• Transactions of the Korean Society of Mechanical Engineers A
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• v.32 no.6
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• pp.488-495
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• 2008

In order to achieve long fatigue lifetimes for cyclically pressurized thick cylinders, multi-layered compound cylinder has been proposed. Such compound cylinder involves a shrink-fit procedure incorporating a monobloc tube which has previously undergone autofrettage. The basic autofrettage theory assumes elastic-perfectly plastic behaviour. Because of the Bauschinger effect and strain-hardening, most materials do not display elastic-perfectly plastic properties and consequently various autofrettage mo dels are based on different simplified material strain-hardening models, which is assumed that combination of linear strain-hardenig and power strain-hardening model. This approach gives a more accurate prediction than the elastic-perfectly plastic model and is suitable for different strain-hardening materials. In this paper, a general autofrettage model that incorporates the material strain-hardening relationship and the Bauschinger effect, based upon the actual tensile-compressive stress-strain curve of a material was proposed. The model was obtained using the von Mises yield criterion and plane strain condition. The tensile-compressive stress-strain curve was obtained by experiment. The parameters needed in the model were determined by fitting the actual tensile-compressive curve of the material. Finally, strain- hardening model was compared with elastic-perfectly plastic model.

• Journal of the Korean Society for Heat Treatment
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• v.2 no.4
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• pp.47-55
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• 1989

The effects of thermal cycle, aging heat treatment and Boron addition on the phase transformation characteristics and mechanical properties of the shape memory alloys of Cu-Zn-Al system, which was designed to operate about $80^{\circ}C$ by this research group, were studied. From the view point of the effects of thermal cycle on the phase transformation temperature change, it was found that up to 100 cycles Ms and Af points increased by $3-7^{\circ}C$ and Mf decreased a little bit and after that all of them were remain constant, and As point was not affected. All of the phase transformation temperatures were decreased $5-7^{\circ}C$ by aging heat treatment, at $140^{\circ}C$ for 24h however the effects of thermal cycle on aged alloys were same as on unaged alloys. As the thermal cycle increased the shape memory ability decreased a little up to 20 cycles, but above that it kept almost same ability. By Boron addition, grain size was refined from $1500{\mu}m$ to about $330{\mu}m$ and the hardness, fatigue property were improved but shape memory ability was lowered.

• Journal of Welding and Joining
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• v.34 no.2
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• pp.22-29
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• 2016

Recently, Application of composite materials are increased in transport area for weight reduction. Also, Related technical developments have been implemented actively at domestic and abroad. In particular, The carbon fiber has high strength and ultra light property higher than stainless steel, aluminum, GFRP as Eco-friendly material. Carbon fiber contribute to improving the environmental effect such as fuel saving, expansion of loadage, reducing the exhaustion of carbon dioxide through the weight reduction of transport area. In addition, The carbon fiber is applied to the ship in the area of race yacht, luxury cruise boat as weight reduction and high added-value materials, but there is limited application for general boat because price of carbon fiber is very expensive. For the weight reduction of general boat hull, being used as structure materials, glass fiber and carbon fiber are applied to hull with form of hybrid composite materials, but application of domestic and research for development are incomlete. In this study, An evaluations of mechanical strength property and fatigue strength are performed on composite materials by hybrid weaving of glass fiber and carbon fiber and composite materials forming method by hybrid forming.

• Elastomers and Composites
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• v.44 no.4
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• pp.401-407
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• 2009

Commercial grades of solution styrene-butadiene rubbers extended with high aromatic oils having high polycyclic aromatic compounds (PCA) and low PCA oils were used to study the effect of the processing oil particularly on the crack propagation resistance and frictional wear resistance of the vulcanizates. The aromatic oil based vulcanizates exhibited superior fracture behavior over the low PCA oil extended vulcanizates based on tensile and trouser tear tests. Compounds with aromatic oil showed superior crack propagation resistance compared with those containing low PCA oil, especially at the lower ranges of tearing energy. In terms of frictional wear resistance, the aromatic oil extended compounds showed superior performance particularly in the lower frictional work ($W_f$) range but in the higher $W_f$ range the low PCA oil extended vulcanizates performed better.

