• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.709-716
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• 2023

In this paper, the shape factors of cellular meta-material plates (MMPs) having diverse cell arrays have been determined as the first attempt to finally examine their stability and vibrational frequencies. The MMPs are actually constructed from cylindrical or cubic cellular cores and two face sheets. Sandwich-like MMPs with circular and square holes in the face sheets have been selected in such a way that the effective material properties depend on the cellular architectures. For verifying the frequency results, finite element (FE) simulations are done in Abaqus software. Several graphical results have been represented to explore the effects of cellular architectures on vibrational frequencies and dynamic responses of the MMPs. Also, the deflection-frequency and stability curves in the case of forced vibrations have been plotted for diverse cell arrays.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.121-122
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• 2023

This study investigates the anti-corrosion properties of two eco-friendly pyridinium ionic liquids; 4DMN and 4DMP, in a 3.5% NaCl solution. Utilizing weight loss tests, EIS, PDP, quantum chemical calculations, and molecular dynamics simulations, the study demonstrates concentration-dependent inhibition efficiencies of 94% and 92% for 4DMN and 4DMP, respectively. The compounds modulate both anodic and cathodic reactions without altering the corrosion mechanism. EIS data suggest that a protective layer forms, supported by FE-SEM and AFM surface analyses, which reveal improved morphology and reduced roughness. Computational validations corroborate these empirical findings, highlighting the feasibility of these ionic liquids for effective, sustainable corrosion mitigation.

• Journal of the Korean Society for Advanced Composite Structures
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• v.2 no.4
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• pp.1-10
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• 2011

This study investigates the performance of composite (steel-concrete) frame structures through numerical experiments on individual connections. The innovative aspects of this research are in the use of connections between steel beams and concrete-filled tube (CFT)columns that utilize a combination of low-carbon steel and shape memory alloy (SMA) components. In these new connections, the intent is to utilize the recentering provided by super-elastic shape memory alloy tension bars to reduce building damage and residual drift after a major earthquake. The low-carbon steel components provide excellent energy dissipation. The analysis and design of these structures is complicated because the connections cannot be modeled as being simply pins or full fixity ones they are partial restraint (PR). A refined finite element (FE) model with sophisticated three dimensional (3D) solid elements was developed to conduct numerical experiments on PR-CFT joints to obtain the global behavior of the connection. Based on behavioral information obtained from these FE tests, simplified connection models were formulated by using joint elements with spring components. The behavior of entire frames under cyclic loads was conducted and compared with the monotonic behavior obtained from the 3D FE simulations. Good agreement was found between the simple and sophisticated models, verifying the robustness of the approach.

• Tunnel and Underground Space
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• v.32 no.6
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• pp.518-529
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• 2022

In Task C of the DECOVALEX-2023 project, nine institutes from six nations are developing their numerical codes to simulate thermo-hydro-mechanical coupled behavior for the FE experiment performed at Mont Terri underground rock laboratory, Switzerland. Currently, Step 1 for comparing the simulation results to field data is the ongoing stage, and we used the OGS-FLAC simulator for a series of numerical simulations. As a result, temperature increase depending on the heating hysteresis was well simulated, and saturation variation in the bentonite depending on phase change was observed. However, due to the suction overestimation, relative humidity and temperature change in the bentonite and the pressure variation in the Opalinus clay showed a difference compared to the field data. From the observation, it is confirmed that the effect of the bentonite capillary pressure is dominant to the flow analysis in the disposal system. We further plan to draw improved results considering tunnel support material and accurate initial water pressure distribution. Additionally, the thermal, hydrological, and mechanical anisotropy of the Opalinus clay was well simulated. From the simulation results, we confirmed the applicability of the OGS-FLAC simulator in the disposal system analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.2
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• pp.113-120
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• 2023

This paper introduces a simulation method for the collision between roadblocks and vehicles using LS-DYNA. The need to evaluate the performance of anti-ram barriers to prepare for vehicle impact has increased since vehicle impact threats have been included as a design criterion for nuclear power plants. Anti-ram barriers are typically certified for their performance through collision experiments. However, because Koreas has no performance testing facilities for anti-ram barriers, their performance can only be verified through simulations. LS-DYNA is a specialized program for collision simulation. Various organizations, including NCAC, distributes numerical models that have been validated for their accuracy with collision tests. In this study, we constructed a finite element model of the most critical vehicle barrier module and simulated collision between roadblocks and vehicles. The calculated results were verified by applying the validation criteria for vehicle safety facility collision simulations of NCHRP 179.

