• Composites Research
• /
• v.32 no.6
• /
• pp.327-334
• /
• 2019

The delamination is a special mode of failure occurring in composite laminates. Several numerical studies with finite element analysis have been carried out on the delamination behavior of unidirectional composite laminates. On the other hand, the fracture for the multi-directional composite laminates may occur not only along the resin-fiber interface between plies known as interply or interlaminar fracture but also within a ply known as interyarn or intralaminar fracture accompanied by matrix cracking and fiber bridging. In addition, interlaminar and intralaminar cracks appear at irregular proportions and intralaminar cracks proceeded at arbitrary angle. The probabilistic analysis method for the prediction of crack growth behavior within a layer is more advantageous than the deterministic analysis method. In this paper, we analyze the crack path when the mode I load is applied to the cross-ply carbon/epoxy composite laminates and collect and analyze the probability data to be used as the basis of the probabilistic analysis in the future. Two criteria for the theoretical analysis of the crack growth direction were proposed by analyzing the stress field at the crack tip of orthotropic materials. Using the proposed method, the crack growth directions of the cross-ply carbon/epoxy laminates were analyzed qualitatively and quantitatively and compared with experimental results.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.1
• /
• pp.48-57
• /
• 2007

The fatigue crack growth behavior of a cracked and patch-repaired Ah2024-T3 panel has been monitored by acoustic emission(AE). The overall crack growth rate was reduced The crack propagation into the adjacent hole was also retarded by introducing the patch repair. AE signals due to crack growth after the patch repair and those due to debonding of the plate-patch interface were discriminated by usiag the principal component analysis. The former showed high center frequency and low amplitude, whereas the latter showed long rise tine, low frequency and high amplitude. This type of AE signal recognition method could be effective for the prediction of fatigue crack growth behavior in the patch-repaired structures with the aid of AE source location.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.32 no.5
• /
• pp.169-174
• /
• 2022

This study is to verify the feasibility of SiC single crystal growth using recycled SiC powder. The fundamental physical properties such as particle size, shape, composition and impurities of the recycled powder were analyzed, and the sublimation behavior occurring inside the reactor were predicted using the basic data. As a result of comprehensive judgment, the physical properties of the recycled powder were suitable for single crystal growth, and single crystal growth experiments were conducted using this. 100 mm 4H-SiC single crystal ingot with a height of 25 mm was grown without polytype inclusion. In the case of micro-pipe density was 0.02 ea/cm² and resistivity characteristics was 0.015~0.020 ohm·cm², commercial level quality was obtained, but additional analysis related to dislocation density and stacking faults is required for device application.

• Journal of the KSME
• /
• v.35 no.7
• /
• pp.593-602
• /
• 1995

수출주도형 산업구조를 가지고 있는 우리 나라의 경제여건은 1960년대 초 경제개발 5개년 계획을 수립한 이래 지속적인 성장을 기록하여 왔다. 그러나 1986년도에 3저라는 국제경제여건을 호기로 삼아 국제무역수지 흑자를 기록한 이후 선진국의 보호장벽 강화, 세계적인 BLOCK 경제화, WTO 출범에 따른 국내시장 개방압력, 국내임금의 급속한 상승 등 수많은 대내외적 여건으로 인하여 우리경제의 성장에 큰 부담으로 작용하고 있다. 1994년의 경우 전체무역적자가 63억 3천만 달 러를 기록함으로써 한국경제의 계속적인 무역역조현상이 큰 문제점으로 대두되고 있고 1994년 기준으로 전체무역적자의 188%이상에 해당하는 118억 7천만 달러가 대일무역에서 발생한 대일 역조라는 사실과 최근 몇년간 대일무역적자는 다소 개선되고 있으나 전체 무역적자에서 차지하는 비중이 더욱더 높아가고 있는 것에 대한 대책이 시급한 실정이다. 이같은 대일무역적자 문제는 1960년대 이후 급속한 경제성장만을 추구하여 노동집약형 사업이 주가된 경제성장의 결과이며, 산업재, 특히 기계분야에 대한 기술축적의 부족으로 대부분의 자본재 및 중간재와 기술력에 대한 대일의존도의 심화 등에 그 원인이 있다고 할 수 있다. 이러한 점에서 수출 주도형의 한국경제 하에서는 대일무역역조 특히 기계공업분야의 역조현상은 반드시 해결해야 할 중요한 정책과제 임을 인식해야 하며, 이 글에서는 이에 대한 다각적인 대책을 검토하여 해결방안을 제시해 보 고자 한다.

