• Journal of the Korean Society of Combustion
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• v.13 no.4
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• pp.16-25
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• 2008

Experiments have been conducted to clarify impacts of curtain flow and velocity ratio on low strain rate flame extinction, and to further display transition of shrinking flame disk to flame-hole. Critical mole fractions at flame extinction are examined in terms of velocity ratio, global strain rate, and nitrogen curtain flow rate. It is shown that multi-dimensional effects at low strain rate flames through global strain rate, velocity ratio, and curtain flowrate dominantly contribute to flame extinction and transition of shrinking flame disk to flame hole. Our concerns are particularly focused on the dynamic behavior of an edge flame in shrinking flame disk.

• Korean Journal of Metals and Materials
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• v.47 no.2
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• pp.71-78
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• 2009

The precipitation behavior of solute carbon and nitrogen strongly affects the mechanical properties of low-carbon automotive panel. In the present study, the effects of aluminum and solute nitrogen on the bake hardenability and strain aging of extremely low-carbon steel with carbon content below 15 ppm has been investigated. The ferrite grain size and distribution of precipitates were varied with the amount of aluminum content of 0.003 to ~ 0.100 wt% in a constant solute carbon and nitrogen. With increasing the aluminum content, the ferrite grain size is increased and strain aging is delayed. The strain aging is also delayed by increasing the annealing temperature, although the ferrite grain size is not much changed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1970-1981
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• 1999

The low-cycle fatigue behaviour of a SiC-particulate-reinforced Al-Si cast alloy with two different volume fractions has been investigated from a series of strain-control led fatigue tests with zero and nonzero tensile mean strains. The composites including the unreinforced matrix alloy, exhibited cyclic hardening behaviour, with more pronounced strain-hardening for the composites with a higher volume fraction of the SiC particles. For the tensile mean strain tests, the initial high tensile mean stress relaxed to zero for the ductile Al-Si alloy, resulting in no influence of the tensile mean strain on the fatigue life of the matrix alloy. However, tensile mean strain for the composite caused tensile mean stresses and reduced fatigue life. The pronounced effects of mean strain on the low-cycle fatigue life of the composite compared to the unreinforced matrix alloy were attributed to the initial large prestrain and non-relaxing high tensile mean stress in the composite with very limited ductility and Cyclic plasticity. Fatigue damage parameter using strain energy, density efficiently accounted for the mean stress effects. Predicted fatigue life using the damage parameter correlated fairly well with the experimental life within a factor of 3. Also, the fatigue damage parameter indicated the inferior life in the low-cycle regime and superior life in the high-cycle regime for the composite, compared to the unreinforced matrix alloy.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.243-244
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• 2014

The opposed flow flame in a mesoscale channel was constructed to observe the flame stabilization behaviors at low strain rate conditions (<$10s^{-1}$). The purpose of this study is to get the overall flame behaviors of partially premixed flames with oxygen enhanced conditions at low strain rates. The oxygen ratio in oxidizer was changed from 18 to 30 %. Conclusively, the flame extinction limit approached to about $1s^{-1}$, and divided into three representative regimes corresponding to self propagating flame, transitional flame, quenching flame regimes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.612-615
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• 2005

Low cycle fatigue tests are performed on the Incollel 617 that be used fur a hot gas casing. The relation between strain energy density and numbers of cycles to failure is examined in order to predict the low cycle fatigue life of Inconel 617. The life predicted by the strain energy method is found to coincide with experimental data and results obtained from the Coffin-Mansun method. Also the cyclic behavior of Inconel 617 is characterized by cyclic hardening with increasing number of cycle at room temperature.

