• Journal of Powder Materials
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• v.15 no.1
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• pp.37-45
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• 2008

This article presents the challenges toward the successful consolidation of $Al_2O_3$ nanopowder using magnetic pulsed compaction (MPC). In this research the ultrafine-structured $Al_2O_3$ bulks have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were investigated. The obtained density of $Al_2O_3$ bulk prepared by the combined processes was increased with increasing MPC pressure from 0.5 to 1.25 GPa. Relatively higher hardness and fracture toughness in the MPCed specimen at 1.25 GPa were attributed to the retention of the nanostructure in the consolidated bulk without cracks. The higher fracture toughness could be attributed to the crack deflection by homogeneous distribution and the retention of nanostructure, regardless of the presence of porosities. In addition, the as consolidated $Al_2O_3$ bulk using magnetic pulsed compaction showed enhanced breakdown voltage.

• Geomechanics and Engineering
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• v.10 no.1
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• pp.109-124
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• 2016

In this paper, process of dynamic powder compaction is investigated experimentally using impact of drop hammer and die tube. A series of test is performed using aluminum powder with different grain size. The energy of compaction of powder is determined by measuring height of hammer and the results presented in term of compact density and rupture stress. This paper also presents a mathematical modeling using experimental data and neural network. The purpose of this modeling is to display how the variations of the significant parameters changes with the compact density and rupture stress. The closed-form obtained model shows very good agreement with experimental results and it provides a way of studying and understanding the mechanics of dynamic powder compaction process. In the considered energy level (from 733 to 3580 J), the relative density is varied from 63.89% to 87.41%, 63.93% to 91.52%, 64.15% to 95.11% for powder A, B and C respectively. Also, the maximum rupture stress are obtained for different types of powder and the results shown that the rupture stress increases with increasing energy level and grain size.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.301-310
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• 2006

A series of laboratory tests was carried out for analyzing compaction characteristics of hydraulic fill soils(or hydraulically filled soils). Hydraulic fill soils were settled down by the weight of soil particle itself in water and consolidated by the extraction of water from the soil structures. Water content and dry unit weight were observed as the depth of sedimentation and consolidation soil. It was found from the result that the optimum water content $(W_{cpt})$ of the maximum unit weight$(\gamma_{dmax})$ is higher than that of laboratory compaction test(KS F 2312 A method). It was due to difference in compaction energy and compaction effect between two methods. And the maximum dry unit of hydraulic fill soil is smaller than that of laboratory compaction test. Especially in terms of compaction effect, the maximum relative compaction degrees$(R_{cmax})$ of Seamangum dredged sand, river sand and mixed sand, half and half of dredged and river sands, were 85%, 91% and 86%, respectively. It means that the compaction effect can be $85\sim91%$ of the maximum unit weight in laboratory compaction test.

• 한국초전도학회:학술대회논문집
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• v.11
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• pp.65-65
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• 2001

• Korean Journal of Materials Research
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• v.18 no.8
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• pp.411-416
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• 2008

In this research, fine-structure TiO2 bulks were fabricated in a combined application of magnetic pulsed compaction (MPC) and subsequent sintering and their densification behavior was investigated. The obtained density of $TiO_2$ bulk prepared via the combined processes increased as the MPC pressure increased from 0.3 to 0.7 GPa. Relatively higher density (88%) in the MPCed specimen at 0.7 GPa was attributed to the decrease of the inter-particle distance of the pre-compacted component. High pressure and rapid compaction using magnetic pulsed compaction reduced the shrinkage rate (about 10% in this case) of the sintered bulks compared to general processing (about 20%). The mixing conditions of PVA, water, and $TiO_2$ nano powder for the compaction of $TiO_2$ nano powder did not affect the density and shrinkage of the sintered bulks due to the high pressure of the MPC.