• Ecology and Resilient Infrastructure
• /
• v.9 no.3
• /
• pp.183-193
• /
• 2022

The growth inhibitory effect of Microcystis aeruginosa according to the ultrasonic irradiation time was evaluated using a large algae sample volume (10 L) for various ultrasonic irradiation times (0.5, 1, 1.5, 2, 2.5 and 3 hr) at a laboratory scale. Based on the analysis of Chl-a and cell number of M. aerginosa, algae growth inhibition was observed with the decrease in Chl-a and cell number in all experimental groups after the ultrasonic irradiation. For the experimental group (T_B, T_C, T_D) with an ultrasonic irradiation time of less than 2 hours, rapid regrowth of algae was observed after growth inhibition, but the experimental group (T_E, T_F, T_G) with an irradiation time of more than 2 hours successfully inhibited algal growth lasting one or two more days. Based on the comparison of the recovery time to initial cell number the experimental group (T_B, T_C, T_D) took less than 20 days whereas the experimental group (T_E, T_F, T_G) took about 30 days. Correspondingly, the experimental group showed a high first order decay rate (𝜅) in proportion to the ultrasonic irradiation time during the growth inhibition period. Additionally, the specific growth rates (𝜇) during regrowth in the experimental group with irradiation time of more than 2 hours were relatively low compared to those in the experimental group with less than 2 hours. Therefore, ultrasonic irradiation for more than 2 hours is required for long-term (30 days) inhibition of algal growth in stagnant waters. However, the appropriate ultrasonic irradiation time for algae growth inhibition should be determined according to various field conditions such as the volume of stagnant water, water depth, flow rate, algae concentration, etc. Finally, damages to the algal cell surface and cell membrane were clearly observed, and both destruction and disturbance of gas vesicles of M. aeruginosa in the experimental group were discovered, indicating the growth inhibitory effect of Microcystis aeruginosa according to the ultrasonic irradiation time was confirmed.

• KSBB Journal
• /
• v.24 no.1
• /
• pp.96-100
• /
• 2009

One of the major drawbacks associated with the high-level expression of the recombinant proteins in Escherichia coli is the formation of insoluble inclusion bodies in the cytoplasm. Production of recombinant protein at reduced temperature has proven effective in improving the solubility of a number of structurally and functionally unrelated proteins, but a major limitation of using low temperatures for recombinant protein production in E. coli is the reduced rate of synthesis of the heterologous protein caused by the significant reduction of cell growth rate. Here we investigated the effect of co-expression of CspA, a cold-shock protein known to be RNA chaperone at low temperature, on the productivity of recombinant protein at various temperatures by using green fluorescence protein (GFP) as a model recombinant protein. We could observe that the co-expression of CspA enhanced the productivity of GFP at $15^{\circ}C$ by accelerating the growth of E. coli at the temperature. On the other hand, the CspA coexpression didn't affect the cell growth rate as well as the specific GFP production rate at other tested temperatures, $20^{\circ}C$, $25^{\circ}C$, and $37^{\circ}C$.

