• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.4
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• pp.421-428
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• 2012

In this study, the effects of surface oxide film formation on the fatigue behavior of 7075-T6 aluminum alloy were analyzed in terms of the corrosion time of the alloy. The aluminum material used is known to have high corrosion resistance due to the passivation phenomenon that prevents corrosion. Aluminum alloys have been widely used in various industrial applications such as aircraft component manufacturing because of their lighter weight and higher strength than other materials. Therefore, studies on the fatigue behavior of materials and passivation properties that prevent corrosion are required. The fatigue behavior in terms of the corrosion time was analyzed by using a four-pointing bending machine, and the surface corrosion level of the aluminum material in terms of the corrosion time was estimated by measuring the surface roughness. In addition, fractographic analysis was performed and the oxide films formed on the material surface were studied by scanning electron microscopy (SEM). The results indicated that corrosion actively progressed for four weeks during the initial corrosion phase, the fatigue life significantly decreased, and the surface roughness increased. However, after four weeks, the corrosion reaction tended to slow down due to the passivation phenomenon of the material. Therefore, on the basis of SEM analysis results, it was concluded that the growth of the surface oxide film was reduced after four weeks and then the oxide film on the material surface served as a protection layer and prevented further corrosion.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.11
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• pp.1011-1020
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• 2017

This study was conducted to investigate the material properties of stainless steel 316L specimens of untreated and UNSM treated material, hydrogen attacked material(100 bar, $300^{\circ}C$ at 120 h) and UNSM treated hydrogen attacked material at room temperature. Results demonstrated that the hydrogen attacked materials showed a tendency toward a slightly decreased fatigue strength, while the hydrogen embrittlement effect was smaller than the S-N curve of conventional untreated material. As compared to untreated material, the fatigue limit of the UNSM treated material increased by 43.8%, while it was 57.1％ higher in the UNSM treated hydrogen attacked material than in untreated hydrogen attacked material. The plastic deformation layer was ${\sim}152{\mu}m$ thick, as confirmed by maps showing the level of local plastic deformation affected by the UNSM treatment in three ways: an image quality map, inverse pole figure map, and kernel average misorientation map captured via electron back scatter diffraction. Owing to hydrogen embrittlement, about 90％ of surface cracks were smaller than the average grain size of $35{\mu}m$.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.37 no.6
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• pp.550-556
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• 1992

Performance of a rice breeding line, Milyang 95 was evaluated at four cultural methods, direct seeding on dry soil covered by making ridges (DS ridged), direct seeding on dry soil covered by rotortilling (DS rotary), direct seeding on flooded soil (FS), and machine transplanting (MT). Days from seeding to emergence in both DS ridged and DS rotary was 15 days. The number of seedlings at DS ridged and DS rotary was lower than that at FS. Heading was earliest at MT, latest at DS rotary and DS ridged, and that at FS was between them. Days from seeding to heading was 115 days at MT, 94-95 days at DS ridged and DS rotary, and 87 days at FS. Lodging index was similar among the cultural methods and lodging was not occurred in the field although fresh weight of tillers and breaking strength at MT were higher than those of direct seedings. Yield and most of yield components were similar among the cultural methods although the number of spikelets per panicle at MT was higher and 1,000 grain weight at FS was lower compared to other cultural methods. Grain appearance (rusty, chalky abortive rice), protein and amylose contents and alkali digestibility were observed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.9-14
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• 2017

In the present work, a mechanical performances under cyclic loading in RC (Reinforced Concrete) beams with normal steel and FRPH (Fiber Reinforced Plastic Hybrid) bar are investigated. For the work, RC beam members with $200{\times}200{\times}2175mm$ of geometry and 24 Mpa of design strength are prepared, and 4-point-bending tests are performed for evaluation of cracking, yielding, and ultimate loads. Through static loading test, 48.9kN and 36.0 kN of yielding loads are measured for normal RC and FRPH beam, respectively. They have almost same ultimate load of 50.0 kN. Typical tension hardening behavior is observed in FRPH beam, which is caused by the behavior of FRPH bar with tension hardening. In cyclic loading conditions, FRPH beam has more smaller crack width and scattered crack pattern, and it shows more elastic recovery than normal RC beam. The energy dissipation ratio in FRPH beam is 0.83, which is greater than 0.62 in normal RC beam and it shows more effective resistance to cyclic loadings.

• Journal of the Korean Wood Science and Technology
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• v.37 no.3
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• pp.184-191
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• 2009

In the southern part of the Korean Peninsula including Jeju-island, the production amount of domestic cedar has increased gradually. However, their low qualities, expected to be caused by the low density and frequent knots, have restricted their practical utilization as the high value-added products. In this study, it is aimed to look for the new uses of domestic cedar and to examine the applicability for lamination lumbers of structural glued laminated timber (glulam). Above all, machine stress ratings for individual sawn lumbers confirmed that modulus of elasticity (MOE) of cedar lumber was lower than that of other common softwood species in Korea. On the other hand, cedar lumbers have enough stiffness to manufacture the structural glulam in accordance with Korean Industrial Standard (KS). The bonding strength and durability also met the KS limitation. Nevertheless, from the result of bending tests for cedar glulam, it was shown that the modulus of elasticity (MOE) did not meet the KS limitation. Therefore, it was concluded that additional researches were needed for reinforcing the stiffness of cedar glulam.

