• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.95-96
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• 2006

This study examined the effects of the tempering temperatures($360-420^{\circ}C$) on the mechanical properties of the carbon tool steel (SK4M) for flat spring. Hardness test, tensile test and fatigue test were performed at room temperature($20^{\circ}C$). The tensile strength and yield strength of $390^{\circ}C\;and\;420^{\circ}C$ tempered SK5M were 0.93-0.97 times and 0.81-0.87 times those of $360^{\circ}C$ tempered SK5M, respectively. The fatigue limit of $360-420^{\circ}C$ tempered SK5M were 35-40% of tensile strength of $360-420^{\circ}C$ tempered SK5M, respectively.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.67-73
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• 2001

Recently the steel parts used at automobiles are required to be used under high stress more than ever before in need of the weight down. To achieve this requirement of a high strength steel, it must be necessary to decrease inclusion content and surface defect as like decarburization, surface roughness etc.. In this study, the surface conditions are measured to know the influence on fatigue properties by two cases of two-stage shot peening iud single-stage shot peening for two kinds of spring steel(SUP7, SAE9254). This study shows the outstanding improvement of fatigue properties at the case of two-stage shot peening in the rotary bending fatigue test and this is assumed to be from decreasing the surface roughness unchanging the surface hardness increasing the compressive residual stress. Results also show fatigue failures originated at inclusion near surface, and this inclusion type is turned out to be a alumina of high hardness.

• Transactions of Materials Processing
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• v.18 no.4
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• pp.336-341
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• 2009

Hydroformed parts have higher dimensional accuracy, structural strength, and dimensional repeatability. Particularly in the automotive industry, manufacturing of parts with complex shapes from tubular materials sometimes requires one or more pre-forming operations such as bending before the hydroforming process. The pre-bending process is an important process for the successful hydroforming in the case where the perimeter of the blank is nearly the same as that of final product. The bendability of a tube depends on the parameters such as the bending radius, welding methods, mechanical properties and hardness. Through the stainless steel tubes bent by rotary draw bending machine, this study shows the following : (1) The influence on spring back ratio variation with stress level in the welded bent tube. (2) The Cross-section ovality variation with weld seam position and bending radius. (3) The relation between elongation and thickness reduction of tension zone with weld seam position and bending radius. (4) Workability evaluation of bent stainless steel tubes through the hardness of materials and hardness increment. The results of this study may help to understanding of characteristics on bendability of stainless steel tubes.

• Journal of The Korean Society of Grassland and Forage Science
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• v.10 no.2
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• pp.96-101
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• 1990

This field experiment was undertaken to find out the effect of grazing and cutting management on the forage quality and soil hardness at different legumes sown swards of the experimental field of Livestock Experiment Station in Suweon, from August 1985 to October 1988. The results obtained are as follows: 1. Crude protein, crude fat and ash contents under grazing were higher than these under cutting, but showed the reverse results in crude fiber and nitrogen free extracts contents. Average in vitro dry matter digestibility (IVDMD) under grazing (72 %) was a little higher than that under cutting (71 %). On the other hand, there was little difference among the mixtures swards in mineral contents and IVDMD. 2. The contents of Ca, P and Mg were a little high in the cutting, but K and Na contents were in gazing. Ca: P ratio in grazing (2.97) was slightly higher than that of cutting (2.94). 3. Production of energies(TDN, StE and NEL) with cutting were appeard to increase by 19.4 %, 13.5 %and 19.0 % than those of grazing, respectively. Mixtures swards including alfalfa showed more production both grazing and cutting. 4. Soil hardness in the top lOcm of soil by cattle grazing was changed from 15.5mm at startihg year to 22.6 mm after 3 years, but in cutting slightly increase from 15.5mm to 16.2mm. Generally it was low in early spring and high in autumn.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1997.10a
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• pp.322-327
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• 1997

This paper investigates the effects of shot peening on mechanical properties of SAE 9254, which is a spring steel used for the suspension system of automobiles. Rotary Bending Fatigue test is accomplished and the results are summarized as fellows : 1. The tensile strength and the hardness do not change so much. 2. The layer of highly residual stress is obtained by multi-stage shot peening. 3. The fatigue strength seems to be improved by residual stress. 4. The fatigue strength of un-peened and multistage shot peened material are 425 MPa and 756 MPa, respectively.

