• KSTLE International Journal
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• v.2 no.1
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• pp.40-45
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• 2001

The paper deals with a non-linear finite element analysis of the thermomechanical distortions of an elastomeric O-ring seal including a temperature gradient. Axial compression of O-ring seals, as well as the influence of the temperature gradients and various O-ring seal models, are investigated based on the axisymmetric analysis. The highest temperature occurs near the interface of the O-ring between the dovetail groove bottom and the O-ring seal. The calculated FEM results indicate that the composite O-ring with the diametral ratio, 0.8 shows very stable and recommendable compared with other seal models far elevated temperatures and corrosive environments.

• Restorative Dentistry and Endodontics
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• v.25 no.3
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• pp.421-434
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• 2000

The purpose of this study was to evaluate the influences of incorporation of zirconium-silicate on diametral tensile strength, shear bond strength to the enamel, and depth of cure of 7 experimental composites. One group contained no filler(group 1 or control group), and the other 6 composites contain 75% filler in which zirconium-silicate(Zr-Si) were 0%, 2%, 4%, 6%, 8%, 10% with reduced contents of silica filler, respectively. Both of fillers were treated with 1% silane (${\gamma}$-methacryloxypropyltrimethoxy silane). Light curable monomers were prepared by mixing Bis-GMA and TEGDMA with 3:1 ratio and adding camphoroquinone(CQ) 0.6% with tertiary amine 0.3%. Diametral tensile strengths of specimens with $3mm{\times}6mm$ were measured with Instron (No.4467, USA) with 1mm/min crosshead speed. Shear bond strengths of composites which bonded to bovine enamel etched with 37% phosphoric acid were measured at Instron Testing Machine with as same speed as in diametral tensile strengths. Depth of cure were measured by a method that composite was filled in cylinder mold, illuminated at one side. and uncured composite was removed with acetone, and the residual thickness of composite was measured. Following results were obtained ; 1. Composites containing 0%, 2%, or 4% zirconium-silicate filler(group 2, 3 and 4) showed the statistically higher diametral tensile strength than the others. (p<0.05) 2. Increase of zirconium-silicate filler contents reduced the diametral tensile strength of experimental composites. ($r^2$=0.8721, p=0.0002) 3. Increase of zirconium-silicate filler contents did not affect the shear bond strength of experimental composites. ($r^2$=0.2815, p=0.4067) 4. Increase of zirconium-silicate filler contents reduced significantly the depth of cure of experimental composites. ($r^2$=0.9700, p<0.0001) These results mean that the mechanical properties of composites could not be improved by incorporation of small amount of zirconium-silicate filler. Also, the increased contents of zirconium-silicates fillers was found to reduce the diametral tensile strength and depth of cure.

• Restorative Dentistry and Endodontics
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• v.26 no.1
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• pp.23-31
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• 2001

The purpose of this study was to search the optimal silane concentrations for filler- silanization of seven experimental composites. Silica filer was a 25micron crushed type. 0.0%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0% silane($\gamma$-methacrylooxypropyltrimethoxysilane)were added into silica-filler with weight percentage (wt%). Mixtures(silica filler/silane)were reacted at 6$0^{\circ}C$ for 72hours, and crushed into fine particles those were used as fillers for 7 experimental composites. Monomer was a 3 : 1 mixture of Bis-GMA and TEGDMA containing 0.2% tertiary amine and 0.4% camphoroquinone for light curability. A ratio for mixing the monomer and filler was 75% and 25% respectively. Seven experimental composites was classified with the concentration of silane treated, and the specimen number for each test was 10. Specimens with 6mm diameter and 3mm height dimension for measuring the diametral tensile strength were destroyed with 1mm/min cross-head speed on Instron universal testing machine (No. 4467, USA). Shear bond strength was measured on the specimens bonded to bovine enamel etched with 37% phosphoric acid solution for 1 minute Fractured surfaces were observed by SEM (Hitachi S-3200, Japan) among that of the highest values measured from each groups. Following results were obtained: 1. Experimental composites containing silanized filter showed the significantly higher diametral tensile strength and shear bond strength than the composites containing un-silanized fillers(Group1) (p<0.05). 2. In silanized filler composite resins(Group 2~7), Diametral tensile strength of Group 3 showed the significantly higher than that of Group 2 and Group 6(p<0.05). 3. Shear bond strength was higher in Group 3 than that of Group 7 (p＜0.05)in silanized fillers composite resins. 4. Fracture surface was formed in resin matrixes on the specimens from composites containing the fillers treated with 0.5% 1.0%, and 1.5% silane. These results mean that the optimal silane concentrations are exist for each fillet with its size and surface area, and that 1.0% is a optimal value for concentration to coat the 25$\mu\textrm{m}$ filler with silane.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.388-395
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• 2000

