• Journal of the Korean Society for Precision Engineering
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• v.27 no.11
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• pp.46-56
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• 2010

The present research works investigated into the low velocity impact characteristics of DP 780 high strength steel sheet with 1.7 mm in thickness subjected to free boundary condition using three-dimensional finite element analysis. Finite element analysis was carried out via ABAQUS explicit code. Hyper-elastic model and the damping factor were introduced to improve an accuracy of the FE analysis. An appropriate FE model was obtained via the comparison of the results of the FE analyses and those of the impact tests. The influence of the impact energy and nose diameter of the impact head on the force-deflection curves, impact time, absorption characteristics of the impact energy, deformation behaviours, and stress-strain distributions was quantitatively examined using the results of FE analysis. The results of the FE analysis showed that the absorption rate of impact energy lies in the range of the 70.7-77.5 %. In addition, it was noted that the absorption rate of impact energy decreases when the impact energy increases and the nose diameter of the impact head decreases. The local deformation of the impacted region was rapidly increased when the impact energy was larger than 76.2 J and the nose diameter was 20 mm. A critical impact energy, which occur the instability of the DP780, was estimated using the relationship between the plastic strain and the impact energy. Finally, characteristics of the plastic energy dissipation and the strain energy density were discussed.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.4
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• pp.211-226
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• 2015

Membrane type Mark III cargo containment system (CCS) is considered in this study to investigate its strength capability under applied loads due to liquefied natural gas (LNG) cargo. A rectangular plated structure supported by inner hull structure is exemplified from Mark III CCS according to classification society's guidance and it is assumed as multi-layered structure by stacking plywood, triplex, reinforced polyurethane (PU) foam and series of mastic upon inner hull structure. Commercially available general purpose finite element analysis package is used to have reliable FE models of Mark III CCS plate. The FE models and anisotropic failure criteria such as maximum stress, Hoffman, Hill, Tsai-Wu and Hashin taking into account the direction dependent material properties of Mark III CCS plate components and their material properties considering a wide variation of temperature due to the nature of LNG together form the strength analysis procedure of Mark III CCS plate. Strength capability of Mark III CCS plate is understood by its initial failure and post-initial failure states. Results are represented in terms of failure loads and locations when initial failure and post-initial failures are occurred respectively. From the results the basic design information of Mark III CCS plate is given.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.10a
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• pp.436-439
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• 2005

Condenser tube has been used as a component of heat exchanger in automobile and air conditioning apparatus. In this paper, porthole die extrusion that is advantageous to form long hollow section tube is analyzed by direct extrusion of condenser tube with 12 holes. A study on extrusion process is performed through the 3D FE simulation at non-steady state and extrusion experiments. Especially, weldability, extrusion load and die defects were estimated try FE-simulation. This study present the redesigned die of direct extrusion in consideration of the results obtained from FE-analysis.

• Journal of Ocean Engineering and Technology
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• v.21 no.2 s.75
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• pp.50-59
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• 2007

Steam generator tubes are degraded from wear, stress corrosion cracking, rupture and fatigue and so on. Therefore, the failure assessment of steam generator tube is very important for the integrity of energy plants. In the steam generator tubes, sometimes, the local wall thinning may result from severe degradations such as erosion-corrosion damage and wear due to vibration. In this paper, the elasto-plastic analysis was performed by FE code ANSYS on steam generator tubes with wall thinning. Also, the four-point bending tests were performed on the wall thinned specimens, and then it was compared with the analysis results. We evaluated the failure mode, fracture strength and fracture behavior from the experiment and FE analysis. Also, it was possible to predict the crack initiation point by estimating true fracture ductility under multi-axial stress conditions at the center of the thinned area from FE analysis.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.320-325
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• 2004

Fracture behaviors and strength of pipes with local wall thinning are very important Jar the integrity of energy plants. In pipes of energy plants, sometimes, the local wall thinning may result from severe erosion-corrosion damage. Recently, the effects of local wall thinning on strength and fracture behaviors of piping system have been well studied. In this paper, the elasto-plastic analysis is performed by FE code ANSIS. We evaluated the failure mode, fracture strength and fracture behavior from FE analysis.

• Journal of Power System Engineering
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• v.10 no.3
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• pp.38-44
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• 2006

Failure assessment of steam generator tube are very important for the integrity of energy plants. In pipes of energy plants, sometimes, the local wall thinning may result from severe erosion-corrosion damage. Recently, the effects of local wall thinning on fracture strength and fracture behavior of piping system have been well studied. In this paper, the elasto-plastic analysis is performed by FE code ANSIS on steam generator tube with wall thinning. We evaluated the failure mode, fracture strength and fracture behavior from FE analysis. It was possible to predict the crack initiation point by estimating true fracture ductility under multi-axial stress conditions at the center of the thinned area.

