• Journal of Animal Science and Technology
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• v.62 no.5
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• pp.659-667
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• 2020

This study was conducted to evaluate the effects of different levels of crude protein (CP) and protease on nitrogen (N) utilization, nutrient digestibility, and growth performance in growing pigs. A total of six crossbred ([Landrace × Yorkshire] × Duroc) barrows were individually accepted in 1.2 m × 0.7 m × 0.96 m stainless steel metabolism cages. The pigs (average initial body weight of 27.91 ± 1.84 kg) randomly assigned to six diets with six weeks (6 × 6 Latin square design). The experiment was carried out in an environment with a temperature of 23 ± 1.5℃, a relative humidity of 83 ± 2.3% and a wind speed of 0.25 ± 0.03 m/s. The dietary treatments were arranged in a 2 × 3 factorial design with two levels of CP (15.3% or 17.1%) and three levels of protease (0 ppm, 150 ppm, or 300 ppm). The average daily gain and gain to feed ratio (G:F) tended to increase (p = 0.074) with increasing amounts of protease. The low CP level diet reduced (p < 0.050) urinary and fecal N concentrations, the total N excretion in feces, and increased (p < 0.050) N retention. Different protease levels in the diet did not affect (p > 0.05) at N intake, but supplementation of the diets with 300 ppm protease decreased (p < 0.050) the N concentration in urine and feces and tended to increase (p = 0.061) the percentage of N retention retained of the total N intake. The dietary CP level did not affect (p > 0.050) the apparent total tract digestibility (ATTD) of dry matter, digestible energy (DE), and metabolic energy (ME), but diet supplementation with 300 ppm protease showed higher (p < 0.050) ATTD of DE and ME than in the protease-free diet. Therefore, a low protein diet with protease could improve the utilization of nitrogen, thereby reducing the negative effect of N excretion into the environment while maintaining or increasing growth performance compared to a high protein diet.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.1
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• pp.126-132
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• 2018

This paper discusses about results of advanced buckling strength design for several kinds of perforated plated in the twin-hull car-ferry. For medium / small sized high speed vessels with a length of more than 50 meters and a length / width ratio of more than 12, such as car-ferries, it is highly possible that the buckling strength becomes weak due to the relatively thin thickness and the use of low strength capacity such as mild steel. Especially, it becomes big problem about weak buckling rigidity around the opening to access purpose in the perforated. As regarding safety design point of view for perforated plate, it is necessary to clarify buckling strength and ultimate strength by the distribution of in-plane load distribution around the opening. In this study, nonlinear series analysis using ANSYS was performed to clarify the influence of parameters such as aspect ratio, opening ratio and opening shape affecting the buckling and ultimate strength characteristics of the perforated plate under axial compression and we are derived the optimum design as buckling strength point of view. Based on these results, the governing factor determining the buckling strength of the perforated plate was the opening ratio, and the aspect ratio and the shape of the hole were not influenced.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.3
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• pp.31-38
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• 2010

In this study, it is suggested that it has to reliability-based design methodology with respect to bridge structure-rail longitudinal interaction and bridge structure-vehicle interaction. For the structural analysis, commercial package, ABAQUS, are used for a three-dimensional finite element analysis. The optimization process utilizes a well-known optimizer, ADS(Automated Design Synthesis). Optimization technique is utilized the ALM-BFGS method for global area search and Golden Section Method for 1-D search. In general, ALM-BFGS method don't need the 1-D search, and that algorithm converge a 0.1~0.2 of Push-Off factor. But in this study, value of Push-Off factor is used 90, therefore 1-D search should be needed for effective convergency. That algorithm contains the "heuristic decision method". As a result of optimum design of 2-main steel girder birdge with 5${\times}$(1@50m), design methodology suggested in this study was demonstrated more economic and efficient than existing design and LCC optimization not considering bridge-rail longitudinal interaction and bridge-vehicle interaction.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.774-780
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• 1999

