• 소성∙가공
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• 제13권1호
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• pp.27-32
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• 2004

Thermomechanical behavior of Al-Mg-Si alloys was studied to investigate the effect of microstructural features such as pre-existing substructure and distribution of particles on the deformation characteristics. The controlled compression tests were carried out to get the information on how the alloy responds to temperature, strain amount and strain rate. Then hot forging of Al-Mg-Si alloys carried out and analyzed by the comparison with the compression tests. Microstructural features after forging were discussed in terms of the thermomechanical response of Al-Mg-Si alloys. As already well mentioned, we found that the deformation of Al-Mg-Si at the elevated temperature brought the recovered structure on most conditions. In a certain time, however, abnormally large grains were found as a result of deformation assisted grain growth, which means that hot forging of Al-Mg-Si alloys could lead to a undesirable microstructural variation and the consequent mechanical properties such as fatigue strength.

• KCI Concrete Journal
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• 제13권1호
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• pp.53-60
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• 2001

Tests of cylindrical concrete specimens under lateral confining pressure of up to 5,000 psi were conducted for two different axial loading cases: monotonic compression and monotonic tension. The purpose of this experimental investigation is to provide stress-strain characteristics of plain concrete in triaxial stress conditions. Lateral confining pressure levels, loading rates, and strength of concrete specimens are varied as parameters. The loading rates are $34.75$\times$10^{-5}$ in/in/sec for fast, $\times$$6.95x10^{-5}$ in/in/sec for normal. and $0.579$\times$10^{-5}$ in/in/sec for slow loading cases. The concrete specimens used in the experiment have compressive strength of 3,500 psi and 6,500 psi, respectively. Findings of this experiment include dependency of the stress-strain behavior of concrete on the above parameters under two different types of loading conditions. The parametric study includes a series of 106 triaxial tests.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2007년도 춘계학술논문 발표대회
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• pp.29-31
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• 2007

Building construction in downtown is ever increasing with a strong demand. Top-Down Method is one of suitable construction method for its advantage in minimizing disturbance to neighborhood. Along with these reasons construction site has developed lots of new methods and materials for Time-Cost Trade-off and improving constructability. Opened Slab is one of these method which resist the horizontal force by slab and it has many merit about construction time and unity. We analyze the compression tests on opened slab for the application.

• 한국세라믹학회지
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• 제32권11호
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• pp.1219-1226
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• 1995

Creep behaviors of Cr3C2 composites containing 90 wt% Cr3C2 and 10 wt% Ni were studied at high temperature. Compression tests at 100$0^{\circ}C$ and bending tests at 100$0^{\circ}C$ and 105$0^{\circ}C$ were done in argon environment. In all test conditions primary and steady-state creep behaviors were observed. Stress exponent and activatiion energy were determined from the experimental data. By microstructural analysis of Cr3C2 composites after creep test, the separate agglomerations of Ni phase were observed. Numerical analysis was also studied to analyze bending creep behaviors of Cr3C2 by assumming different tensile and compressive creep behavior in a bending sample. From the analysis, it was found that the stress state at the compressive region as applied stress increased. The observed creep rates were compared with the predicted creep rates by estimating power-law creep parameters from bending test data.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.605-612
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• 2002

The objective of this study is to investigate the behavior of Visco-Elasto-Plastic materials of Silicate Grouted Sands due to external load. Uniaxial compression strength of silicate grouted sands was increased accordingly with curing time, but it was almost unchanged after 7days. A series of uniaxial compression creep tests were peformed for $\sigma$/$\sigma$$\sub$f/ = 8%,16% and 24%. The tested Silicated Grouted Sands exhibits three types of strains : elastic, plastic, viscoelastic. It is seen that the magnitude of the instantaneous recoverable strains $\varepsilon$$\sub$r/(o) is approximately independent of the unloading time. In this tests, The total creep strains( elastic, plastic, viscoelastic) are proportional to the stress level. Based on the constant creep test results, relationships between the time and the creep compliance are developed.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2002년도 가을 학술발표회 논문집
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• pp.673-680
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• 2002

The mechanical characteristics and compressibility of Light-Weighted Foam Soil (LWFS) are investigated. LWFS is composed of the dredged soil from offshore, cement and foam to reduce the unit-weight and increase compressive strength. For this purpose, the unconfined compression tests and triaxial compression tests are carried out on the prepared specimens of LWFS with various conditions such as initial water contents, cement contents, and confining stresses. The test results of LWFS indicated that the stress-strain relationship and the compressive strength are strongly influenced by the cement contents rather than the intial water contents of the dredged soils. In this study, the normalized factor considering the ratio of initial water contents, cement contents, and foam contents is suggested to evaluate the relationship between compressive strength and normalized factor.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.1181-1192
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• 2008

A laboratory investigation was carried out into effects of strain rate on undrained shear behavior of Holocene clay underneath Kobe Airport with an objective to evaluate the factor of safety of the retaining structure built on it. It was examined in a series of triaxial compression and extension tests performed using different rate of axial straining. A comparative compression test in which the strain rate was changed in steps was also carried out. Similar tests were performed in constant-volume direct shear box (DSB) test. And, the deformation characteristics of the clay were also examined in order to evaluate the variation of stiffness during undrained shearing. It was found that the undrained strength increased with not only the shear rate but also the consolidation period. ISOTACH properties seemed a key to govern the undrained shear behavior.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.69-72
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• 2005

The crystal structure of magnesium is hexagonal close-packed (HCP), so its formability is poor at room temperature. But formability is improved in high temperature with increasing of the slip planes. Purpose of this paper is to know about the mechanical properties of magnesium alloy (AZ31B), before warm and hot forming process. The mechanical properties were defined by the tension and compression tests in various temperature and strain-rate. As the temperature is increased, yield${\cdot}$ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) are decreased. But strain rate sensitivity (m) is increased. As strain-rate increased, yield${\cdot}$ultimate strength, K-value, and work hardening exponent (n) are increased. Also, microstructures of grains fine away at high strain-rate. These results will be used in simulations and manufacturing factor for warm and hot forming process.

• 한국정밀공학회지
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• 제15권9호
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• pp.75-81
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• 1998

Simulations of warm and hot forming processes need reliable expressions of flow stress at high temperatures. To get flow stress of the materials usually tension, compression and torsion tests are conducted. In this study, hot compression tests were adopted to get flow stress of medium carbon steel. Experiments have been conducted under both isothermal, near constant strain rate in the temperature ranges 650～100$0^{\circ}C$. Phase transformation takes place by temperature changes for steels in hot and warm forging stage. So Constitutive equation are formulated as the function of strain, strain rate and temperature for isothermal conditions and phase transformation.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1997년도 Lecture Notes by Two Distinguished Scholars
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• pp.1.2-22
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• 1997

Anisotropic behaviour in soils and soft rocks may be either fabric of stress related ultra in practice is invariably a combination of both. Theoretical studies in the paper include tile iMluence oil untrained strength of assuming both the critical state and Mo21r-Coulomb concepts to hold, and the influence of elastic anisotropy oil predicted undrained effective stress paths. The predictions stemming from these theoretical concepts are examined in the light of evidence from triaxial compression and extension tests oil laboratory prepared, compacted and natural clays and from triaxial compression tests on clay shales. The experimental studies also show the Buence of sample orientation on untrained snear strength, as wen as the iIBluence of anisotropy old the effective stress angle cishearing resistance and of stress patn on measured stiffness.