• Journal of the Korean Institute of Gas
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• v.24 no.6
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• pp.61-69
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• 2020

This paper is a study of the behavior characteristics that occur in the hydrogen storage vessel TYPE 1 according to pressure and temperature conditions by FEM(Finite element method). Von Mises stress (VMS) generated at the highest pressure was compared with Yield strength (YS) of the material for structural safety assessment of the container, and the results of plastic strain energy density (PSED) were analyzed as basic data for life expectancy. According to the analysis results, the safety of the hydrogen gas storage vessel is not ensured due to the occurrence of VMS higher than the yield strength on the bottom of the storage container at a gas pressure of 40 Mpa or higher. In addition, the results of VMS caused by temperature conditions are very low and the behavior by temperature can be ignored. The maximum pressure of VMS/YS below 1 is calculated to be about 30 Mpa, indicating that the hydrogen storage container subject to this paper should be managed with a gas charging pressure of less than 30 Mpa.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.6
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• pp.1417-1431
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• 1994

In this study, shear strength characteristics of the Nak-Dong river sand in Taegu area are investigated by triaxial compression test, considering shear strain control velocity, relative density, and confining pressure. The results from Lade model and Modified Lade model are compared with the measured value in the laboratory test. The results by the change of shear strain control velocity, relative density, and confining pressure are as follows; 1) The stress limit, which can be Coulomb's law about the Nak-Dong river sand, have ranged 120~200 kpa at 0.08%/min and 120~150 kpa at 0.5%/min. These limits are smaller than that of the calcareous sand and the well-graded, quartz sand. 2) The parameters needed to Lade model and Modified Lade model are much affected by the strain control velocity and the relative density. Consequently, in the field, it is important to use parameters aptly after accurately understanding both the loading condition and subsoil condition. 3) Overall, the principal stress ratio obtained from constitutive model equations is not affected by the control velocity, but both the relative density and confining pressure affect the result of constitutive model equations. Consequently, the study on the various conditions about the relative density and confining pressure is needed to accurately predict the stress-strain behavior on the Nak-Dong river sand. 4) For the range of the used confining pressure in the study, the Lade model shows better agreements with the measured value than the Modified Lade model, comparing the measured value with the principal stress ratio at failure and the internal friction angle of failure envelope obtained from the Lade model and Modified Lade model.

• Computers and Concrete
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• v.21 no.2
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• pp.209-217
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• 2018

The dynamic compressive behavior of concrete after freezing and thawing tests are investigated by using the split Hopkinson pressure bar (SHPB) technique. The stress-strain curves of concrete under dynamic loading are measured and analyzed. The setting numbers of freeze-thaw cycles are 0, 25, 50, and 75 cycles. Test results show that the dynamic strength decreases and peak strain increases with the increasing of freeze-thaw cycles. Based on the Weibull distribution model, statistical damage constitutive model for dynamic stress-strain response of concrete after freeze-thaw cycles was proposed. At last, the fragmentation test of concrete subjected to dynamic loading and freeze-thaw cycles is carried out using sieving statistics. The distributions of the fragment sizes are analyzed based on fractal theory. The fractal dimensions of concrete increase with the increasing of both freeze-thaw cycle and strain rate. The relations among the fractal dimension, strain rates and freeze-thawing cycles are developed.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.335-342
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• 2000

In this study, the swelling characteristics of reconstituted clayey soil were investigated by STD and CRS test. The strain rate during loading was constant i.e. 0.05 %/min, 0.03 %/min and during unloading was varied in proportion to 1/1, 1/5, 1/10 and 1/15 of strain rate during loading. From this study the following conclusions were obtained; (1) There were similar values, especially, during unloading in case of 1/10 or 1/15 of strain rate during loading and the test results between STD and CRS were much to be alike. (2) The cross point of effective stress versus excess pore water pressure ratio curve, was increased during unloading, while the stress level of the cross point was decreased. The stress level can be separated into two zones according to the swelling index named Cs1 and Cs2. From the test results, the values of Cs1 were approximately constant irrespective of strain rate during unloading, but the values of Cs2 were much influenced by strain rate. (3) In CRS consolidation tests, it was found that unloading strain rate did not affect on the existence of zone.

• Journal of the Korean Society of Combustion
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• v.5 no.1
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• pp.7-18
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• 2000

Numerical simulations of counterflow non-premixed $CH_4/C_2HCl_3/Air$ flames added 8%(by volume) C2HCl3 on the fuel side are conducted at atmospheric pressure using a detailed chemical reaction mechanism in order to understand the effect of strain rates. A detailed sensitivity analysis is also performed in order to assess the relative influence of each reaction on the flame established at a strain rate of 200s-1. The structure of flames (i.e., temperature, velocity, and concentration of species) established at both a strain rate of 150s-1 and 300s-1 are investigated. As the strain rate increases, the "flame zone" is restricted to a narrower range and the position of maximum temperature is shifted to the fuel side. The concentrations of major species, H2O, CO, H2, HCl, Cl2, and Cl are decreased with increased strain rate. The reaction involving chlorine, CH4 + Cl $\rightarrow$ CH3 + HCl, instead of the reaction, CH4 + H $\rightarrow$ CH3 + H2 influences the consumption of methane. C2HCl3 + OH $\rightarrow$ CHCl2 + CHOCl and HCl + OH $\rightarrow$ H2O + Cl, are major reactions, through which OH radicals are consumed.

