• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.1
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• pp.11-19
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• 2015

We present the results of a multi-material numerical investigation of the propagation of a combustible gas mixture detonation in narrow metal tubes. We use an experimentally tuned one step Arrhenius chemical reaction and ideal gas equation of state (EOS) to describe stoichiometric $H_2-O_2$ and $C_2H_4-O_2$ detonations. The purely plastic deformations of copper and steel tubes are modeled using the Mie-Gruneisen EOS and Johnson-Cook strength model. To precisely track the interface motion between the detonating gas and the deforming wall, we use the hybrid particle level-sets within the ghost fluid framework. The calculated results are validated against the experimental data because the results explain the process of the generation and subsequent interaction of the expansion wave with the high-strain-rate deformation of the walls.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.6 s.249
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• pp.670-677
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• 2006

Vacuum interrupters are used in various switch-gear components such as circuit breakers, distribution switches, contactors. The electrodes of a vacuum interrupter are manufactured of sinter-forged Cu-Cr material for good electrical and mechanical characteristics. Since the closing velocity is 1-2m/s and impact deformation of the electrode depends on the strain-rate at the given velocity, the dynamic material property of the sinter-forged Cu-Cr alloy is important to design the vacuum interrupter reliably and to identify the impact characteristics of a vacuum interrupter accurately. This paper is concerned with the dynamic material properties of sinter-forged Cu-Cr alloy for various strain rates. The amount of chrome is varied from 10 wt% to 30 wt% in order to investigate the influence of the chrome content on the dynamic material property. The high speed tensile test machine is utilized in order to identify the dynamic property of the Cu-Cr alloy at the intermediate strain-rate and the split Hopkinson pressure bar is used at the high strain-rate. Experimental results from both the quasi-static and the high strain-rate up to the 5000/sec are interpolated with respect to the amount of chrome in order to construct the Johnson-Cook and the modified Johnson-Cook model as the constitutive relation that should be applied to numerical simulation of the impact behavior of electrodes.

• Journal of Aerospace System Engineering
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• v.17 no.4
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• pp.43-57
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• 2023

The hypervelocity impact simulations of space objects and structures are performed using LS-DYNA. Space objects with spherical, conical, and hollow cylindrical shapes are modeled using the Smoothed Particle Hydrodynamics (SPH). The direct and indirect impact zones of a space structure are modeled using the SPH and finite element methods, respectively. The Johnson-Cook material model and Mie-Grüneisen Equation of State are used to represent the nonlinear behavior of metallic materials in hypervelocity impact. In the hypervelocity impact simulations, various impact conditions are considered, such as the shape of the space object, the thickness of the space structure, the impact angle, and the impact velocity. The shapes of debris clouds are quantitatively classified based on the geometric parameters. Conical space objects provide the worst debris clouds for all impact conditions.

• Advances in nano research
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• v.17 no.1
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• pp.33-49
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• 2024

Using the mechanical treatments for mechanical properties improvement was rarely in the development scope before. This research approves through analytical ways that surface impacts can improve the quality of the surface significantly. This fact is approved for deposited titanium on silicone substrate. The new algorithm called minimum resultant error method (MREM) which is a direct combination of nanoindentation, FEM and dimensional analysis through a reverse method is utilized to extract the mechanical characteristics of the coating surface before and after impact. This method is extended to the time dependent behavior of the material to obtain strain rate coefficient. To implement this new approach, a new analysis technic is developed to define the residual stress field caused by surface impact as initial condition for nanoindentation. Analyzing the model in micro and macro scale at the same time was one of the main resolved challenges in this study. The result was obtaining of the constants of Johnson-Cook constitutive equation. Comparing the characteristics of the coating surface before and after impact shows high improvement in yield stress (34%), Elastic modulus (7.75%) and strain hardening coefficient (2.8%). The main achievement is that the strength improvement in titanium thin layer is much higher than bulk titanium. The yield strength shows 41.7% improvement for coated titanium comparing with 24% for bulk material. The rate of enhancement is about 6 times when it comes to the Young's modulus.

• The Journal of Society for e-Business Studies
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• v.18 no.4
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• pp.241-255
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• 2013

Convergence service, which is a combination of various services, is becoming more important. Among the many examples of convergence service, this study aims to analyze telematics service. By dividing Telematics service into information services and entertainment services, it was empirically proved that the relationship between each dimensions of TAM (perceived ease of use, perceived usefulness, purchase intention) and each service satisfaction, price, design factor. According to the result of structure equation model, service satisfaction and design factor have a significant effect on perceived ease of use, but not on perceived usefulness. It means that the perceived ease of use factor should be emphasized, because of service characteristics that are used during driving.

