• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.10a
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• pp.55-63
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• 1994

The analysis of superplastic sheet forming process is studied by the use of the finite element method using a convected coordinate system and a skew boundary condition. In the formulation, the large inelastic behavior of the superplastic material is described as incompressible, nonlinear, viscous flow. The formulation is then approximated to the finite dimensional space with the use of membrane elements, which results in algebraic linear equations. In addition to the finite element formulation, a pressure cycle control algorithm is combined in the analysis for optimization of the forming time, which deals with the maximization of the strain rate sensitivity, the protection of the thickness reduction, the consistency of the desired strain rate and improvement of formability.

• Proceedings of the KWS Conference
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• 1999.05a
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• pp.241-244
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• 1999

The purpose of this study is to examine the characteristics of stress corrosion cracking(SCC) and acoustic emission(AE) signals for the weld HAZ of HT-60 steel under corrosion control in synthetic seawater. Corrosive environment was controlled by potentiostat, and SCC experiment was conducted using a slow strain rate test method at strain rate of 10$^{-5}$ /sec. In order to verify the miroscopic fracture behaviour of the weldment during SCC phenomena, AE test was done simultaneously. Besides, correlationship between mechanical parameters and AE ones was investigated. In case of the parent, reduction of area(ROA) at -0.5V was samller than any other applied voltage such as -0.8V and -1.1V. In addition, reduction of area for the PWHT specimens at -0.8mV was larger than that of the weldment due to the softening effect according to PWHT. In case of the weldment, a lots of events was produced because of the singularities of the weld HAZ compared with the parent.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.84-88
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• 1997

The Jonhnson-Cook constitutive relation has been used in dynamic plasticities. The constants of the Jonhson-Cook relation of sheet metals for an autobody is not known yet. In this paper, the material properties of SPCEN, SPCC and SPRC in the high strain rate states have been acquired. A new tension split Hopkinson bar was used in high speed tensile tests of sheet metals. The experimental results acquired from the apparatus are used to determine the constants of Johnson-Cook constitutive relation of sheet metals. This results can be used to analysis of crashworthness.

• Korean Journal of Environmental Agriculture
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• v.26 no.4
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• pp.332-336
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• 2007

Pseudomonas stutzeri strain KCCM 34719 was used in this experiment to determine the effects of increasing Pb(II) concentrations on its growth rate. To obtain optimum growth conditions, strain KCCM 34719 was cultivated in nutrient broth under various conditions, such as temperature, pH, and NaCl concentration. Optimal conditions for cell growth were $30^{\circ}C$ of temperature, 8.0 of pH, and 3% of NaCl concentration, respectively. Growth response of bacterial cell to Pb(II) showed tolerance to concentrations ranging from 10 to 100 mg ${\ell}^{-1}$ in liquid culture, following a growth pattern similar to the control. Growth rate was greatly inhibited at 200 mg ${\ell}^{-1}$ of Pb(II).

• Computers and Concrete
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• v.6 no.5
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• pp.377-390
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• 2009

In this paper an improved one-dimensional frame element for modelling of reinforced concrete beams and columns subjected to impact is presented. The model is developed in the framework of a flexibility fibre element formulation that ignores the shear effect at material level. However, a simple shear cap is introduced at section level to take account of possible shear failure. The effect of strain rate at the fibre level is taken into account by using the dynamic increase factor (DIF) concept for steel and concrete. The capability of the formulation for estimating the element response history is demonstrated by some numerical examples and it is shown that the developed 1D element has the potential to be used for dynamic analysis of large framed structures subjected to impact of air blast and rigid objects.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.455-462
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• 2002

There exist several kinds of continuous consolidation tests to analyze the consolidation behavior of soft clay. The constant rate of strain (CRS) test has been adopted as a standard method by several countries, and some researches also have been peformed by domestic researchers. Among those, the constant pressure ratio (CPR) test is peformed with the constant ratio of excess porewater pressure to vertical effective stress. The test has the advantage of considerable reduction of duration time. In the study, the consolidation characteristics are analyzed by performing the CPR test as validate the pressure ratio with undisturbed soft clay and remolded clay, Also, results of the standard consolidation test and CRS test are compared to verify the CPR test can be employed for practical use. As a result, effects of variation of the pressure ratio on consolidation parameter are similar to the strain rate in the CRS test. Therefore, the test can be used to analyze the consolidation behavior of soft clay But the test have some problems such as expensive cost of equipment and highly skilled workmanship.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.176-179
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• 1999

The high temperature deformation behaviour of 15vol% SiCp/A16061 composites has been studied in the temperature range of 300-50$0^{\circ}C$ and the strain rate range of 0.1-3.0/sec by torsion test. On he basis of the flow stress data the strain rate sensitivity(m) of the material is evaluated and used for calculating the deformation efficiency(η) [η=2m/(m+1)] A domain of dynamic recrystallization(DRX) could be identified in these maps by using the deformation efficiency. The characteristicvs of these results has been investigated with the help of determining the region of optimum hot working condition.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.10a
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• pp.14-19
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• 1996

This study presents development of finite element simulation program and analysis of hot extrusion through square dies with mandrel. The design of extrusion dies is still an art rather than science. Die design for a new extrusion is developed from through in-plant trials. In the present paper, three-dimensional steady-state finite element simulation program is developed. The developed system is effectively used to simulate extrusion of clamp shaped hollow section. The objective of the present paper is to study the possibility of integrating this method into the design of dies for extrusion of complex section. To obtain sound product, the distributions and effects of temperature, effective strain rate, mean strain rate and mean stress are studied.

• Transactions of Materials Processing
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• v.10 no.5
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• pp.383-388
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• 2001

In describing the plastic deformation behaviour of ultrafine-grained materials, a phase mixture model in which a polycrystalline material is regarded as a mixture of a crystalline phase and a grain boundary phase has been successful. The deformation mechanism for the grain boundary phase, which is necessary for applying the phase mixture model to polycrystalline materials, is modelled as a diffusional flow of matter along the grain boundary. A constitutive equation for the boundary diffusion creep of the boundary phase was proposed, in which the strain rate is proportional to (stress/grain siz $e^{2}$). The upper limit of the stress of the boundary phase was set to equal to the strength to the amorphous phase. The proposed model can explain the strain rate and grain size dependence of the strength of the grain boundary phase. Successful applications of the model compared with published experimental data are described.

• Journal of the Korean Applied Science and Technology
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• v.28 no.1
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• pp.29-34
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• 2011

The sterilization of strain and algae in sea water was studied to see the possibility to apply the redox reaction of metal alloy to meet the international marine organization(IMO) regulation, which was to regulate deballasting concentration of strain and algae above 99% of sterilization. Two different kinds of brass were heat treated at different temperature and cooled rapidly to conserve the specific character of ${\beta}$ brass. Untreated Muntz metal showed the best result of antimicrobial rate in sea water, and 7:3 brass showed similar result to Muntz metal. Heavy metal elution rate was inversely proportional to the sterilization capability.