• 대한기계학회논문집B
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• 제35권8호
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• pp.831-838
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• 2011

마이크로채널 표면의 핵에서 생성된 기포는 물을 작동유체로 이용하는 경우 채널의 좁은 단면적에 의해 압착되어 유동불안정성을 유발한다. 직관 마이크로채널에서 압착된 기포는 관성 유동의 역방향인 채널 상류로 진행한다. 마이크로채널에서 역방향 유동을 없애기 위해 채널 하류의 단면적을 확장시키는 것이 효과적이다. 그 이유는 압착된 기포의 전후단 계면의 표면장력에 의한 압력차이가 계면의 반지름에 역비례해서 자연적으로 기포가 채널 하류로 이동하려는 힘이 발생하기 때문이다. 확장 증발 마이크로채널에서 정적 유동불안정성 모델이 제시되었으며, 실험으로 모델을 검증하였다. 또한, 안정된 확장 시스템을 설계하기 위해 국부 설계 개념을 도입하였다. 검증된 모델과 개념을 바탕으로 안정된 확장 증발 마이크로채널 설계를 성공적으로 수행하였다.

• Interaction and multiscale mechanics
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• 제3권1호
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• pp.23-37
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• 2010

Concrete is a heterogeneous material consisting of coarse aggregate, mortar matrix and interfacial zones at the meso level. Though studies have been done to interpret the fracture process in concrete using meso level models, not much work has been done for simulating the macroscopic behaviour of reinforced concrete structures using the meso level models. This paper presents a procedure for the mesoscopic analysis of reinforced concrete beams using a modified micro truss model. The micro truss model is derived based on the framework method and uses the lattice meshes for representing the coarse aggregate (CA), mortar matrix, interfacial zones and reinforcement bars. A simple procedure for generating a random aggregate structure is developed using the constitutive model at meso level. The study reveals the potential of the mesoscopic numerical simulation using a modified micro truss model to predict the nonlinear response of reinforced concrete structures. The modified micro truss model correctly predicts the load-deflection behaviour, crack pattern and ultimate load of reinforced concrete beams failing under different failure modes.

• 대한기계학회논문집
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• 제7권2호
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• pp.123-129
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• 1983

The effect of the micro-internal stress which is induced in the ferrite grain by plastic constraint, on fracture behavior was investigated. The specimen used has combined microstructure with matrix of ferrite encapsulated by second phase of martensite. The micro-internal stress in the ferrite grain was estimated using a simple mechanical model, and its effect on micro and macro fracture behaviors was discussed. The results obtained are summarized as follows; The micro-internal stress promotes the formation of cleavage cracks in the ferrite during deformation. Consequently, it was concluded that the internal stress is one of the significant factors which cause the fracture ductility to decrease.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.509-510
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• 2006

Simulation of micro electrical discharge machining (micro-EDM) process using finite element analysis is proposed. Multiphysics model which has three steps; heat transfer analysis, structural analysis and electric field analysis is developed for simulation. Machined surface for successive five discharges is simulated using developed multiphysics model. Machined surface roughness was simulated under two discharge conditions and the simulated results are compared with actual machined surfaces. From the comparison it is demonstrated that the model can accurately predict the machined surface with the error less than $0.5{\mu}m$.

• 소성∙가공
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• 제24권3호
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• pp.194-198
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• 2015

Microstructure based FE simulations were conducted to investigate the micro-mechanical properties of ferrite-martensite dual-phase steels. The FE model was built based on real microstructure images which were characterized by optical microscopy through the thickness direction. Serial sectioned 2D images were converted into semi-2D representative volume elements (RVEs) model. Each RVE model was subjected to a non-proportional loading condition and the mechanical response was analyzed on both the macroscopic and microscopic levels. Macroscopically, stress-strain curves were described under tension-compression and tension-orthogonal tension conditions and the Bauschinger effect was well captured for both loading paths. In addition, micromechanical properties were investigated in the view of stress-strain partitioning and strain localization during monotonic tension.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.183-186
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• 2003

