• Transactions of Materials Processing
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• v.6 no.4
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• pp.279-290
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• 1997

The sectional forming analysis of stamping pocesses for aluminum alloy sheet metals was investigated. For the modeling of the anomalous behavior of aluminum alloy sheet. the Barlat's strain rate potential and Hill's 1990 non-quadratic yield theory with an isotropic hardening rule were employed. The rigid-viscoplastic FEM formulation which solves equilibrium equation for plane-strain stage with mesh-normal geometric constraints was derived. A new method to determine the Barlat's anisotropic coefficients was also suggested. To verify the validity of the formulation, the stretch and draw forming processes of a square cup were simulated.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.1
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• pp.103-118
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• 2018

When collision accident between ships or between ship and offshore platform occurs, a common phenomenon that occurs in structures is the plastic deformation accompanied by a large strain such as fracture. In this study, for the rational design against accidental limit state, the plastic material constants of steel plate which is heated by line heating and steel plate formed by cold bending procedure have been defined through the numerical simulation for the high speed tension test. The usefulness of the material constants included in Cowper-Symonds model and Johnson-Cook model and the assumption that strain rate can be neglected when strain rate is less than the intermediate speed are verified through free drop test as well as comparing with numerical results in several references. This paper ends with describing the future study.

• Microbiology and Biotechnology Letters
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• v.44 no.3
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• pp.349-354
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• 2016

A variety of nuruks collected in different areas in Korea were explored to isolate sixty yeast strains that was able to grow at 44℃. MBY/L1569 strain, which showed the highest growth rate, was selected and identified as Pichia farinosa (Millerozyma farinosa). The isolated strain exhibited superior resistance to heat, acid, and alkali compared with those of P. farinosa KCTC27412 as a control strain. The specific growth rate of P. farinosa MBY/L1569 at 46℃ was 0.37 ± 0.05 h⁻¹, and the highest specific growth rate of 0.50 ± 0.02 h⁻¹ was obtained when it was grown at pH 7.0 and 37℃ with 50 g/l (w/v) glucose as the carbon source. Under optimum growth conditions, strain MBY/L1569 produced ethanol 19.66 ± 0.68 g/l from glucose 50 g/l, with an approximate yield of 40%. P. farinosa MBY/L1569 was deposited at the Korean Collection for Type Cultures as pichia farinosa KCTC27753.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.275-278
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• 2006

Systematic experiments in $CH_4/Air$ counterflow diffusion flames diluted with He have been undertaken to study the oscillatory instability in which lateral heat loss could be remarkable at low global strain rate. The oscillatory instability arises for Lewis numbers greater than unity and occurs near extinction condition. The dynamic behaviors of extinction in this configuration can be classified into three modes; growing, harmonic and decaying oscillation mode near extinction. As the global strain rate decreases, the amplitude of the oscillation becomes larger. This is caused by the increase of lateral heat loss which ran be confirmed by the reduction of lateral flame size. Oscillatory edge flame instabilities at low global strain rate are shown to be closely associated with not only Lewis number but also heat loss (radiation and lateral heat loss).

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.95-98
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• 2008

In the present work, cross-roil rolling was rallied out using a rolling mill in which the roll axes are tilted by $5^{\circ},\;7.5^{\circ},\;10^{\circ}$ towards the transverse direction of the roiled sample. The evolution of strain states during cross-roll rolling was investigated by three-dimensional finite element method (FEM) simulation. Parallel to cross-roll rolling, normal-rolling using a conventional rolling mill was also carried out in the same rolling condition for clarifying the effect of cross-roll rolling. It turned out that three shear rate components were all introduced to the rolled sample by the cross-roll rolling process, while only one shear rate component operated during normal-rolling.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.05a
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• pp.404-407
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• 2008

In the present work, cross-roll rolling was carried out using a rolling mill in which the roll axis is tilted by $7.5^{\circ}$ towards the transverse direction of the rolled sample. The evolution of strain states during cross-roll rolling was investigated by three-dimensional finite element method (FEM) simulation. Parallel to cross-roll rolling, normal-rolling using a conventional rolling mill was also carried out in the same rolling condition for clarifying the effect of cross-roll rolling. It turned out that three shear rate components were all introduced to the rolled sample by the cross-roll rolling process, while only one shear rate component operated during normal-rolling.

