• Journal of the korean academy of Pediatric Dentistry
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• v.43 no.4
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• pp.427-434
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• 2016

The aim of this study was to compare the mechanical properties of high viscosity bulk-fill resin composites, $Filtek^{TM}$ Bulk Fill Posterior Restorative (FBF) and $Tetric^{(R)}$ N-Ceram Bulk Fill (TBF), with conventional composite ($Filtek^{TM}$ Z-350 XT, Z-350). The Vickers hardness test which indicates the degree of conversion was performed and the dye penetration test was performed to measure the microleakage which indicates polymerization shrinkage amount. To minimize experimental error, the standardized 3D-printed molds and the bovine teeth were used. Obtained data were analyzed by the Kruskal-Wallis test and Mann-Whitney test with the confidence interval of 95%. In the microhardness test within 1 hour of polymerization, lower surface of FBF and TBF showed significantly lower value than that of Z-350 (p < 0.05). But after 24 hours, the microhardness of FBF had increased and showed no significant difference with Z-350 (p > 0.05). In top and 2 mm depth surface, mean microhardness values were in the following order: Z-350 > FBF > TBF (p < 0.05). The mean microleakage value of TBF was significantly lower than others (p < 0.05). For clinical application of bulk-fill resin composites, caution for applying masticatory forces during 24 hours after polymerization is advised and further studies to decrease microleakage should be conducted.

• Progress in Superconductivity
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• v.9 no.1
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• pp.107-110
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• 2007

Bi/CNT composite and resin/CNT were chosen to improve the mechanical properties of $YBa_2Cu_3O_7$(YBCO) superconductor. In order to elucidate the effects of Bi/CNT composite and resin/CNT in YBCO superconductors, melt texture superconductor were impregnated by mixed compound of Bi and CNT into the artificial holes parallel to the c-axis, which were drilled on the YBCO superconductor. Various amount of Bi/CNT and resin/CNT were impregnated to YBCO superconductor with different holes diameters. Typical artificial holes diameters were 0.5, 0.7, and 1.0 mm respectively. Result of three-point bending test measurement, the bending strength with resin/CNT impregnation was improved up to 59.64 MPa as compared with 50.79 MPa of resin/CNT free bulk. Resin/CNT impregnation has been found to be one of the effective ways in improving the mechanical properties of bulk superconductor.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2006.05a
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• pp.417-420
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• 2006

The composition and structure of dendrite phase within $Zr_{76.11}Ti_{4.20}Cu_{4.51}Ni_{3.16}Be_{1.49}Nb_{10.53}$ bulk metallic glass (BMG) were confirmed by using an EPMA, XRD and TEM, respectively. The chief elements of dendrite phase were Zr-Ti-Nb and had a BCC structure. The thermal properties of this BMG have been then subsequently investigated by using a differential scanning calorimeter (DSC). The glass transition and crystallization onset temperatures were determined as $339.7^{\circ}C$ and $375.8^{\circ}C$ for this alloy, respectively. Mechanical properties have also been examined by conducting a series of uniaxial compression tests at various temperatures within supercooled liquid region under the strain rates between $10^{-4}/s$ and $3{\times}10^{-2}/s$. The deformation behavior of BMG composite within supercooled liquid region is similar to one of Vit-1 exhibiting amorphous single phase alloy. The flow stresses of BMG composite, however, are entirely higher than those of Vit-1 because dendrite phases are interfere with moving of atoms.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.2
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• pp.185-198
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• 2017

The application of composites as an alternative material for marine steel hatch covers is the subject of this study. Two separate approaches are considered; weight reduction approach and strengthening approach. For both approaches Finite Element Analysis (FEA) was performed using ANSYS software. Critical design parameters of the composite hatch cover and FEA are discussed in details. Regarding the weight reduction approach; steel hatch covers of a bulk carrier were replaced by composite covers and a weight reduction of 44.32% was achieved leading to many benefits including fuel saving, Deadweight Increment and lower center of gravity of the vessel. For the strengthening approach; the foremost hatch cover was strengthened to withstand 150% of the load required by IACS for safer navigation while no change in weight was made between the steel and composite covers. Results show that both approaches are feasible and advantageous.

• Korean Journal of Materials Research
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• v.14 no.3
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• pp.181-185
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• 2004

The mechanical properties of a bulk amorphous alloy ($Zr_{41.2}$ $Ti_{13.8}$ /$Cu_{10}$ $Ni_{10}$ $Be_{22.5}$ /at.%) before and after an annealing treatment were investigated. For the bulk amorphous alloy, the compressive strength was about 2.0 GPa, irrespective of the strain rates in the range of $10^{-4}$ to $10^3$$ sec^{-1}$ . Fine-sized nanocrystalline particles (10～100 nm) were precipitated homogeneously in the bulk amorphous matrix after the annealing treatments. Compared to the bulk amorphous materials, these composite materials, composed of the nanocrystalline phases and a bulk amorphous matrix had much different mechanical properties. The strength and strain of coposite materials measured by a compressive test showed a peak-maximum values at 7 vol.% of the nanocrystalline phases. The values in higher volume fraction of the crystalline phases in the amorphous matrix were decreased, as measured by both quasi-static and high strain rate. The decrease in fracture strength is due to presence of the dispersed large-crystalline phases in the amorphous matrix.

