• Transactions of Materials Processing
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• v.20 no.3
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• pp.229-235
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• 2011

The formability of magnesium alloy sheets at room temperature is generally low because of the inherently limited number of slip systems, but higher at temperatures over $150^{\circ}C$. Therefore, prior to the practical application of these materials, the forming limits should be evaluated as a function of the temperature and strain rate. This can be achieved experimentally by performing a series of tests or analytically by deriving the corresponding modeling approaches. However, before the formability analysis can be conducted, a model of flow stress, which includes the effects of strain, strain rate and temperature, should be carefully identified. In this paper, such procedure is carried out for Mg alloy AZ31 and the concept of flow stress surface is proposed. Experimental flow stresses at four temperature levels ($150^{\circ}C$, $200^{\circ}C$, $250^{\circ}C$, $300^{\circ}C$) each with the pre-assigned strain rate levels of $0.01s^{-1}$, $0.1s^{-1}$ and $1.0s^{-1}$ are collected in order to establish the relationships between these variables. The temperature-compensated strain rate parameter which combines, in a single variable, the effects of temperature and strain rate, is introduced to capture these relationships in a compact manner. This study shows that the proposed concept of flow stress surface is practically relevant for the evaluation of temperature and strain dependent formability.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.4
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• pp.494-502
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• 1997

Experiments on corresponding jet flames with stagnant point diffusion flames have been carried out in initial injection periods. A compensated measurement of maximum flame temperature, which is based on the ion signal, has been employed to inspect flame responses to time-varying strain rates. The flame responses are obtained at two conditions for the slowly time-varying strain rate and the case of flame extinction, and analyzed to confirm similarity between a stagnant point diffusion flame and an evolving jet diffusion flame. Nonsteady effects are addressed via the comparison between several time scales. The time variation with low strain rates, in which illustrates the flame behavior of the upper branch far from extinction in the well-known S-curve, is confirmed to produce a quasi-steady flame response through the nonsteady experiments. The time variation with strain rates in the case of flame extinction indicates an unsteady effect of flame response. It is therefore found that the flame responses near jet tip depend on time histories of characterized strain rates in the developing process.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.10
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• pp.813-820
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• 2021

In this study, a low-velocity impact test was performed to obtain the dynamic properties of solid propellants. The dynamic behavior of the solid propellant was examined by measuring the force and displacement of the impactor during the low-velocity impact test. The bending displacement was calculated by compensating for the local displacement caused by the low-velocity impact test in the form of three point bending and the shear displacement caused by using a short and thick solid propellant specimen. Stress and strain were calculated using compensated displacements and measured force, and dynamic properties of solid propellants were obtained from the stress-strain curve and compared with static bending test. The dynamic properties of solid propellant under the low-velocity impact loading at various operating temperature conditions such as room temperature(20 ℃), high temperature(63 ℃), and low temperature(-32 ℃) were compared and investigated.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.32A no.6
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• pp.75-81
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• 1995

InGaAsP/InP uncooled LDs emitting at 1.3$\mu$m wavelength are of interest for several application of fiber-to-the-home, optical interconnection, long-haul high-bit-rate optical transmission systems, etc. The strain compensated PBH-MQW-LD employing 1.4% compressive strained well (${\lambda}=1.3{\mu}m$) and 0.7% tensile strained barrier (${\lambda}=1.12{\mu}m$) layers grown by low pressure metallicorganic vapor phase epitaxy was found to be low threshold current and stable temperature characteristics. The average threshold current of 5.6mA and average slope efficiency of 0.27mW/mA at room temperature were obtained for uncoated uncooled-LD.