• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.854-858
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• 2002

In this study, Fatigue crack growth behavior of the laser welded sheet metal due to a single overload was investigated. From Fatigue crack propagation test, it was observed that the retardation of fatigue crack growth has been more effective in the welded specimen than in the base metal. And if the distance between the welded part and the position of overload is too close the retardation of fatigue crack growth at the welded part has been decreased. From FEM analysis, it was observed the retardation has been more effective compressive residual stress than plastic zone.

• 한국안전학회지
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• 제8권1호
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• pp.54-58
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• 1993

The fatigue growth behavior of short cracks were studied various load ratios. Computer-aided unloading elastic compliance method was employed to measure the closure and the length of short cracks. In the dc/dN-$\Delta$K relationships. the decreasing behavior of the growth rate of short cracks is due to the decrease of crack opening ratio with increasing crack length. Irrespective of load ratio. the growth rate of short cracks can be well decribed in terms of the effective stress intensity factor range $\Delta$K$_{eff}$, which is calculated on the base of crack closure. dc/dN-$\Delta$K$_{eff}$ relationships of short cracks are found to coincide well with the corresponding long crack relationships. accordingly. the growth rate of short cracks can be predicted using that of long cracks.ort cracks can be predicted using that of long cracks.cks.

• Macromolecular Research
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• 제9권6호
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• pp.319-326
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• 2001

Fatigue crack growth (FCG) behavior of natural rubber/ethylene-propylene-diene rubber (NR/EPDM) blend vulcanizates under dynamic tearing condition was investigated by using a fracture mechanics approach. It appeared that variation of crack growth rate with blend compositions was dependent on the level of imposed tearing energy G. At low tearing energy region, the FCG rates of the blend were lower as the EPDM content was increased, while at high tearing energy region, the trend was reversed. Over the measured range of tearing energy G, all blend compositions showed the lower crack growth rates compared to the average of properties of component elastomers. When the blends were thermally aged, the fatigue resistance of the blends was deteriorated in proportion to the concentration of EPDM phase. Fatigue crack growth behavior of the blends was supposed to be associated with the inhomogeneities of the crosslink structure of the blends arising from cure incompatibility of the EPDM and NR when they are sulphur cured.

• 대한기계학회논문집
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• 제18권3호
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• pp.548-554
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• 1994

The high temperature fatigue crack growth behavior of SUS 304 stainless steel at $550^{\circ}C$ and $650^{\circ}C$ was investigated under various kinds of stress ratio and frequency in sinusoidal waveform on the basis of the non-linear fracture mechanics. The result arranging crack growth rate by modified J-integral J' showed influence of stress ratio and frequency. All the data obtained under the test at $550^{\circ}C$ were plotted within data band of da/dN-${\triangle}J_f$ relationship for cycle-dependent crack growth. On the basis of static creep and cycle-dependent data band; both time- and cycle-dependent crack growth behavior was observed under loading conditions at $650^{\circ}C$, but cycle-dependent crack growth behavior predominantly appeared and time-dependent crack growth behaviour was little observed under loading conditions at $550^{\circ}C$. Fractographic examinations for fracture surface indicated that the fracture mode was generally transgranular. The stripes were found on fracture surface and each stripe was accompanied by a crack tip blunting and an abrupt increase in the load-point displacement. The $J'_{an}$ had a validity in case of $650^{\circ}C, but scarcely had it in case of $550^{\circ}C$.

• 대한지역사회영양학회지
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• 제26권1호
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• pp.1-11
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• 2021

Objectives: This study was conducted to assess the eating behavior, growth, and dietary practices of children aged 3~5 years living in the Seoul and Gyeonggi Provinces. Methods: Self-administered questionnaires were completed by 237 mothers of preschool children between April and June 2018. Z-scores for weight-for-age, height-for-age, and BMI-for-age were calculated to determine the children's growth status. Dietary practices were evaluated using the nutrition quotient for Korean preschoolers (NQ-P). Results: In our study, 29.5% of children were in the eating-small-amounts group, 46.8% of children were in the neophobic behavior group, and 61.2% of children were in the refusal-of-specific food group. Specific foods found to have a high frequency of rejection are listed in descending order as follows: shellfish, soy, mushroom, shrimp, vegetables, milk, eggs, yogurt, seaweed, meat, fruits, and fish. The eating-small-amounts group had lower Z-scores for weight-for-age, height-for-age, and BMI-for-age than the non-picky eaters' group. Compared to the non-picky eaters' group, the eating-small-amounts group of picky eaters had lower scores on the moderation and environment items of the NQ-P, the neophobic behavior group had lower scores on the balance and environment items of the NQ-P, and the refusal-of-specific food group had lower scores on the balance, moderation, and environment items of the NQ-P. Conclusions: Children classified with picky eating behavior had lower growth and development, lower diet diversity, less balanced food intake, and had greater difficulty in abstaining from eating unhealthy foods than non-picky eaters. Therefore, a lot of patience and intensive efforts are needed to encourage children to encounter, experience, and accept unfamiliar food. It is more effective to provide eating behavior guidance by gently encouraging children, than by being strict and forceful. Besides, since the eating behavior of children is influenced maximally by the dietary lifestyle at their homes, it is important to ensure that a healthy dietary lifestyle is maintained at home.