• Computers and Concrete
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• v.8 no.2
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• pp.229-241
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• 2011

In this work, cement paste samples with 1% (by cement mass) of a conductive carbon fiber admixture have been studied under uniaxial compression. Three different arrangements were used to measure the resistivity of the samples. According to the results obtained, the resistance should be measured using the four wire method in order to obtain good sensitivity and repeatability. The effect of the load value and the load rate on the fractional change of the volume resistivity has been determined. It has been observed that the gage factor (fractional change in resistance respect to strain) increases when the maximum load is increased, and the loading rate does not affect significantly this parameter. The effect of the sample ambient humidity on the material piezoresistivity has also been studied, showing that the response of the composite is highly affected by this parameter.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10a
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• pp.529-534
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• 1998

To find out an adequate failure criterion in two-dimensional linear elastic crack problems, finite element programs, SED, which determine stress intensity factors $K_I, K_{II}$, crack angle and peak load by the minimum strain energy density failure criterion were developed. In this program, the conventional quadratic isoparametric elements were used in all regions except the crack tip zone where triangular singular elements with 6 nodes were used. The results of SED were compared with the results of those which followed by the maximum circumferential tensile stress criteria and those by the maximum energy release rate criteria and those by Jenq and Shah`s experiments of the same geometry and material properties. The maximum energy release rate criteria were better close to those of the Jenq and Shah`s experiments than the maximum circumferential tensile stress criteria and the minimum strain energy density criteria.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.9
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• pp.75-81
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• 1998

Simulations of warm and hot forming processes need reliable expressions of flow stress at high temperatures. To get flow stress of the materials usually tension, compression and torsion tests are conducted. In this study, hot compression tests were adopted to get flow stress of medium carbon steel. Experiments have been conducted under both isothermal, near constant strain rate in the temperature ranges 650～100$0^{\circ}C$. Phase transformation takes place by temperature changes for steels in hot and warm forging stage. So Constitutive equation are formulated as the function of strain, strain rate and temperature for isothermal conditions and phase transformation.

• Journal of Yeungnam Medical Science
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• v.6 no.1
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• pp.47-57
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• 1989

T. verrucosum infection has been reported for the first time in 1986 in Korea and has been increasing progressively. To evaluate the progress of clinical and histopathological change of dermatophytosis caused by T. verrucosum, inoculation study, using T. verrucosum isolated from infected human(human strain) and from infected cattle(cattle strain), was done in 24 male albino Hartley guinea pig. Their clinical and histopathological changes were evaluated. In addition, comparison for the growth rate between human strain and cattle strain on Sabouraud's glucose agar was made. The results were as follows: 1. Growth rate on Sabouraud's glucose agar : Cattle strain showed significantly more rapid growth rate than human strain on Sabouraud's glucose rate at $25^{\circ}C$ and $37^{\circ}C$. And cattle strain showed more rapid growth rate at $37^{\circ}C$ than $25^{\circ}C$. But human strain showed no significant difference of growth rate at both temperature. 2. Clinical findings: Initial erythema, scale and crust were developed about 8th after inoculation. All three findings reached maximum severity about 12th to 16th day and disappeared about 30th to 34th day after inoculation. There was no significant difference in progress of erythema, scale and crust between cattle strain and human strain. 3. Histopathological findings: Although mild acanthosis was noticed on the 3rd day after inoculation, the other findings including parakeratosis, intraepidermal abscess, spongiosis and vascular change, cellular infiltration were found on 9th day after inoculation. They reached maximum severity on the 12th day and lasted to the 25th day after inoculation. After that, all three findings were decreased gradually between 29th day and 33th day. On the PAS stainings, hyphae and spores were found on the 6th day and disappeared on the 21th day after inoculation. 4. In trichophytin skin test, all of the 24 guinea pigs became positive within average $9.83{\pm}1.17$ lays. These findings suggested that dermatophytosis caused by T. verrucosum induced rapid cell mediated immunity and contributed to rapid resolution of the lesion.