• Microbiology and Biotechnology Letters
• /
• v.16 no.4
• /
• pp.327-333
• /
• 1988

For optimal production of recombinant human interleukin-2 (IL-2) in E. coli the effect of fermentation conditions on cell growth, IL-2 production, and stability of recombinant cells were investigated. Among the complex nutrients tested in this work, yeast extract, peptone and corn steep liquor were found to be effective for recombinant cell growth. The recombinant cells were maintained stably under repression condition (3$0^{\circ}C$), but the stability of recombinant cells were drastically reduced upon induction of IL-2 expression (42$^{\circ}C$) even under the selection pressure. Addition of antibiotics to the culture medium resulted in the cell growth inhibition without significant improvement in recombinant stability. When the expression of IL-2 gene was induced at different growth phases, highest IL-2 production was achieved by the induction of IL-2 at the middle-exponential growth phase. It was found that the production of IL-2 significantly inhibited the cell growth and the ex-pression of other genes in the plasmid.

• Electrical & Electronic Materials
• /
• v.4 no.2
• /
• pp.175-184
• /
• 1991

급속 열처리 방법으로 두께가 약 80.angs.C인 산화막을 성장시킨 후 950.angs.C와 1150.angs.C의 온도에서 15초-120초 동안 질화 및 재산화 공정을 수행하여 초 박막 구조의 질화 및 재산화된 질화 산화막을 성장하였다. 성장한 질화산 화막과 재 산화된 진화 산화막의 전기적 특성은 C-V, I-V, 전하 포획 및 TDDB 측정등을 통하여 분석하였다. 측정된 소자의 특성으로부터 질화 조건이 950.angs.C, 60초이고 재산화 조건이 1150.angs.C, 60초인 재산화된 질화 산화막은 전기적 스트레스 인가후에 전하 포획에 의한 평탄전압변화(.DELTA. $V_{fb}$ )와 계면 상태밀도( $D_{itm}$)의 증가가 산화막보다 적은 우수한 특성을 나타내는 것을 알 수 있었다.

• Cement
• /
• s.202
• /
• pp.9-14
• /
• 2014

남북통일은 국가 경제활동의 기반을 질적으로 변화시킴으로써 새로운 성장의 기회를 창출할 것으로 보인다. 특히 국내 경제는 인프라 확충, 산업생산 기반 정비, 생산재 수요 증가, 소비재 및 서비스 수요 증가로 이어지며 다양한 산업에 새로운 성장의 계기를 제공할 것으로 기대된다. 여기서는 현대경제연구원의 '통일 한국의 12대 유망 산업' 보고서를 통해 통일 이후 경제활동 기반의 변화, 산업발전 경로, 성장이 기대되는 주요 산업 등에 대해 살펴본다.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.4 s.97
• /
• pp.13-18
• /
• 1999

섬유강화금속적층재(Fiber Reinforced Metal Laminates. FRMLs)는 고강도금속과 섬유강화복합재료(Fiber Reinforced Composite Materials)를 적층한 새로운 종류의 하이브리드 재료이다. 국산 아라미드 섬유인 헤라크론(Heracron, 코오롱)과 국내 복합재료 제작기술(한국화이바)을 사용하여 섬유강화금속적층재를 제작하고, 이를 HERALL(Heracron Reinforced Aluminum Laminate)이라 명명하였다. HERALL(Heracron Reinforced Aluminum Laminate)의 피로균열성장특성 및 피로균열진전 방해기구를 ARALL(Aramid-fiber Reinforced Aluminum alloy Laminates) 및 Al 2024-T3과 비교해석하였다. HERALL과 ARALL은 균열진전을 저지하는 아라미드 섬유로 인해 뛰어난 피로균열성장특성 및 피로저항성을 보여주었다. 아라미드 섬유의 균열브리드징으로 인한 $K_{max}$의 감소량과 Al 2024-T3의 균열닫힘으로 인한 $K_{max}$의 증가량을 구할 수 있는 응력-COD법을 사용하여 실제로 균열성장에 영향을 준 유효응력확대계수범위를 측정하였다. 균열선단으로부터 균열을 가공하면서 COD 변화량을 측정하여 균열브리징 영역을 구하였다.