This study was performed to examine the effects of infrared (IR)/heated-air combination drying on some quality attributes of Korean white ginsengs. Ginseng roots were dried in a dryer where both the far infrared ray and heated-air are available as drying energy sources. Diametral shrinkage, external color, total saponin content, and ginsenosides and free sugar composition of the IR/heated-air combination dried ginsengs were measured and compared with those of commercial white ginseng products. The external color became lower in lightness and higher in saturation as the IR radiating plate temperature increased. IR/heated-air combination dried white ginsengs at IR plate temperature of 100$^{\circ}C$ was comparable to the commercial white ginseng products in color characteristics. Diametral shrinkage ratios ranged from 20 to 36% and appeared to be independent on the different drying methods. No definite evidence could be found whether the IR/heated-air combination drying and the conventional. hot-air drying practice resulted in white ginsengs having different ginsenoside contents and compositions. No conclusion could be made on whether the various drying treatments used in the study had effects on the free sugar contents and compositions of white ginsengs.

• Korean Journal of Dental Materials
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• v.44 no.1
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• pp.69-77
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• 2017

The aim of this study was to investigate the effects of chitosan powder addition on the strengthening of conventional glass ionomer cement. Two types of chitosan powders with different molecular weight were mixed with conventional glass ionomer cement (GIC): low-molecular weight chitosan (CL; 50~190 kDa), high-molecular weight chitosan (CH; 310~375 kDa). The chitosan powders (CL and CH) were separately added into the GIC liquid (0.25-0.5 wt%) under magnetic stirring, or mixed with the GIC powder by ball-milling for 24 h using zirconia balls. The mixing ratio of prepared cement was 2:1 for powder to liquid. Net setting time of cements was measured by ISO 9917-1. The specimens for the compressive strength (CS; $4{\times}6mm$), diametral tensile strength (DTS; $6{\times}4mm$), three-point flexure (FS; $2{\times}2{\times}25mm$) with flexure modulus (FM) were obtained from cements at 1, 7, and 14 days after storing in distilled water at $(37{\pm}1)^{\circ}C$. All mechanical strength tests were conducted with a cross-head speed of 1 mm/min. Data were statistically analyzed by one-way ANOVA and Tukey HSD post-hoc test. The mechanical properties of conventional glass ionomer cement was significantly enhanced by addition of 0.5 wt% CL to cement liquid (CS, DTS), or by addition of 10 wt% CH (FS) to cement powder. The CL particles incorporated into the set cement were firmly bonded to the GIC matrix (SEM). Within the limitation of this study, the results indicated that chitosan powders can be successfully added to enhance the mechanical properties of conventional GIC.

• Journal of the Korean GEO-environmental Society
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• v.10 no.3
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• pp.37-45
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• 2009

The experimental study was carried out to evaluate the characteristics of the point load index and the uniaxial compressive strength of inherently anisotropic shale in the laboratory. In the testing program the effects of size and the shape on the point load index were investigated both in the axial and diametral direction. In general, the point load index of the shale was constant when the length/diameter (L/D) ratio of the specimen is greater than 1.0 in the diametral direction. The point load index in axial direction shows slight decrease as the L/D ratio is increased and the corner breakage was observed when L/D ratio is greater than unity. The minimum point load index was observed in the bedding angle of $\beta=15^{\circ}{\sim}30^{\circ}$ in the axial point load tests and of $\beta=30^{\circ}$ in the uniaxial compression tests. The relationship between the point load index and the uniaxial compressive strength was linear to ${\sigma}_c=25.0 I_{s(50)}$ for the specimen with the bedding plane angle, $\beta$ at the range of $0^{\circ}{\sim}90^{\circ}$. On the other hand, this relationship was appeared linear to ${\sigma}_c=14.4 I_{s(50)}$ when the bedding angle, $\beta$ is fixed to 90${^{\circ}}$ and this correlation is much different from ${\sigma}c=22 I_{s(50)}, which is generally applied to the rock specimen with no bedding plane in ISRM (1985). The anisotropic strength with different $\beta$ angle shows the shoulder type and this can be suitably modelled by the corrected Ramamurthy'(1993)s equation with the index value of 'n' equal to 3.0.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.3
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• pp.39-43
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• 2010