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.304-309
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• 2001

A Fiber optic strain sensor for the measurement of the internal strain of a concrete specimen was developed. This sensor was a 11 mm Fiber-optic Fabry-Perot interferometer attached inside a stainless steel pipe of 2 mm diameter. The fabricated strain sensors were embedded in a reinforced concrete structure of $100{\times}100{\times}500\;mm^3$ size and were measured the internal strain of a concrete structure when the external pressure was applied to the structure. For a field application, the strain sensors were attached on the bottom of a real bridge and dynamic loading test were executed. In the test, they showed good sensitivity as a deformation sensor and capability of remote monitoring.

• Transactions of the Korean Society of Automotive Engineers
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• v.6 no.4
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• pp.166-177
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• 1998

Combustion characteristics of natural gas premixed flames is studied experimently and numerically by adopting a counterflow as a flamelet model in turbulent flames. Flame speeds are measured by employing LDV, and the results show that flame speed increases linearly with strain rate, which agrees well with numerical results. Parametric dependences of extinction strain rates are studied numerically with detailed kinetic mechanism to show that the addition of ethand to a methane premixed flame makes the flame more resistant to strain rate. The effect of pressure on the extinction strain rate is that the extinction strain rate increases up to 10 atm and them decreases, which is explained by competition of chain branching H+O2=OH+O and recombination reaction H+O2+M=HO2+M. Detailed mechanism having seventy-four step is systematically reduced to a nine-step and a five-step thermal NOx chemistry is reduced to two-step. Comparison between the results of the detailed and the reduced mechanisms demonstrates that the reduced mechanism successfully describes the essential features of natural gas premixed flames including extinction strain rate and NOx production.

• Geomechanics and Engineering
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• v.21 no.4
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• pp.327-336
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• 2020

Conventional researches on the behavior of fiber-reinforced and unreinforced soils often investigated the failure point. In this study, a concept is proposed in the comparison of the fiber-reinforced with unreinforced sand, by estimating the strength and strength ratio at different levels of strain. A comprehensive program of laboratory drained triaxial compression test was performed on compacted sand specimens, with and without date palm fiber. The fiber inclusion used in triaxial test specimens was form 0.25%-1.0% of the sand dry weight. The effect of the fiber inclusion and confining pressure at 0.5%, 1.0%, 1.5%, 3.0%, 6.0%, 9.0%, 12%, and 15% of the imposed strain levels on the specimen were considered and described. The results showed that, the trend and magnitude of the strength ratio is different for various strain levels. It also implies that, using failure strength from peak point or the strength corresponding to the axial strain of approximately 15% for evaluating the enhancement of strength or strength ratio, due to the reinforcement, may cause hazard and uncertainty in practical design. Therefore, it is necessary to consider the strength of fiber-reinforced specimen at the imposed strain level, compared to the unreinforced specimen.

• Geomechanics and Engineering
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• v.18 no.2
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• pp.133-140
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• 2019

Strain-rate and temperature have significant effects on the one-dimensional (1D) compression behavior of soils. This paper focuses on the bonding degradation effect of soil structure on the time and temperature dependent behavior of soft structured clay. The strain-rate and temperature dependency of preconsolidation pressure are investigated in double logarithm plane and a thermal viscoplastic model considering the combined effect of strain-rate and temperature is developed to describe the mechanical behavior of unstructured clay. By incorporating the bonding degradation, the model is extended that can be suitable for structured clay. The extended model is used to simulate CRS (Constant Rate of Strain) tests conducted on structural Berthierville clay with different strain-rates and temperatures. The comparisons between predicted and experimental results show that the extended model can reasonably describe the effect of bonding degradation on the stain-rate and temperature dependent behavior of soft structural clay under 1D condition. Although the model is proposed for 1D analysis, it can be a good base for developing a more general 3D model.

• Transactions of Materials Processing
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• v.20 no.1
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• pp.73-78
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• 2011

The flashing reduces the part quality and the productivity of the molding process. We developed a contact pressure sensor to detect the flashing immediately. The performance of the sensor was analyzed in a simple 2D simulation. The sensor was applied to an automotive bumper mold with cavity pressure sensors. It showed sensitive output signal for the mold response by the cavity pressure change. It was confirmed that the flashing at the gate area occurred in the filling stage by the pressure increase due to growth of the melt flow length. The sensor output was correlated with the cavity pressure sensor output.