• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.421-429
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• 1985

This study has been made to investigate into the relation between fatigue crack behavior and ferrite grain size. As experimental observation of the low-carbon steel specimen with the drilled micro-hole under rotating bending stress was made to accomplish this investigation. Obtained results are as follows; (1) The fatigue limit of micro-hole depends upon the magnitude of ferrite grain size, as indicated by the Hall-Petch formula. (2) The fatigue crack occurring around the micro-hole is of shear type, and the frequency of fatigue crack initiation depends upon the ferrite grain size. (3) The magnitude of ferrite grain size affects the behavior of fatigue crack propagation up to the crack size of 0.3mm. The effect, however, is negligible for the crack size larger than 0.3mm.

• Journal of the Korean institute of surface engineering
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• v.24 no.1
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• pp.24-24
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• 1991

Cr-N films were deposited on low-carbon steel sheets by the reactive arc-induced ion plating (AIIP). The influence of the deposition conditions (nitrogen pressure and substrate bias voltage) on the crystal orientation, morphology and microhardness of the Cr-N films has been investigated using x-ray diffractometer and scanning electron microscope. The impurities and contaminations on the surface and at the interface, and the layer-by-layer compositions of the film have been analyzed using scanning Auger multiprobe (SAM) and glow discharge spectroscope (GDS). The mixed state of Cr and Cr2N turned out to have a fine fibrous structure. The Cr2N films were deposited at a wide range of nitrogen flow rates. The orientations of Cr2N films were mainly (110) and (111), and the intensity of the (111) peak increased as the substrate bias voltage increased. The micorstructure of the Cr2N film was dense and no columnar structure was observed. The films in the mixed state of Cr2N and CrN were also dense without columnar structure. The maximum microhardness of the Cr-N films was 2400 kg/$\textrm{mm}^2$ at 10gf load.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.4
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• pp.113-119
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• 2001

Ammonia emissions during composting of hog manure mixed with sawdust were studied in four runs comprising a total of 22 pilot-scale reactor vessels. These four runs extended previous work and both verified and extended the previous conclusions. The pilot-scale vessels were 205 L insulated stainless steel drums that were aerated either continuously (high/low thermostatically controlled fans) or intermittently (5 min high fan 55 min off). Temperature ammonia emissions air flow rates carbon dioxide production and oxygen utilization moisture and dry matter reduction initial and final chemical compositions were measured. Ammonia emissions from the intermittently aerated vessels were only about 50% as great as those from the continuously aerated ones but this was found to be a result more related to total air flow than to aeration technique. All of the data for total result more related to total air flow were fitted with a linear regression line y=0.139x+29.835 where y is ammonia expressed as g of N and x is air flow in kg with $R^2$=0.6808. this general trend indicates that about 50% reduction in ammonia emissions can be achieved with 75% reduction in air flow. For the aeration techniques used the minimum oxygen level in te exhaust gas from the vessels was 5% and this is probably a resonable lower limit constraining air flow reduction. However within this constraint lower air flow now appears to be a technique that can reduce odorous ammonia emissions.

• Applied Chemistry for Engineering
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• v.10 no.8
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• pp.1119-1123
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• 1999

In this paper, electrorefining of uranium metal was studied to develop pyrometallurgical processing technology in molten salt system. The reaction between uranium metal and $CdCl_2$ was taken about 3 hours and the uranium metal deposits were obtained in the form of dendrite grown on the cathode surface in every electrotransport experiment. The shapes of dendrite were changed according to the applied voltages. Current efficiency was decreased with the increase of current density. Deposition rate was not changed after 6 hours and its maxium was obtained at $100{\sim}150mA/cm^2$ of current density and about 75 rpm of stirring speed, respectively. Also, the current efficiency was increased with decrease of the pitch of spiral groove curved on cathode.

• Journal of the Korean Society for Heat Treatment
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• v.13 no.2
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• pp.91-97
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• 2000

The structure and mechanical properties of TiN and TiCN thin films deposited on STD61 steel substrates by the RF-sputtering methods has been studied by using XPS, XRD, micro-hardness tester, scratch tester, and wear-resistance tester. XPS results showed that the TiCN thin film formed with chemical bonding state. The TiN thin films grew with (111) orientation having the lowest strain energy by compressive stress, whereas the TiCN thin films grew with both (111) and (200) orientation, but (200) orientation having the lowest surface energy becomes dominant as carbon contents increase. The pre-etching treatment of substrate did not affect on the preferred orientation of thin films, but it played an important role in improving mechanical properties of thin films such as the hardness, adhesion and wear- resistance. Especially, the TiCN thin films showed the superior wear resistances due to high hardness and low friction coefficient compared with TiN thin films.

