• 소성∙가공
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• 제9권4호
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• pp.372-378
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• 2000

A process model including the effects of both the texture development and ductile damage evolution In plane strain rolling is presented. In this process model, anisotropy from deformation texture and deterioration of mechanical properties due to growth of micro voids are directly coupled Into the virtual work expressions for the momentum and mass balances. Special treatments in obtaining the initial values of field variables in the nonlinear simultaneous equations for the anisotropic, dilatant viscoplastic deformation are also given. Mutual effects of the texture development and damage evolution during plate rolling are carefully examined in terms of the distribution of strain components, accumulated damage, R-value as well as yield surfaces.

• 터널과지하공간
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• 제34권2호
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• pp.169-184
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• 2024

본 연구에서는 심부 지하공간의 안정성을 평가하고자 심부 응력조건을 반영한 암석블록의 이축압축실험을 통하여 지하공동에서 손상 발생시 발생하는 음향방출 및 미소변형의 특성을 분석하였다. 음향방출 특성 분석 결과 지하공동에서 손상 발생 직전에 음향방출 신호의 주파수, 카운트, 에너지, 진폭 특성이 급격히 증가하였다. 특히 주파수와 카운트는 손상 전후에서 특성 차이가 크게 나타나 원형 공동의 손상 특성 분석에 적합한 음향방출 인자인 것으로 나타났다. 이미지상관기법 적용결과 실험 중 공동 주변에 변형이 집중되었음을 변형률의 공간적 분포를 통해 알 수 있었으며, 실험 종료 지점에서는 스폴링 현상이 발생하였음을 확인할 수 있었다. 본 연구에서 제시된 원형 공동 손상시 음향방출 및 미소변형 특성은 심지층 활용을 위한 지하공동 안정성 평가의 기초자료로 활용될 것으로 기대된다.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 추계학술발표대회 개요집
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• pp.170-172
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• 2000

In this research, newly proposed heat source equations were calculated to predict micro distortion of small structure in laser welding and compared with experimental results which were measured using laser speckle metrology. A finite element code, ABAQUS is used for the heat transfer analysis with a three-dimensional plane assumption. The results suggest that weld distortion is varied according to the heat source of the. laser beam.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.706-711
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• 2003

A numerical method is presented for computing unsteady incompressible two-phase flows with immersed solids. The method is based on a level set technique for capturing the phase interface, which is modified to satisfy a contact angle condition at the solid-fluid interface as well as to achieve mass conservation during the whole calculation procedure. The modified level set method is applied for numerical simulation of bubble deformation in a micro channel with a cylindrical solid block and liquid jet from a micro nozzle.

• 한국정밀공학회지
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• 제22권9호
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• pp.27-33
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• 2005

This study deals with the truing of diamond wheel fur the manufacture of micro v-shaped grooves with fine sharp edges in the grinding. Fine micro v-shaped grooves are key components to fabricate LGP(light guide plate), optical fiber connector and so on. Conventional v-shaped groove methods such as etching and lithography are difficult to make grooves with accuracy and cutting by lathe is difficult to select target materials. Therefore, as a preliminary stage to developing the grinding technology that will be expected fabrications for micro 3-dimensional structure of high effectivity and accuracy and freed up the restrictions of machinability to the materials for micro v-shaped grooves, truing is carried out with resin bond diamond wheel and electroforming diamond wheel using a cup-type truer. From the experimental results, it is found that the effects according to working direction of the cup-type truer and the restrainable methods of plastic deformation that is generated at wheel edge are examined. As a result, fine micro v-shaped diamond wheel was obtained, which are applicable to micro grinding for optical devices.

