• Journal of the Korean GEO-environmental Society
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• 제11권12호
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• pp.5-11
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• 2010

If the groundwater in rock joint is changed into ice, it induces the stress increment by volume increase. Also, if the ice is changed into groundwater again, the stress in joint decreases by volume decrease. The accumulated displacement and fatigues of joints are increased by the stress-hysterisis, induced from the continuous frost-thawing. Also the shear strength is decreased by them continuously. The stress-hysterisis is affected by the atmospheric temperature changes, whose behavior is visco-elasticity, usually. Therefore, Kelvin model could be used to analyze the frost-thawing behavior in winter. The measured data of total 5 points are examined, which are composed of 3 points of shallow joints and 2 points of deep joints. Because shallow weathered rocks have many joints, a lot of Kelvin model are connected and the behaviors are complicated. In case of deep joints, simple Kelvin model is applied and the behaviors are also simple.

• KOREAN JOURNAL OF CROP SCIENCE
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• 제47권2호
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• pp.75-79
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• 2002

This study conducted to elucidate the change of the cation content (Na$^{+}$, $K^{+}$, and $Ca^{2+}$), the L-proline content, and the sugar and starch content in the stems, roots, and leaves of three cultivars of the 30 days old seedling soybeans (Glycine max L. cv. Danwonkong, Hwang-keumkong, and Kwangankong) after 100 mM NaCl stress containing 1/2 Hoaglands nutrient solution in the sand culture. The reduction of the dry matter weight after 100 mM NaCl treatment among cultivars was higher in the order of Kwangankong, Danwonkong, and Hwang-keumkong. The highest reduction of the dry matter weight was occurred at the roots among three parts of plant. The Na$^{+}$ content increased with NaCl treatment in overall and specially greatly increased in roots and stems. The $K^{+}$ and $Ca^{2+}$ content decreased with NaCl treatment at the roots and stems. The $K^{+}$ content, however, at the leaves increased in all three cultivars with the NaCl treatment. The L-proline content with NaCl stress increased greatly. The increment of the L-proline content at the stems and roots of Hwangkeumkong was lower than that of other two cultivars, K wangankong and Danwonkong. The sugar content decreased with NaCl treatment at the stems and leaves. The starch content also decreased at the stems and leaves with NaCl treatment.aCl treatment.

• Structural Engineering and Mechanics
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• 제32권3호
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• pp.459-475
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• 2009

This paper presents analytical methodologies for remaining life prediction of plain concrete structural components considering tension softening and size effects. Non-linear fracture mechanics principles (NLFM) have been used for crack growth analysis and remaining life prediction. Various tension softening models such as linear, bi-linear, tri-linear, exponential and power curve have been presented with appropriate expressions. Size effect has been accounted for by modifying the Paris law, leading to a size adjusted Paris law, which gives crack length increment per cycle as a power function of the amplitude of a size adjusted stress intensity factor (SIF). Details of tension softening effects and size effect in the computation of SIF and remaining life prediction have been presented. Numerical studies have been conducted on three point bending concrete beams under constant amplitude loading. The predicted remaining life values with the combination of tension softening & size effects are in close agreement with the corresponding experimental values available in the literature for all the tension softening models.

• Journal of Welding and Joining
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• 제32권6호
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• pp.41-46
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• 2014

In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s (WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with ${\gamma}+Cr7C3$ eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.

• Proceedings of the Korean Society For Composite Materials Conference
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• 한국복합재료학회 2001년도 추계학술발표대회 논문집
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• pp.158-162
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• 2001

The effects of chemical treatment on Kevlar-29 fibers have been studied in a composite system. The surface characteristics of the Kevlar-29 fibers were characterized by pH, acid-base value and X-ray photoelectron spectroscopy (XPS). The mechanical interfacial properties of final composites were studied by interlaminar shear strength (ILSS) and critical stress intensity factor ($K_{IC}$). Also, the impact properties of the composites were investigated in the differentiating studies between initiation and propagation energies, and ductile index (DI) along with maximum farce and total energy. It was found that the chemical treatment with phosphoric acid ($H_3PO_4$) solution significantly affected the degree of adhesion at interfaces between fibers and resin matrix, resulting in improving the mechanical interfacial strength of the composites. This was probably due to the presence of chemical polar groups on Kevlar surfaces, leading to an increment of interfacial binding force in a composite system.

• Proceedings of the KSME Conference
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• 대한기계학회 2004년도 추계학술대회
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• pp.202-207
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• 2004

An elastic-plastic finite element analysis of fatigue crack closure is performed for plane strain conditions. The stabilization behavior of crack opening level and the effect of mesh size on the crack opening stress are investigated. In order to obtain a stabilized crack opening level for plane strain conditions, the crack must be advanced through approximately four times the initial monotonic plastic zone. The crack opening load tends to increase with the decrease of mesh size. The mesh size nearly equal to the theoretical plane strain cyclic plastic zone size may provide reasonable numerical results comparable with experimental crack opening data. The crack opening behavior is influenced by the crack growth increment and discontinuous opening behavior is observed. A procedure to predict the most appropriate mesh size for different stress ratio is suggested. Crack opening loads predicted by the FE analysis based on the procedure suggested resulted in good agreement with experimental ones within the error of 5 %. Effect of the distance behind the crack tip on the crack opening load determined by the ASTM compliance offset method based on the load-displacement relation and by the rotational offset method based on the load-differential displacement relation is investigated. Optimal gage location and method to determine the crack opening load is suggested.

