• 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 $1000^{\circ}C$.

• Proceedings of the Korean Geotechical Society Conference
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• 1998.05a
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• pp.3-34
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• 1998

The stability condition of rock slopes is greatly affected by the geometry and strength parameters of discontinuities in the rock masses. Rock slopes Involving movement of rock blocks on discontinuities are failed by one or combination of the three basic failure modes-plane, wedge, and toppling. In rock mechanics, practically all the parameters such as the joint set characteristics, the rock strength properties, and the loading conditions are always subject to a degree of uncertainty. Therefore, a reasonable assessment of the rock slope stability has to include the excavation of the multi-failure modes, the consideration of uncertainties of discontinuity characteristics, and the decision on stabilization measures with favorable cost conditions. This study was performed to provide a new numerical model of the deterministic analysis, reliability analysis, and reliability-based optimization for rock slope stability. The sensitivity analysis was carried out to verify proposed method and developed program; the parameters needed for sensitivity analysis are design variables, the variability of discontinuity properties (orientation and strength of discontinuities), the loading conditions, and rock slope geometry properties. The design variables to be optimized by the reliability-based optimization include the cutting angle, the support pressure, and the slope direction. The variability in orientations and friction angle of discontinuities, which can not be considered in the deterministic analysis, has a greatly influenced on the rock slope stability. The stability of rock slopes considering three basic failure modes is more influenced by the selection of slope direction than any other design variables. When either plane or wedge failure is dominant, the support system is more useful than the excavation as a stabilization method. However, the excavation method is more suitable when toppling failure is dominant. The case study shows that the developed reliability-based optimization model can reasonably assess the stability of rock slopes and reduce the construction cost.

• Magazine of the Korean Society of Agricultural Engineers
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• v.26 no.1
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• pp.29-37
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• 1984

This study was made to find several significant relations among various physical and mechanical properties including cone penetration resistance. The alluvial clay samples were taken at the Daebul Reclaimed Tideland in Samhomyeon, Yeongamgun, Jeonranamdo. The results of the study are summarized as follows; 1.Most samples belong to medium or high plastic, inorganic, silty clay(clay contents;32-64%, silt contents; 36-68%, sand contents; 0-3%). The specific gravities range from 2.70 to 2.73, the unit weights from 1.45 to 1. 75g/cm$^3$, the natural moisture contents from 45 to 77%, the liquid limits from 32 to 56%. It is certain that the foundation is weak because the natural moisture contents are much higher than the liquid limits. 2.It is known from the shear tests that the unconfined compression strenghs vary from 0.09 to 0. 38kg/cm2, the cohesions from 0.05 to 0. 21kg/cm2, the internal friction angles from 0 to 3˚. 3.The consolidation tests show that the initial void ratios range from 1.25 to 2.28, the compression indeices from 0.43 to 0.84, the preconsolidation loads from 0.21 to 0.74kg/cm$^2$. 4.Cone penetration resistances are usually less than 5kg/cm$^2$ from ground surface to the depth of about 8m, and from S to l0kg/cm$^2$ in the layer below about 8m to hard layer. 5.The cohesion and cone penetration resistance are in proportion to the depth of soil layer. 6.The correlations between various physical and mechanical properties including cone penetration resistance for the alluvial clay samples are as follows; a) Wn=0.944C+ l2.733 (r=0.829) b) LL=0. 728Cy+6. 991 (r=0. 873) c) PI=0.659Cy-8.168 (r=0.860) d) rt=0. 0077(272-Wn) =2.092-0. 0077Wn (r=0. 859) e) 60=0. 035wn-0 447 (r=0. 893) f) C=0.380qw+0.031 (r=0.816) g) qu=0.0707qc+0.029 (r=0.810) h) C=0.018Z+0.055 (r=O.802) I) qc=0. 415Z+1, 438 (r=0. 943)

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.1
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• pp.99-109
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• 2015

