• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.445-450
• /
• 2003

This study was performed 10 develop the accelerated life test method using Weibull-IPL(Inverse Power Law) model for mechanical components. Weibull-IPL model is concerned with determining the assurance life with confidence level and the accelerated life test time From the relation of weibull distribution factors and confidence limit, the testing times on the no number of failure acceptance criteria arc determined. The mechanical components generally represent wear and fatigue characteristics as a failure mode. IPL based on the cumulative damage theory is applied effectively the mechanical components to reduce the testing time and to achieve the accelerating test conditions. As the actual application example, accelerated life test method of agricultural tractor transmission was described. Life distribution of agricultural tractor transmission was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (MTBF) 3,000 hours and 90% confidence level for one test sample. According to IPL, because test time call be shorten in case increase test load test time could be reduced by 482 hours when we put the load 1.1 times of rated load than 0.73 times of rated load that is equivalent load calculated by load spectrum of the agricultural tractor. This time, acceleration coefficient was 11.7.

• 한국기계가공학회지
• /
• 제2권3호
• /
• pp.26-33
• /
• 2003

The term 'High Speed Machining' has been used for many years to describe end milling with small diameter tools at high rotational speeds, typically 10,000-100,000rpm. The process was applied in the aerospace industry for the machining of light alloys, notably aluminum. In recent year, however, the mold and die industry has begun to use the technology for the production of components, including those manufactured from hardened tool steels. With increasing cutting speed used in modern machining operation, the thermal aspects of cutting become more and mole Important. It not only directly influences in rate of tool weal, but also affects machining precision recognized as thermal expansion and the roughness of the surface finish. Hence, one needs to accurately evaluate the rate of cutting heat generation and temperature distributions on the machining surface. To overcome the heat generation, we used to cutting fluid. Cutting fluid plays a roles in metal cutting process. Mechanically coupled effectiveness of cutting fluids affect to friction coefficient at tool-workpiece interface and cutting temperature and chip control, surface finish, tool wear and form accuracy. Through this study, we examined the behavior of heat generation in high-speed machining and the cooling performance of various cooling methods.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2009년도 하계학술발표대회 논문집
• /
• pp.916-921
• /
• 2009

In this study, lubrication characteristics of sliding members were compared with the change of the hardness of friction surfaces and the application of nano-oil. The materials of the specimens were gray cast iron (AISI 35, AISI 60) and nickel chromium molybdenum steel (AISI 4320). The Friction coefficients and the temperature variations of on the frictional surfaces were measured by disk-on-disk tribotester under the condition of fixed rotating speed. The friction surfaces were observed by scanning electron microscope (SEM). In the results, the friction coefficients of the disk surface were increased as hardness difference was increased. The friction coefficient lubricated in nano-oil was less than mineral oil. This is because a spherical nano particle plays a tiny ball bearing between the frictional surfaces, improved the lubrication characteristics.

• Journal of Mechanical Science and Technology
• /
• 제18권3호
• /
• pp.388-394
• /
• 2004

Composites of Si$_3$N$_4$-SiC containing up to 30 wt% of dispersed SiC particles were fabricated via hot-pressing with an oxynitride glass. To determine the effect of sintering time and SiC content on the mechanical properties and the cutting performance, the composites with fixed 8hr-sintering time and 20 wt% SiC content were fabricated and tested. Fracture toughness of the composites increased with increasing sintering time, while the hardness increased as the SiC content increased up to 20 wt%. The hardness of the composites was relatively independent of the grain size and the sintered density. For machining heat-treated AISI4140, the insert with 20 wt% SiC sintered for 8hr showed the longest tool life while the insert with 20 wt% SiC sintered for 12hr showed the longest tool life for machining gray cast iron. An effort was made to relate the mechanical properties, such as hardness, fracture toughness and wear resistance coefficient with the tool life. However, no apparent relationship was found between them. It may be stated that tool life is affected by not only the mechanical properties but also other properties such as surface roughness, density, grian size and the number of the inherent defects in the inserts.

• 유통과학연구
• /
• 제10권11호
• /
• pp.31-37
• /
• 2012

Purpose - This study was conducted under the assumption that brand A, a store of company Z of Pangyo, with a new store at Pangyo station is targeting the Bundang-gu area of the newly developed city of Seongnam. Research design, data, methodology - As a result of demand forecasting using geometric series models, an extrapolation of past trends provided the coefficient estimates, without utilizing regression analysis on a constant increase in children's wear, for which the population size and estimated parameter were required. Results - Demand forecasting on the basis of past trends indicates the likelihood that sales of discount stores in the Bundang area, where brand A currently has a presence, would fetch a higher estimated value than that of the average discount store in the country during 2015. If past trends persist, future sales of operational stores are likely to increase. Conclusions - In evaluating location using the simple weighting model, Seohyun Lotte Mart obtained a high rating amongst new stores in Pangyo, on the basis of accessibility, demand class, and existing stores. Therefore, when opening a new counter at a relevant store, a positive effect can be predicted.

