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[en] Mechanical and impact properties of stitched S2 glass fiber reinforced polyester woven laminates composites have been studied. Laminates were stitched using Kevlar 49 thread with 1/2, 1, and 2 inch stitch spacing. Tensile and 3-point bending tests have been performed to evaluate the mechanical properties of stitched and unstitched laminates. Impact tests at applied energy of 234.7J were performed to examine the impact behavior and toughness changes of the specimen. The same specimens were also tested repeatedly at low impact energy level of 110.2J for 3 times to evaluate damage tolerance properties. The tensile and 3-point bending test results showed that one inch spacing specimen had the highest tensile and flexural strength. It also showed the highest energy absorption capability and the best damage tolerance property at the repeated impact test. The half inch spacing specimen showed the lowest tensile strength and energy absorption property at the energy level of 234.7J, even though it had the highest frequency of stitching thread. (Author)
[en] The thermal properties of metal composite fabrics (MCFs) are governed by the high thermal conductivity and low emissivity of the metal component. Metal type, metal yarn density, metal mesh openness and layering arrangement of the MCFs were varied to study how they affect the thermal insulation properties of the fabrics. Three types of thermal resistance (solid to solid, solid to convective air, and stagnant air to convective air) were measured. All MCFs tested showed higher solid to air thermal resistance compared to non-metal fabric. The solid to air thermal resistance of the MCFs showed either higher or lower values than those predicted from the metal content of the MCFs, depending on the openness aspect ratio of the metal mesh. The solid to air thermal resistance of stainless steel composite fabric was greatly enhanced by proper layering with non-metal fabrics. The results showed that the thermal insulation properties of MCFs can be improved by modifying the metal content, metal mesh openness and layering arrangement of MCFs with other fabrics
[en] The annual operation time and thermal output of Research Reactor No. 1 were 207 hours and 874 kWh in 1994, and the bulk of operation was for reactor training for university students. Research Reactor No. 2 was used for sample irradiation for radioisotope production, activation analysis, etc., having 2,593 hours of annual operation time and 3,266 MHh of gross thermal output in this year. Number of samples irradiated was 1,118; 371 samples for radioisotope production, 648 samples for activation analysis and 99 for other purpose. It was planned Research Reactor No. 1 and No. 2 to be stopped sometime during next year, then a new reactor (HANARO) will take all missions of these two reactors. According to this policy, the reactor training course using reactor No. 1 was decide to be called off from 1995, and all spent fuels will be transported to the storage pool of (HANARO). Currently, preliminary arrangements for fuel transporting and discuss reporting for these two reactors are under operation, and reactor operation project will place the focus on this matter. 15 tabs., 21 figs. (Author) .new
[en] The annual operation time of research reactor No. 1 and No. 2 were 248 and 2,549 hours, and the thermal output were 24 kWh and 3,519 MWh respectively. Research reactor No. 1 was mainly used for student training and research reactor No. 2 was used for sample irradiations for radioisotope production, activation analysis, etc., and for researches using neutron beam ports. The operation and utilization of both reactors were nearly similar level with past years, but the operation of research reactor No. 2 was stoped for about one month due to replacement of crane. Several problems have been found through the inspection for safety with the over head cranes of both reactors in 1992.The capacity of the new crane has increased to 7.5 tons from 5 tons, but the other one at research reactor No. 1 remains as it is prohibited from using. As the plan about future management and utilization of these two reactors it is clearing to be memorial building after dicommissioning of No. 1 reactor, and to used No. 2 reactor continuously for student training. Considering the deterioration of the most part of facilities and number of equipments, repairing or replacement of them as well as tremendous paper work such as various documents and procedures which are demanded by current raw. 14 tabs., 17 figs. (Author) .new
[en] With various applicability of shear thickening fluids (STFs), control of rheological properties of STFs has been a major interest to industry. While carbon nanotubues and graphene have often been employed as fillers of STFs, little has been examined for their individual and combined effects on shear thickening behavior. In this study, the onset of viscosity increase of STFs was examined for the addition of: 1D functionalized multi-walled carbon nanotubes (fMWCNTs); 2D reduced graphene oxides (rGO); 3D network of MWCNTs-rGO hybrids (H); and spherical iron oxides (Fe3O4). To overcome the poor dispersibility of carbon particles, carbon nanotubes were functionalized to attach carboxylic groups (fMWCNTs), and graphene oxides (GOs) were reduced using TiO2 particles. Large hydrodynamic diameters of fMWCNT, rGO, and their hybrids of percolated network facilitated the interactions with silica particles in STF, decreasing the onset of shear thickening. Among the tested particles, STF with hybrids (H-STF) exhibited the lowest critical shear rate and the highest viscosity, due to the hybrid’s 3D network structure in which long and tortuous fMWCNTs bridged adjacent rGOs. The addition of Fe3O4 to HSTF shifted the shear thickening onset to a higher shear rate. The results demonstrate that the shear thickening onsets can be controlled by the selective additions of nanoparticles.