The main objective of this research is to develop a mechanistic performance predictive model for fatigue cracking of asphalt-aggregate mixtures. Controlled-stress diametral fatigue tests were performed to characterize fatigue cracking of asphalt-aggregate mixtures. Performance prediction model for fatigue cracking was developed using the internal damage ratio (IDR) growth method. In the IDR growth method, the general concepts of the dissipated energy, the reference tensile strain, the threshold tensile strain, and the strain shift factor were introduced. The source of the dissipated energy in the fatigue test is from the intrinsic viscoelastic material property of an asphalt concrete mixture and the damage growth within the asphalt concrete specimen. In controlled-stress mode test, the dissipated energy is gradually increased with an increasing number of load applications.

• Restorative Dentistry and Endodontics
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• v.45 no.4
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• pp.50.1-50.11
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• 2020

Objectives: In this study, we investigated the potential of amoxicillin-loaded polymeric microspheres to be delivered to tooth root infection sites via a bioactive reparative cement. Materials and Methods: Amoxicillin-loaded microspheres were synthesized by a spray-dray method and incorporated at 2.5% and 5% into a mineral trioxide aggregate cement clinically used to induce a mineralized barrier at the root tip of young permanent teeth with incomplete root development and necrotic pulp. The formulations were modified in liquid:powder ratios and in composition by the microspheres. The optimized formulations were evaluated in vitro for physical and mechanical eligibility. The morphology of microspheres was observed under scanning electron microscopy. Results: The optimized cement formulation containing microspheres at 5% exhibited a delayed-release response and maintained its fundamental functional properties. When mixed with amoxicillin-loaded microspheres, the setting times of both test materials significantly increased. The diametral tensile strength of cement containing microspheres at 5% was similar to control. However, phytic acid had no effect on this outcome (p > 0.05). When mixed with modified liquid:powder ratio, the setting time was significantly longer than that original liquid:powder ratio (p < 0.05). Conclusions: Lack of optimal concentrations of antibiotics at anatomical sites of the dental tissues is a hallmark of recurrent endodontic infections. Therefore, targeting the controlled release of broad-spectrum antibiotics may improve the therapeutic outcomes of current treatments. Overall, these results indicate that the carry of amoxicillin by microspheres could provide an alternative strategy for the local delivery of antibiotics for the management of tooth infections.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.3
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• pp.591-599
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• 1994

A design system for power transmission bevel gears(straight, zerol, and spiral) is developed, in which the strength and durability of bevel gears can be estimated and the size of bevel gears can be minimized by introducing optimal techniques. The size of bevel gear pair as the object function to be minimized is the volume of equivalent spur gear pair at mean normal section, and the design variables to be determined are considered as the number of teeth, face width, diametral pitch, and spiral angle in spiral bevel gear. The strength(bending strength, pitting resistance) according to the AGMA standards, geometrical quantities, and operating characteristics(interference of pinion, contact ratio, etc.) are considered as the constraints in design optimization. The optimization with these constraints becomes nonlinear problem and that is solved with ALM(Augmented Lagrange Multiplier) method. The developed design method is applied to the example designs of straight, zerol, and spiral bevel gears. The design results are acceptable from the viewpoint of strength and durability within the design ranges of all other constraint, and the bevel gears are designed toward minimizing the size of gear pair. This design method is easily applicable to the design of bevel gears used as power transmitting devices in machineries, and is expected to be used for weight minimization of bevel gear unit.

• Journal of the Korean Geotechnical Society
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• v.22 no.8
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• pp.63-72
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• 2006

In the ASTM and ISRM, an uniaxial compressive strength(${\sigma}_{c}$) has been estimated to be 23(ASTM) or $20{\sim}25$(ISRM) times of point load strength index using a diametral test regardless of the rock rating or geological conditions. This paper presents a relationship between $I_{s}$ and ${\sigma}_{c}$ of a weak sedimentary rocks on Ulsan of the Kyung-Sang Basin in Korea. In the results of 291 for ${\sigma}_{c}$ test and 2310 for $I_{s}$ test from 77 spots, the predicted errors of ${\sigma}_{c}$ determined by strength ratio of ${\sigma}_{c}/I_{s}$ have been relatively less than those determined by linear regression analysis. And in case of weak sedimentary rocks such as mudstones, shales and sandstones, ${\sigma}_{c}$ should be lower than those suggested by ISRM and ASTM.