• Transactions of the Korean Society of Automotive Engineers
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• v.22 no.2
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• pp.141-147
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• 2014

This study aims to investigate the influence of bevel angles on the fatigue life of V-groove butt-welded joints with back-plates made by SM490A steel material, generally used for excavators, because changes in the geometry, material and surface properties of welded regions affect the fatigue life of welded structures. Butt type test specimens were prepared by the $CO_2$ welding of rolled steel plates (SM50A steel) with a thickness of 13.5 mm at a welding speed of 30 cm/min and these Butt type test specimens had two different groove angles, which are $40^{\circ}$ (A type) and $30^{\circ}$ (B type). In order to investigate differences in fatigue life between two types, 4-point bending fatigue tests were conducted with a stress ratio of R=0.1 under the cyclic loading environment at a frequency of 5 Hz at room temperature. The fatigue life of A type specimens was approximately 7% higher than that of B type specimens. The stress concentration factors calculated by finite element analysis were 2.16 for A type and 2.25 for B type, whose difference was caused by the influence of the back-plates of butt-welded structures. The current results could provide important guidelines to determine the V-groove angle of butt-welded joints with a satisfactory fatigue life, although under severe operating conditions.

• Journal of the Korean Wood Science and Technology
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• v.24 no.3
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• pp.18-27
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• 1996

The feasibility of using stress-wave technique in the transverse direction for the assessment of early stages of decay was investigated using compression test specimens having different annual ring orientations subjected to decay by Tyromyces palustris for various time intervals. Decay detection, quantitative assessment of decay, and the prediction of residual strength of decayed wood with less than five percent weight loss can be feasible using stress-wave parameters (wave velocity, wave impedance, and stress-wave elasticity) and their percent reduction due to decay, measured by stress-wave technique in the transverse direction. The use of stress-wave technique in the transverse direction for the application of this technique to structural members in service is desirable, when considering the easiness of attachment of accelerometers of stress-wave measuring device on the surface of members and also accurate detection of localized decayed areas. In stress-wave technique in the transverse direction, stress-wave parameters measured were different according to the angles between wave propagation path and annual ring, due to the anisotropy of wood structure. Therefore, it is recommended to use percent reduction in stress-wave parameters instead of stress-wave parameters. This evaluation method using percent reduction in stress-wave parameters is ideal when it is impossible to observe annual ring orientation on the transverse surface of wood.

• Korean Journal of Soil Science and Fertilizer
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• v.46 no.4
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• pp.260-269
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• 2013

Two single-crystals of fully dehydrated, partially $Li^+$-exchanged zeolites X (Si/Al = 1.09, crystal 1) and Y (Si/Al = 1.56, crystal 2), were prepared by flow method using 0.1 M $LiNO_3$ at 393 K for 48 h, respectively, followed by vacuum dehydration at 673 K and $1{\times}10^{-6}$ Torr. Their structures were determined by single-crystal X-ray diffraction techniques in the cubic space group $Fd\bar{3}$ and $Fd\bar{3}m$ at 100(1) K for crystals 1 and 2, respectively. They were refined to the final error indices $R_1/wR_2$ = 0.065/0.211 and 0.043/0.169 for crystals 1 and 2, respectively. In crystal 1, about 53 $Li^+$ ions per unit cell are found at three distinct positions; 9 at site I', 19 at another site I', and the remaining 25 at site II. The residual 25 $Na^+$ ions occupy three equipoints; 2 are at site I, 7 at site II, and 16 at site III'. In crystal 2, about 31 $Li^+$ ions per unit cell occupy sites I' and II with occupancies at 22 and 9, respectively; 3, 4, 23, and 3 $Na^+$ ions are found at sites I, I', II, and III', respectively. The extent of $Li^+$ ion exchange into zeolite X (crystal 1) is higher than that of zeolite Y (crystal 2), ca. 73% and 56% in crystals 1 and 2, respectively.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.407-414
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• 2007

