• Transactions of Materials Processing
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• v.10 no.4
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• pp.347-354
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• 2001

Compression tests were carried out to investigate the hot-deformation behavior of Ti-6Al-4V alloy in the temperature range of $915^{\circ}C$ to $1015^{\circ}C$ and the strain rate range of $10^{-3}s^{-i}$ to $10s^{-1}$. Under the given test conditions, the hot-deformation of Ti-6Al-4V alloy was mainly led by dynamic recovery rather than by dynamic recrystallization. The activation energy for the plastic deformation in $\alpha+\beta$ field was about 894 kJ/mol and $\beta$ field was 332kJ/mo1. Processing map for hot working are developed on the basis of the variations of efficiency of power dissipation($\eta$=2m/m＋1) and flow instability criterion using the dynamic material model. The optimum process condition in the ($\alpha＋\beta$) field was obtained at the temperature ranges of $930^{\circ}C$ to $955^{\circ}C$$^{\circ}C$ and a strain rate of $10^{-3}s{-1}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.9 s.252
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• pp.905-912
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• 2006

Experiments in low strain rate methane-air counterflow diffusion flames diluted with $CO_2$ have been conducted to investigate the flame extinction behavior and edge flame oscillation in which flame length is less than the burner diameter and thus lateral conductive heat loss in addition to radiative loss could be remarkable at low global strain rates. The critical mole fraction at flame extinction is examined in terms of velocity ratio and global strain rate. It is seen that flame length is closely relevant to lateral heat loss, and this sheets flame extinction and edge flame oscillation considerably. Lateral heat loss causes flame oscillation even at fuel Lewis number less than unity. Edge flame oscillations are categorized into three: a growing-, a harmonic- and a decaying-oscillation mode. Onset conditions of the edge flame oscillation and the relevant modes are examined with global strain rate and $CO_2$ mole fraction in fuel stream. A flame stability map based on the flame oscillation modes is also provided at low strain rate flames.

• Genomics & Informatics
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• v.1 no.2
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• pp.101-107
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• 2003

Loss of heterozygosity (LOH) has been used to detect deleted regions of a specific chromosome in cancer cells. LOH on chromosome 16q has been reported to occur frequently in progressed hepatocellular carcinoma (HCC). Liver tissues from 37 Korean HCC patients were analyzed for LOH by using 25 polymorphic microsatellite markers distributed along 16q. Out of the 37 HCC patients studied, 21 patients (56.8%) showed LOH in various regions of 16q with at least one polymorphic marker. Puring the analysis of these 21 LOH cases, 6 patients showed interstitial LOHs in which the boundary of the LOH region was defined. With two rounds of LOH analysis, five commonly occurring interstitial LOH regions were identified; 16q21-22.1, 16q22.2 - 22.3, 16q22.3, 16q23.2 and 16q23.3 - 24.1. Among the five LOH regions the 16q23.3 - 24.1 region has been reported to be related with chromosome instability. A complete physical map, which covers the 3.2 Mb region of 16q23.3 - 24.1 (D16S402 and D16S486), was constructed to identify novel candidate tumor suppressor genes. We provide the minimally tiling path map consisting of 28 BAC clones. There was one gap between NT_10422.11 and NT_019609.9 of the human genome sequence contig (NCBI sequence build 33, April 29, 2003). This gap can be filled by sequencing the R-1425M20 clone which bridges these sequence contigs.

• Journal of the Korean Geotechnical Society
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• v.30 no.6
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• pp.51-59
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• 2014

Shallow landslides and debris flows are a common form of soil slope instability in South Korea. These events may be generally initiated as a result of intense rainfall or lengthening rainfall duration because of the effects of climate change. This paper presents the evaluation of rainfall-induced natural soil slope stability and reinforced soil slope instability under vertical load (railway or highway load) throughout South Korea based on quantitative analysis obtained from 58 sites rainfall observatories for 38 years. The slope stability was performed for infinite and geogrid-reinforced soil slopes by taking an average of maximum rainfall every ten years from 1973 to 2010. Seepage analysis is carried out on unsaturated soil slope using the maximum rainfall at each site, and then the factor of safety was calculated by coupled analysis using saturated and unsaturated strength parameters. The contour map of South Korea shows four stages in 10-year-time for the degree of landslide hazard. The safety factor map based on long term observational data will help prevent rainfall-induced soil slope instability for appropriate design of geotechnical structures regarding disaster protection.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.399-408
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• 2010

The characteristics of lifted laminar propane flames diluted with nitrogen have been investigated experimentally to elucidate self-excitation and the effects of flame curvature. Flame oscillation modes are classified as follows: oscillation induced by heat loss, a combination of oscillations induced by heat loss and buoyancy, and a combination of the oscillations induced by heat loss and diffusive thermal instability. It is shown that the oscillation induced only by heat loss is not relevant to the diffusive thermal instability and hydrodynamic instability caused by buoyancy; this oscillation is observed under all lift-off flame conditions irrespective of the fuel Lewis number. These experimental evidences are displayed through the analysis of the power spectrum for the temporal variation of lift-off height. The possible mechanism of the oscillation induced by heat loss is also discussed.

