• Journal of Mechanical Science and Technology
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• 제18권1호
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• pp.12-19
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• 2004

Using LSM (laser scanning method) , the radius of curvature due to thermal deformation in polyimide film coated on Si substrate is measured. Since the polyimide film shows viscoelastic behavior, i.e., the modulus and deformation of the film vary with time and temperature, we estimate the relaxation modulus and the residual stresses of the polyimide film by measuring the radius of curvature and subsequently by performing viscoelastic analysis. The residual stresses relax by an amount of 10％ at 100$^{\circ}C$ and 20% at 150$^{\circ}C$ for two hours.

• Structural Engineering and Mechanics
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• 제75권2호
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• pp.133-144
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• 2020

This investigation is to study the effect of gravitational field and diffusion on a microstretch thermoelastic medium heating by a non-Gaussian laser beam. The problem was studied in the context of the dual-phase-lag model. The normal mode analysis is used to solve the problem to obtain the exact expressions for the non-dimensional displacement components, the micro-rotation, the stresses, and the temperature distribution. The effect of time parameter, heat flux parameter and gravity response of three theories of thermoelasticity i.e. dual-phase-lag model (DPL), Lord and Shulman theory (L-S) and coupled theory (CT) on these quantities have been depicted graphically for a particular model.

• International Commerce and Information Review
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• 제12권4호
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• pp.25-45
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• 2010

The objective of this paper is to review the mechanics of how global e-trade practices can affect a firm's performance. It is well known that the introduction of global e-trade systems can save transaction costs at the macro level. However this study is extended at micro level by determining whether global trade transaction costs influence positively or negatively in exporting firms performances at firm level. A theoretical framework is suggested for determining the usage and performance of global e-trade with the global e-trade barriers. An empirical analysis of South Korean exporting firms has been undertaken. This paper concludes that the global e-trade has yet to overcome the barriers resulting from the transaction costs and asset specificity. In this regard, appropriate action like intensive education and training program should be implemented in order to make South Korea's global e-trade more matured.

• Proceedings of the KSME Conference
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.507-510
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• 2001

Brittle failure mechanism has been well known as growth of initial micro-damage, that causes macro crack and failure in the end. Several precise criteria are suggested recently, based on experiments values in a whole load range. Among them, Mohr-Coulomb's criterion is used widely these days, but it has a big error compared with the real failure behavior since it does not show reciprocal actions of stresses. In this study, a new brittle failure criterion is proposed, which includes the effects of brittle damage evolution by taking a brittle damage parameter specifically. Comparisons between the proposed model and the previous ones are also given.

• Journal of the Korean Society of Industry Convergence
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• 제2권2호
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• pp.139-146
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• 1999

Combustion Characteristics of the wood chips(balsa chips) were experimental studied as fundamental investigation of the thermal recycle system of the urban dust. The urban dust contains plastics vegetable and lot of wood material. Then, a wood was chosen as an example of the component of urban dust. A small wood chip was burned in a electric furnace and mass reduction rate during volatile and combustion states were recorded by the micro-electric balance and the combustion flame shape took a photograph by video camera at the mass of wood chips and ambient temperature in the furance. Ignition delay took the minimum value when the mass of the test chip was 0.3g. When a mass of the test chip was smaller then 0.001g, combustion with flame did not burnt.

• Economic and Environmental Geology
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• 제32권1호
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• pp.93-100
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• 1999

In rock, there are many microsopic structures which influence the mechnical behavior of rock. Many microstructures interact with each other, and furthermore, material constants vary discontinuously within rock, as most rocks are composed of several minerals. Taking into account this feature, it may be possible to contemplate a microstructure of rock as a unit cell by which the rock is constituted periodically. If this idealization is acceptable, the homogenization method can be applied. In this research, various microcracks on rock specimens were observed through a stereoscopic microscope under uniaxial compression. On the other hand, local stress distribution in the periodic-micro structure was calculated by the homogenization method. Then it is shown that there is a possibility to establish a relation between the behavior of microcrack and macroscopic load quantitatively by the linear fracture mechanics.

• Journal of Surface Science and Engineering
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• 제44권5호
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• pp.207-212
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• 2011

In this study, the change in diffusion coefficient and wear characteristic with depth in the carbonitriding layer of SCM415 steel was discussed. To determine the diffusion coefficient, depth profile of carbon was measured from the surface using the Glow Discharge Spectrometer. In otherwise, measurements of carbide fraction, micro vickers hardness of surface and observation of microstructure have been implemented through the SEM image. $Fe_3$(C,N) layer and effective depth were increased as the time for carbonitriding takes longer. According to wear experiment, the results showed that wear resistance was improved by $Fe_3$(C,N) layer and effective depth.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.473-479
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• 1996

Until now, we assumed in the time-dependent analysis of concrete structure that tensile creep has same characteristics as compressive creep has. But, in according to results of researches, it appears that tensile creep is different from compressive creep in quantity and in mechanics because tensile creep is affected significantly by micro cracking. The test results indicate that the creep behavior of concrete in compression and tension is rather different. The test data shows that the amount of creep under tensile loading is larger than that under compressive loading. In this paper, a realistic tensile creep model is suggested and incorporated in the formulation. In order to get more accurate results of time-dependent analysis. The present study indicates that the long-term deflection of concrete structures under realistic tensile creep model is somewhat larger than that under ordinary compressive creep model.

• International Journal of Concrete Structures and Materials
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• 제3권1호
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• pp.47-56
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• 2009

The first diagonal cracking and ultimate shear load of reinforced girder made of ultra high performance fiber reinforced concrete (UHPFRC) were investigated in this paper. Eleven girders were tested in which eight girders failed in shear. A simplified formulation for the first diagonal cracking load was proposed. An analytical model to predict the ultimate shear load was formulated based on the two bounds theory. A fiber reinforcing parameter was constituted based on the random assumption of steel fiber uniform distribution. The predicted values were compared with the conventional predictions and the test results. The proposed equation can be used for the first cracking status analysis, while the proposed equations for computing the ultimate shear strength can be used for the ultimate failure status analysis, which can also be utilized for numerical limit analysis of reinforced UHPFRC girder. The established fiber reinforcing theoretical model can also be a reference for micro-mechanics analysis of UHPFRC.

• Journal of the Society of Naval Architects of Korea
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• 제29권4호
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• pp.179-192
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• 1992

An elasto-plastic-damage constitutive model for ductile materials was derived under the framework of thermodynamic approach of contimuum damage mechanics(CDM) in which internal irreversible thermodynamic change of micro-structure of materials such as plastic deformation and damage evolution were considered as thermodynamic state variables. New constitutive model can predict not only the elasto-plastic behaviors but also the sequential degradation process of ductile materials more rationally.