• 한국분말재료학회지
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• 제28권4호
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• pp.287-292
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• 2021

In this study, the layered structures of immiscible Fe and Cu metals were employed to investigate the interface evolution through solid-state mixing. The pure Fe and Cu powders were cold-consolidated by high-pressure torsion (HPT) to fabricate a layered Cu-Fe-Cu structure. The microstructural evolutions and flow of immiscible Fe and Cu metals were investigated following different iterations of HPT processing. The results indicate that the HPT-processed sample following four iterations showed a sharp chemical boundary between the Fe and Cu layers. In addition, the Cu powders exhibited perfect consolidation through HPT processing. However, the Fe layer contained many microcracks. After 20 iterations of HPT, the shear strain generated by HPT produced interface instability, which caused the initial layered structure to disappear.

• Geomechanics and Engineering
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• 제10권2호
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• pp.225-245
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• 2016

Settlement of foundations in permafrost regions primarily results from three physical and mechanical processes such as thaw consolidation of permafrost layer, creep of warm frozen soils and the additional deformation of seasonal active layer induced by freeze-thaw cycling. This paper firstly establishes theoretical models for the three sources of settlement including a statistical damage model for soils which experience cyclic freeze-thaw, a large strain thaw consolidation theory incorporating a modified Richards' equation and a Drucker-Prager yield criterion, as well as a simple rheological element based creep model for frozen soils. A novel numerical method was proposed for live computation of thaw consolidation, creep and freeze-thaw cycling in corresponding domains which vary with heat budget in frozen ground. It was then numerically implemented in the FISH language on the FLAC platform and verified by freeze-thaw tests on sandy clay. Results indicate that the calculated results agree well with the measured data. Finally a model test carried out on a half embankment in laboratory was modeled.

• Pediatric Infection and Vaccine
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• 제5권2호
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• pp.302-307
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• 1998

Hemolytic anemia due to cold agglutinin disease is a known complication of Mycoplasma pneumoniae infection but is rarely observed, particularly in children. A case of Mycoplasma pneumonia complicated with hemolytic anemia is presented. A 7 year-old girl was adimitted because of fever, cough, sputum and pale appearance. Chest X-ray showed pneumonic consolidation of Rt. upper lobe, lingular division. Laboratory studies disclosed the following values : Hb 5.3g/dL, Hct 11.1%, reticulocyte 2.9%, indirect Coombs test negative, direct Coombs test(monovalent) Anti-C3d positive, Anti-IgG negative, Anti-IgM negative, cold agglutinin titer 1 : 256, mycoplasma antibody titer 1 : 640, total bilirubin 1.0mg/dL. Initial PBS before wanning showed agglutination of red blood cells. The diagnosis of cold agglutinin hemolytic anemia complicating mycoplasma pneumonia was made. And treatment with roxithromycin, prednisolone and avoiding cold exposure was initiated, and complete recovery ensued. We report a case of cold agglutinin hemolytic anemia complicating mycoplasma pneumonia in children.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2001년도 추계 학술발표강연 및 논문개요집
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• pp.39-39
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• 2001

• 한국분말재료학회지
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• 제9권3호
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• pp.153-160
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• 2002

A nitrogen gas atomized aluminum powder was consolidated by powder-in sheath rolling method. A pure aluminum tube with outer diameter of 12 mm and wall thickness of 1mm was used as a sheath. The aluminum tube filled with the aluminum powder, first, was cold-rolled to the thickness of 6mm for performing, and then consolidated by the cold rolling and/or subsequent hot rolling at 360, 460 and $560^{\circ}C$. The aluminum powder compact fabricated by the sheath rolling showed high relative density more than 0.96 at any rolling conditions. The 0.2% proof stress increased with increasing hot rolling reduction and hot rolling temperature. Tensile strength was hardly affected by change in the hot rolling reduction, whereas it decreased with increasing hot rolling temperature. The powder compact showed the large elongation when cold rolling or hot rolling reduction was large. It was found that the sheath rolling was an effective method for consolidation of aluminum powder.