The study of bond behavior between concrete and rebar has been performed for a long time. On this study, we tried to analysed variation of bond behaviors quantitatively with varying the strength of concrete. Bond stress which observed below the neutral surface of beam and at connecting part of beam and column is affected by various bond parameters. Resistance of deformed bars which embedded in concrete to the pullout force is divided 1) chemical adhesive force 2) frictional force 3) mechanical resistance of ribs to the concrete and these horizontal components of resistance is being bond strength. We selected the most common and typical variable which is concrete strength among various variables. So we used two kinds of concrete strength like as 25MPa(NSC) and 65MPa(HSC). Tension Test was performed to verify how bond behavior varied with two kinds of concrete strength. Concentration of bond stress was observed at load-end commonly in Tension Test of the initial load stage. At this stage stress distribution was almost coincident at each strength. As tension load added, this stress distribution had difference gradually and movement of pick point of bond stress to free-end and central section was observed. This tendency was observed at first and moving speed was more fast in NSC. At the preceeding result the reason of this phenomenon is considered to discretion of chemical adhesion and local failure of concrete around rebar in load-end direction. Especially, when concrete strength was increased 2.6 times in tension test, ultimate bond strength was increased 1.45 times. In most recent used building codes, bond strength is proportioned to sqare root of concrete compressive strength but comparison of normalized ultimate bond strength was considered that the higher concrete strength is, the lower safety factor of bond strength is in each strength if we use existing building codes. In Tension Test, in case of initial tensile force state, steel tensile stress of central cross section is not different greatly at each strength but tensile force increasing, that of central cross section in NSC was increased remarkably. Namely, tensile force which was shared in concrete in HSC was far greater than that of concrete in NSC at central section.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.10
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• pp.1265-1273
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• 1999

PIV(Particle Image Velocimetry) velocity field measurements inside the snout of a1/10 scale model of the Zn plating process were carried out at the strip speed $V_s=1.5m/s$. Aluminum powder particles ($1{\mu}m$) and atomized olive oil ($3{\mu}m$) were used as seeding particles to simulate the molten Zinc flow and deoxidization gas flow, respectively. A pulsed Nd:Yag laser and a $2K{\times}2K$ high-resolution CCD camera were synchronized for the PIV velocity field measurement. From flow visualization study, it is found that the liquid flow in the Zn pot is dominantly governed by the uprising flow caused by the rotating sink roll, with its effect on the steel strip inside the snout largely diminished by installing of the snout. The deoxidization gas flow in front of the strip inside the snout can be characterized by a large-scale vortex rotating clockwise direction formed by the moving strip. In the rear side of the strip, a counter-clockwise vortex is formed and some of the flow entrained by the moving strip impinges on the free surface of molten zinc. The liquid flow in front of the strip is governed by the flow entering the snout, caused by the spinning sink roll. Just below the free surface a counter-clockwise vortex is formed near the snout wall. The moving strip affects dominantly the flow behind the strip inside the snout, and large amount of the liquid flow follows the moving strip toward the sink roll. The thickness of the flow following the strip is very thin in the front side due to the uprising flow, however thick boundary layer is formed in the rear side of the strip. Its thickness is increased as moving downstream toward the sink roll. Inside the snout, the deoxidization gas flow above the free surface is much faster than the liquid flow in the zinc pot. Due to the larger influx of the flow following the moving strip in the rear side of the strip, higher percentage of imperfection can be anticipated on the rear surface of the strip.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.762-771
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• 1987

Friction welding is a fusion process in which the necessary heat is generated by clamping one of the two pieces to be welded in a stationary chuck and rotating the other at high speed with an axially applied load. It is essentially a variation of the pressure welding process but utilizes a novel heating method. In addition to the foregoing advantages, it has also been reported excellent for welding dissimilar materials. Therefore, this study reported on investigating the strength behavior for the frictionally welded domestic structural steel SM45C and SUS304. The results obtained by the experiments are as follows. (1) The highest tensile strength of the best friction welded specimen (B4) is about 3% lower than that of SM-45C base metal, and 9% lower than that of SUS304 base metal. The heat treated specimens (850.deg.C 1hr A.C) have almost same value of tensile strength. (2) The strain of SM45C base metal is 27.3% and that of SUS304 is 42%, that of the best friction welded specimen (B4) appeared as 11.9% which is about 50% lower than the base metal, so, this same phenomenon apeared in all the other welding conditions. (3) The bending strength of SM45C base metal is 123kgf/mm$^{2}$ and that of SUS304 is 127kgf/mm$^{2}$. The best specimen (B4) appeared as 121kgf/mm$^{2}$ which is almost same bending strength for both base metals. (4) The friction welded condition involving maximum strength is determined by P$_{1}$=8kgf/mm$_{2}$, P$_{2}$=22kgf/mm$_{2}$, T$_{1}$=10sec, T$_{2}$=2sec, and amount of upset 7.6mm. (5) The interface of two dissimilar materials are mixed strongly, and welded zone is about 1.03mm and also the heat affected zone is about 2.36mm at SM45C while about 1.85mm at SUS304, therefore the welded zone and heat affected zone are very narrow to compare with those of the other welding materials.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.1
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• pp.6-13
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• 2012

