• Journal of Welding and Joining
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• v.31 no.2
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• pp.26-29
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• 2013

The latest research & development trend on friction stir welding and friction stir processing technologies presented in the international symposium, 'Friction Stir Welding & Processing VII'. Papers and presentations about high temperature materials such as advanced high strength steel, stainless steel and titanum alloy shoot up this year. Papers on modeling of metal flow and control of process parameters also increased. The FSP technologies for manufacturing of carbon materials reinforced metal matrix composites were reported, too.

• Journal of Adhesion and Interface
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• v.22 no.3
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• pp.106-110
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• 2021

Recently, research using waste among eco-friendly materials has been attracting attention. In this study, we investigated the physical properties of blends in which high density polyethylene (HDPE) was filled with waste gypsum (CaSO₄) generated during fertilizer manufacturing. Composites were prepared by adding the gypsum content 0~20 wt% using a twin screw extruder. The mechanical, rheological, and thermal properties of the composites were evaluated. It was found that the tensile strength of the composites was less than 4.1% compared to that of unfilled HDPE, so there is no significant deterioration in physical properties. The thermal stability of the composites was improved as the gypsum content increased and the gypsum content had little effect on the viscosities of the composites.

• Composites Research
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• v.35 no.6
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• pp.412-418
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• 2022

Flame-retardant vinyl ester (VE) resin films were developed from the mixtures of brominated and non-brominated epoxy resins via esterification with methacrylic acid without reactive diluents. The films were used to fabricate carbon fiber (CF) prepregs via a hot melt impregnation process. The viscosity of VE resins suitable for film production was optimized by mixing low-viscosity bisphenol-A and high-viscosity brominated bisphenol-A epoxy precursors. Increasing the bromine content of the cured VE resin further increased the limited oxygen index (LOI) (39%), storage modulus (2.4 GPa) at 25℃ and residual carbonization (16.1%) values compared to non-brominated VE. Manual layup of as-prepared VE prepregs with subsequent curing led to the successful fabrication of CF-reinforced composites with high tensile and flexural strength. The results from the study hold high promise for a styrene-free, environmentally friendly VE composite process in the future.

• Journal of the Korean Recycled Construction Resources Institute
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• v.7 no.4
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• pp.128-135
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• 2012

Autoclaved lightweight concrete, also known as autoclaved aerated concrete(AAC) or autoclaved cellular concrete (ACC), is made with fine silica powder, quik lime, cement, and an Al powder. ALC contains 70~80% air. The lightweight material offers excellent sound and thermal insulation, and like all cement-based materials, is strong and fire resistant. However, ALC have high water absorption, low compressive strength and popout the origin of the low surface strength in its properties. These properties make troubles under construction such as cracking and popout. Thus, this study is to improve the fundamental strength by controls of increasing of admixtures, gypsum and silica powder size. Admixtures make use of metakaolin and silica fume. From the test result, the ALC using admixture have a good fundamental properties compared with plain ALC. Compressive strength, specific strength and abrasion's ratio were improved depending on increasing admixtures ratio's, gypsum and silica powder size.

• The Journal of Korean Academy of Prosthodontics
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• v.32 no.3
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• pp.411-430
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• 1994

The denture may be fractured accidentally by an impact while outside the mouth, or may be cracked or broken while in service in the mouth. The latter is generally a fatigue failure caused by repeated flexure over a period of time. This investigation compared the flexural fatigue resistance, the impact force and the transverse strength of two denture base materials with and without the grid strengthener, the T300, the T800 and the Kevlar fiber to evaluate the fracture resistance. The distribution and behavior of fibers across fracture lines were examined by Hi-Scope Compact Microvision System. Through analyses of the data from this study, the following conclusions were obtained. 1. The flexural fatigue resistance, impact strength and transverse strength of high impact strength resin were higher than those of conventional heat polymerizing resin, but statistically there was no significant difference(p>0.05). 2. All specimens with and without the grid strengthener did not show significant differences in the flexural fatigue, the impact and the transverse strength test(p>0.05). 3. All specimens reinforced with the T300, the T800 and the Kevlar fiber showed significant increase of the fatigue resistance and the impact force(p<0.05). 4. All specimens reinforced with the T800 and the Kevlar fiber showed significant increase of the transverse strength(p<0.05). 5. All specimens reinforced with the T300, the T800 and the Kevlar fiber exhibited greenstick fractures. The fibers tended to remain enveloped in the resin, resisting pull-out.

• Journal of the Korean Geosynthetics Society
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• v.17 no.2
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• pp.19-31
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• 2018

Recently the ground subsidence which seriously weakens the safety of cities tends to increase. The purpose of this paper is to develop the materials by using industrial by-products for the application to emergency restoration process in case of ground subsidence. In this paper the laboratory tests including pH test, initial setting test, unconfined compressive strength test, and flow test were performed in order to evaluate the design properties of Controlled Low Strength Material (CLSM). The field test was carried out for evaluating the performance for the early strength of CLSM and the workability for emergency restoration. Test results showed that the strength will be too high to re-excavate the ground when the cement ratio is more than 4%. The optimum mixing ratio appears to be most effective when the mixing ratio of the bottom ash and the gypsum is approximately 50:50 and the cement content is 2%.