A finite element-based, integrated process model is presented for a three dimensional, coupled analysis of the thermal and mechanical behavior of type 304 stainless slab during hot charge rolling (HCR) and cold charge rolling (CCR) processes. The validity of the proposed model is examined through comparison with measurements. The susceptibility on micro-crack initiation or propagation due to the thermal stress in these two different process conditions was examined. The model's capability of revealing the effect of diverse process parameters is demonstrated through a series of process simulation.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.1278-1281
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• 2004

Several workers reported the relationship between osteoporosis and age-related reductions in the BV/TV (bone volume fraction) of vertebral trabecular bones. However, there were few micro finite element (micro-FE) models to account for the treatments of the osteoporotic trabecular bone. In the present study, micro-FE models of osteoporotic and hormone-treated bone models were constructed to analyze the effect of specimen location and boundary condition on mechanical characteristics of hormone treatment model for osteoporotic trabecular bone. Top and bottom sections of specimens were also investigated individually to study the effect of specimen location. Hormone-treated models were allowed to have the same relative BV/TV (13.4％) as that used in models of previous researchers. The present study reported the elastic and plastic characteristics of the osteoporosis and hormone-treated bone models. In the present study, in-situ boundary condition was applied to the simulated compression tests for in-vivo condition of vertebral trabecular bone. The present study indicated that the hormone therapy was likely to improve the mechanical characteristics of osteoporotic bones and the mechanical characteristics of vertebral trabecular bone specimen were dependent on the captured location and boundary condition.

• 한국기계가공학회지
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• 제21권3호
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• pp.77-85
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• 2022

In this study, to diagnose the grinding state of a micro drill bit, a sensor attachment location was selected through random vibration analysis of the grinding unit of the micro drill-bit grinding system. In addition, the vibration data generated during the drill bit grinding were collected from the grinding unit for the grinding wheels under the steady and worn conditions, and data feature extraction and dimension reduction were performed. The wear of the micro-drill-bit grinding wheel was diagnosed by applying KNN, a machine-learning algorithm. The classification model showed excellent performance, with an accuracy of 99.2%. The precision, recall and f1-score were higher than 99% in both the steady and wear conditions.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2763-2768
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• 2007

Recently, as the semiconductor production technology develops, there has been growing interest in the cooling system using micro fluid pump. Among the various types of micro fluid pump, the valve-less diffuser/nozzle has been extensively studied in recent years. However, the flat-walled diffuser/nozzle flow has not been clearly looked into due to its non-linear characteristics. In this paper, the flow characteristics of the flat-walled diffuser/nozzle have been analyzed using similitude model and simulations. Similitude models are designed so that the flow pattern is same as that of 1/10 scale flow by using high viscous fluid as working fluid. The results are compared to the simulations. It is shown that the flow characteristics of 2D simulation are different from 3D simulations at high Re region, and the measured pump efficiency is highly dependent on the pressure difference as well as the channel geometry. From these results, the desirable conditions for the efficient pump is discussed.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2005년도 ICCAS
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• pp.139-144
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• 2005

A rigorous research is underway in our team, for the design and development of high figure of merits (ZT= 1.5${\sim}$2.0) micro-thermoelectric coolers. This paper discusses the fabrication process that we are using for developing the $Sb_2Te_3-Bi_2Te_3$ micro-thermoelectric cooling modules. It describes how to obtain the mechanical properties of the thin film TEC elements and reports the results of an equation-based multiphysics modeling of the micro-TEC modules. In this study the thermoelectric thin films were deposited on Si substrates using co-sputtering method. The physical mechanical properties of the prepared films were measured by nanoindentation testing method while the thermal and electrical properties required for modeling were obtained from existing literature. A finite element model was developed using an equation-based multiphysics modeling by the commercial finite element code FEMLAB. The model was solved for different operating conditions. The temperature and the stress distributions in the P and N elements of the TEC as well as in the metal connector were obtained. The temperature distributions of the system obtained from simulation results showed good agreement with the analytical results existing in literature. In addition, it was found that the maximum stress in the system occurs at the bonding part of the TEC i.e. between the metal connectors and TE elements of the module.