• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.4
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• pp.621-629
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• 1992

This study is concerned with an application of the Boundary Element Method to 2-dimensional elastoplastic stress analysis on the material nonlinearities. The boundary integral formulation adopted an initial stress equation in the inelastic term. In order to determine the initial stress increment, the increment of initial elastic strain energy due to elastic increment in stressstrain curve was used as the convergence criterion during iterative process. For the validity of this procedure, the results of B.E.M. with constant elements and NISA with linear elements where compared on the thin plate with 2 edge v-notches under static tension and the thick cylinder under internal pressure. And this paper compared the results of using unmedical integral with the results of using semi-analytical integral on the plastic domain integral.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.155-159
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• 2000

Microstructural processes during high cycle fatigue are investigated according to plastic-strain hardening, crack formation, crack propagation and fracture. It is shown that the fatigue test resembles the uniaxial tensile test. The logarithm of the number of cycles to failure is proportional to the elongation in the tensile test. Under high cycle fatigue test, the strain is normally elastic. If the strain is absolutly elastic, fatigue could not result. But this is over simplication. Nearly all metals undergo a minor amount of plastic strain even at low stress. Damage accumulation leadling to crack formation can continue in the persistent slip bands at very low average plastic strain amplitude. In the ten­s sile test the overall specimen follows the failure procedure whilst in the high cycle fatigue test the local persistent slip band follows the failure procedure. However accumulations of strain per unit volume in the deforming region before failure in both cases are equal locally.

• Geotechnical Engineering
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• v.14 no.1
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• pp.93-108
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• 1998

In this study, the analytic solutions and numerical methods were used to estimate the shape and size effects on the stability of underground openings. The stability of underground openings was evaluated by scrutinizing the effects of the rock mass quality, the state of in-situ stresses and the lateral earth pressure coefficient on the displacement, the stress concentration and the plastic region developed in the vicinity of the openings. The analytic solutions have shown that the stress concentration factor is inversely proportional to the radius of curvature of openings. Through parametric study on the various shapes and sizes of underground openings the characteristics of the controlling factors concerned with the stability were analyzed. Then, the study was extended to the horseshoe-shaped openings commonly used for under ground storage. Through the extended study the effects of the stress ratio and the height-towidth ratio of openings on the maximum displacement and plastic region developed around the openings were estimated. The results have shorn that the height-to-width ratio of domestic storage caverns can be increased economically without stability problem, as far as the lateral earth pressure coefficient is appropriate.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.6391-6396
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• 2015

In order to investigate characteristics of the von Mises yield criterion under 2 dimensional stress condition, two cases of plane strain were studied. One of which was for zero elastic strain and the other was for zero plastic strain increment. Yield functions for the plane strain condition for zero elastic strain and for the plane stress condition were represented as ellipse and the two yield functions were compared by ratios of major axis, minor axis and eccentricity and it was seen that the ratio of minor axis was the same between the two cases and the ratios of major axis and eccentricity were functions of Poisson's ratio. Region of elastic behavior obtained from considering plane strain condition of zero elastic strain increases as the Poisson's ratio increases. Yield function for plane strain obtained from considering zero plastic increment and associate flow rule was displayed as straight line and the region of elastic behavior was greater than that for the case of plane stress.

• Geotechnical Engineering
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• v.11 no.3
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• pp.113-122
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• 1995

The purposes of this study are to investigate the mechanical prospeities of the inter mediate soils through consolidation tests and triaxial compression shear tests. The intermediate soils used in this study are artificial soils which are composed of sea clay, sand and it's crushed component. The relationship between plastic index and mechanical prosperties (permeability and compressibility) is investigated through series of consoli dation tests. Strain hardening phenomenon under shearing is explored based on several overconsideration ratios and strain rates in undrained shear tests. To make a comparative study difference of drain condition and strain rate, drain shear tests are performed with overconsolidation ratio.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.93-96
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• 2003

Recently, various bulk metallic glasses (BMG's) haying good mechanical and chemical properties were developed. BMG's can easily be deformed in the supercooled liquid region, via viscous flow mechanism. In our previous work, we evaluated the deformation behavior and some other basic properties of Z $r_{41.2}$ $Ti_{13.8}$C $u_{12.5}$N $i_{10}$B $e_{22.5}$ alloy. In this study, we investigated the micro forming of Z $r_{41.2}$ $Ti_{13.8}$C $u_{12.5}$N $i_{10}$B $e_{22.5}$ alloy. The process condition was chosen based on the viscosity data from TMA, and superalloy and Si wafer with micro patterns on the surface were used as forming die. The alloy showed good replication of the patterns. However, some stripe patterns, resembling scratches, appeared on the deformed alloy surface. These scratches can be reduced or eliminated by polishing before forming.ing.ore forming.ing.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1507-1508
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• 2011

