• Magazine of the Korean Society of Agricultural Engineers
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• v.39 no.1
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• pp.83-92
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• 1997

An experimental study of the application of Silica fume for the high strength concrete was conducted. Nine specimens with three different contents of silica fume, 0%, 10%, 20% and with three water-cement ratio 30%, 40%, 50% were tested. Results shows that 10% of silica fume and 30% of water-cement ratio has a maximum strength with 700kg/$cm^2$ of compressive strength and 64kg/$cm^2$ of splitting tensile strength and 100kg/$cm^2$ of flexural strength. Slump value of the tested samples decreases with increasing water-cement ratio and elapsed time of silica fume. Splitting tensile strength$({\sigma}_f)$ and flexural strength $({\sigma}_f)$ and static modulus of elasticity(E) can be correlated with compressive strength $({\sigma}_c)$ from a regression analysis.

• Current Research on Agriculture and Life Sciences
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• v.18
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• pp.61-69
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• 2000

This study was conducted to investigate most effective the optimum lime content for lime-clay modification. To achieve the aim, characteristics of compaction and compressive strength were tested by adding of 0, 5, 10, 15 and 20% lime (Hydrated lime) of dry weight of the clay. Distilled water was added 10, 15, 20 and 25% of dry weight of lime-clay mixture. In this test, the compressive strength of the specimens was measured according to the following curing period : 7, 21, 28, 35 and 49 days. The results are as follows. (1) As lime additive increased, the optimum moisture content of lime-clay mixture was increased and the maximum dry density was decreased. (2) The soil mixture of 20% of the moisture content and 10% of lime additive was shown the maximum compressive strength. (3) As curing period longer, the compressive strength was increased but after 21 curing days, the increasing rate of compressive strength was low as compared with earlier its value. (4) In the range of 20% of the moisture content, compressive strength of mixture of 10% lime additive increased twice compared with that of mixture of 0% lime additive. (5) All of the lime-clay are possible to use for an sub-base material and 20% of moisture content of lime-clay mixture is possible to use for a base material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.4 s.175
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• pp.1055-1064
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• 2000

First, various specimen geometries, namely, coupon type, waisted type and dog-bone type, were examined to determine appropriate fatigue specimen of thermoplastic composite material AS4/PEEK and the n, fatigue strength of smooth and notched specimens of AS4/PEEK [-45/0/+45/90]2s was investigated. Fatigue tests were performed under load controlled condition at a stress ratio of 0. 1 at a frequency of 5Hz. Stiffness degradation of specimens with fatigue cycling was monitored using an automated unloading compliance technique. The waisted type specimen is found appropriate for smooth fatigue specimen geometry of AS4/PEEK. As for the effect of stress concentration, it is found that fatigue strength is higher for a 2mm-diameter hole notched specimen than a 5mm-diameter one. Fatigue notch factor decreases with the increase of fatigue life. These results are far different from the trend of fatigue strength of metallic materials. The stiffness variation of smooth specimen was only 4% at maximum until final fracture. On the other hand, the stiffness of hole notched specimen was reduced by 45% at maximum. Notched fatigue strength was compared between thermoplastic composite AS4/PEEK and thermosetting composite Graphite/Epoxy. In long-life fatigue (>104), the AS4/PEEK composite shows superior fatigue strength, but in short-life fatigue, the fatigue strength of the Graphite/Epoxy composite is nearly equal or somewhat higher than that of the AS4/PEEK composite.

• The korean journal of orthodontics
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• v.20 no.2
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• pp.381-390
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• 1990

The purpose of this study was to evaluate the effects of heat treatment on mechanical properties in $0.016^{{\prime}{\prime}}{\times}0.022^{{\prime}{\prime}}$ blue Elgiloy wires and to measure the amounts of nickel and chromium released from the wires in artificial saliva. Ultimate tensile strength, yield strength and elongation were measured with universal testing machine (Instron). and the amounts of nickel and chromium released from the sample were measured with atomic absorption spectrophotometer after one week immersion in the artificial saliva. Ultimate tensile strength and yield strength were progressively increased below $1000^{\circ}F$, but elongation was decreased. And the results were reversed above $1100^{\circ}F$. After heat treatment of the sample for 9 minutes at $1000^{\circ}F$, the maximum tensile strength and yield strength were $213.6kg/mm^2$, $140.1kg/mm^2$, respectively. Both tensile strength and yield strength were decreased progressively above $1100^{\circ}F$. Elongation was appeared the minimum value (8.6%) after heat treatment for 9 minutes and 12 minutes at $1000^{\circ}F$. There was a pronounced increase in nickel and chromium liberation with increasing time and temperature. The maximum amounts of nickel and chromium released form the sample were $4.947{\mu}m/cm^2$, $3.088{\mu}g/cm^2$, respectively after heat treatment for 12 minutes at $1300^{\circ}F$. Heat treatment is applied to orthodontic wires, especially cobalt-chromium alloys, for the purpose of stress-relievning and hardening. When the heat-treatment of orthodontic wires, the heating procedure should be well controlled in order to have no effect on corrosion resistance and mechanical properties.