• Transactions of Materials Processing
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• v.21 no.3
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• pp.179-185
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• 2012

In this paper, it is proposed to produce high precision screws with a diameter of $800{\mu}m$ and a thread pitch of $200{\mu}m$ ($M0.8{\times}P0.2$) by means of a cold thread rolling process. In this part II of the study, the focus is on the production and reliability testing of the prototype $M0.8{\times}P0.2$ micro-screw. Designs for two flat dies were developed with the aid of the literature and previous studies. Process parameters during the cold thread rolling process were established through FE simulations. The simulation results showed that the threads of the micro-screw are completely formed through the rolling process. Prototype $M0.8{\times}P0.2$ micro-screw were fabricated with a high precision thread rolling machine. In order to verify the simulation results, the deformed shape and dimensions obtained from the experiment were compared with those from the simulations. Hardness and failure torque of the fabricated micro-screw were also measured. The values obtained indicate that the CAE based process design used in this paper is very appropriate for the thread rolling of micro-sized screws.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.539-546
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• 2016

In this paper, the effect of J-R curve changes on the determination of parameters in a failure model owing to the presence or absence of a side groove in a C(T) specimen is investigated. A stress-modified fracture strain model is implemented for FE damage simulations. C(T) specimens were taken from SA508 grade 1a low-alloy steel piping material, and some of them were processed with a side groove. Fracture toughness tests were performed at room temperature and at $316^{\circ}C$. The parameters of the failure model were determined by damage simulations using the J-R curves obtained from the tests. Finally, the results show that the determination of failure model parameters is not affected by variations in J-R curves owing to the presence or absence of a side groove.

• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2682-2695
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• 2021

This paper aims to evaluate the structural dynamic responses and damage/failure of the nuclear fuel reprocessing plant under the free drop impact of spent fuel cask (SFC) and fuel assembly (FA) during the on-site transportation. At the present Part I of this paper, the large-scale SFC model free drop test and the corresponding numerical simulations are performed. Firstly, a composite target which is composed of the protective structure, i.e., a thin RC plate (representing the inverted U-shaped slab in the loading shaft) and/or an autoclaved aerated concrete (AAC) blocks sacrificial layer, as well as a thick RC plate (representing the bottom slab in the loading shaft) is designed and fabricated. Then, based on the large dropping tower, the free drop test of large-scale SFC model with the mass of 3 t is carried out from the height of 7 m-11 m. It indicates that the bottom slab in the loading shaft could not resist the free drop impact of SFC. The composite protective structure can effectively reduce the damage and vibrations of the bottom slab, and the inverted U-shaped slab could relieve the damage of the AAC blocks layer dramatically. Furthermore, based on the finite element (FE) program LS-DYNA, the corresponding refined numerical simulations are performed. By comparing the experimental and numerical damage and vibration accelerations of the composite structures, the present adopted numerical algorithms, constitutive models and parameters are validated, which will be applied in the further assessment of drop impact effects of full-scale SFC and FA on prototype nuclear fuel reprocessing plant in the next Part II of this paper.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.149-154
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• 2007

The zinc prosphate film treatments used to lubricating treatment of mostly cold forging processes. But there are several problems happened to lubricating treatment process such as happening harmful environment on person, complex lubrication processing occurring in energy and time consumption, eco-destructive and chemical by-product generation, the needs of waste disposal etc. As a result, a water-soluble lubricant was developed to replace the perfect or some of the zinc prosphate film in the world. In order to solve these problems, this study evaluated the performance of the typical water-soluble. In this study, for these requirement inquiry of two part. First, about possibility of replace zinc phosphate lubricant, quantitatively evaluation developed of water-soluble lubricant for cold forging vs zinc phosphate lubricant. Second, About optimization of coating Process use to equipment with practicable automatic coating Process. The performance evaluation of these lubricants was conducted using the double cup extrusion test and spike forging test. With the use of the commercial FE code DEFORM, friction factor calibration curves, i.e. cup height ratio vs. punch stroke and spike height vs. punch stroke, were established for different friction factor values. By matching the cup height ratio and the punch stroke and spike height vs. punch stroke from experiment to that obtained from FE simulations, the friction factor of the lubricants was determined. Survey of comparative analysis use to SEM that sprayed lubricant surface structure of grain shape and characteristic of lubricant performance based on grain shape and deformed lubricant surface expansion. As a result, developed lubricant were found to perform comparable to or better than zinc phosphate. And thought this result, innovatively cope with generated problem of existing lubrication process.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.4
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• pp.567-572
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• 1998

The crystalline structure of $LaTi_{0.8}V_{0.2}O_3$ solid solutions, prepared by arc-melting palletized mixtures of predried $La_2O_3,\;V_2O_3,\;TiO_2$, and Ti, was investigated by transmission electron microscopy and computer image simulation. Computer image simulations were performed by the multislice method for a wide range of sample thickness and defocusing value. The structure of $LaTi_{0.8}V_{0.2}O_3$ was determined as a $GdFeO_3$-type orthorhombic $(a\approx5.58{\AA},\;b\approx7.89{\AA},\;and\;c\approx5.58{\AA})$ with a space group $P_{nma-}$. No evidence of ordering of Ti and V atoms in $SaTi_{0.8}V_{0.2}O_3$ was found.