• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.92-97
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• 2000

Low-velocity impact damage of a thick pressure vessel by composite materials was studied using the modified Herzian contact radius theory. Impactors of various masses and various tup shapes were dropped freely in the range of 20m to 200mm height. With acceleration gage and strain gage installed on the impactor, impact force and acceleration and Contact radius were measured. After a test, the samples were radiographed to scan the state of damage. Compared with hemispherical tup of 12.7mm diameter, the contact radius of hemispherical tup of 25.4mm diameter was bigger. And the experimental data and the theoretical data was different due to the mechanical properties difference. The acceleration value was changed linearly according to the height.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.11 s.254
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• pp.1335-1347
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• 2006

Surface energies calculated from measured contact angles between several solutions and test samples, such as Si wafer, $Al_2O_3$, $SiO_2$, PTFE(Polytertrafluoroethylene), and DLC(Diamond Like Carbon) films, based on geometric mean method and Lewis acid base method. In order to relate roughness to adhesion force, surface roughness of test samples were scanned large area and small by AFM(Atomic Force Microscopy). Roughness was representative of test samples in large scan area and comparable with AFM tip radius in small scan area. Adhesion forces between AFM tip and test samples were matched well with order of roughness rather then surface energy. When AFM tips having different radius were used to measure adhesion force on DLCI film, sharper AFM tip was, smaller adhesion force was measured. Therefore contact area was more important factor to determine adhesion force.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.05a
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• pp.539-542
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• 2002

The role of disk clamp is to fasten disks to motor and to prevent the slip of disks during operation. This paper examined the effects of the design parameters of disk clamp - thickness, contact radius and cross-sectional shape -on the clamping force and circumferential stress distribution of disk. The large stress variation in circumferential direction results in large disk waveness and will increase repeatable run-out (RRO) finally. The disk clamp-disk-disk spacer system is modeled and the FE analysis is performed by ANSYS. The disk clamp with large contact radius shows more uniform stress distribution than the one with small contact radius and the stiffness variation around circumferential direct ion or the addition of the bending sect ion can make stress distribution uniform.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.69-73
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• 2001

Damage induced by low-velocity impact on the curved composite laminates was experimentally evaluated for CFRP cylindrical shells with the radius of curvatures of 50, 150, 300, and 500 mm. The result was then compared with that of flat laminates. The radius of curvatures and the effective shell stiffness appeared to considerably affect the dynamic impact response of curved shells. Under the same impact energy level, the maximum contact force increased with the decreasing radius of curvatures, with reaching 1.5 times that for plates at the radius of curvature of 50 mm. Since the maximum contact force is directly related to the impact damage, curved laminates can be more susceptible to delamination and less resistant to the low-velocity impact damage. The distribution of delamination along the thickness direction of curved laminates are also different from that of flat plates. Delamination was distributed rather even]y at each interface along the thickness direction of curved laminates. This implies that the effect of curvatures has to be considered for the design of a curved composite laminate.

• Journal of Korean Ophthalmic Optics Society
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• v.2 no.1
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• pp.127-131
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• 1997

An analysis on the corneal diopter power and corneal radius has been carried out the Korean female in the twenties age. The results were as follows. The most contact lens wears have the early stage of the twenties age, but the increase of aging have a decrease. The mean corneal diopter power on the right eye have 44.04 diopter, but left eye have 43.92 diopter. The mean of corneal radius on the right eye have the 7.66 mm, but left eye have the 7.69 mm. As a results, In increasing of the age, Most mean corneal diopter power have increase, but the mean of corneal radius have not change.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.613-617
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• 2000

This paper descries the effect of the stylus tip size on the measuring error in surface topography measurement. To analyze the distortional effect of an actual surface geometry originating from the finite stylus size, the surface is modeled as a sinusoid and the stylus tip as a circle. the measuring error is defined as the ratio of the standard deviation of a tracing profile and an original profile. It is shown that this measuring error depends on the amplitude and wavelength of an original profile. In this paper, the spectrum analysis is applied to investigate the distortional effect due to the mechanical filtering of the stylus in the frequency domain. and, the cumulative power spectrum is applied to determinate the minimum wavelength limits to be measured with the various stylus tip radius from these results, a new method to select proper stylus tip radius is proposed.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.11a
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• pp.18-22
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• 2000

An experimental study was carried out to investigate the effect of nano-contact condition on the nano-adhesion phenomena. SPM(scanning probe microscope) tips with different radius of curvature were fabricated by a series of masking and etching processes. DLC(diamond-like carbon) and W-DLC (tungsten-incorporated diamond-like carbon) were coated on (100) silicon wafer by PACVD(plasma assisted chemical vapor deposition). Pull-off forces of Pure Si-wafer, DLC and W-DLC were measured with SPM(scanning probe microscope). Also, the same series of tests were carried out with the tips with different radius of curvature. Results showed that DLC and W-DLC showed much lower pull-off force than Si-wafer and Pull-off force increased with the tip radius.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1589-1590
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• 2013

• Tribology and Lubricants
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• v.15 no.2
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• pp.164-170
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• 1999

Gerotor is widely used as a hydraulic pump or motor, by virtue of its volume changing ability. Performance deterioration of a gerotor hydraulic motor mainly due to the wear come from the contact between inner rotor with trochoidal curve and outer rotor with circular arc profile. This research covers the basic investigation about the contact forces of a gerotor hydraulic motor using analytic method. The influence of the eccentricity and the radius of circular arc teeth on the contact stress was evaluated.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.43-57
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• 2005

The authors have assembled a sample of 80 W UMa binary systems (42 W-subtype and 38 A-subtype) whose light curves have all been solved by means of the recent W-D code and combined with up-to-date radial velocity solutions. The absolute parameters (masses, radii and luminosities) have been derived (without any constraint on the physical parameters). The main results of this paper are: (1) the mass-luminosity relations for both W&A-subtypes. as well as for all W UMa contact binaries have been shown, (2) the mass-radius relations have been found for both subtypes, (3) some remarks on the evolution status have been presented.