In the construction industry, the interest for recycling aggregates is rising as more people demand for alternatives due to lack of supply of natural aggregates and environmental problems. However, in order for recycled aggregates to be used in infrastructures, stability and other factors need to be verified. Therefore, the objective of this study is to analyze the sensitivity of soil properties to secure slope safety according to various heights of embankment when bottom ash and dredged soil mixture is applied in the embankment. In most cases, all heights were safe for the slide for the embankment whether the water level is full or sudden draw down. The result of the sensitivity analysis revealed that the unit weight of embankments is highest among all factors to be considered. However, the sensitivity of the unit weight became smaller and the sensitivity of the friction angle of embankments increased with the height of embankments. The sensitivity of factors of core materials is very small because the core has weaker physical properties than those of the embankment. The effect of the height for each factor is different for each slope and water levels. The sensitivity of the unit weight of embankments is most affected when the height is 60m in the upstream slope. To conclude, bottom ash and dredged soil mixture can be applied in the embankment and different factors must be considered in different scale because the sensitivity depends highly on the height of embankments.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.221-227
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• 2001

Both strength and stiffness of RC structures strengthened by a steel plate greatly increase and however, their ductility might not be sufficient because premature failures usually occur at the adhesive-concrete interface. In this study, Mohr-Coulomb criterion was adopted to examine the bonding failure mechanism, and the diagonal shear bonding test, the direct shear bonding test, and the flexural test on RC beams strengthened by a steel plate were carried out to measure the bonding properties. It is found from the experimental and numerical results that the cohesive strengths of epoxy-concrete interfaces are ranging from 50 kgf/㎠ to 70 kgf/㎠ when the friction angle is 45°. Bonding failure loads can be predicted by applying the bonding properties to the structural analysis of RC beams strengthened by steel plate. By considering them in the design of strengthened beams, the premature failure would be effectively prevented.

• Geomechanics and Engineering
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• v.5 no.6
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• pp.575-594
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• 2013

Organic soils exhibit problematic properties such as high compressibility and low shear strength; these properties may cause differential settlement or failure in structures built on such soils. Organic soil removal or stabilization are the most important methods to overcome geotechnical problems related to peat soils' engineering characteristics. This paper presents soil mechanical intervention for stabilization of peat with sand columns and focuses on a comparison between the mechanical characteristics of undisturbed peat and peat stabilized with 20%, 30% and 40% of sand on the laboratory scale. Cylindrical columns were extruded in different diameters through a nearly undisturbed peat sample in the laboratory and filled with sand. By adding sand columns to peat, higher permeability, higher shear strength and a faster consolidation was achieved. The sample with 70% peat and 30% sand displayed the most reliable compressibility properties. This can be attributed to proper drainage provided by sand columns for peat in this specific percentage. It was observed that the granular texture of sand also increased the friction angle of peat. The addition of 30% sand led to the highest shear strength among all mixtures considered. The peat samples with 40% sand were sampled with two and three sand columns and tested in direct shear and consolidation tests to evaluate the influence of the number and geometry of sand columns. Samples with three sand columns showed higher compressibility and shear strength. Following the results of this laboratory study it appears that the introduction of sand columns could be suitable for geotechnical peat stabilization in the field scale.

• Journal of Fashion Business
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• v.11 no.3
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• pp.79-86
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• 2007

The purpose of this study is to understand the dyeing properties and color analysis of fabrics knitted with ramie, cotton, wool and acrylic by using scoria and to analyze whether the knitted fabrics can be used for industrialization by measuring color fastness after and before sliver-nano process. The following is the conclusions. Firstly, when ramie fabric regarding cotton, wool and acrylic was dyed at the temperature of $50^{\circ}C$ for fifteen minutes by using 10, 25, 50, 100g/ $\ell$ of scoria, dyeing absorption gradually increased up to 50g/ $\ell$, and over the point of 50g/ $\ell$ it showed slow increase. Secondly, regarding saturation, among ramie fabric, wool, cotton and acrylic, wool appears as the lowest brightness. Therefore, it can be dyed with bright color and the highest value. In terms of the value of chromaticity, wool also emerges as the lowest brightness. On the contrary, acrylic showed the lightest red as it had the value of the smallest b. Cotton takes the lightest yellow as the b value of the cotton showed the smallest. Thus, scoria dyestuff is a material that showed strong red and yellow on knitted fabric mixed with wool that is the biggest a. b value. Thirdly, in terms of dyeing fastness, sunlight fastness did not show noticeable differences before and after silver-nano processes, but in terms of washing and friction fastness, the material processed by silver-nano indicated that all knitted fabrics are over 4-5 point. which means silver-nano process can be effective for the industrial applications. As mentioned above, as a result of dyeing knitted fabrics with scoria, this study found a possibility of dyeing in the fabric materials, and if there is deeper dyeing experiments, fastness experiments and speculations, it might be possible to be a big issue just like loess and charcoal.