• 한국정밀공학회지
• /
• 제15권6호
• /
• pp.124-138
• /
• 1998

Particles reinforced MMCs have many advantages over monolithic metals including a higher specific modulus, higher specific strength, better properties at elevated temperatures and better wear resistance. SiC$_p$/A16061 composites have good results in its mechanical properties. This work investigates SiC$_p$/A16061 composites in the microscopic view and compares the analytical results with the experimental ones. The discrepancy of the material properties between the reinforced particle, SiC$_p$, and the matrix material, A16061 appears to be so significant. Especially the coefficient of thermal expansion(CTE) of A16061 is 5 times larger than that of SiC$_p$. Thermal residual stress in MMCs is induced at high temperatures. The shape of particle is various but the theoretical model is not able to consider the nonuniform shape. Particle distribution is not homogeneous in experimental specimen. However, it is assumed to be homogeneous in simulation model. The shapes of particles are assumed to be not only perfect global but hexahedral shapes. The types of particle distribution are two - simple cubic array(SC array) and face-centered cubic array(FCC array).

• 대한가정학회지
• /
• 제24권3호
• /
• pp.43-50
• /
• 1986

This study is toidentify what makes people uncomfortable when people wear new shoes and to gain fundamental data for establishing shoe sizes. Data materal from the 16 measurement investigation conducted on 796 college girl students shows the following. 1) More than 96% of the subjects have experienced footache when they wore new shoes. It is significant that 45.76% of the subjects answered shoe width, especially pump-lining part cause them to feel more pain in their feet than any other measurement elements. 2) According to multiple correlation analysis to know which parts of feet determine shoe size, both multiple correlation coefficient of feet length to other parts of foot and joint girth to other parts of foot show the highest of R=0.93. 3) According to the ANOVA-tested result of estimated function when both foot-length-joint girth and foot length-joint girth-foot width are independent variables in each case, the level of α〈0.001 is very significant. 4) The comparision between KS G3116 adult women's shoe size establishment table and my table in this study reveals that the cases of more increased joint girth measurements than standard joint girth measurements in KS G 3116 table are easy to find.

• 한국전기전자재료학회논문지
• /
• 제29권8호
• /
• pp.516-521
• /
• 2016

Mo-Cu alloys have been widely used for heat sink materials, vacuum technology, automobile, and many other applications due to their excellent physical and electric properties. Especially, Mo-Cu composites with 5 ~ 20 wt.% copper are widely used for the heavy duty service contacts due to their excellent properties like low coefficient of thermal expansion, wear resistance, high temperature strength, and prominent electrical and thermal conductivity. In most of the applications, highly-dense Mo-Cu materials with homogeneous microstructure are required for better performance. In this study, Mo-Cu alloys were prepared by PBM (planetary ball milling) and SPS (spark plasma sintering). The effect of Cu with contents of 5~20 wt.% on the microstructure and thermal properties of Mo-Cu alloys was investigated.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2008년도 춘계학술대회 논문집
• /
• pp.2080-2093
• /
• 2008

대표적으로 높은 운동에너지를 가지는 고속철도와 항공기의 제동장치에 적용되는 금속계 소결마찰재와 내열강 간의 트라이볼로지 특성 연구를 목적으로 각각 2종류의 고속철도용 금속계 마찰재와 항공기용 금속계 마찰재를 Lab-Scale Dynamometer를 이용하여 시험하였다. 그 결과 철도용 금속계 마찰재가 항공기용 마찰재에 비해 높은 마찰계수 및 마찰계수 안정성을 나타내었고, 마모량도 철도용 금속계 마찰재는 항공기용 마찰재에 비해 약 50%수준에 불과하여 본 시험조건에서는 철도용 소결마찰재가 뛰어난 것으로 나타났다. 또한, 동계 마찰재가 철계 마찰재보다 제동시 급격하게 온도가 상승하며, 냉각도 동계 마찰재가 빨리 되지만, 동계 마찰재라도 마찰재의 기지의 량에 따라 달라지는 것으로 나타났다. 마찰재에 따라 마찰면에 형성되는 산화피막의 안정성은 달라지는 것으로 나타났으며, 산화피막은 $Fe_2O_3$와 $Fe_3O_4$계통이며, 마찰재에 따라서 마모메카니즘이 달라지는 것으로 판단된다.

• 복식문화연구
• /
• 제17권4호
• /
• pp.548-560
• /
• 2009

This study was conducted to investigate purchasing behavior of jeans consumers and to find differences in jeans evaluative criteria according to consumers' characteristics. Male and female university students participated in the study. Quota sampling method was used to collect the data. Data from 492 questionnaires were used for the statistical analysis. Descriptive analysis, factor analysis, Cronbach's alpha coefficient, ANOVA, Duncan test, and t-test were conducted. Three factors of jeans evaluative criteria classified (i.e., external criteria, internal/aesthetic criteria, internal/quality criteria). Results indicated that most of respondents put on jeans wear more than three times per a week and 38.1% of respondents reported that they owned three to four jeans products on average. Department store was the most used place to buy jeans product with 44.2%. 27.5% of respondents spent from 50,000 won to 100,000 won on purchasing jeans. Style was the highest important jeans evaluative criterion with 36.2%, followed by fitness, price, color, condition of washing treatment. Women respondents considered aesthetic criteria and quality criteria more importantly than men did. Respondents who were on a high income and spent more than 200,000 won per a month on apparel more concerned aesthetic criteria and external criteria than the other respondents did. Results of this study provide a basis for understanding jeans consumers' purchase behavior and evaluative criteria.