• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 춘계학술대회 논문집
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• pp.271-276
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• 2002

Continuous loading is applied the sample has been developed to overcome some of the problems associated with the incremental loading consolidation test. Therefore, it is able to reduce the test time and provide a well defined the curve of effective stress versus strain due to continuous stress-strain points. Also, the constant rate of strain consolidation(CRSC) test has been accepted widely as a standard method in foreign countries because of its many advantages. However, in Korea the CRSC test has not been used in engineering practice and experimentally verified. Because there is not a precise criterion of testing despite consolidation characteristics are influenced on strain rate and Pore pressure ratio. Consequently, it is difficult to apply in engineering practice. In this study, artificial neural networks are applied to the estimation of th proper strain rate and pore pressure ratio of the CRSC test. This study shows the possibility of utilizing the artificial neural networks model of estimation of the strain rate and pore pressure ratio in the CRSC test.

• 소성∙가공
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• 제17권8호
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• pp.579-585
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• 2008

Numerous experimental investigations on metallic materials and solid polymers have shown that relaxation behavior is nonlinearly dependent on prior strain rate. The stress drops in a constant time interval nonlinearly increase with an increase of prior strain rate. And the relaxed stress associated with the fastest prior strain rate has the smallest stress magnitude at the end of relaxation periods. This paper deals with the performance of three classes of unified constitutive models in predicting the characteristic behaviors of relaxation. The three classes of models are categorized by a rate sensitivity of kinematic hardening rule. The first class uses rate-independent kinematic hardening rule that includes the competing effect of strain hardening and dynamic recovery. In the second class, a stress rate term is incorporated into the rate-independent kinematic hardening rule. The final one uses a rate-dependent format of kinematic hardening rule.

• 대한기계학회논문집
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• 제15권2호
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• pp.537-543
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• 1991

In this study, the strain rate effects are considered in the formulation by introducing the constitutive equation of the strain rate sensitive materials and rigid-viscoplastic finite element program is developed for axisymmtric extrusion. The effect of strain rate sensitivity on the flow characteristics and forming pressure are investigated and the experiments are carried out for extrusion with pure lead specimens. The theoretically predicted forming pressure showed reasonably good agreement with the experimental values.

• 한국자동차공학회논문집
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• 제3권1호
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• pp.97-107
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• 1995

Global postbuckling analysis is accomplished for one-dimensional and two-dimensional delaminations. A new finite element model, which can be used to model the global postbuckling analysis of one-dimensional and two-dimensional delaminations, is presented. In order to calculate the strain energy release rate, geometrically nonlinear analysis is accomplished, and the incremental crack closure technique is introduced. To check the effectiveness of the finite element models and the incremental crack closure technique, the simplified closed-form sloution for a through-the-width delamination with plane strain condition is derived and compared with the finite element result. The finite element results show good agreement with the closed-foul1 solutions. The present method was extended to calculate the strain energy release rate for two-dimensional delamination. For a symmetric circular delamination, the strain energy release rate shows great variation along the delamination front. and the delamination growth appears to occur perpendicular to the loading direction.

• International Journal of Safety
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• 제2권1호
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• pp.12-16
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• 2003

In Part 1, the flame structure of the counterflow nonpremixed flames computed by using Fire Dynamics Simulator was compared with that of OPPDIF for different concentrations of methane in the fuel stream. In this study, comparisons were made for the global strain rate that is an important parameter for diffusion flames for further evaluation of FDS. At each of the three fuel concentrations, $20% CH_4＋ 80% N_2, 50% CH_4 ＋ 50% N_2, 90% CH_4 ＋ 10% N_2$ in the fuel stream, the temperature and axial velocity profiles were investigated for the global strain rate in the range from 20 to $100s^{-1}$. Changes in flame thickness and radius were also compared with OPPDIF. There was good agreement in the temperature and axial velocity profiles between the axisymmetric simulations and the one-dimensional computations except for the regions where the flame temperature reach its peak and the axial velocity rapidly changes. The simulations of the axisymmetric flames with FDS showed that the flame thickness decreases and the flame radius increases with increasing global strain rate.

• 소성∙가공
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• 제14권7호
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• pp.635-641
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• 2005

The crystal structure of magnesium was hexagonal close-packed (HCP), so its formability was poor at room temperature. But formability was improved in high temperature with increasing of the slip planes. Purpose of this paper was 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 was increased, yield·ultimate strength, K-value, work hardening exponent (n) and anisotropy factor (R) were decreased. But strain rate sensitivity (m) was increased. As strain-rate increased, yield·ultimate strength, K-value, and work hardening exponent (n) were increased. Also, microstructures of grains fined away at high strain-rate. These results would be used in simulations and manufacturing factor fer warm and hot forming process.

• 대한기계학회논문집B
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• 제25권1호
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• pp.29-35
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• 2001

Radiation-induced oscillatory instability in CH$_4$/Air diffusion flames is numerically investigated by adopting detailed chemistry. Counterflow diffusion flame is employed as a model flamelet and optically thin gas-phase radiation is assumed. Attention is focused on the extinction regime induced by radiative heat loss, which occurs at low strain rate. Once a steady flame structure is obtained for a prescribed value of initial strain rate, transient solution of the flame is calculated after a finite amount of strain-rate perturbation is imposed on the steady flame. Depending on the initial strain rate and the amount of perturbed strain rate, transient evolution of the flame exhibits various types of flame-evolution behaviors. Basically, the dynamic behaviors can be classified into two types, namely oscillatory decaying solution and diverging solution leading to extinction.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.106-110
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• 1997

A split Hopkinson bar has been used for obtaining material properties in high strain rate state, In this paper, the apparatus was modified to obtain the high strain rate properties of sheet metal for an autobody. From the experiments with the new apparatus, the material properties of SPCEN in the high strain rate state have been acquired and compared with quasi-static experimental results.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2017년도 춘계 학술논문 발표대회
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• pp.214-215
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• 2017

Extreme loads such as impact and explosion have higher strain rate than static loading condition. Therefore, it is necessary to evaluate mechanical properties at high strain rate in order to apply fiber reinforced cement composites to ensure safety performance against impact and explosion. In this study, the compressive properties of fiber reinforced cement composites by strain rate were evaluated.

• 터널과지하공간
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• 제18권3호
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• pp.214-218
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• 2008

본 연구에서는 SHPB(Split Hopkinson Pressure Bar)를 이용하여 변형률 속도에 따른 이방성 화강암의 동적파괴 과정을 조사하였다. 실험결과 변형률 속도가 증가할수록 에너지 흡수량 및 최대응력이 증가하였다. 최대응력은 모든 방향에서 변형률 속도에 의존적이나 역학적 이방성에 민감하지는 않았다. 변형률 속도가 증가할수록 탄성파속도가 많이 감쇠되고, 모든 방향에서 변형률 속도에 의존적이며 강한 암석일수록 감쇠가 빠르게 일어났다.