• Journal of the Korean institute of surface engineering
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• v.51 no.4
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• pp.249-255
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• 2018

High temperature and low temperature gaseous nitriding was performed in order to study of the surface hardening and wear properties of the nitrided AISI 410 Martensitic stainless steels. High temperature gaseous nitiridng (HTGN) was carried out using partial pressure $N_2$ gas at $1,100^{\circ}C$ for 10 hour, and Low temperature gaseous nitiridng (LTGN) was conducted in a gas mixture of NH3 and N2 at $470^{\circ}C$ for 10 hour. The nitrided samples were characterized by microhardness measurements, optical microscopy and scanning electron microscopy. The phases were identified by X-ray diffraction and nitrogen concentration was analyzed by GD-OES. The HTGN specimen had a surface hardness of about $700HV_{0.1}$, $350{\mu}m$ of case depth. A ${\sim}50{\mu}m$ thick, $1,250HV_{0.1}$ hard nitrided case formed at the surface of the AISI 410 steel by LTGN, composed nitrogen supersaturated expanded martensite and ${\varepsilon}-Fe_{24}N_{10}$ iron nitrides. Additionally, the results of the wear tests, carried out LTGN specimen was low friction coefficient and high worn mass loss of ball. The increase in wear resistance can be mainly attributed to the increase in hardness and to the lattice distortion caused by higher nitrogen concentration.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.206-211
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• 2012

Graphene has recently received high attention as a promising material for various applications, and many related studies have been undertaken to reveal its basic mechanical properties. However, the tribological properties of graphene film fabricated by the chemical vapor deposition (CVD) method are barely known. In this study, the contact angle and frictional wear characteristics of graphene coated copper film were investigated under room temperature, normal air pressure, and no lubrication condition. The contact angle was measured by sessile drop method and the wear test was carried out under normal loads of 660 mN and 2940 mN, respectively. The tribological behaviors of a graphene coating layer were also examined. Compared to heat treated bare copper foil, the graphene coated one shows a higher contact angle and lower friction coefficient.

• Corrosion Science and Technology
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• v.18 no.5
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• pp.212-219
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• 2019

This paper reviews recent approaches to develop composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE). The features of the unique approaches to form the composite polymer-containing coating on the surface of MA8 magnesium alloy were summarized. Improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of the surface layers and solid lubrication effect of the SPTFE particles. Such multifunctional coatings have high corrosion resistance ($R_p=3.0{\times}10^7{\Omega}cm^2$) and low friction coefficient (0.13) under dry wear conditions. The effect of dispersity and ${\xi}$-potential of the nanoscale materials ($ZrO_2$ and $SiO_2$) used as electrolyte components for the plasma electrolytic oxidation on the composition and properties of the coatings was investigated. Improvement in the protective properties of the coatings with the incorporated nanoparticles was explained by the greater thickness of the protective layer, relatively low porosity, and the presence of narrow non-through pores. The impedance modulus measured at low frequency for the zirconia-containing layer (${\mid}Z{\mid}_{f=0.01Hz}=1.8{\times}10^6{\Omega}{\cdot}cm^2$) was more than one order of magnitude higher than that of the PEO-coating formed in the nanoparticles-free electrolyte (${\mid}Z{\mid}_{f=0.01Hz}=5.4{\times}10^4{\Omega}{\cdot}cm^2$).