• Tribology and Lubricants
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• v.28 no.1
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• pp.1-6
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• 2012

In this paper, a three elastic body sliding contact problem is modeled to investigate more precise wear mechanisms related with the sealing surface. A 3-D finite element contact model, a small spherical elastic particle, PTFE seal and steel surface, is solved using a nonlinear finite element code MARC. The deformed seal and steel surface shapes, von-Mises and principal stress distributions are obtained for different seal sliding distances. The entrapped small particle within PTFE seal results in very high stresses on the steel surface which exceeded its yield strength and produce plastic deformation such as groove and torus. The sealing surface could also be worn down by sub-surface fatigue due to intervening small particles together with the well-known abrasive wear. Therefore the proposed contact model adopted in this paper can be applied in design of various sealing systems, and further studies are required.

• Journal of the Korean Electrochemical Society
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• v.17 no.3
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• pp.187-192
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• 2014

In this article, we report the fabrication and characterization of $CNT/Co_3O_4$ nanocomposite for lithium ion batteries. We expected that the composition with CNT is effective method to compensate for the low electronic conductivity of $Co_3O_4$ and suppress the stress from phase transition of $Co_3O_4$ during cycling. $CNT/Co_3O_4$ nanocomposites were composed of nano-sized $Co_3O_4$ particles, which were homogeneously distributed on the surface of CNTs. The $CNT/Co_3O_4$ electrode presented higher capacity than commercial graphite, good rate capability and stable cyclic performance. This implies that the $CNT/Co_3O_4$ could be a promising anode material for lithium ion batteries.

• Journal of Ginseng Research
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• v.45 no.3
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• pp.442-449
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• 2021

Background: Panax ginseng is an important crop in Asian countries given its pharmaceutical uses. It is usually harvested after 4-6 years of cultivation. However, various abiotic stresses have led to its quality reduction. One of the stress causes is high content of heavy metal in ginseng cultivation area. Plant growth-promoting rhizobacteria (PGPR) can play a role in healthy growth of plants. It has been considered as a new trend for supporting the growth of many crops in heavy metal occupied areas, such as Aluminum (Al). Methods: In vitro screening of the plant growth promoting activities of five tested strains were detected. Surface-disinfected 2-year-old ginseng seedlings were dipping in Rhizobium panacihumi DCY116^T suspensions for 15 min and cultured in pots for investigating Al resistance of P. ginseng. The harvesting was carried out 10 days after Al treatment. We then examined H₂O₂, proline, total soluble sugar, and total phenolic contents. We also checked the expressions of related genes (PgCAT, PgAPX, and PgP5CS) of reactive oxygen species scavenging response and pyrroline-5-carboxylate synthetase by reverse transcription polymerase chain reaction (RT-PCR) method. Results: Among five tested strains isolated from ginseng-cultivated soil, R. panacihumi DCY116^T was chosen as the potential PGPR candidate for further study. Ginseng seedlings treated with R. panacihumi DCY116^T produced higher biomass, proline, total phenolic, total soluble sugar contents, and related gene expressions but decreased H₂O₂ level than nonbacterized Al-stressed seedlings. Conclusion: R. panacihumi DCY116^T can be used as potential PGPR and "plant strengthener" for future cultivation of ginseng or other crops/plants that are grown in regions with heavy metal exposure.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.465-472
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• 2017

The ingot fabrication conditions related with the thermal shock bearing phase and microstructure have investigated for the rare earth zirconate ceramic material, lanthanum gadolinium zirconate, as a thermal barrier coating using electron beam evaporation method. The thermal shock resistance of the prepared ingot was evaluated by high energy electron beam irradiation. The rare earth zirconate ceramic powder was prepared by controlling the raw material powder composition of $La_2O_3$, $Gd_2O_3$ and $ZrO_2$ so as to have a composition of $(La_{0.3}Gd_{0.7})_2Zr_2O_7$ which was selected from the former study. Ingot samples were prepared under two conditions. The first condition is prepared by sintering the prepared powder mixture to form an ingot. The second condition is prepared by calcining the prepared powder mixture to form a composite phase and then sintering to form an ingot. X-ray diffraction(XRD) and Scanning Electron Microscope(SEM) were used to analyze phase forming behavior and microstructure of ingot samples. Nanoindentation method used to obtain elastic modulus and hardness of each ingot specimen. Also the stress distribution of ingot was simulated by using FEM method assuming the ingot surface was exposed to electron beam. As a results, in the case of an ingot having a network-shaped microstructure in which relatively coarse pores are included, it seems that the thermal shock resistance was higher than in the case of an ingot having a microstructure composed of relatively fine grains only or particles with the similar level size when the high energy electron beam irradiation.

• Korean Journal of Materials Research
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• v.10 no.2
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• pp.111-116
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• 2000

Fracture mode and carbide reactions of cast alloy 738LC during thermal exposure and creep at 816$^{\circ}C$/440MPa and 982$^{\circ}C$/152MPa were investigated. Crystallographic transgranular failure was observed in the specimen crept at 816$^{\circ}C$ due to shearing on the slip plane. Because selective oxidation at the grainboundaries which was exposed at the surface leads reduction in surface energy, however, early initiation of crack at the grainboundaries and intergranular failure were observed in the specimen crept at 982$^{\circ}C$/152MPa. As a result of decomposition of MC carbide at the tested temperatures, M(sub)23C(sub)6 carbide precipitated either on the grainboundaries or on the deformation band. The applied stress enhanced decomposition of MC. $\sigma$phase nucleated from Cr(sub)23C(sub)6 then grew to the ${\gamma}$+${\gamma}$\\` matrix. Precipitation of $\sigma$was accelerated by increasing temperature and applied stress.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.156-161
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• 2002