• Journal of the Korean institute of surface engineering
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• v.48 no.6
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• pp.315-321
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• 2015

Rare-earth zirconates, such as $La_2Zr_2O_7$ and $Gd_2Zr_2O_7$, have been investigated as one of the candidates for replacing conventional yttria-stabilized zirconia (YSZ) for thermal barrier coating (TBC) applications at higher turbine inlet temperatures. In this study, double-ceramic-layer (DCL) TBCs of YSZ 1st layer and $La_2Zr_2O_7$ top coat layer are fabricated by suspension plasma spray with serial liquid feeders. Microstructures, hardness profiles, and thermal durability of DCL-TBCs are also characterized. Fabricated DCL-TBCs of YSZ/$La_2Zr_2O_7$ exhibit excellent properties, such as adhesion strength (>25 MPa) and electrical thermal fatigue (~1429 cycles), which are comparable with TBCs fabricated by atmospheric plasma spray.

• Journal of Korea Foundry Society
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• v.20 no.4
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• pp.240-246
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• 2000

Surface layer properties such as composition, phase, hardness, and oxide layer condition are very important if the main failure mechanism of metals is wear. Generally, stable and dense oxide layers are known to decrease the wear rate of metals by prohibition of metallic junction occurred between bare metals. Addition of Si above 4 wt% to DCI(Ductile Cast Iron) is reported to enhance the significant oxidation resistance by forming the silicon-rich surface layer which inhibits further oxidation. And addition of up to 2 wt% Mo to high Si ductile iron produces significant increases in high temperature tensile strength, creep strength, thermal fatigue resistance and oxidation resistance. High pressure wear characteristics of unalloyed DCI(Ductile cast Iron), 4.46 wt% Si ductile iron, 4.3 wt% Si-0.52 wt% Mo ductile iron were investigated through unlubricated pin-on-disc wear test. Wear test was carried out at speed of 23m/min, under pressure of 3 MPa and 3.3 MPa. Wear surfaces of each specimen were observed by SEM to determine the wear mechanism under high pressure wear condition. Addition of Si 4.46 wt% severely deteriorated wear property of ductile iron compared to unalloyed DCI. But combined addition of Si 4.3 wt%andMo0.52wt%decreasedthefrictioncoefficient(${\mu}$)ofductileironsandremarkablydelayedthemild-severeweartransition.

• Proceedings of the ESK Conference
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• 1997.10a
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• pp.406-413
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• 1997

근전도(EMG:Electromyogram)를 사용하여 국부 근육 피로(Localized Muscle Fatigue)를 정량화으로 분석 하기 위해 널리 이용되고 있는 AR(Autoregressive)모델의 1차 계수, RMS(Root Mean Square), ZCR(Zero Crossing Rate), MPF(Mean Power Frequency), MF(Median Frequency)를 선택하여, 근육이 발휘하는 힘과 시간의 흐름에 따라 근육 피로의 정도를 민감하게 나타내는 매개변수를 규명하였다. 피실험자 10명의 좌우 척추세움근(Erector Spinae Muscle)을 대상으로 등장수축(Sustained Isometric Contraction)조건에서 허리의 신전(Extension)운동을 실시하였다. 이때 발휘해야 하는 힘의 수준은 15%, 30%, 45%, 60%, 75% MVC 로 정하였고 각 수준마다 20초 동안 근전도를 측정하 였다. 데이터 분석은 총20초 구간의 근전도를 0.5초 간격으로 나누어 매개변수들을 각각 구하고 분석을 실시하였다. 시간의 흐름에 대한 피로도 분석 결과, AR 모델의 1차 계수와 MPF가 유의한 차이를 보였으며, 낮은 수준의 %MVC에서는 AR 계수가, 높은 수준에서는 MPF가 민감한 반응 결과를 나타냈다. 그리고 근육이 발휘하는 힘의 정도를 분석하기 위해 주로 사용되고 있는 RMS 보다는 더 AR 계수가 모든 수준에서 뚜렷하게 차이를 보인 것이 확인되었다. 따라서 AR 모델의 1차 계수가 근육의 피로 정도와 힘의 수준을 다른 매개변수에 비해 더욱 민감하게 구별함이 입증되었다. 이러한 결과는 다른 분야에서도 근육 피로를 정량적으로 측정하는데 사용될 수 있을 것으로 생각되며, 개인적 변이도를 고려한 확률 기법을 사용한다면 보다 정확한 근전도 분석이 이루어질 것으로 기대된다.있음을 알 수 있었다. 사료된다.의 결과는 자전거 에르고노미터의 결과가 트레드밀의 결과에 87.60%정도 나타났다.음을 관찰하였다. 특히 vitamin C와 E의 병용투여는 상승적으로 적용하여 간세포손상을 더욱 억제시킴을 알 수 있었다.mance and on TFP(Total Factor Productivity) growth which is a pure measure of firm performance. To utilize the advantage of panel data, FEM(Fixed Effect Model) and REM(Random Effect Model) were used. The empirical result shows that the entropy index as a measurement of inter-business relatedness is not significant but technological relatedness index is significant. OLS estimates on pooled data were considerably different from FEM or REM estimates on panel data. By introducing interaction effect among the three variables for business portfolio properties, we obtained three findings. First, only VI (Vertical integration) has a significant positive correlation with ROS. Second, when using TFP growth as an dependent variable, both TR(Technological Relatedness) and f[ are signif