• Horticultural Science & Technology
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• v.18 no.3
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• pp.348-352
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• 2000

Four different Chinese cabbage cultivars were compared for their physicochemical quality characteristics including crude fiber, chlorophyll, firmness, hardness, sugar, and flavor at different parts of the cabbages. No significant difference in crude fiber content was observed among cultivars. Chlorophyll content in midrib was not significantly different among cultivars, however Chlorophyll content in leaf of 'Golden House' and 'Golden Spring' were greater than that of 'Alpine Summer' Firmness was the highest in 'Golden House' and 'Golden Spring' but hardness was not significantly different among cultivars. Sugar content was higher in midrib than in leaf. 'Golden Spring' a showed the highest sugar content in midrib. Glucose content was higher than the fructose content in leaf, but was opposite in midrib. Sensory evaluation showed that 'Golden House' and 'Golden Spring' were the best in yellowness, and 'Golden House' and 'Alpine Summer' were the best for their taste and aroma in midrib, however, no significant difference in texture was observed among cultivars.

• Korean journal of food and cookery science
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• v.17 no.5
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• pp.464-471
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• 2001

Physicochemical and sensory properties of Kakdugi prepared with spring cultivars of radish were compared during fermentation. Among 5 cultivars,` ‘Bagkwang’‘Chunhadaehyung’and ‘Bakbong’ were heavier in average weight and longer in length than others. Sugar content and hardness were the highest in ‘91144’and ‘Bakbong’, while moisture content, in ‘Bagkwang’ and ‘Bakbong’, During fermentation at 20$\^{C}$ for 11 days, a great decrease in pH and great increase of acidity were observed in five Kakdugi samples after day 2. The acidity of ‘Bagkwang’ and ‘Housebommoo’ increased rapidly after day 2 until day 5 and then reached around 1.04-1.08% (lactic acid) at day 11, while those of ‘91144’ and ‘Bakbong’ increased slowly until day 5, but after day 7 increased rapidly up to 1.2-1.3%(lactic acid). ‘91144’ showed the highest ‘a’ value(redness), but ‘Bagkwang’, the lowest. Decrease in hardness during fermentation was the least in ‘Bakbong’, while ‘Chunhadaehyung’, the greatest. The result of sensory evaluation suggested that ‘Bakbong’and ‘Housebommoo’ were the best among spring cultivars of radish for Kakdugi preparation.

• Journal of the Korean Society for Heat Treatment
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• v.30 no.6
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• pp.279-284
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• 2017

Mechanical properties of titanium alloy can be improved by controlling microstructure through heat treatment. In this study, Ti-3Al-8V-6Cr-4Mo-4Zr metastable beta titanium alloy, was controlled for excellent mechanical property and sound formability through various high temperature heat treatment and aging conditions and the optimum heat treatment conditions were determined. The specimens were heat-treated at $950^{\circ}C$, followed by various aging treatments from $430^{\circ}C$ to $500^{\circ}C$ for 1 to 24 h. As aging temperature and holding time increased, hardness increased by ${\beta}^{\prime}$ phase formation and precipitation of secondary ${\alpha}$ phase in ${\beta}$ matrix. However, the optimum aging temperature and holding time for mechanical properties were at $450{\sim}470^{\circ}C$ for 8~16 hr. Hardness values of the specimen aged at $450^{\circ}C$ for 8 h were found to be the highest. These results can be effectively applied to fabrication of spring with better formability and mechanical property.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1320-1329
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• 1990

A static performance tester for a torque rod assembly was developed to evaluate the three characteristics of the rod rubber bushing : radial spring characteristic, thrust spring characteristic, and rotational torque characteristic. Among the various schemes considered in the conceptual design stage, the final versatile type was determined to perform three different tests in one machine. The performance testing machine carried out radial spring test, thrust spring test, and torque test of the torque rod assembly. Static performance of the torque rod assembly was evaluated with the tester developed and fatigue strength of the assembly was also tested with the servo-hydraulic structural fatigue testing machine. The life of the component was found to be related with the rubber quality and adhesionability between the rubber and the steel rod. The optimum rubber hardness was experimentally found by changing the chemical compositions of rubber, and the adhesion was improved by optimizing the shape of the outer section of a the rubber, this study ensured the development of a reliable torque rod assembly.

• Journal of the Korean Wood Science and Technology
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• v.39 no.2
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• pp.148-155
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• 2011

Thermal treatment techniques are used for modifying wood and wood-based materials to improve dimensional stability and hygroscopicity. This study investigated the effects of press pressure and temperature on density, vertical density profile, thickness swelling and surface hardness of eucalyptus wood boards. The experimental wood boards were prepared from Turkish River Gum ($Eucalyptus$ $camaldulensis$ Dehn.). The surface hardness value increased with increasing press pressure in the treated groups. The application of a higher pressure at the same temperature level increased the amount of swelling of wood. It means that it is not needed for application of higher pressure to enhance the dimensional stability of wood. It is expected that it is possible to produce increased hardness, dimensional stability and durability by application of hot pressing treatment. This research showed that different press pressure and temperature values should be used to improve the performance properties of eucalyptus wood so that the end-use of the wood materials could be expanded.