• Journal of the Korean institute of surface engineering
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• v.25 no.1
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• pp.24-33
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• 1992

Cr-N films were deposited on low-carbon steel sheets by the reactive arc-induced ion plating (AIIP). The influence of the deposition conditions (nitrogen pressure and substrate bias voltage) on the crystal orientation, morphology and microhardness of the Cr-N films has been investigated using x-ray diffractometer and scanning electron microscope. The impurities and contaminations on the surface and at the interface, and the layer-by-layer compositions of the film have been analyzed using scanning Auger multiprobe (SAM) and glow discharge spectroscope (GDS). The mixed state of Cr and Cr₂N turned out to have a fine fibrous structure. The Cr₂N films were deposited at a wide range of nitrogen flow rates. The orientations of Cr₂N films were mainly (110) and (111), and the intensity of the (111) peak increased as the substrate bias voltage increased. The microstructure of the Cr₂N film was dense and no columnar structure was observed. The films in the mixed state of Cr₂N and CrN were also dense without columnar structure. The maximum microhardness of the Cr-N films was 2400 kg/㎟ at 10 gf load.

• Journal of Welding and Joining
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• v.20 no.5
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• pp.78-86
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• 2002

A metallurgical model for the prediction of prior austenite grain size considering the dissolution kinetics of M$_3$C precipitates at the heat affected zone of SA508-cl.3 was proposed. The isothermal kinetics of grain growth and dissolution were respectively described by well-known equation, $dD/dT=M({\Delta}F_{eff})^M$ and Whelan's analytical model. The isothermal grain growth experiments were carried out for measure the kinetic parameters of grain growth. The precipitates of the base metal and the specimens exposed to thermal cycle were examined by TEM-carbon extraction replica method. The model was assessed by the comparison of BUE simulation experiments and showed good consistencies. However, there was no difference between the model considering and ignoring $M_3C$ precipitates. It seems considered that pinning force exerted by $M_3C$ Precipitates was lower than driving force for grain growth due to large size and small fraction of precipitates, and mobility of grain boundary was low in the lower temperature range.

• International Journal of Concrete Structures and Materials
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• v.11 no.2
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• pp.247-259
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• 2017

This paper presents a fatigue assessment model that was developed for corroded reinforced concrete (RC) beams strengthened using prestressed carbon fiber-reinforced polymer (CFRP) sheets. The proposed model considers the fatigue properties of the constituent materials as well as the section equilibrium. The model provides a rational approach that can be used to explicitly assess the failure mode, fatigue life, fatigue strength, stiffness, and post-fatigue ultimate capacity of corroded beams strengthened with prestressed CFRP. A parametric analysis demonstrated that the controlling factor for the fatigue behavior of the beams is the fatigue behavior of the corroded steel bars. Strengthening with one layer of non-prestressed CFRP sheets restored the fatigue behavior of beams with rebar at a low corrosion degree to the level of the uncorroded beams, while strengthening with 20- and 30%-prestressed CFRP sheets restored the fatigue behavior of the beams with medium and high corrosion degrees, respectively, to the values of the uncorroded beams. Under cyclic fatigue loading, the factors for the strengthening design of corroded RC beams fall in the order of stiffness, fatigue life, fatigue strength, and ultimate capacity.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.4
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• pp.56-68
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• 2014

This paper presents an experiment on the modeling, analysis, prediction and optimization of machining parameters used during the turning process of the low-carbon steel known as ST40. The parameters used to develop the model are the cutting speed, the feed rate, and the depth of the cut. The experiments were carried out under various conditions, with three level of parameters and two different treatments for each level (with and without a lubricant), to determine the effects of the parameters on the surface roughness and electric current consumption. These effects were investigated using response surface methodology (RSM). A second-order model is used to predict the values of the surface roughness and the electric current consumption from the results of experiments which collected preliminary data. The results of the experiment and the predictions of the surface roughness and electric current consumption under both treatments were found to be nearly identical. This result shows that the feed rate is the main factor that influences the surface roughness and electric current consumption.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.12 no.6
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• pp.84-92
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• 2013

This study improves the formability in fine-blanking the lock plate of car seat belts using a low carbon steel(SM35C) plate. The optimal die design for the forming process is proposed using rules for process planning based on theories and field experiences. The optimal design is analyzed using commercial finite element software in order to solve the fracture problems in the extrusion process. Through the improved layout based on the FEM results, the fracture of the extruded part and the roll over problem are solved. Furthermore, it is demonstrated through the shown from experiments that the extruded part does not break in the modified die.