechanism using ramp, impact situation in the presence of a bump on disk surface and other contact phenomena including particle interaction. It was shown that the influence of impact can be characterized effectively in the AE frequency spectrum. As a result of this work, frequency spectrum analysis will be utilized with better understanding for studying the head/disk interface (HDI) characteristics and monitoring the particle interaction in HDI effectively.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2010.11a
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• pp.747-748
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• 2010

• Journal of the Korean Society for Precision Engineering
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• v.25 no.4
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• pp.140-147
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• 2008

This paper represents an ultra precision rotational device where the smooth impact drive mechanism (SIDM) is utilized as driving mechanism. Linear motions of piezoelectric elements are converted to the rotational motion of disk by frictional forces generated between the rotational disk and the friction part that is attached to the piezoelectric element. This device was designed to drive the rotational disk using slip-slip motion mechanism instead of stick-slip motion mechanism occurred in conventional impact drive mechanism. Experimental results show that the angular velocity is increased in proportion to the magnitude and frequency of supplied voltage to piezoelectric element and decreased as the preload is increased. In our device, the smooth rotational motion was obtained when the driving frequency has been reached to 500Hz under the driving voltage of 100V.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.1
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• pp.482-494
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• 2019

In this paper, the oblique water-entry impact of a vehicle with a disk cavitator is studied experimentally and numerically. The effectiveness and accuracy of the numerical simulation are verified quantitatively by the experiments in this paper and the data available in the literature. Then, the numerical model is used to simulate the hydrodynamic characteristics and flow patterns of the vehicle under different entry conditions, and the axial force is found to be an important parameter. The influences of entry angle, entry speed and cavitator area on the axial force are studied. The variation law of the force coefficient and the dimensionless penetration distance at the peak of the axial force are revealed. The research conclusions are beneficial to engineering calculations on the impact force of a vehicle with a disk cavitator over a wide range of water-entry parameters.

• Composites Research
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• v.29 no.2
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• pp.73-78
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• 2016

In this paper, The concept of a wheel with carbon fiber composite is to replace the conventional material used for a wheel hub, such as plastic, with a disk-type hub made of carbon fabric and epoxy resin. The impact load from the ground under real conditions was considered; a low-velocity impact test was conducted to evaluate the impact performance of the carbon wheel and compare it with that of a conventional plastic wheel. This study applied a 70 J impact load as a test condition. The impact energy was controlled in the test by adjustment of height and weight of impactor. The use of a carbon disk wheel hub was confirmed to reduce weight and generate an excellent repulsive force at low energy under conditions similar to real driving conditions. The results showed that the maximum load increased proportionally depending on the impact load, but the growth of the maximum load was reduced at a 20 J impact load and tended to decrease at a 45 J impact load. The carbon wheel showed excellent properties ; the level of rebounding was 35.3% and 19.1% of the total impact energy at impact loads of 5 J and 10 J, respectively. On the other hand, the carbon disk wheel rebounded less than 5% of the total energy due to crack generation of the thin carbon hub for impact loads of more than 20 J.

• International Journal of Highway Engineering
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• v.18 no.4
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• pp.37-45
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• 2016

PURPOSES : The objective of this study was to develop an impact resonance (IR) test procedure for thin disk-shaped specimens in order to determine the ${\mid}E^*{\mid}$ and phase angle values of various asphalt mixtures. METHODS : An IR test procedure was developed for evaluating thin disk-shaped specimens, in order to determine the dynamic modulus (${\mid}E^*{\mid}$) of various asphalt mixtures. The IR test method that was developed to determine the elastic modulus values of Portland cement concrete was evaluated, which method uses axisymmetric flexural vibration proposed by Leming et al. (1996). The IR tests were performed on three different mixtures of New York with varying nominal maximum aggregate sizes (NY9.5, NY19, and NY25) at six different temperatures ($10-60^{\circ}C$). The ${\mid}E^*{\mid}$ values obtained from the IR tests were compared with those determined by the commonly used AASHTO T342-11 test. RESULTS AND CONCLUSIONS : The IR test method was employed to determine the ${\mid}E^*{\mid}$ values of thin-disk-shaped specimens of various asphalt mixtures. It was found that the IR test method when used with thin disk-like specimens is a simple, practical, and cheap tool for determining the ${\mid}E^*{\mid}$ values of field cores. Further, it was found the ${\mid}E^*{\mid}$ values obtained from the IR tests using thin disk-like specimens were almost similar to those obtained using the AASHTO T342-11 test.

• Journal of the Korea Institute of Building Construction
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• v.23 no.1
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• pp.11-22
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• 2023

In this work, a depth-by-depth evaluation on the deterioration of concrete is suggested by utilizing disk shaped concrete specimens. Dynamic elastic modulus of cylindrical concrete was measured using a free-free resonance column method and compared with dynamic elastic modulus of disk-shaped concrete measured by impulse excitation technique(IET) and impact resonance(IR). According to the results of the experiment, both IET and IR methods showed a smaller difference in dynamic elastic modulus with smaller deviation in data when thickness of the disk specimen was increased. This trend was more evident from dynamic elastic modulus measured by IR method compared to that measured by IET. Variation in data was also smaller with the IR result. To increase the accuracy of the data, it is recommended to use the IR method for disk specimen with a diameter of 100mm and a thickness of 25mm.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.23-28
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• 2005

This paper investigates the effects of disk thickness and Pemto slider on PES(position error signal) for high TPI(track per inch) drives above 150kTPI at early stage of their development. In order to reduce the disk flutter which becomes a dominant contributor to the TMR, the thicker disks with both 63 and 69mi1 have been used. Also, PES of a Pemto slider with thinner thickness than Pico slider has been estimated to decrease the conversion factor of disk motion in axial direction to head off-track motion. A frequency-domain PES estimation and prediction tool has been developed via measurement of disk flutter and HSA(head stack assembly) forced vibration. It has been validated by the measured PES in drive level. Based on the model and measurement of disk flutter, PES of a drive with the thicker disk and Pemto slider is predicted and their impact is investigated.