• Transactions of Materials Processing
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• v.29 no.3
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• pp.151-156
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• 2020

In general, the cause of slab cracking during heat treatment has been analyzed with focus on processing conditions. However, in the present work, the cause of cracking is analyzed based on the microstructural evolution during heat treatment. The microstructural analysis indicates that the structure of the slab consists of three main regions as the top, quarter, and center parts. The tensile properties are investigated in each region of the slab in the temperature range from 25 to 350 ℃. Results demonstrate that the cracking is mainly attributed to the thermal stress and specific morphology of the microstructure. It is proposed that the cracking during the heat treatment is related to the presence of inclusion at the ferrite phase which is located at the boundary of pearlite grains.

• Advanced Composite Materials
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• v.16 no.4
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• pp.377-384
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• 2007

'Green' composites were fabricated from poly lactic acid (PLA) and bamboo fibers by using a conventional hot pressing method. The insulating properties of the PLA-bamboo fiber 'green' composites were evaluated by determination of the thermal conductivity, which was measured using a hot-wire method. The thermal conductivity values were compared with theoretical estimations. It was demonstrated that thermal conductivity of PLA-bamboo fiber 'green' composites is smaller than that of conventional composites, such as glass fiber reinforced plastics (GFRPs) and carbon fiber reinforced plastics (CFRPs). The thermal conductivity of PLA-bamboo fiber 'green' composites was significantly influenced by their density, and was in fair agreement with theoretical predictions based on Russell's model. The PLA-bamboo fiber composites have low thermal conductivity comparable with that of woods.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.578-578
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• 2012

Graphene, a flat one-atom-thick two-dimensional layer of carbon atoms, is considered to be a promising candidate for nanoelectronics due to its exceptional electronic properties. Most of all, future nanoelectronics such as flexible displays and artificial electronic skins require low cost manufacturing process on flexible substrate to be integrated with high resolutions on large area. The solution based printing process can be applicable on plastic substrate at low temperature and also adequate for fabrication of electronics on large-area. The combination of printed electronics and graphene has allowed for the development of a variety of flexible electronic devices. As the first step of the study, we prepared the gate electrodes by printing onto the gate dielectric layer on PET substrate. We showed the performance of graphene field-effect transistor with electrohydrodynamic (EHD) inkjet-printed Ag gate electrodes.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.05c
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• pp.106-109
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• 2001

In this paper, we have investigated the degradation of shed materials of outdoor insulators by UV-radiation by using corona-charging and XPS analysis. The accumulated charges on polymeric surface having intrinsic hydrophobic property have a negative impact on retaining its hydrophobicity. Therefore, shorter decay times of surface charges are preferred. The surface voltage decay on UV-treated silicone rubber and EPDM show a different decay trend with UV treated time. From the XPS analysis, the oxidized groups of silica-like structure in silicone rubber increase with UV treatment time. For EPDM, the oxidized carbon groups of C=O, O=C-O increase as elapse of UV radiation time. These oxidized surface for each material have different electrostatic characteristics, so deposited charges may be expected to have different impacts on their surface hydrophobicity. The degradation mechanism based on our results is discussed.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.942-943
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• 2006

To meet the demands for use in extremely abrasive and corrosive environments, a new material was developed. The VeKo25Cr distinguishes itself through specifically selected amounts of carbon and carbide forming elements such as Cr, Mo, V, W and Nb. The alloy is based on a Fe matrix. The strength after heat treatment and the wear and corrosion properties are compared to those of other materials. VeKo25Cr can be combined with easy-to-process materials such that the difficult handling is minimized to those places on the piece most subjected to operational wear.

• Advanced Composite Materials
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• v.16 no.2
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• pp.167-180
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• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.

• Journal of the Korean Ceramic Society
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• v.35 no.1
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• pp.33-40
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• 1998

A MgO-CaO-based coating material for ferrous melt refining is applied to the tundish operation for mol-ten steel having low carbon. The changes in the total oxygen content insoluble aluminum content and the content of inclusions in molten steel during tundish operation were measured at the pouring part strand of tundish and mold. On the basis of the experimental results the interfacial reaction occurring between the coating materials and the molten steel in tundish was discussed and compared with the theoretical con-sideration. It is concluded that interfacial reaction is not active at the strand part of tundish but is active at the pouring part because of the turbulent flow in the molten steel.

• Interaction and multiscale mechanics
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• v.1 no.3
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• pp.317-328
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• 2008

When carbon-filled rubber specimens are subjected to cyclic loading, they do not return to their initial state after loading and subsequent unloading, but exhibit a residual strain or permanent deformation. We propose a specific form of the pseudo-elastic energy function to represent cyclic loading for incompressible, isotropic materials with stress softening and residual strain. The essence of the pseudo-elasticity theory is that material behaviour in the primary loading path is described by a common elastic strain energy function, and in unloading, reloading or secondary unloading paths by a different strain energy function. The switch between strain energy functions is controlled by the incorporation of a damage variable into the strain energy function. An extra term is added to describe the permanent deformation. The finite element implementation of the proposed model is presented in this paper. All parameters in the proposed model and elastic law can be easily estimated based on experimental data. The numerical analyses show that the results are in good agreement with experimental data.

• Current Photovoltaic Research
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• v.6 no.3
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• pp.74-80
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• 2018

Recently, perovskite solar cells have shown tremendous improvement in power conversion efficiencies. Moreover, they have potential in semitransparent solar cell applications due to their high absorption coefficients. In order to fabricate semitransparent perovskite solar cells with good performance, it is essential to consider the suitability of transparent electrode materials in various aspects, such as transparency, conductivity and fabrication process. In this review, candidate materials for transparent electrodes in perovskite solar cells including carbon-based nanomaterials, conductive polymers and metallic nanostructures are discussed.

• Applied Science and Convergence Technology
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• v.26 no.6
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• pp.149-156
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• 2017

Recently, stretchable and transparent electrodes have received great attention owing to their potential for realizing wearable electronics. Unlike the traditional transparent electrodes represented by indium tin oxide (ITO), stretchable and transparent electrodes are able to maintain their electrical and mechanical properties even under stretching stress. Lots of research efforts have been dedicated to the development of stretchable and transparent electrodes since they represent the most important engineering platform for the production of wearable electronics. Various approaches using silver nanowires, nanostructured networks, conductive polymers, and carbon-based electrodes have been explored by many world leading research groups. In this review, present and recent advances in the fabrication methods of stretchable and transparent electrodes are discussed.