• 한국보육지원학회지
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• 제10권2호
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• pp.153-174
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• 2014

본 연구는 유아가 함께 참여할 수 있도록 녹색성장교육에 기초한 프로그램을 구성하고 이 프로그램이 유아의 환경보전지식, 태도 및 행동에 미치는 효과를 분석하는데 목적이 있다. 녹색성장교육에 기초한 프로그램은 '생태계', '에너지', '자원', '녹색시민의식'으로 크게 4가지 내용 영역으로 구성하였고, 각 내용 영역에 가장 적합하다고 판단되는 구체적인 활동을 20회기로 계획하여 만 5세 유아를 대상으로 프로그램을 실시하였다. 프로그램 실시 후 환경보전지식, 환경보전태도, 환경보전 행동에서 실험집단 유아의 점수가 비교집단 유아보다 유의하게 높은 것으로 나타나 녹색성장교육에 기초한 프로그램이 유아의 환경보전지식 습득과 환경보전태도 및 행동의 향상에 효과적임을 알 수 있었다. 본 연구는 유아교육현장에서 녹색성장교육을 실행하는데 많은 어려움을 호소하고 있는 현실을 반영하여, 녹색성장교육을 실행하고자 하는 유아 교사에게 구체적이고 실질적인 정보를 제공할 수 있을 것으로 기대한다.

• 한국분말재료학회지
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• 제11권2호
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• pp.165-170
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• 2004

Growth behavior of two different types of grains, faceted and rounded, in a liquid matrix has been studied in the (75WC-25TiCN)-30Co system. Powder samples were sintered above the eutectic temperature for various times under a carbon saturated condition. (Ti,W)(C,N) grains with a rounded shape and WC grains with a faceted shape coexisted in the same Co based liquid. With increasing sintering time, the average size of (Ti.W)(C,N) grains increased continuously and very large WC grains appeared. The growth of rounded (Ti,W)(C,N) grains followed a cubic law, r^3-r^3_0$=kt, where r is the average size of the grains, $r_0$ the initial average size, k the proportionality constant and t the sintering time. indicating a diffusion-controlled growth. On the other hand, the growth of the faceted WC grains resulted in a bimodal grain size distribution, showing an abnormal grain growth. These observations show that the growth behavior of different types of grains is governed by their shape, faceted or rounded, even in the same liquid matrix.

• 한국결정성장학회지
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• 제26권2호
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• pp.53-57
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• 2016

저항가열 방식으로 제작된 설비를 이용하여 SiC 단결정을 성장하였다. 성장 조건에 따라 결정의 성장 양상이 달랐으며, 원료부의 온도와 결정 성장부의 온도에 따라 각각 온도 설정이 필요함을 알았다. 본 논문에서는 SiC 결정의 성장 온도에 따른 성장 결과에 대하여 고찰해 보았으며, 이에 대한 결과를 보고하고자 한다.

• Communications for Statistical Applications and Methods
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• 제17권6호
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• pp.909-916
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• 2010

A trend in software reliability engineering is to take into account the coverage growth behavior during testing. A coverage growth function that represents the coverage growth behavior is an essential factor in software reliability models. When multiple competitive coverage growth functions are available, there is a need for a criterion to select the best coverage growth functions. This paper proposes a selection criterion based on the prediction error. The conditional coverage growth function is introduced for predicting future coverage growth. Then the sum of the squares of the prediction error is defined and used for selecting the best coverage growth function.

• 대한토목학회논문집
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• 제11권1호
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• pp.29-36
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• 1991

장섬유 강화 마그네슘 복합제(FP/ZE41A)의 피로 균열 성장 거동에 대한 열처리 효과를 규명한 것으로 TEM관측에 의해 알루미나 섬유와 마그네슘 복합 매트릭스간의 상호 접변을 완화시키기 위하여 풀림을 실시하였다. 피로 균열 성장 방향에 수직한 섬유와 평행한 섬유들에 대한 피로 균열 성장 거동에 관한 실험을 실시 한 바, 피로 균열 성장 방향에 수직한 시험편의 경우 열처리를 실시한 시험편은 잔류 응력을 제거시키지 않은 시험편에 비해 피로 균열 성장에 대한 더 많은 저항성을 갖고 있음을 알수 있었다. 그러나, 이에 반해 피로 균열 성장 방향에 평행한 시험편의 경우는 잔류 응력을 제거시키지 않은 시험편 이 열처리를 실시한 시험편에 비해 더 많은 피로 균열 성장 저항성을 내포하고 있다는 피로 균열 성장 거동에 대한 차이점을 발견할 수 있었다. 피로 파괴 표면에 대한 연성 파열과 섬유 박리를 SEM관찰한 결과 열처리는 피로균열 성장 거동에서 지적된 바와 같이 섬유와 매트릭스 상호면의 강도를 약화시킨다는 것을 알 수 있었다.