• Journal of Powder Materials
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• v.12 no.5 s.52
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• pp.345-350
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• 2005

In this study the nanostructured ${\alpha}-Al_{2}O_3$ ceramics have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent spark plasma sintering (SPS), and their density and hardness properties were investigated. The ${\alpha}-Al_{2}O_3$ prepared by the combined processes showed an increase by $8.4\%$ in density, approaching the value close to the true density, and an enhancement by $210\~400\;Hv$ in hardness, compared to those fabricated by MPC or static compaction method followed by sintering treatment.

• Nuclear Engineering and Technology
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• v.34 no.1
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• pp.60-67
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• 2002

The effects of ball-milling time(0 ~4 hrs) have been investigated on the change of powder characteristics, compaction behavior (compaction pressure range : 200 ~400MPa) and sinterability (1700'c in Ha atmosphere) of two different UO$_2$ powders (ex-ADU and ex-AUC) prepared by the wet process. It is observed that, while the ex-ADU UO$_2$ was little affected, the ex-AUC UO$_2$ was largely affected by the ball-milling treatment. This may be attributed to the characteristics of particle size formed during the preparation step, i.e.., the former has a small average size of about 1.0${\mu}{\textrm}{m}$, while the latter has a relatively large average size of about 301n. It appeared that the effective size reduction by ball-milling treatment is limited to the particle size larger than l${\mu}{\textrm}{m}$, and to the extent of maximum decrease in size of about 0.5tn. In the case of ex-AUC UO$_2$, it is observed that the particle size decreased with ball-milling time and green density and sintered density of the pellets prepared from ball-milled powder increased compared with those of pellets prepared from the as-received powder under the same conditions. This may be attributed mainly to the fine particles formed during the ball-milling treatment.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.967-968
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• 2006

This research reports for the successful consolidation of $Al_2O_3$ powder with retained ultra-fine structure using MPC and sintering. Measurements in the consolidated $Al_2O_3$ bulk indicated that hardness, fracture toughenss, and breakdown voltage have been much improved relative to the conventional polycrystalline materials. Finally, optimization of the compaction parameters and sintering conditions will lead to the consolidation of $Al_2O_3$ nanopowder with higher density and even further enhanced mechanical properties.

• Progress in Superconductivity
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• v.3 no.2
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• pp.218-223
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• 2002

The void volume fraction of cables is one of the effective parameters to characterize the joints of superconducting magnet. Because electrical resistance and cooling stability in the CICC (Cable-in-Conduit Conductors) joint are governed by the void volume fraction, it should be controlled constantly in the termination of cable. The change of cross-section shape in the cable was fecund during the unidirectional compaction of terminal sleeve. The non-uniform thickness of the sleeve after compaction is expected because the loading is not taxi-symmetric, and the plastic flow is also not axi-symmetric. The CICC was compacted from 45% void volume fraction to 15% by using two-piece compaction jig, which could be pressed mini-directionally. Commercial code, ABAQUS, was used to analyze the plastic flow in the sleeve during the unidirectional compaction. The increment of radius of curvature of compaction jig could minimize the change of the deformed shape of cables. The calculated results were agreed with the experimental observations.

• Journal of the Korean Geotechnical Society
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• v.31 no.10
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• pp.17-28
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• 2015

The strict regulations on eco-friendly construction and the significant reduction of natural aggregate resources have raised public concerns on the utilization of recycled aggregates for backfilling a power transmission pipeline trench. In this paper, the particle breakage of concrete-based recycled aggregates and river sand has been experimentally studied during the standard compaction test. The applied compaction energy does not significantly break the river sand particles down, and thus causes no change in the compaction curve, thermal resistivity, and particle gradation characteristics. On the other hand, considerable particle breakage was observed in case of the three recycled aggregates. Such particle breakage leads to enhancing compaction effort, reducing thermal resistivity, and changing particle gradation curve with finer particles that are broken during the first compaction. In addition, particle breakage is more dramatic in lower water contents because pore water may damp down the compaction energy.