[en] One-dimensional magnetic nanostructures have recently attracted much attention because of their intriguing properties that are not realized by their bulk or particle form. These nanostructures are potentially useful for the application to ultrahigh-density data storages, sensors and bulletproof vest. The magnetic particles in magnetic nanofibers of blend types cannot fully align along the external magnetic field because magnetic particles are arrested in solid polymer matrix. To improve the mobility of magnetic particles, we used magneto-rheological fluid (MRF), which has the good mobility and dispersibility. Superparamagnetic core/sheath composite nanofibers were obtained with MRF and poly (ethylene terephthalate) (PET) solution via a coaxial electrospinning technique. Coaxial electrospinning is suited for fabricating core/sheath nanofibers encapsulating MRF materials within a polymer sheath. The magnetic nanoparticles in MRF were dispersed within core part of the nanofibers. The core/sheath magnetic composite nanofibers exhibited superparamagnetic behavior at room temperature and the magnetic nanoparticles in MRF well responded to an applied magnetic field. Also, the mechanical properties of the nanofiber were improved in the magnetic field. This study aimed to fabricate core/sheath magnetic composite nanofibers using coaxial electrospinning and characterize the magnetic as well as mechanical properties of composite nanofibers. - Highlights: ► The composite nanofibers including the MRF and PET. ► The fabrication of core/sheath structured nanofibers using coaxial electrospinning. ► Superparamagnetic composite nanofibers.
[en] As the demand for wearable intelligent textile systems continues to expand, it is now essential to achieve a high-level of electronic circuit integration into textiles. By applying a commercial yarn manufacturing technique and a computer numerical control (CNC) embroidery process, metal composite embroidery yarns (MCEYs) comprised of three strands of fine metal filaments and polyester filaments, and embroidered circuits have been successfully produced. Using MCEYs, circular and square spiral inductors were embroidered on a textile substrate. Their inductive characteristics, i.e. inductance, self-resonance frequency, and quality factor, were investigated under three different environments, i.e. in free space, on a human body, and with a metal fabric ground. Their inductive characteristics could be easily modified by adjusting the circuit design. The validity of the MCEY inductors was demonstrated with Wheeler's formula and design equations for the MCEY inductors were proposed. When in contact with the human body, the self-resonance frequency of the circuit decreased but the inductance was not affected. Although the inductance and maximum quality factor decreased with a metal ground, the inductor gave a stable performance irrespective of the environment. The results also suggest that MCEY embroidery is a simple and eco-friendly process for producing flexible, light-weight, wearable circuitries in various designs
[en] Graphical abstract: New methodology for suspended graphene sheets of high-quality (oxide-free), high-yield (high concentration) using amide solvent exfoliation and thermal treatment at 800 °C. We confirmed that the van der Waals force between the graphene layers decreases as increasing thermal treatment temperatures as shown XRD data (b). Highlights: ► Propose of new methodology to prepare oxide-free graphene sheets suspension. ► The graphene suspension concentration is enhanced by thermal treatment. ► Decrease of van der Waals force between the graphene layers by high temperature and pressure. ► This method has the potential as technology for mass production. ► It could be applied in transparent and flexible electronic devices. - Abstract: High quality graphene sheets were produced from graphite by liquid phase exfoliation using N-methyl-2-pyrrolidone (NMP) and a subsequent thermal treatment to enhance the exfoliation. The exfoliation was enhanced by treatment with organic solvent and high thermal expansion producing high yields of the high-quality and defect-free graphene sheets. The graphene was successfully deposited on a flexible and transparent polymer film using the vacuum filtration method. SEM images of thin films of graphene treated at 800 °C showed uniform structure with no defects commonly found in films made of graphene produced by other techniques. Thin films of graphene prepared at higher temperatures showed superior transmittance and conductivity. The sheet-resistance of the graphene film treated at 800 °C was 2.8 × 103 kΩ/□ with 80% transmittance.