Using the MPI (Moldflow Plastics Insight) software from Moldflow Co., the optimum conditions for producing the upper part of the automobile air cleaner were obtained for 20% talc filled polypropylene (PP). The analysis was carried out to solve the cracking problem between upper and lower parts and the improved process was proposed using the flow balance. The comparative results between the conventional process, CASE-1, with one-pin gate and the new process (CASE-2) comprising two-pin gate system are the followings. In the case of CASE-2, the shorter filling time and reduced cycle time induced an improved production and processibility. In addition, the orientation and volumetric shrinkage are similar to those observed in the lower part, but the assembly, deformation, and physical characteristics are enhanced. The problem induced by the CASE-1 did not originate from the residual stress, but from the difference in the size of the upper part air cleaner after shrinkage. Thus, the orientation problem was expected to improve by optimizing the gate structure.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.21 no.2
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• pp.137-145
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• 2003

Currently, the availability of 3-D topographical survey by combination of GPS and Echo Sounder has been increased in the various field like as the construction of structure, the dredging and the reclamation in the ocean and river, and observation of topographic change in seabed or riverbed. In this case, the error of depth sounding can divide in form that is happened by combination of GPS and Echo Sounder, and form that is happened in Echo Sounder itself, In this study, in the case happen by Echo Sounder itself, analyzed error by specially about geological features of the seabed and riverbed that is specular surface of sound wave and wished to present solution way. The sounding error about the echo sounder and characteristic of estuary riverbed was found by understanding the relation of average diameter and residual error and we defined correction formula, Y=-0.00474$^{*}$In(X) -0.0045 by the regression analysis. and then we verified applicability of correction formula. As the result, if measure Preliminary investigation or pre-survey the geological features for the survey area at topographical survey of estuary riverbed, we presented the error correction formula that estimate and can correct of error by Echo Sounderer.

• Journal of the Korean institute of surface engineering
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• v.32 no.2
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• pp.144-156
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• 1999

Thermal Barrier Coating with Functional Gradient Materials (FGM-TBC) can play an important role to protect the parts from harmful environments in high temperatures such as oxidation, corrosion, and wear and to improve the efficiency of aircraft engine by lowering the surface temperature on turbine blade. FGM-TBC can increase the life spans of product and improve the operating properties. Therfore, in this study the evaluations of mechanical and thermal properties of FGM-TBC such as fatigue, oxidation and wear-resistance at high temperatures have been conducted. The samples of both the TBC with 2, 3, 5 layers (YSZ/NiCrAlY) to be produced by Air Plasma Spray method (APS) and the bulk TBC with 6 layers to be produced by Plasma Assisted Sintering method (PAS) were used. Furthermore, residual stress, bond strength, and thermal conductivity were evaluated. The average thickness of the APS was 500$\mu\textrm{m}$ to 600$\mu\textrm{m}$ and the average thickness of the PAS was 3mm. The hardness number of the top layer of APS was 750 Hv to 810Hv and that of PAS was 950 Hv to 1440Hv. The $ZrO_2$ coating layer of APS was composed of tetragonal structure after spraying as the result of XRD analysis. As shown in the results of the high temperature wear test, the 3 layer coating of APS had the best wear resistance at $800^{\circ}C$ and the 5 layer coating of APS had the best wear resistance at $600^{\circ}C$. But, these coatings had the tendency of the low-temperature softening at $300^{\circ}C$. The main mechanism of wear was the adhesive wear and the friction coefficient of coatings was increased as increasing the test temperatures. A s results of thermal conductivity test, the ${\Delta}T$ of the APS coating was increased as number of layer and the range of thermal conductivity of the PAS was $800^{\circ}C$ to $1000^{\circ}C$.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.5-12
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• 2006

This study was conducted to investigate the effect of operational parameters such as dosage of magnesium and phosphate, pH, reaction time and existence crystal core for the removal of nitrogen and phosphorus in anaerobic fermentation supernatant by struvite crystallization. Optimal mole ratio of $Mg^{2+}:NH_4{^+}:PO_4{^{3-}}$ was 1.2:1.0:1.2. Under the optimal molar ratio, removal ratio and reaction rate constant of $NH_4{^+}-N$ and $PO_4{^{3-}}-P$ were 79.2, 96.8%, 0.157 and $0.344min^{-1}$, respectively. Optimal pH and reaction time were 11 and 10 minutes, respectively, in the optimal molar ratio. Residual concentration of $NH_4{^+}-N$ and $PO_4{^{3-}}-P$ showed lowest value with 1 g/L of crystal core addition. SEM analysis of struvite crystallization with crystal core showed higher crystal core growth than that of without crystal core. Struvite precipitate proved to be orthorhomic crystal structure by XRD analysis.

