• 열처리공학회지
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• 제10권1호
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• pp.55-62
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• 1997

The morphology of deformation induced dislocations in polycrystalline $Ni_3$(Al, Cr) containing $M_{23}C_6$ precipitates has been investigated in terms of transmission electron microscopy(TEM). Fine Polyhedral precipitates of $M_{23}C_6$ appeared in the matrix by aging at temperatures around 973 K after solution annealing at 1423 K. TEM examination revealed that the $M_{23}C_6$ phase and the matrix lattices have a cube-cube orientation relationship and keep partial atomic matching at the {111} interface. After deformation at temperature below 973 K, typical Orowan loops were observed surrounding the $M_{23}C_6$ particles. At higher deformation temperatures, the Orowan loops disappeared and the morphology of dislocations at the particle-matrix interfaces suggested the existence of attractive interaction between dislocations and particles. The change of the interaction modes between dislocation and particles with increasing deformation temperature can be considered as a result of strain relaxation at the interface bet ween matrix and particles.

• 한국게임학회 논문지
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• 제17권1호
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• pp.89-98
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• 2017

본 논문에서는 물리기반 동적 변형을 실시간에 안정적으로 시뮬레이션하는 새로운 ARAP(as-rigid-as-possible) 방법을 제안한다. 1, 2, 3차원 물체의 변형을 안정적이며, 빠르고, 일관성 있게 다루기 위하여 방향성 입자로 이루어진 변형 그래프를 도입하고 그에 따른 ARAP 변형에너지를 공식화한다. 방향성 입자의 안정적인 시간 적분을 위해서는 변분 공식화에 기반을 둔 내재적 시간 적분 기법을 개발한다. 또한 국지적/전역적 최적화를 교대로 반복 적용하여 방향성 입자의 최적 위치 및 회전을 구한다. 제안된 방법은 구현이 쉽고 복잡한 변형을 실시간에 시뮬레이션할 수 있을 정도로 빠르다.

• 한국컴퓨터그래픽스학회논문지
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• 제18권4호
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• pp.35-40
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• 2012

컴퓨터 그래픽스 분야에서 변형 및 파괴 시뮬레이션은 매우 중요한 기법으로 영화 및 게임 등에서 그 응용 범위가 매우 넓다. 본 논문에서는 방향성 입자를 이용한 고체 시뮬레이션 기법[1]을 확장하여 과도한 변형에 의한 파괴 현상을 실시간에 안정적으로 근사할 수 있는 실용적인 기법을 제안한다. 제안된 기법은 방향성 입자 집합의 최적 회전을 엄밀히 계산함으로써 순수 신축을 정확히 얻을 수 있으며 이를 이용하여 파괴 현상을 손쉽게 정형화할 수 있다. 본 논문의 실험에서는 대규모 모델의 변형 및 파괴 시뮬레이션도 실시간에 수행되었다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1090-1094
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• 2009

Many problems in geotechnical engineering such as slop failure, debris flow, ground heaving due to embankment, and lateral flow caused by liquefaction are related to large deformation rather than small deformation. Traditional numerical methods such as finite element and finite difference methods have a difficulty to solve such large deformations because they use grids. A particle method was developed for fluid dynamics. The particle method can solve large deformation problems because it uses particles to discretize differential equations. It can also include soil constitutive model and thus solve soil behavior on various boundary conditions. In this study, a particle method, which is based on particles rather than grids, is introduced and used to simulate large deformation including soil failure. The developed method can be applied for various large deformation problems in geotechnical engineering because it incorporates soil constitutive models.

• Advances in nano research
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• 제13권4호
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• pp.313-323
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• 2022

The microstructure and mechanical properties of Cr-Ni steel and Cr-Ni steel-matrix nanocomposites reinforced with nano-ZrO₂ particles were investigated in this study. Cr-Ni steel and Cr-Ni/ZrO₂ nanocomposites were produced using a combination of high-energy ball milling, pressing, and sintering processes. The microstructures of the specimens were analyzed using EDX and XRD. Compression and hardness tests were performed to determine the mechanical properties of the specimens. Nano-ZrO₂ particles were effective in preventing chrome carbide precipitate at the grain boundaries. While t-ZrO₂ was detected in Cr-Ni/ZrO₂ nanocomposites, m-ZrO₂ could not be found. Few α'-martensite and deformation bands were formed in the microstructures of Cr-Ni/ZrO₂ nanocomposites. Although nano-ZrO₂ particles had a negligible impact on the strength improvement provided by deformation-induced plasticity mechanisms in Cr-Ni/ZrO₂ nanocomposites, the mechanical properties of Cr-Ni steel were significantly improved by using nano-ZrO₂ particles. The hardness and compressive strength of Cr-Ni/ZrO₂ nanocomposite were higher than those of Cr-Ni steel and enhanced as the weight fraction of nano-ZrO₂ particles increased. Cr-Ni/ZrO₂ nanocomposite with 5wt.% nano-ZrO₂ particles had almost twofold the hardness and compressive strength of Cr-Ni steel. The nano-ZrO₂ particles were considerably more effective on particle-strengthening mechanisms than deformation-induced strengthening mechanisms in Cr-Ni/ZrO₂ nanocomposites.