• 한국분말재료학회지
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• 제11권4호
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• pp.341-347
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• 2004

In the study, a hybrid constitutive model for densification of metallic powders was applied to cold isostatic pressing. The model is based on a pressure-dependent plasticity model for porous materials combined with a dislocation density-based viscoplastic constitutive model considering microstructural features such as grain size and inter-particle spacing. Comparison of experiment and calculated results of microscale and nanoscale Cu powders was made. This theoretical approach is useful for powder densification analysis of various powder sizes, deformation routes and powder processing methods.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.668-673
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• 2008

In this paper, we developed a physically-based micromechanical model for inelastic deformation of ceramic powders. The aggregate response of ceramic particles was modeled using the two-surface yield function which considered the shear-induced dilatancy caused by friction, rolling resistance and cohesion between powder particles and consolidation caused by plastic deformation of powder themselves under high compression. The constitutive equations were implemented into the user-subroutine VUMAT of finite element program ABAQUS/Explicit. The material parameters in the constitutive model were identified by calibrating the model to reproduce data from triaxial compression tests and simple compression tests. The density distribution obtained by using the proposed model was in good quantitative agreement with the experimental results of the triaxial compression and cold isostaic compression as well.

• 대한금속재료학회지
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• 제46권3호
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• pp.182-188
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• 2008

Carbon nanotubes(CNTs) have outstanding mechanical, thermal, and electrical properties. Thus, by placing nanotubes into appropriate matrix, it is postulated that the resulting composites will have enhanced properties. Cold spray can produce thick metal-based composite coatings with very high density, low oxygen content, and phase purity, which leads to excellent physical properties. In this study, we applied cold spray coating process for the consolidation of Cu/CNT composite powder. The precursor powder mixture, in which CNTs were filled into copper particles, was prepared to improve the distribution of the CNT in copper matrix. Pure copper coating was also conducted by cold spraying as a reference. Annealing heat treatment was applied to the coating to examine its effect on the properties of the composite coating. The hardness of Cu/CNT composite coating represented similar value to that of pure copper coating. It was importantly found that the electrical conductivity of the Cu/CNT composite coating significantly increased from 53% for the standard condition to almost 55% in the optimized condition, taking annealed ($500^{\circ}C/1hr$.) copper coating as a reference (100%). The thermal conductivity of Cu/CNT composite coating layer was higher than that of pure Cu coating. It was also found that the electrical and thermal conductivities of Cu/CNT composite could be improved through annealing heat treatment. The microstructural evolution of Cu/CNT coating was also investigated and related to the macroscopic properties.

• Journal of Magnetics
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• 제11권3호
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• pp.126-129
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• 2006

The phosphate coating on the $(Fe_{0.97}Cr_{0.03})_{76}(Si_{0.5}B_{0.5})_{22}C_2$ amorphous powders with an average size of 10 ${\mu}m$ in diameter has been carried out in aqueous 1.0-2.0 wt% $H_3PO_4$ solutions, and the consolidation behavior and magnetic properties of their compressed powder cores has been investigated. The phosphate coating could provide efficient electrical insulation between amorphous powders and improved consolidation ability at room temperature. Especially when the powders were treated in more concentrated phosphoric acid solution, enhanced phosphate covering and higher frequency/dc-bias stability were achieved. The powder cores phosphate-coated in 2.0 wt% $H_3PO_4$ solution exhibited constant permeability of 21 up to 10 MHz, 110 of the quality factor at 0.9 MHz, 610 mW/cm3 core loss at 100 kHz/0.1 T and 89 of percent permeability at 100 kHz.

• 한국지반환경공학회 논문집
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• 제13권3호
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• pp.21-27
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• 2012

동토를 대상으로 건설되는 지반구조물과 방사능 폐기물 처리장의 점토벽체의 성능을 결정하기 위해서는 정확한 세립토의 열전도계수 산정이 중요하다. 그러나 세립토의 경우 시료 성형과정에서의 교란, 포화상태 유지, 그리고 측정 장치의 장기발열로 인해 함수비 구배 발생과 같은 기존 열전도계수 측정 장비의 문제점으로 인해 열전도계수 측정에 오차가 발생한다. 본 연구에서는 압밀장비를 개조하여 열전도계수 측정용 니들프로브를 삽입한 상태에서 압밀시험을 활용하여 하중조건과 건조밀도의 변화에 따른 열전도계수를 연속적으로 측정하였다. 또한 실내실험 결과를 토대로 흙입자 구성성분의 열전도계수를 고려한 예측 모델의 신뢰성을 분석하였다.