본 논문에서는 전기장이 염료감응형 태양전지 광전극의 산화반도체($TiO_2$)에 미치는 영향에 대해 설명하고 DSC의 효율과 밀접한 관련이 있는 산화반도체의 결정구조 개선에 초점을 맞추어 효율을 향상시키고자 하였다. DSC의 광전극 제조에서 FTO 기판에 doctor-blade 방법을 통해 $TiO_2$ paste 도포 한 후 소성 직전 전기장을 인가하여 입자의 결정화를 돕는다. 이때 인가 전압과 전압을 인가하는 시간을 변화시키면서 실험하였다. 그 후 $450^{\circ}C$에서 30분 동안 소성하였다. FE-SEM으로 $TiO_2$의 형태를 보고 전기장이 $TiO_2$ 결정화에 미치는 영향을 확인하였고, current-voltage 특성 분석을 통해 에너지 변환 효율과 각 요소들을 비교하였다. UV-vis spectrophotometer, EIS 측정으로 각 DSC의 광 흡수율과 $TiO_2$/염료/전해질 영역에서의 저항을 분석하였다. 그 결과 전기장이 가해진 $TiO_2$의 결정이 더 잘 배열된 것을 확인하였고, 그로인해 에너지 변환 효율이 7.09%에서 8.65%로 증가한 것을 알 수 있었다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.417-420
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• 2006

The composition and structure of dendrite phase within $Zr_{76.11}Ti_{4.20}Cu_{4.51}Ni_{3.16}Be_{1.49}Nb_{10.53}$ bulk metallic glass (BMG) were confirmed by using an EPMA, XRD and TEM, respectively. The chief elements of dendrite phase were Zr-Ti-Nb and had a BCC structure. The thermal properties of this BMG have been then subsequently investigated by using a differential scanning calorimeter (DSC). The glass transition and crystallization onset temperatures were determined as $339.7^{\circ}C$ and $375.8^{\circ}C$ for this alloy, respectively. Mechanical properties have also been examined by conducting a series of uniaxial compression tests at various temperatures within supercooled liquid region under the strain rates between $10^{-4}/s$ and $3{\times}10^{-2}/s$. The deformation behavior of BMG composite within supercooled liquid region is similar to one of Vit-1 exhibiting amorphous single phase alloy. The flow stresses of BMG composite, however, are entirely higher than those of Vit-1 because dendrite phases are interfere with moving of atoms.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.138-143
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• 1998

The continuous casting process has been adopted increasingly in recent years to save both energy and labor. It has experienced a rapid development in the production of semi-finished steel products, replacing the conventional route of ingot casting plus rolling. To achieve this good merit, however, more studies about a heat transfer mechanism between roll and slab are needed. So this paper shows the results of the deformation behavior of steel cast slabs, which are about the solidification and heat transfer. This study is used to prevent internal cracks of a slab in a bending and unbending zone. The value of moving strand shell bulging between two supporting rollers under ferrostatic pressure and slab-self weight has been computed in terms of creep and elastic-plasticity. The high strand distributions in solidified shell undergoes a series of bulging are calculated with boundary condition a very closed to continuous steel cast slabs productions.

• Transactions of Materials Processing
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• v.13 no.1
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• pp.9-14
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• 2004

Recently, various bulk metallic glasses (BMG's) having good mechanical and chemical properties were developed. BMG's can easily be deformed in the supercooled liquid region, via viscous flow mechanism. By using the viscous flow, the very low pressure is needed to deform the materials. In this study, we investigated the structural transition and deformation behavior of Vitreloy 1 (Zr/sub 41.2/Ti/sub 13.8/Cu/sub 12.5/Ni/sub 10/Be/sub 22.5/) using TMA and DSC. We applied the results to the micro forming process. The forming condition was chosen based on the viscosity data from TMA, and Si wafer with micro patterns on the surface was used as a forming die. The deformed surface was analyzed by SEM and 3D Surface Profiling System. The alloy showed good replication of the patterns. Quantitative measurement of roughness was useful to evaluate the replication. Surface condition of the deformed surface was determined by the initial surface condition.