• 한국컴퓨터그래픽스학회논문지
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• 제28권4호
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• pp.13-22
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• 2022

본 논문에서는 최소 입자 단위의 역동적인 회전 움직임을 나타낼 수 있는 MPM(Material Point Method) 기반 단일 프레임워크를 소개한다. 우리가 표현하고자 하는 입자는 다양한 형상(Shape)을 가질 수 있음과 동시에, 선형(Linear momentum), 회전(Angular momentum) 운동을 함께 묘사할 수 있다. 그 결과 기존 구형 입자의 선형 움직임만을 나타내던 입자 기반 시뮬레이션과는 달리, 시각적으로 단일 입자의 역동적인 모습을 표현할 수 있다. 제안하는 프레임워크는 회전 운동을 큰 변형(Large Deformation)으로부터 분해 및 추출 할 수 있다는 점에서 MPM을 활용하였다. 본 기법은 MPM 적분 과정 중 계산되는 변형 구배 텐서(Deformation Gradient Tensor)를 극 분해(Polar Decomposition)하는 과정을 통해 회전 텐서(Rotation Tensor)를 추출하고, 각 입자의 선형 운동과 함께 이를 적용하여 결과적으로 입자 자체의 회전, 선형 운동을 동시에 표현 하는 것이 가능하다. 본 연구에서는 제안하는 기법의 검증을 위해 바람에 흩날리며 회전하는 입자의 모습 및 움직이는 물체와 정지한 입자간의 상호작용 시뮬레이션을 기존 MPM을 이용한 시뮬레이션과의 비교를 통해 진행하였다.

• Applied Microscopy
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• 제45권2호
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• pp.37-43
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• 2015

In present work, work-hardening behavior of TiCu-based bulk metallic glass composite with B2 particles has been studied by systemic structural and mechanical investigations. After yield, pronounced work-hardening of the alloy was clearly exhibited, which was mainly related to the martensitic transformation as well as the deformation twinning in B2 particles during deformation. At the early plastic deformation stage (work-hardening stage), the stress-induced martensitic transformation from B2 phase to B19' phase and deformation-induced twinning of B19' phase was preferentially occurred in the around interface areas between B2 phase and amorphous matrix by stress concentration. The higher hardness value was observed in vicinity of interface within the B2 particles which are probably connected with martensitic transformation and deformation twinning. This reveals that the work-hardening phenomenon of this bulk metallic glass composite is a result of the hardening of B2 particles embedded in amorphous matrix.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.750-751
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• 2006

We investigated the mechanism how the high green density can be provided during die lubricated warm compaction (WD). We observed and analyzed the densification processes of iron powders including different contents of an inner lubricant, and measured the lateral pressure at the die wall during WD in comparison with conventional compaction and warm compaction. As a result, the high density in WD was due to not only the particles-deformation enhanced by warming powders but also the particles-rearrangement promoted by reducing an amount of the inner lubricant rather than the die lubrication.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.1301-1302
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• 2006

Sintered composites of Al-8wt%Cu-10vol%SiCp were deformed by repressing or equal channel angular pressing(ECAP) at room temperature, $500^{\circ}C$ and $600^{\circ}C$. Repressing produced more densification than ECAP but resulted in much lower transverse rupture strengths. In both cases, deformation at room temperature and $500^{\circ}C$, resulted in much lower strengths than deformation at $600^{\circ}C$, and also caused the fracturing of some SiC particles. The higher bend strengths and less SiC fracturing at $600^{\circ}C$ are attributable to the presence of an Al-Cu liquid phase during deformation. The employment of copper coated SiC instead of bare SiC particles for preparing the composites was found not improving the properties.

• 한국재료학회지
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• 제23권10호
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• pp.574-579
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• 2013

The milling and particulate characteristics of Al alloy-$Al_2O_3$ powder mixtures for a reaction-bonded $Al_2O_3$ (RBAO) process were studied. A commercially available prealloyed Al powder with Zn, Mg, Cu and Cr alloying elements (7475 series) was mixed with a calcined sinter-active $Al_2O_3$ powder and then milled in centrifugal milling equipment for ~48 hrs. The Al alloy-$Al_2O_3$ powder mixtures after milling were characterized and evaluated in various ways to reveal their particulate characteristics during milling. The milling efficiency of the Al alloy increased with a longer milling time. Comminution of the Al alloy particles started with its elongation, showing a high aspect ratio. With a longer milling time, the elongated Al alloy particle changed in terms of its shape and size, becoming equiaxially fine particles. Regardless of the milling efficiency of the Al alloy particles, all of the Al alloy particles repeatedly experienced strong plastic deformation during milling, giving rise to higher density of surface defects, such as microcracks, and leading to higher residual microstress within the Al alloy particles. The chemical reactions, oxidation behavior and hydration behavior of the Al alloy particles and the hydrolysis characteristics of their reaction with the environment were also observed during the milling process and during the subsequent powder handling steps.