• Journal of the korean academy of Pediatric Dentistry
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• v.32 no.3
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• pp.481-490
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• 2005

The aim of this study was to investigate the relationship between the C-factor and shrinkage strain values of composite resin and examine the strain values in different incremental filling techniques. The strain gauge method was used for measurement of polymerization shrinkge strain. Experiment was divided two step. In a first experiment, we compared with strain value in three different depth (2mm, 3mm, 4mm) and microhardness of each samples after 24hours were measured. In a second experiment, we examined the strain values in five different filling techniques(Group 1: bulk filling, Group 2: oblique incremental filling, Group 3: horizontal incremental filling, Group 4: vertical incremental filling, Group 5: lining of flowable resin and bulk filling) The results of the present study can be summarized as follows: 1. Composite resin in acrylic molds showed the initial expansion at the early phase of polymerization. 2. Contraction stress was not revealed significant difference between depth of 2mm and 3mm(P>0.05). 3. Contraction stress in sample of 4mm was showed the lowest value(P<0.05). 4. Microhardness of specimen was revealed more difference between upper and lower surface in depth of 4mm than 2 and 3mm(P<0.05). 5. Lining of flowable resin and bulk filling (Group 5) was showed the lowest contraction stress, Group 2 and 3 was showed the highest contraction stress(P<0.05). On the basis above results, the stress that result from the polymerization shrinkage, when incremental curing techniques are used, showed that there is no advantage in incremental placement and curing.

• Restorative Dentistry and Endodontics
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• v.31 no.5
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• pp.352-358
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• 2006

The purpose of this study was to investigate the influence of thickness on the degree of cure of dual-cured composite core. 2, 4, 6, 8 mm thickness Luxacore Dual and Luxacore Self (DMG Inc, Hamburg, Germany) core composites were cured by bulk or incremental filling with halogen curing unit or self-cure mode The specimens were stored at $37^{\circ}C$ for 24 hours and the Knoop's hardness of top and bottom surfaces were measured. The statistical analysis was performed using ANOVA and Tukey's test at p = 0.05 significance level. In self cure mode, polymerization is not affected by the thickness. In Luxacore dual, polymerization of the bottom surface was effective in 2, 4 and 6 (incremental) mm specimens. However the 6 (bulk) and 8 (bulk, incremental) mm filling groups showed lower bottom/top hardness ratio (p < 0.05). Within the limitation of this experiment, incremental filling is better than bulk filling in case of over 4 mm depth, and bulk filling should be avoided.

• Bulletin of the Korean Chemical Society
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• v.31 no.2
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• pp.344-350
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• 2010

The improved photocatalytic performance of a carbon/$TiO_2$ composite was studied for the Bisphenol A (BPA) decomposition. Titanium tetraisopropoxide (TTIP) and a rice husk from Korea were heterogeneously mixed as the titanium and carbon sources, respectively, for 3 h at room temperature, and then thermally treated at $600^{\circ}C$ for 1 h in $H_2$ gas. The transmission electron microscopy (TEM) images revealed that the bulk carbon partially covered the $TiO_2$ particles, and the amount that was covered increased with the addition of the rice husk. The acquired carbon/$TiO_2$ composite exhibited an anatase structure and a novel peak at $2{\theta}=32^{\circ}$, which was assigned to bulk carbon. The specific surface area was significantly enhanced to 123~164 $m^2/g$ in the carbon/$TiO_2$ composite, compared to $32.43m^2/g$ for the pure $TiO_2$. The X-ray photoelectron spectroscopy (XPS) results showed that the Ti-O bond was weaker in the carbon/$TiO_2$ composite than in the pure $TiO_2$, resulting in an easier electron transition from the Ti valence band to the conduction band. The carbon/$TiO_2$ composite absorbed over the whole UV-visible range, whereas the absorption band in the pure$TiO_2$ was only observed in the UV range. These results agreed well with an electrostatic force microscopy (EFM) study that showed that the electrons were rapidly transferred to the surface of the carbon/$TiO_2$ composite compared to the pure $TiO_2$. The photocatalytic performance of the BPA removal was optimized at a Ti:C ratio of 9.5:0.5, and this photocatalytic composite completely decomposed 10.0 ppm BPA after 210 min, whereas the pure $TiO_2$ achieved no more than 50% decomposition under any conditions.

• Applied Microscopy
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• v.45 no.2
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• pp.52-57
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• 2015

Bulk metallic glass (BMG) shows higth strength, high elastic limit, corrosion resistance and good wear resistance and soft magnetic properties and has been considering as a candidate for new structural materials. But they show limited macroscopic plasticity and lack of tensile ductility due to highly localized shear deformation, which should be solved for real structural application. In this paper researches on the enhancement of plasticity of BMG were reviewed briefly. Introducing heterogeneous structure in glass is effective to induce more shear transformation zones (STZs) active for multiple shear band initiation and also to block the propagating shear band. Several methods such as BMG alloy design for high Poisson's ratio, addition of alloying element having positive heat of mixing, pre-straining BMG and variety of BMG composites have been developed for homogenous distribution of locally weak region, where local strain can be initiated. Therefore enhancement of plasticity of BMG is normally accompanied with some penalty of strength loss.

• Journal of Powder Materials
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• v.23 no.3
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• pp.213-220
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• 2016

In this study, bulk nickel-carbon nanotube (CNT) nanocomposites are synthesized by a novel method which includes a combination of ultrasonication, electrical explosion of wire in liquid and spark plasma sintering. The mechanical characteristics of the bulk Ni-CNT composites synthesized with CNT contents of 0.7, 1, 3 and 5 wt.% are investigated. X-ray diffraction, optical microscopy and field emission scanning electron microscopy techniques are used to observe the different phases, morphologies and structures of the composite powders as well as the sintered samples. The obtained results reveal that the as-synthesized composite exhibits substantial enhancement in the microhardness and values more than 140 HV are observed. However an empirical reinforcement limit of 3 wt.% is determined for the CNT content, beyond which, there is no significant improvement in the mechanical properties.