It depends on the joint configuration, dimensions and constraints on the joint whether the residual stress at the root of single-sided butt weld is tensile or not. Therefore, recommendation is generally made that high R ratio should be used in the fatigue test of this type of joint in order to prevent excessively long life caused by compressive residual stress. in this research, the residual stress profile in butt weld joint was obtained through compliance method, using successive extension of a slot and measurement of the variation of strain during the slot extension. The residual stress profile was firstly assumed to be the linear summation of Legendre polynomials up to 9th order excluding 0th and 1st order. Strain variation on the surface was measured while the slot was being extended by cutting to find out the 8 unknown coefficients of each polynomial tenn. The cut was made by the electric discharge machine. It was concluded that the residual stress near the surface stayed positive, however, it turned into the negative value as soon as it passed through 2 or 3 mm depth. Several fatigue tests were also carried out under zero stress ratio. Test results showed that fatigue life coincides well with the design cuive of butt joint in British Standards, which supports that it is tensile residual stress that exists near the weld root.

• Nuclear Engineering and Technology
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• v.40 no.3
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• pp.233-238
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• 2008

This study investigates the surface modification of a Hastelloy X plate and diffusion bonding in the assembly of surface modified plates. These types of plates are involved in the key processes in the fabrication of a process heat exchanger (PHE) for a $SO_3$ decomposer. Strong adhesion of a SiC film deposited onto Hastelloy X can be achieved by a thin SiC film deposition and a subsequent N ion beam bombardment followed by an additional deposition of a thicker film that prevents the Hastelloy X surface from becoming exposed to a corrosive environment through the pores. This process not only produces higher corrosion resistance as proved by electrolytic etching but also exhibits higher endurance against thermal stress above 9$900^{\circ}C$. A process for a good bonding between Hastelloy X sheets, which is essential for a good heat exchanger, was developed by diffusion bonding. The diffusion bonding was done by mechanically clamping the sheets under a heat treatment at $900^{\circ}C$. When the clamping jig consisted of materials with a thermal expansion coefficient that was equal to or less than that of the Hastelloy X, sound bonding was achieved.

• Structural Engineering and Mechanics
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• v.47 no.4
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• pp.531-544
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• 2013

Compared with pavement structures of ordinary road sections, pavement structures in the intersection are exposed to more complex traffic characteristics which may exacerbates pavement distresses such as fatigue-cracking, shoving, shear deformation and rutting. Based on a field survey about traffic characteristics in the intersection conducted in Shanghai China, a three dimensional dynamic finite-element model was developed for evaluating the mechanistic responses in the pavement structures under different traffic characteristics, namely uniform speed, acceleration and deceleration. The results from this study indicated that : (1) traffic characteristics have significant effects on the distributions of the maximum principal strain (MPS) and the maximum shear stress (MSS) at the pavement surface; (2) vehicle acceleration or deceleration substantially impact the MPS and MSS at pavement surface and could increase the magnitude of them by 20 percent to 260 percent; (3) in the vertical direction, with the increase of vehicle deceleration rate, the location of the MPS peak value and the MSS peak value changes from the sub-surface layer to the pavement surface.

• Polymer(Korea)
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• v.37 no.1
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• pp.61-65
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• 2013

In this work, the anodic oxidation of carbon fibers was carried out to enhance the mechanical interfacial properties of carbon fibers-reinforced epoxy matrix composites. The surface characteristics of the carbon fibers were studied by FTIR, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Also, the mechanical interfacial properties of the composites were studied with interlaminar shear strength (ILSS), critical stress intensity factor ($K_{IC}$), and critical strain energy release rate ($G_{IC}$). The anodic oxidation led to a significant change in the surface characteristics of the carbon fibers. The anodic oxidation of carbon fiber improved the mechanical interfacial properties, such as ILSS, $K_{IC}$, and $G_{IC}$ of the composites. The mechanical interfacial properties of the composites anodized at 20% sulfuric/nitric (3/1) were the highest values among the anodized carbon fibers. These results were attributed to the increase of the degree of adhesion at interfaces between the carbon fibers and the matrix resins in the composite systems.

• Proceedings of the Korean Society of Crop Science Conference
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• 2022.10a
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• pp.157-157
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• 2022

Plants being sessile are prone to various abiotic challenges, including salinity. Plants generally cope with salt stress by regulating their endogenous NO levels. NO exogenously applied in various forms also successfully impedes the salt stress, but its small size, short half life, and high volatility rate hamper its application in agriculture. NO application via CS as a nanocarrier is an alternate option to ensure the optimal kinetic release of NO for a long period compared to the free NO form. Herein, we synthesized and characterized GSNO-CS NP by ionic gelation of TPP with CS and then reacting with GSH, followed by reaction with NaNO₂ suspension. The synthesized NPs were characterized using non-destructive analytical techniques such as DLS, FTIR, and SEM to ensure their synthesis and surface morphology. NO-release profile confirmed optimal kinetic NO release for 24 h from NO-CS NP as compared to free NO form. The efficiency of NO-CS NP was checked on Arabidopsis plants under salinity stress by gauging the morphological, physiological, and enzymatic antioxidant system and SOS pathway gene expression levels. Overall, the results revealed that NO-CS NP successfully mitigates salinity stress compared to free GSNO. Concluding, the findings provide sufficient experimental evidence for the application of nanotechnology to enhance NO delivery, thus inducing more benefits for the plants under stress conditions by mitigating the deleterious impacts of salt stress on the morphological and physiological status of the plants, and regulating the ions exchange by overexpression of SOS pathway candidate genes.