• Geomechanics and Engineering
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• v.25 no.4
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• pp.341-345
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• 2021

1D sand compression response to ko-loading experiences volume contraction from low to high effective stress regimes. Previous study suggested compressibility model with physically correct asymptotic void ratios at low and high stress levels and examined only for both remolded clays and natural clays. This study extends the validity of Enhanced Terzaghi model for different sand types complied from 1D compression data. The model involved with four parameters can adequately fit 1D sand compression data for a wide stress range. The low stress obtained from fitting parameters helps to identify the initial fabric conditions. In addition, strong correlation between compressibility and the void ratio at low stress facilitates determination of self-consistent fitting parameters. The computed tangent constrained modulus can capture monotonic stiffening effect induced by an increase in effective stress. The magnitude of tangent stiffness during large strain test should not be associated with small strain stiffness values. The use of a single continuous function to capture 1D stress-strain sand response to ko-loading can improve numerical efficiency and systematically quantify the yield stress instead of ad hoc methods.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.535-541
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• 1999

Low-dislocation-density large-diameter GaAs single crystals with low-residual-strain have been strongly required. We have developed dislocation-free 3-inch Si doped GaAs crystals for photonic devices, and low-dislocation-density low-residual-strain 4-inch to 6-inch semi-insulating GaAs crystals for electronic devices by Vertical Bridgman(VB) technique. We confirmed that VB substrates with low-residual-strain have higher resistance against slip-line generation during MBE process. VB-GaAs single crystals show uniform radial profile of resistivity reflecting to the flat solid-liquid interface during the crystal growth. Uniformity of micro-resistivity of VB-GaAs substrate is much better than of the LEC-GaAs substrate, which is due to the low-dislocation-density of VB-GaAs single crystals.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.129-157
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• 1999

Low-dislocation-density large-diameter GaAs single crystals with low-residual-strain have been strongly required. We have developed dislocation-free 3-inch Si-doped GaAs crystals for photonic devices [1], and low-dislocation-density low-residual-strain 4-inch to 6-inch [2, 3] semi-insulating GaAs crystals for electronic devices by Vertical Boat (VB) technique. We confirmed that VB substrates with low-residual-strain have higher resistance against slip-line generation during MBE process. VB-GaAs single crystals show uniform radial profile of resistivity reflecting to the flat solid-liquid interface during the crystal growth. Uniformity of micro-resistivity of VB-GaAs substrate is much better than that of the LEC-GaAs substrate, which is due to the low-dislocation-density of VB-GaAs single crystals.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.5
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• pp.1192-1202
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• 1994

Fatigue behavior and life prediction were presented for thermal-mechanical and isothermal low cycle fatigue of 12Cr forged steel used for high temperature applications. In-phase and out-of-phase thermal-mechanical fatigue test at 350 to 600.deg. C and isothermal low cycle fatigue test at 600.deg. C were conducted using smooth cylindrical hollow specimen under strain-control with total strain ranges from 0.006 to 0.015. Cyclic softening behavior was observed regardless of thermal-mechanical and isothermal fatigue tests. The phase difference between temperature and strain in thermal-mechanical fatigue resulted in significantly shorter fatigue life for out-of-phase than for in-phase. The difference in fatigue lives was dependent upon the magnitudes of inelastic strain ranges and mean stresses. Increase in inelastic strain range showed a tendency of intergranular cracking and decrease in fatigue life, especially for out-of-phase thermal-mechanical fatigue. Thermal-mechanical fatigue life prediction was made by partitioning the strain ranges of the hysteresis loops and the results of isothermal low cycle fatigue tests which were performed under the combination of slow and fast strain rates. Predicted fatigue lives for out-of-phase using the strain range partitioning method showed an excellent agreement with the actual out-of-phase thermal-mechanical fatigue lives within a factor of 1.5. Conventional strain range partitioning method exhibited a poor accuracy in the prediction of in-phase thermal-mechanical fatigue lives, which was quite improved conservatively by a proposed strain range partitioning method.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.295-298
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• 2006

Experiments in methane-air low strain rate counterflow diffusion flames diluted with nitrogen have been conducted to study the behavior of flame extinction and edge flame oscillation in which lateral conduction heat loss in addition to radiative heat loss could be remarkable at low global strain rates. Onset conditions of edge flame oscillation and flame oscillation modes are also provided with global strain rate. It is seen that flame length is closely relevant to lateral heat loss, and this affects flame extinction and edge flame oscillation. Edge flame oscillations in low strain rate flames are categorized into three: a growing oscillation mode, a decaying oscillation mode, and a harmonic oscillation mode. The regime of flame oscillation is also provided at low strain rate flames.