• Journal of the Korean Geotechnical Society
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• v.33 no.10
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• pp.5-14
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• 2017

The hazard maps for predicting collapse on natural slopes consist of a combination of topographic, hydrological, and geological factors. Topographic factors are extracted from DEM, including aspect, slope, curvature, and topographic index. Hydrological factors, such as soil drainage, stream-power index, and wetness index are most important factors for slope instability. However, most of the urban areas are located on the plains and it is difficult to apply the hazard map using the topography and hydrological factors. In order to evaluate the risk of subsidence of flat and low slope areas, soil depth and groundwater level data were collected and used as a factor for interpretation. In addition, the reliability of the hazard map was compared with the disaster history of the study area (Gangnam-gu and Yeouido district). In the disaster map of the disaster prevention agency, the urban area was mostly classified as the stable area and did not reflect the collapse history. Soil depth, drainage conditions and groundwater level obtained from boreholes were added as input data of hazard map, and disaster vulnerability increased at the location where the actual subsidence points. In the study area where damage occurred, the moderate and low grades of the vulnerability of previous hazard map were 12% and 88%, respectively. While, the improved map showed 2% high grade, moderate grade 29%, low grade 66% and very low grade 2%. These results were similar to actual damage.

• Steel and Composite Structures
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• v.28 no.2
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• pp.195-207
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• 2018

First-order reliability method (FORM) is enhanced based on the search direction using relaxed conjugate reliability (RCR) approach for the embedded nanocomposite beam under buckling failure mode. The RCR method is formulated using discrete conjugate map with a limited scalar factor. A dynamical relaxed factor is proposed to control instability of proposed RCR, which is adjusted using sufficient descent condition. The characteristic of equivalent materials for nanocomposite beam are obtained by micro-electro-mechanical model. The probabilistic model of nanocomposite beam is simulated using the sinusoidal shear deformation theory (SSDT). The beam is subjected to external applied voltage in thickness direction and the surrounding elastic medium is modeled by Pasternak foundation. The governing equations are derived in terms of energy method and Hamilton's principal. Using exact solution, the implicit buckling limit state function of nanocomposite beam is proposed, which is involved various random variables including thickness of beam, length of beam, spring constant of foundation, shear constant of foundation, applied voltage, and volume fraction of ZnO nanoparticles in polymer. The robustness, accuracy and efficiency of proposed RCR method are evaluated for this engineering structural reliability problem. The results demonstrate that proposed RCR method is more accurate and robust than the excising reliability methods-based FORM. The volume fraction of ZnO nanoparticles and the applied voltage are the sensitive variables on the reliable levels of the nanocomposite beams.

• Tribology and Lubricants
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• v.13 no.1
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• pp.28-33
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• 1997

Results of theoretical investigations of the stability characteristics of externally pressurized air journal bearing, of which bearing is synchronously vibrate with respect to rotor, are presented. Linearized perturbation method is used to get the dynamic coefficients of air bearing, and the Routh-Hurwitz criterion is used to obtain stability map. The stability characteristics operating at zero steady-state eccentricity is investigated of various phase difference of bearing to rotor. It is shown that stability of air bearing is greatly influenced by synchronous motion of bearing, there exists optimum phase difference which gives maximum stability threshold.

• Transactions of Materials Processing
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• v.31 no.6
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• pp.365-375
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• 2022

The microstructure and high-temperature plastic deformation behavior of the modified Al-0.7Mn alloy were investigated and compared with the conventional Al-0.3Mn (Al3102) alloy. α-Al (matrix) and Al₆(Mn, Fe) phases were identified in both alloys. As a result of microstructure observation, both alloys showed equiaxed grains, and Al-0.7Mn alloy showed larger grain size and higher Al₆(Mn, Fe) fraction than Al-0.3Mn alloy. High temperature compressive tests, the deformation temperatures of 410℃, 450℃, 490℃, 530℃ and strain rats of 10^-2/s, 10^-1/s, 1/s, 10/s, were conducted using Gleeble equipment. The flow stress values of Al-0.7Mn alloy were higher than that of Al-0.3Mn alloy at all strain rates and temperature conditions. Constitutive equations were presented using the flow stresses obtained from experimental results and the Zener-Hollomon parameter. In the true stress-true strain curves of the two alloys, the experimental and predicted values were in good agreement with each other. Based on the dynamic material model, eutectic deformation maps of Al-0.7Mn and Al-0.3Mn alloys were suggested, and the plastic instability region was presented. The modified Al-0.7Mn alloy showed a wider plastic instability region than that Al-0.3Mn alloy. Based on the process deformation maps, the MPE tube parts could be manufactured through the actual extrusion process using the suggested conditions.

• Transactions of Materials Processing
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• v.14 no.2 s.74
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• pp.126-132
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• 2005

The isothermal forging design of a Ti-6Al-4V wing shape was performed by 3D FE simulation. The design focuses on near-net shape forming by the single stage. The process variables such as the die design, pre-form shape and size, ram speed and forging temperature were investigated. The main design priorities were to minimize forging loads and to distribute strain uniformly in a given forging condition. The FE simulation results for the final process design were compared with the isothermal forging tests. The instability of deformation was evaluated using a processing map based on the dynamic materials model(DMM), including flow stability criteria. Finally, a modified process design for producing a uniform Ti-6Al-4V wing product without forming defects was suggested.