• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.240-247
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• 2005

In order to analyze effects of strain rate on consolidation characteristics on Busan clay, a series of constant rate of strain(CRS) consolidation tests with different strain rate and incremental loading test(ILT) were performed. From experimental test results, it was found that the preconsolidation pressure was dependent on the corresponding strain rate occurred during consolidation process. Also, consolidation curves normalized with respect to preconsolidation pressure gave a unique stress-strain curve. Coefficient of consolidation and permeability estimated from CRS test had a tendancy to converge to a certain value at normally consolidated range regardless of strain rate. An increase in excess pore pressure without change of total stress was noted on the incremental loading test after the end of loading.

• Tunnel and Underground Space
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• v.18 no.3
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• pp.214-218
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• 2008

Dynamic fracturing of anisotropic granite was investigated by SHPB (Split Hopkinson Pressure Bar). Energy absorption during the test and maximum stress were increased as strain rate increased. Maximum stresses in every direction were dependent on the strain rate but not so sensitive to anisotropy. Elastic wave velocity was decreased as strain rate increased and dependent on strain rate in every direction. Especially, elastic wave velocity decreased more rapidly in a strong rock.

• Computers and Concrete
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• v.15 no.2
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• pp.183-198
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• 2015

Chloride ingress implies a complex interaction between physical and chemical process, in which heat, moisture and chloride ions transport through concrete cover. Meanwhile, reinforced concrete structure itself undergoes evolution due to variation in temperature, relative humidity and creep effects, which can potentially change the deformation and trigger some micro-cracks in concrete. In addition, all of these process show time-dependent performance with complex interaction between structures and environments. In the present work, a time-dependent behavior of chloride transport in reinforced concrete beam subjected to flexural load is proposed based on the well-known section fiber model. The strain state varies because of stress redistribution caused by the interaction between environment and structure, mainly dominated by thermal stresses and shrinkage stress and creep. Finally, in order to clear the influence of strain state on the chloride diffusivity, experiment test were carried out and a power function used to describe this influence is proposed.

• Journal of the Korean Ceramic Society
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• v.29 no.2
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• pp.136-142
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• 1992

The effects of cyclic stress, frequency and bias-pressure on densification of Al2O3 powder cyclic compaction are investigated. The effect of frequency was not significant on densification of Al2O3 powder under cyclic compaction. The higher the cyclic stress and the lower the bias pressure, the higher densification was achieved. To obtain a higher densification, cyclic compaction was more efficient than 1 stroke compaction. A densification equation was proposed to describe an cyclic time dependent pressure-volume relation for Al2O3 powder under cyclic compaction. This equation was obtained empirically, based on the pressure-volume equation proposed by Cooper and Eaton, the time dependent densification equation by Kim and Suh and experimental data for Al2O3 powder under cyclic compaction. The agreement between the proposed equation and experimental data for Al2O3 powder under cyclic compaction was very good.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.7
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• pp.1107-1118
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• 2001

The forming limit diagram introduced by Keeler and Goodwin has been used generally to analyze the formability of sheet metal. However, path dependent forming limit curves based on the state of strain can be explained only by a single criterion which is based on the state. In this study, experimental forming limits in strain space of some metal sheets are transformed into forming limit curves in stress space. Effects of yield criterion are investigated in transforming the forming limit curves. Some important design aspects which are based on the close prediction of movements in forming limit curves during sheet forming are concluded.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.457-460
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• 1999

The effects of electrical positive stress on n-channel LDD and offset structured poly-Si TFT\`s have been systematically investigated in order to analyze the transfer curve\`s shift mechanism. It has been found that the LDD and offset regions behave as a series resistance that reduce the electric field near drain. Hot carrier effects are reduced because of these results. After electrical stress transfer curve’s shift and variation of the off-current are dependent upon the offset length rather than offset region’s doping concentration. Variation of the subthreshold slope is dependent upon offset region’s doping concentration as well as offset length.

• The Journal of Engineering Research
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• v.6 no.2
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• pp.33-38
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• 2004

To investigate the reliability of the MTJs on the roughness of insulating tunnel barrier, we prepared two MTJs with the different uniformity of barrier thickness. Namely, the one has uniform insulating barrier thickness; the other has non-uniform insulating barrier thickness as compared to different thing. As to depositing amorphous layer CoZrNb under the pinning layer IrMn, we achieved MTJ with uniform barrier thickness. Toinvestigate the reliability of the MTJs dependent on the bottom electrode, time-dependent dielectric breakdown (TDDB) measurements were carried out under constant voltage stress. The Weibull fit of out data shows clearly that $t_{BD}$ scales with the thickness uniformity of MTJs tunnel barrier. Assuming a linear dependence of log($t_{BD}$) on stress voltages, we obtained the lifetime of $10^4$years at a operating voltage of 0.4 V at MTJs comprising CoNbZr layers. This study shows that the reliabilityof new MTJs structure was improved due to the ultra smooth barrier, because the surface roughness of the bottom electrode influenced the uniformity of tunnel barrier.

• Transactions of Materials Processing
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• v.21 no.4
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• pp.221-227
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• 2012

The automotive and electronic industries have seriously considered the use of magnesium alloys because of their excellent properties such as strength to weight ratio, EMI shielding capability, etc. However, it is difficult to form magnesium alloys at room temperature because of the mechanical deformation related to twinning. Hence, magnesium alloys are normally formed at elevated temperatures. In this study, a temperature dependent constitutive model, the C-H/V model, for the magnesium alloy AZ31B sheet is proposed. A hardening law based on nonlinear kinematic and H/V(Hollomon/Voce) hardening model is used to properly characterize the Bauschinger effect and the stabilization of the flow stress. Material parameters were determined from a series of uni-axial cyclic experiments(C-T-C) with the temperature ranging between 150 and $250^{\circ}C$. The developed models are fit to experimental data and a comparison is made.

• Steel and Composite Structures
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• v.46 no.2
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• pp.253-261
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• 2023

The goal of this paper is to investigate dynamic responses of simply-supported laminated micro beams under moving load. In the considered micro-scale problem, the modified coupled stress theory which includes the length scale parameter is used. The governing equations of problem are derived by using the Lagrange procedure. In the solution of the problem the Ritz method is used and algebraic polynomials are used with the trivial functions for the Ritz method. In the solution of the moving load problem, the Newmark average acceleration method is used in the time history. In the numerical examples, the effects of stacking sequence of laminas, fibre orientation angles and the length scale parameter on the dynamic responses of laminated micro beams are examined and discussed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.243-247
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• 2008

An analytical approach to calculate time-dependent stresses and strains in initially cracked reinforced concrete section with biaxial bending was proposed. The method utilized the aging coefficient approach of Bazant and the linear creep theory. The position of neutral axis and strain and stress distributions of cracked section after creep and shrinkage were determined from the requirements of strain compatibility and equilibrium of a section. With this proposed algorithm, examples were given for rectangular section and a comparative analysis for stress and strain was also made.