• Journal of Forest and Environmental Science
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• v.34 no.2
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• pp.119-125
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• 2018

The tropical forests in developing countries are faced with the problem of illegal exploitation of trees. However, dearth of empirical means of expressing the dimensions, structure, quality and quantity of a removed tree has imped conviction of offenders. This study aimed at developing a model that can effectively estimate individual tree basal area (BA) from stump diameter (Ds) for Tectona grandis stands in Omo Forest Reserve, Nigeria, for timber valuation in case of illegal felling. Thirty-six $25m{\times}25m$ temporary sample plots (TSPs) were laid randomly in six age strata; 26, 23, 22, 16, 14, and 12 years specifically. BA, Ds and diameter at breast height were measured in all living T. grandis trees within the 36 TSPs. Least square method was used to convert the counted stumps into harvested stem cross-sectional areas. Six basal area models were fitted and evaluated. The BA-Ds relationship was best described by power model which gave least values of Root mean square error (0.0048), prediction error sum of squares (0.0325) and Akaike information criterion (-15391) with a high adjusted coefficient of determination (0.921). This study revealed that basal area estimation was realistic even when the only information available was stump diameter. The power model was validated using independent data obtained from additional plots and was found to be appropriate for estimating the basal area of Tectona grandis stands in Omo Forest Reserve, Nigeria.

• Journal of Hydrogen and New Energy
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• v.29 no.1
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• pp.90-96
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• 2018

Reaction characteristics and kinetics of a oxygen carrier (OCN717-R1SU) for chemical looping combustion (CLC) have been investigated using TGA by changing gas concentration (10-30 vol.% $CH_4$) and reaction temperature ($825-900^{\circ}C$). Reaction rate of OCN717-R1SU increased as temperature increased and it was found that reaction is delayed at the initial reaction regime. Johnson-Mehl-Avrami (JMA) model was adopted to explain the reaction phenomenon. The activation energy (E) determined by JMA model in reduction reaction of OCN717-R1SU is $151.7{\pm}2.03kJ/mol$ and pre-exponential factor and JMA exponent were also obtained. The parameters calculated in this study will be applied in design of the reactor and operation conditions for CLC process.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.137-143
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• 2017

A tensile failure criterion that can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept is introduced, and conventional plasticity based damage models for concrete such as CSC model and HJC model, which are generally used for the blast analyses of concrete structures, are compared with orthotropic model in blast test to verify the proposed criterion. The numerical prediction of the time-displacement relations in mid span of the beam during blast loading are compared with experimental results. Analytical results show that the numerical error is substantially reduced and the accuracy of numerical results is improved by applying a unique failure strain value determined according to the proposed criterion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.182-189
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• 2007

This paper is concerned with the empirical flow stress constitutive equation of steel sheets for an auto-body with the variation of temperature and strain rate. In order to represent the strain rate and temperature dependent behavior of the flow stress at the intermediate strain rates accurately, an empirical hardening equation is suggested by modifying the well-known Khan-Huang-Liang model. The temperature and strain rate dependent sensitivity of the flow stress at the intermediate strain rate is considered in the hardening equation by coupling the strain, the strain rate and the temperature. The hardening equation suggested gives good correlation with experimental results at various intermediate strain rates and temperatures. In order to verify the effectiveness and accuracy of the suggested model quantitatively, the standard deviation of the fitted result from the experimental one is compared with those of the other two well-known empirical constitutive models such as the Johnson-Cook and the Khan-Huang-Liang models. The comparison demonstrates that the suggested model gives relatively well description of experimental results at various strain rates and temperatures.

• Geomechanics and Engineering
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• v.28 no.2
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• pp.171-180
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• 2022

Time-dependent stress-strain behaviour significantly influences the compressibility characteristics of the clayey soil. In this paper, a series of oedometer tests were conducted in two loading patterns and investigated the time-dependent compressibility characteristics of Indian Montmorillonite Clay, also known as black cotton soil (BC) soil, during loading-unloading stages. The experimental data are analyzed using a new non-linear function of the Elasto-Visco-Plastic Model considering Swelling behaviour (EVPS model). From the experimental result, it is found that BC soil exhibits significant time-dependent behaviour during creep compared to the swelling stage. Pore water entrance restriction due to consolidated overburden pressure and decrease in cation hydrations are responsible factors. Apart from it, particle sliding is also evident during creep. The time-dependent parameters like strain limit, creep coefficient and C_αe/C_c are observed to be significant during the loading stage than the swelling stage. The relationship between creep coefficients and applied stresses is found to be nonlinear. The creep coefficient increases significantly up to 630 kPa-760 kPa (during reloading), and beyond it, the creep coefficient decreases continuously. Several parameters like loading duration, the magnitude of applied stress, loading history, and loading path have also influenced secondary compressibility characteristics. The time-dependent compressibility characteristics of BC soil are presented and discussed in detail.