• Elastomers and Composites
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• v.38 no.4
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• pp.295-302
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• 2003

The amount of shrinkage of injection molded parts is different from operational conditions of injection molding such as injection temperature, injection pressure and mold temperature, and mold design such as gate size. It also varies depending on the presence of crystalline structure in resins. In this study, part shrinkage was investigated for various operational conditions and resins. Poly(butylene terephthalate) (PBT) for crystalline polymer, and polycarbonate (PC) and poly(methyl methacrylate) (PMMA) for amorphous polymers were used. Crystall me polymer showed higher part shrinkage by about three times than that of amorphous polymers. Part shrinkage increased as melt and molt temperatures increased, and injection pressure decreased. Part shrinkage decreased as gate size increased since the pressure delivery is mush easier for larger gate sizes. Part shrinkage at the position close to the gate was larger than that or the position far from gate. This phenomenon might be occur by difference of residual stress.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.70.1-70.1
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• 2012

In-situ X-ray photoelectron spectroscopy (XPS) and infrared (IR) spectroscopy studies of SOFC cathode materials will be discussed in this presentation. The mixed conducting perovskites (ABO3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC). However, the details of the oxygen reduction reaction are still not clearly understood. The information about the type of adsorbed oxygen species and their concentration is important for a mechanistic understanding of the oxygen incorporation into these cathode materials. XPS has been widely used for the analysis of adsorbed species and surface structure. However, the conventional XPS experiments have the severe drawback to operate at room temperature and with the sample under ultrahigh vacuum (UHV) conditions, which is far from the relevant conditions of SOFC operation. The disadvantages of conventional XPS can be overcome to a large extent with a "high pressure" XPS setup installed at the BESSY II synchrotron. It allows sample depth profiling over 2 nm without sputtering by variation of the excitation energy, and most importantly measurements under a residual gas pressure in the mbar range. It is also well known that the catalytic activity for the oxygen reduction is very sensitive to their electrical conductivity and oxygen nonstoichiometry. Although the electrical conductivity of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (Po2), in-situ measurements of the conductivity of these materials in contact with the electrolyte as a SOFC configuration have little been reported. In order to measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance is required for excluding the leakage current of the substrate. It is also hardly possible to measure the conductivity of cracked thin film by electrical methods. In this study, we report the electrical conductivity of perovskite $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in-situ IR spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current to the substrate and cracks in the film.

• Polymer(Korea)
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• v.26 no.6
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• pp.701-709
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• 2002

To synthesize a new positive photosensitive polyimide precursor, parts of carboxylic acid groups in poly (amic acid) were esterified with 4,5-dimethoxy-2-nitrobenzyl bromide in the presence of K$_2$CO$_3$/HMPA followed by the chemical imidization of residual carboxylic acid units. The chemical structure of resulting polymer was characterized by $^1$H-NMR, UV/vis and FT-IR spectroscopic methods, and its thermal properties were examined by DSC and TGA. Upon UV irradiation, 4,5-dimethoxy-2-nitrobenzyl moiety underwent the photodegradation. As a result, the polymer became soluble in alkaline developer due to the formation of carboxylic acid moiety, which was used to make a micron-sized positive pattern. Sensitivity curves were obtained from the gel fraction experiments with respect to the various 4,5-dimethoxy-2-nitrobenzyl ester contents. From those curves, the sensitivity was ranged iron 4000 to 6000 mJ/㎠, and the contrast was measured to be from 3.1 to 4.9.