• Steel and Composite Structures
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• v.25 no.5
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• pp.545-556
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• 2017

The tubed steel reinforced concrete (SRC) column is a composite column in which the outer steel tube is mainly used to provide confinement on the core concrete. This paper presents experimental and analytical studies on the behavior of circular tubed SRC (TSRC) columns subjected to axial compression. Eight circular TSRC columns were tested to investigate the effects of length-to-diameter ratio (L/D) of the specimens, diameter-to-thickness ratio (D/t) of the steel tubes, and use of stud shear connectors on the steel sections. Elastic-plastic analysis on the steel tubes was used to investigate the mechanism of confinement on the core concrete. The test results indicated that the tube confinement increased the strength and deformation capacity for both short and slender columns, and the effects on strength were more pronounced for short columns. A nonlinear finite element (FE) model was developed using ABAQUS, in which the nonlinear material behavior and initial geometric imperfection were included. Good agreement was achieved between the predicted results using the FE model and the test results. The test and FE results were compared with the predicted strengths calculated by Eurocode 4 and the AISC Standard. Based on the analytical results, a new design method for this composite column was proposed.

• Journal of the Korean institute of surface engineering
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• v.31 no.1
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• pp.34-44
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• 1998

Stainless steel is being used widely lor various purposes due to its good corrosion resistance. There has becn much research to produce colored stainless sterl by several methods. In this experiment, we coated TixN film on the SUS304 substrate with thc DC magnetron sputtering system and studied the internal structurc and adhesive strength of the films as a function of the coating conditions. Before lhe specimen was coated, a sputter etching was very effective in removing the$\delta$ Fe(BCC) phase as well as the contaminant and oxide layer as well as increasing rotghness. Five-stage failure mode appeared with increased scratch load with the TIN films coated on the SUS304 in this manner ; tensile failure-,conformal failure-,buckling failure->chipping failurc and spalling Failure. When the failure was terminated at the initial stage, the film will have good adhesion. But, if syalling failure has occurred at the initial scratch, then the adhesion will be poor. The interlayer between thc coated film and thc substratc was homogeneously adhcsive when the $\gamma'-Fe_4N$ phase wasn't detected in the XRD analysis and the adhesive strength only was reduced by surPace defects. But, when the ,$\gamma'-Fe_4N$N phasc was detected in the XRD analysis, the adhesive strength was very poor.

• Computers and Concrete
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• v.25 no.5
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• pp.461-470
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• 2020

This paper presents a numerical study on structural behavior of hammer head pier cap beams, extended on verges and reinforced with carbon fiber reinforced polymer (CFRP) plates. A 3-D finite element (FE) model along with a simplified analytical model are presented. Concrete damage plasticity (CDP) was adapted in the FE model and an analytical approach predicting the CFRP anchor strength was adapted in both FE and analytical model. Total five quarter-scaled pier cap beams with various CFRP reinforcing schemes were experimentally tested and analyzed with numerical approaches. Comparison between experimental results, FE results, analytical results and current ACI guideline predictions was presented. The FE results showed good agreement with experimental results in terms of failure mode, ultimate capacity, load-displacement response and strain distribution. In addition, the proposed strut-and-tie based analytical model provides the most accurate prediction of ultimate strength of extended cap beams among the three numerical approaches.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.3
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• pp.47-58
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• 2024

This study were conduced experimentally to analyze the heat-generating performance, flexural strength, and microstructure of conductive mortar mixed with micro steel fiber and multi-wall carbon nanotube (MWCNT). In the conductive mortar heat-generating performance and flexural strength tests, the mixing concentration of MWCNT was selected as 0.0wt%, 0.5wt%, and 1.0wt% relative to the weight of cement, and micro steel fibers were mixed at 2.0vol% relative to the volume. The performance experiments were conducted with various applied voltages (DC 10V, 30V, 60V) and different electrode spacings (40 mm, 120 mm) as parameters, and the flexural strength was measured at the curing age of 28 days and compared and analyzed with the normal mortar. Furthermore, the surface shape and microstructure of conductive mortar were analyzed using a field emission scanning electron microscope (FE-SEM). The results showed that the heat-generating performance improved as the mixing concentration of MWCNT and the applied voltage increased, and it further improved as the electrode spacing became narrower. However, even if the mixing concentration of MWCNT was added up to 1.0 wt%, the heat-generating performance was not significantly improved. As a result of the flexural strength test, the average flexural strength of all specimens except the PM specimen and the MWCNT mixed specimens was 4.5 MPa or more, showing high flexural strength due to the incorporation of micro steel fibers. Through FE-SEM image analysis, Through FE-SEM image analysis, it was confirmed that a conductive network was formed between micro steel fibers and MWCNT particles in the cement matrix.