• Journal of the Korea Concrete Institute
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• v.28 no.6
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• pp.655-663
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• 2016

The present study shows the moment-average curvature relationship and effective inertia moment of RC beams obtained from the nonlinear analysis based on the parabola-rectangular stress-strain curve defined in EC-2 code. The variables examined are concrete strength and steel ratio, and moment-average curvature relationship and effective inertia moment obtained are compared with those of the current KCI provisions. As the results of the comparison, the followings could be said: Since the KCI provisions(the Branson method) were originally derived based on the experimental data ranged from 2.2 to 4 of $M/M_{cr}$ and 1.3 to 3.5 of $I_{ut}/I_{cr}$, thereby within these ranges the inertia moments obtained from the nonlinear analysis are closely agreed with those predicted by the Branson method. However, beyond those range the remarkable difference could be found between the two results. In particular, for beams having low steel ratio the inertia moment resulted from the nonlinear analysis are significantly smaller than those obtained from the KCI(Branson) method. This result may imply that the deflection of lightly reinforced members, such as slabs in buildings, becomes much larger than those calculated according to the current design provisions.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.97-105
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• 1999

In the binary system of SiC and carbon, porosity and pore size distribution of green body was controlled by varying pH, by the addition of polyelectrolyte dispersants, and by using different particle size of starting powders. The preforms having different green microstructure were fabricated by slip casting from suspensions having different dispersion condition. The reaction bonding process was carried out for these preforms. The condition of reaction bonding was 1600$^{\circ}C$ and 20 min. under vacuum atmosphere. The analyses of optical and SEM were studied to investigate the effect of green microstructure on that of reaction bonded silicon carbide and subsequently the mechanical properties of sintered body was investigated. Different green microstructures were obtained from suspensions having different dispersion condition. It was found that the pore size could be remarkably reduced for a fine SiC(0.5$\mu\textrm{m}$). The bimodal microstructure was not found in the present study, which is frequently observed in the typical reaction bonded silicon carbide. It is considered that the ratio between SiC and C was responsible for the formation of bimodal microstructure. For the preform fabricated from the well dispersed suspension, the 3-point bending strength of reaction-bonded silicon carbide was 310${\pm}$40 MPa compared to the specimen fabricated from relatively agglomerated particles having lower value 260${\pm}$MPa.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.4
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• pp.369-376
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• 2003

In this paper, a nonlinear structural analysis for the composite structure composed of the spent nuclear fuel disposal canister and the 50㎝ thick bentonite buffer is carried out to predict the collapse of the canister while the horizontal symmetric sudden rock movement of 10㎝ is applied on the composite structure. This sudden rock movement is anticipated by the earthquake etc. at a deep underground. Elastoplastic material model is adopted. Drucket-Prager yield criterion is used for the material yield prediction of the bentonite buffer and von-Mises yield criterion is used for the material yield prediction of the canister(cast iron, copper). Analysis results show that even though very large deformations occur beyond the yield point in the bentonite buffet, the canister structure still endures elastic small strains and stresses below the yield strength. Hence, the 50㎝ thick bentonite buffet can protect the canister safely against the 10㎝ sudden rock movement by earthquake etc.. Analysis results also show that bending deformations occur in the canister structure due to the shear deformation of the bentonite buffer.

• Korean Journal of Construction Engineering and Management
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• v.16 no.6
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• pp.136-143
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• 2015

Snow-melting system has been applied not only to roads for car traffic but also to pavement for the pedestrians safety reason in some of the developed countries such as USA and Canada based on countermeasures against Natural Disasters Act revised in 2000. Even though this system was introduced in korea in 2006 and has been partly applied to car traffic roads, there is few places that the system has been applied. Therefore, in this research a snow-melting system with a block-type to cover a pavement that efficiently transfers heat form heat rays to the top of a pavement and protects the heat rays. A quality check showed that compression and bending strength was improved approximately 5 times stronger and 7 to 10 times more absorption rate than the KS(Korea Industrial Standard) requirement. Moreover, only 10 minute was required to increase temperature above zero with a block-type snow-melting system whereas approximately 180 minute was spent with the existing system. This research is expected to contribute to environmental issues and reduce accidents on a slippery road.

• Journal of the Microelectronics and Packaging Society
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• v.17 no.1
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• pp.9-17
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• 2010

In this study, von Mises stress and total strain energy density characteristics of lead pin in PGA (Pin Grid Array) packages have been calculated by using the FEM (Finite Element Method). FEM computation is carried out with various heat treatment conditions of lead pin material under $20^{\circ}$ bending and 50 mm tension condition. Results show that von Mises stress locally concentrated on lead pin corners and interface between lead pin head and solder. von Mises stress and total strain energy density decrease as heat treatment temperature of lead pin increases. Also, round shaped corner of lead pin decreases both von Mises stress and total strain energy density on interface between lead pin head and solder. This means that PGA package reliability can be improved by changing the mechanical property of lead pin through heat treatment. This has been known that solder fatigue life decreases as total strain energy density of solder increases. Therefore, it is recommended that both optimized lead pin shape and optimized material property with high lead pin heat treatment temperature determine better PGA package reliability.