HVOF thermal spray coating of 80%WC-CoFe powder is one of the most promising candidate for the replacement of the traditional hard chrome plating and hard ceramics coating because of the environmental problem of the very toxic $Cr^{6+}$ known as carcinogen by chrome plating and the brittleness of ceramics coatings. 80%WC-CoFe powder was coated by HVOF thermal spraying for the study of durability improvement of the high speed spindle such as air bearing spindle. The coating procedure was designed by the Taguchi program, including 4 parameters of hydrogen and oxygen flow rates, powder feed rate and spray distance. The surface properties of the 80%WC-CoFe powder coating were investigated roughness, hardness and porosity. The optimal condition for thermal spray has been ensured by the relationship between the spary parameters and the hardness of the coatings. The optimal coating process obtained by Taguchi program is the process of oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min and spray distance 8 inch. The coating cross-sectional structure was observed scanning electron microscope before chemical etching. Estimation of coating porosity was performed using metallugical image analysis. The Friction and wear behaviors of HVOF WC-CoFe coating prepared by OCP are investigated by reciprocating sliding wear test at $25^{\circ}C$ and $450^{\circ}C$. Friction coefficients (FC) of coating decreases as sliding surface temperature increases from $25^{\circ}C$ to $450^{\circ}C$.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.6
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• pp.752-757
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• 2017

Analysis has been performed for the penetration of a long-rod into MMC/Ceramic layered armour system with several shot test and a series of simulations. Two types of MMC plate have been fabricated by a liquid pressing method; A356/45%vol.%SiCp with a uniform distribution of SiC particle and Al7075/45%vol.B4Cp with B4C particle. The mechanical properties were measured with the high-speed split Hopkins bar test, hardness test and compression test. The popular Simplified Johnson-Cook model was adopted to represent the material characteristics for FEM simulations. The performance of the MMC applied armour system has been made by comparing with the semi-infinite mild steel target using the depth of penetration(DOP). The results show that placing ceramic front layer provides a certain gain in protection, and that placing another ductile front layer provides a further gain. The application of MMC is found to be attractive.

• Journal of the Korean Society for Railway
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• v.17 no.5
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• pp.355-364
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• 2014

The restrained volume changes of concrete due to variations of temperature and moisture produce transverse cracks in continuously reinforced concrete tracks (CRCTs). Such cracks are known to significantly affect the behaviors and long-term performance of CRCT. To investigate the effects of the transverse cracks on the behavior of CRCT and to develop more reasonable maintenance standards for cracks, in this study, the stress distribution of the track concrete layers (TCL) and the hydraulically stabilized base course (HSB) with transverse cracks were numerically predicted by a three dimensional finite element analysis when CRCT was subjected to train loads. The results indicate that the bending stresses of TCL and vertical stresses at the interfaces between TCL and HSB increased as the cracks were deepened. In addition, vertical stresses were locally concentrated near reinforcing steel in cracks in TCL when full-depth cracks developed, which may lead to punch-outs in CRCTs. Comparably, the effects of crack width and spacing were not as significant as crack depth. This study indicates that ensuring the long-term performance of CRCTs requires adequate maintenance not only for crack width and spacing but also for crack depth. Our results also show that locating HSB joints between sleepers is beneficial to the long-term performance of CRCTs.

• Korean Journal of Materials Research
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• v.28 no.12
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• pp.763-768
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• 2018

In this study, glass fibers are fabricated via a continuous spinning process using manganese slag, steel slag, and silica stone. To fabricate the glass fibers, raw materials are put into an alumina crucible, melted at $1550^{\circ}C$ for 2 hrs, and then annealed at $600^{\circ}C$ for 2 hrs. We obtain a black colored glass. We identify the non-crystalline nature of the glass using an XRD(x-ray diffractometer) graph. An adaptable temperature for spinning of the bulk marble glass is characterized using a high temperature viscometer. Spinning is carried out using direct melting spinning equipment as a function of the fiberizing temperature in the range of $1109^{\circ}C$ to $1166^{\circ}C$, while the winder speed is in the range of 100rpm to 250rpm. We investigate the various properties of glass fibers. The average diameters of the glass fibers are measured by optical microscope and FE-SEM. The average diameter of the glass fibers is $73{\mu}m$ at 100rpm, $65{\mu}m$ at 150rpm, $55{\mu}m$ at 200rpm, and $45{\mu}m$ at 250rpm. The mechanical properties of the fibers are confirmed using a UTM(Universal materials testing machine). The average tensile strength of the glass fibers is 21MPa at 100rpm, 31MPa at 150rpm, 34MPa at 200rpm, and 45MPa at 250rpm.