• The Journal of Advanced Prosthodontics
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• v.10 no.3
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• pp.205-210
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• 2018

PURPOSE. The purpose of this study was to evaluate the efficiency of a gas-phase fluorination method under different fluorination periods through using two resin cements. MATERIALS AND METHODS. 84 zirconia specimens in dimensions of $5mm{\times}5mm{\times}2mm$ were prepared and surface treated with $50{\mu}m$ aluminum oxide particles or gas phase fluorination for 2 min, 5 min, or 10 min. One specimen in each group was surface analyzed under scanning electron microscope. The remaining specimens were bonded to composite cylinders in dimensions of 2 mm diameter and 3 mm high with Panavia SA Plus or Variolink N. Then, the specimens were stored in $37^{\circ}C$ distilled water for 24 hours and shear bond strength test was applied at a speed of 1 mm/min. RESULTS. The highest shear bond strength values were observed in the samples fluorinated for 5 minutes and cemented with Panavia SA Plus. Variolink N did not elicit any statistical differences between surface treatments. Panavia SA Plus resin cement and Variolink N resin cements featured statistically significant difference in shear bond strength values only in the case of 5 minutes of fluorination treatment. CONCLUSION. According to the results of this study, application of 5 minutes of fluorination with 10-methacryloyloxydecyl dihydrogen phosphate monomer (MDP) containing Panavia SA Plus resin cement increased the resin bond strength of zirconia. Fluorination of the zirconia surface using conventional resin cement, Variolink N, did not lead to an increase in bond strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.147-153
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• 2006

Photocatalyst reaction has limit of its usage because application range mostly centered on atmosphere purification area. Thus, it is true that an alternative plans are necessary to increase usage of $TiO_2$ as photocatalyst material. (1) The result of flow felt according to $TiO_2$ replacement rate has shown that both of anatase type and rutile type over 12% deviated from desired flow, $110{\pm}5mm$. Consequently, the range below 9% will be suitable when the anatase type $TiO_2$ if used for functional additives if workability is considered. (2) After compressive strength test, replacement rate 6-9% is estimated as suitable range if $TiO_2$ is used as compressive strength material. Rutile type and anatase type are suitable for in early-age strength and long-age strength respectively. (3) It was revealed that bending strength was dramatically decreased when replacement rate was increased. The main reason were the increase of $TiO_2$ doesn't influence hydration reaction and the decrease of bending strength. (4) The result from the water purification properties test using ion-chromatograhpy has shown that the condition with anatase type $TiO_2$ was normally better than rutile type on the same replacement rate.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.101-112
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• 2019

The grouting method is utilized to reinforce and waterproof poor grounds, enhance the bearing capacity of geo-structures damaged from differential settlement. The purpose of this research is to improve the compressive strength and degree of grout using reinforcing fibers and blast furnace slag powder. In this regard, this study has conducted uniaxial compression tests for the specimens with high ratios (higher than 50%) of blast furnace slag powder. The carbon fiber content was increased by 0, 0.5, and 1.0% to coMpare its compressive strength with that of aramid fiber. The uniaxial compressive strength increased with the increase of fiber content and the bridging activity by fiber in cement tended to increase uniaxial compressive strength. Based on the results, it was confirmed that the aramid fiber has a gel time of 14 seconds and the uniaxial compressive strength is more than 3 Mpa coMpared to carbon fiber.

• The Journal of Advanced Prosthodontics
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• v.15 no.5
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• pp.248-258
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• 2023

PURPOSE. This study aims to evaluate the effects of exposure energy on the lateral resolution and mechanical strength of dental zirconia manufactured using digital light processing (DLP). MATERIALS AND METHODS. A zirconia suspension and a custom top-down DLP printer were used for in-office manufacturing. The viscosity of the suspension and uniformity of the exposed light intensity were controlled. Based on the exposure energy dose delivered to each layer, the specimens were classified into three groups: low-energy (LE), medium-energy (ME), and high-energy (HE). For each energy group, a simplified molar cube was used to measure the widths of the outline (X_o and Y_o) and isthmus (X_i and Y_i), and a bar-shaped specimen of the sintered body was tested. A Kruskal-Wallis test for the lateral resolution and one-way analysis of variance for the mechanical strength were performed (α = .05). RESULTS. The zirconia green bodies of the ME group showed better lateral resolution than those of the LE and HE groups (both P < .001). Regarding the flexural strength of the sintered bodies, the ME group had the highest mean value, whereas the LE group had the lowest mean value (both P < .05). The ME group exhibited fewer agglomerates than the LE group, with no distinctive interlayer pores or surface defects. CONCLUSION. Based on these findings, the lateral resolution of the green body and flexural strength of the sintered body of dental zirconia could be affected by the exposure energy dose during DLP. The exposure energy should be optimized when fabricating DLP-based dental zirconia.