• Composites Research
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• 제13권2호
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• pp.51-60
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• 2000

Filament wound pressure vessels have been studied for the efficient design tool to consider the variation of fiber angles through-the thickness direction. Filament winding patterns were simulated from semi-geodesic fiber path equation to calculate fiber path on arbitrary surface. Finite element analyses were performed considering fiber angle variation in longitudinal and thickness directions by ABAQUS. For the finite element modeling of the pressure tank, the 3-dimensional layered solid element was utilized. From the stress results of pressure tanks, maximum stress criterion in transverse direction was applied to modify material properties for failed region. In the end of each load increment, resultant layer stresses were compared with a failure criterion and properties were reduced to 1/10 for a failed layer. Results of progressive failure analysis were compared with two experimental data.

• KSTLE International Journal
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• 제6권1호
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• pp.28-32
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• 2005

The electrorheoloRical (ER) fluids are composed of a colloidal dispersion of polarizable particles in insulating oil, and it's the rheological property changes by the applied electric field. These changed are reversible and occur fast within a fewmilliseconds. The ER properties of the ER fluid such as increment of viscosity and yield stress come from the particle chain structure induced by electric fleld. When formulating the ER fluid for a speciflc application, some requirement must besatisfled, which are high yield stress under electric field, rapid response, and dispersion stability. While this characteristic makes valuable ER fluids in valious industrial applications, their lung term and quiescent application has been limited because ofproblems with particle sedimentation. In an effort to overcome sedimentation problem of ER fluids, the anhydrous ER materials of monodispersed hollow polyaniline (PANI) and adipate derivative respectively with submicron-sized suspension providing wide operating temperature range and other advantage were synthesized in a four-step procedure. The ER fluidswere characterized by FT-lR, TGA, DLS, SEM, and TEM. Stability of the suspensions was examined by an UV spectroscopy.The rheological and electrical properties of the suspension were investigated Couette-type rheometer with a high voltagegenerator, current density, and conductivity. And the behavior of ER suspensions was observed by a video camera attached toan optical microscope under 3kV/mm. The suspensions showed good ER properties, durability, and particle dispersion.

• Geomechanics and Engineering
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• 제19권6호
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• pp.533-542
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• 2019

Geosynthetic reinforced soil method in coarse-grained soils has been widely used in last decades. Two effective factors on soil-geosynthetic interaction are confining stresses and loading rate in clay. In terms of methodology, one pull-out test with four different strain rates, namely 0.75, 1.25, 1.75 and 2.25 mm/min, and three different normal stresses equal to 20, 50, and 80 kg have been performed on specimens with dimensions of 30×30×17 cm in the saturated, consolidated condition. The obtained results have demonstrated that activation of geosynthetic strength at contact surface depends on the applied stress. In addition, the increase in normal stress would increase the shear strength at contact surface between clay and geogrid. Moreover, it is concluded that the strain rate increment would increase the shear strength.

• The Journal of Korean Medicine
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• 제23권2호
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• pp.139-150
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• 2002

OBJECTIVES : Schizandra chinensis is well known for its efficacy at liver function reinforcement, relieving thirst and recovery from fatigue. In this study, we examined the effects of sports drink containing Schizandra chinensis on serum metabolic substrate, electrolyte, stress indicators, related-enzyme and exercise performance, rectal temperature, and heat shock proteinb70 (HSP70). METHODS : Elite long-distance runners (male, 21.3yrs, n=16) were selected and divided into two groups; an experimental group (EXP, n=8) and a control group (CON, n=8). A beverage containing Schizandra chinensis was supplemented 3 times per day to EXP for 4 weeks. Serum biochemical elements (glucose, lactate, total cholesterol, triglyceride, high density lipoprotein cholesterol, glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, creatinine, creatine phosphokinase, lactate dehydrogenase, blood urea nitrogen, Na, K, Cl) were analyzed by auto blood analyzer. Exercise performance was measured by treadmill exercise test, HSP70 was detected by electrophoresis and Western blotting, and rectal temperature was measured by rectal temperature probe. RESULTS : Administration of the beverage increased significantly the rest level of blood Na, Cl and glucose and decreased significantly lactate dehydrogenase, glutamate oxaloacetate transaminase. No difference was found in exercise performance, rectal temperature increment or HSP70 concentration between groups. CONCLUSIONS : Administration of a sports drink containing Schizandra chinensis altered blood glucose, lactate dehydrogenase, glutamate oxaloacetate transaminase, Na and Cl levels.