• Polymer(Korea)
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• v.26 no.1
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• pp.53-60
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• 2002

Polypropylene(PP : continuous phase)/poly (styrene-co-acrylonitrile)(SAN : dispersed phase) blends, and PP/poly(acrylonitrile-butadiene-styrene) (ABS : dispersed phase)blends, containing various amounts of compatibilizer(PP-SAN graft copolymer), were prepared at various shear rates by using twin-screw extruder. In the PP/SAN blend, the average size of the dispersed particles(SAN) was increased with SAN content, while the flexural strength and tensile strength were decreased with SAN content. When the screw rpm was increased from 10 to 60 rpm, the size of the dispersed phase was decreased while the flexural strength and the tensile strength were increased. Maximum mechanical strength and minimum droplet size were observed when the 5 phr compatibilizer was added to the PP/SAN blends. The mechanical strength of PP/ABS blends such as flexural strength and tensile strength increased by adding compatibilizer was reached maximum when blends contained 5 phr compatibilizer.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.79-88
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• 1993

The purpose of this study is to provide a firm base for the quality improvement of high strength concrete and the development of ultra high strength concrete as well as enviromental con-servation and utilization of byproducts from industrial processing such as Fly ash and Silica fume. A comprehensive experimental study was performed to investigate the effects on the quality improvement of high strength concrete using mineral admixtures. As results, 400~500kg/$\textrm{cm}^2$ compressive strength and excellent flowability can be obtained if fly ash is replaced with cement in the range of 305. In case of using powder type silica fume, 600~700 kg/$\textrm{cm}^2$ compressive strength is showed and 600~800kg/$\textrm{cm}^2$ compressive strength cam be obtained with liquid type silica fume. But it is necessary to increase dosage of high range water reducer for flowability using powder type silica fume. Especially, higher strength concrete cam be obtained when maximum size of coarse aggregate is lower than 25mm.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2002.05a
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• pp.69-74
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• 2002

The following results are achieved from a mortar flow test depending on stainless steel slag fineness, replacement ratio, and a research on material age compressive strength, strength activity index. 1. Flow is proportional to the stainless steel slag fineness within the limits of 4000~8000$\textrm{cm}^2$/g, but in the case of fineness 20000$\textrm{cm}^2$/g flow decreases at all conditions except the case of replacement ratio 10%. 2. As stainless steel slag replacement ratio increases, Mortar of flow somewhat decreases. 3. As stainless steel slag blends, compressive strength decreases, but in proportion to the increase of age, compressive strength increases. 4. As stainless steel slag replacement ratio, compressive strength decreases. 5. In the case of stainless steel slag fineness 6000$\textrm{cm}^2$/g and 20.000$\textrm{cm}^2$/g, compressive strength of revelation ratio has the maximum value when it's replacement ratio is 10%.

• Proceedings of the ESK Conference
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• 1996.10a
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• pp.238-243
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• 1996

Grip strength is a very important basic data for ergonomic design of hand tools, grips, handles and etc.. Excessive grip strength is contineously exerted to handle the machines or tools, it might cause a musculoskeletal disorder such as cumulative trauma disorders. Capal tunnel syndrome is a typical nerve disorder anomg CTDs. In this paper we have measured the grip strength under sitting and standing posture for Korean adults ; 113 male and 105 female aged from 20' to the above 50' . And this paper performed statistical analysis for driving out characteristics between grip strength and anthropometric data. The results are as follows ; (1) The maximum girp strength is exerted under standing posture with the elbow in full extension(180 .deg. ) for both of male and female (2) There is significant difference in posture, sex and right left hand (3) Grip strength decreases with age for male, but it traces an inverted U curve for female (4) Grip strength has a correlation with age, weight, height, BSA, forearm length, hand length, thickness of wrist, circumference of wrist and breadth of wrist for male

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.2
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• pp.15-22
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• 1998

The effects of shot peening an the fatigue strength are studied in this paper. Applying the multistage shot peening on the material. the relation between the residual stress and fatigue strength compressive is investigated. Observing tensile strength elongation. reduction of area. hardness. and roughness. the results can be summarized as follows ; 1.The change of mechanical properties is small before and after the shot peening is carried out. The change of hardness is also small in high hardness material. 2.The surface roughness does not affect the fatigue strength. but the surface roughness is improved by multi-stage shot peening. 3.The fatigue strength of multi-stage shot peening material is 756MPa and is 1.78 times higher than that of un-peened material. 4.The maximum compressive residual strength of multi-stage shot peening material is -792MPa the fatigue strength seems to be improved by residual stress.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.315-320
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• 2007

An effective reinforcement method for steel tubular joints having a large chord diameter is the use of internal ring stiffeners. This paper presents the results of a numerical study on the static strength of internally ring-stiffened tubular X- and T-joints subjected to brace axial compression loading. Nonlinear finite element analyses are used to compute the joint strength. The influence of geometrical parameters has been studied and the maximum reinforcement effect of a ring stiffener has been evaluated. A strength ratio is defined. by the ratio of ring-stiffened joint strength to unstiffened joint strength, and an equation for this strength ratio is derived by regression analysis. Design optimization for ring stiffener of tubular joints is carried out using metropolis genetic algorithm.