• Magazine of the Korea Concrete Institute
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• v.8 no.6
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• pp.151-161
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• 1996

Recently, polypropylene fiber reinforced mortar and concrete as civil and architectural materials have been used in major countries in the world. Polypropylene fiber reinforced concrete has many advantages in terms of economical aspect, chemical stability and durability. It has been reported that polypropylene fiber can control restrained tensile stresses and cracks and increase toughness, resistance to impact, corrosion, fatigue and durability. The purpose of the present study is, therefore, to investigate the strength as well as many mechanical characteristics including toughness and shrinkage control properties. A specially devjsed shrinkage test has been applied to measure the crack control characteristics of polypropylene fiber reinforced concrete. The present study indicates that the polypropylene fiber reinforced concrete curbs greatly the crack occurrence due to shrinkage and enhances toughness resistance. The present study provides a firm base for the efficient use of polypropylene fiber reinforced concrete in actual construction such as pavements and slab structures.

• Research in Community and Public Health Nursing
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• v.6 no.2
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• pp.183-196
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• 1995

The purpose of this study was to construct a substantive theory about the substantials of stress of Korean Wives in the community. The subjects were 10 wives. In the process of data analysis, 'burden' was found to be the core phenomenon. And the properties of burden were 'burden of domestic economy', 'a sence of duty about the esteemed family of her husband', 'role burden in a family and her work place', and 'burden of conception'. Twenty five hypotheses were derived from the integration of categories. It is as follows : 1. The stronger the difference as perceiced by subjects, the stronger the burden will be. 2. The stronger the dissatisfaction, the stronger the burden will be. 3. The stronger the trouble, the stronger the burden will be.4. The stronger the worry, the stronger the burden will be. 5. The stronger the forcible demand, the stronger the burden will be. 6. The stronger the regret, the stronger the burden will be. 7. The rarer the communication, the stronger the burden will be. 8. The stronger the fatigue, the stronger the burden will be. 9. The stronger the anger, the stronger the burden will be. 10. The stronger the worrisome feeling, the stronger the burden will be. 11. The stronger the unbearable feeling, the stronger the burden will be. 12. The stronger the resentment. the stronger the burden will be. 13. The stronger the sence of insufficiency, the stronger the burden will be. 14. The stronger the estrangement, the stronger the burden will be. 15. The stronger the attachment, the stronger the burden will be.

• Journal of Ocean Engineering and Technology
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• v.26 no.2
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• pp.48-57
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• 2012

This paper deals with numerical analyses in the context of estimations of hydrodynamic motions and dynamic loads for a floating type offshore platform using some exclusive simulation code such as code for the simulation of a floating type of offshore crane based on multi-body dynamics, along with the commercial code AQWA. Verifications of numerical models are carried out by comparing the RAO results from the simulation code. In the verification analyses, hydrodynamic motions are examined in the frequency domain for the floating type offshore platform according to the mooring lines. Both the hydrodynamic motions and dynamic loads are estimated for floating type offshore platforms equipped with the catenary type and taut mooring lines. A review and comparison are carried out for the numerically estimated results. The structural safety of the connection parts in an offshore structure such as a floating type offshore platform is one of the most important design criteria in view of fatigue life. The dynamic loads in the connecting area between a floating type offshore platform and its mooring lines are estimated in detail according to variations in the mechanical properties of the mooring lines. The dynamic tension load on the mooring lines is also estimated.