• Computers and Concrete
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• 제17권1호
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• pp.107-127
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• 2016

Concrete is a heterogeneous material containing many weaknesses such as micro-cracks, pores and grain boundaries. The crack growth mechanism and failure behavior of concrete structures depend on the plastic deformation created by these weaknesses. In this article the non-linear finite element method is used to analyze the effect of presence of micro pore near a crack tip on both of the characteristics of crack tip plastic zone (its shape and size) and crack growth properties (such as crack growth length and crack initiation angle) under pure shear loading. The FE Code Franc2D/L is used to carry out these objectives. The effects of the crack-pore configurations and the spacing between micro pore and pre-excising crack tip on the characteristics of crack tip plastic zone and crack growth properties is highlighted. Based on the obtained results, the relative distance between the crack tip and the micro pore affects in very significant way the shape and the size of the crack tip plastic zone. Furthermore, crack growth length and crack initiation angle are mostly influenced by size and shape of plastic zone ahead of crack tip. Also the effects of pore decrease on the crack tip by variation of pore situation from linear to perpendicular configuration. The critical position for a micro pore is in front of the crack tip.

• 한국공작기계학회논문집
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• 제16권5호
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• pp.77-83
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• 2007

The study on damaged layer is necessary for machinability improvement in micro machining. The damaged layer in metal cutting is derived from plastic deformation and transformation of metal structure. The damaged layer affects micro mold life and micro machine parts. In this study, the damaged layer of micro machined surface of copper is evaluated according to various machining condition. The damaged layer structure and metallurgical characteristics are measured by optical microscope, and evaluated by cutting forces and surface roughness. The scale of this damaged layer depends on cutting process parameters and machining environments. By experimental results, depth of damaged layer was increased with increasing of cutting depth, also the damaged layer is less occurred in down-milling compared to up-milling during micro endmilling operation.

• Current Photovoltaic Research
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• 제4권4호
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• pp.140-144
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• 2016

In this paper, core-shell structure of nickel/gold (Ni/Au) conductive layer on poly-methyl-methacrylate (PMMA) micro-ball was fabricated and its conduction property was investigated. Firstly, PMMA micro-ball was synthesized by using dispersion polymerization method. Size of the ball was $2.8{\mu}m$ within ${\pm}7%$ deviation, and appropriate elastic deformation of the PMMA micro-ball ranging from 31 to 39% was achieved under 3 kg pressure. Also, 200 nm thick Ni/Au conductive layer was fabricated on the PMMA micro-ball by uniformly depositing with electroless-plating. Adhesion of the conductive layer was optimized with help of surface pre-treatment, and the layer adhered without peeling-off despite of thermal expansion by collision with accelerated electrons. Composite paste containing core-shell structured particles well cured at low temperature of $130^{\circ}C$ while pressing the test chip onto the substrate to make electrical contact, and electrical resistance of the conductive layer showed stable behavior of about $6.0{\Omega}$. Thus, it was known that core-shell structured particle of the Ni/Au conductive layer on PMMA micro-ball was feasible to flexible electronics.

• 자원환경지질
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• 제27권5호
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• pp.499-505
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• 1994

기존 미소결함에서의 국소적 응력집중은 새로운 미시적 손상의 원인이 되고, 이러한 미시적 손상은 또한 거시적 손상으로 발달하게 된다. 이들 미시적 손상에서 거시적 손상으로의 바달은 그 암석 및 암반의 변형특성으로 나타난다. 지금까지 응력하에서의 미소크랙의 거동에 대한 연구는 많이 되어왔으나, 실제암석의 파괴전 상태에서 미소크랙거동에 대한 역학적 해석은 아직 미비한 실정이다. 본 연구에서는 새로이 개발한 시험장치에 의한 정밀한 관찰로 손상 발달에 대한 이해를 더하였으며, 수학적 균질화 이론에 의해 수치해석 함으로서 그 역학성을 검토하였다.

• 한국정밀공학회지
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• 제31권3호
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• pp.181-187
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• 2014

Micro patterns are used to maximize the performance and efficiency of the product in many industries such as energy, display, printing, biology, etc. Nowadays, the fabrication technology for micro patterns has been developed in various ways such as photolithography, laser machining, electrical discharge machining and mechanical machining. Recently, mechanical machining the size of smaller than 1 micrometer could be tried, because the technology related to the machining was developed brilliantly. This paper shows the experiments using cutting processes in order to fabricate the micro pattern. Micro patterns of the size of several micrometers were machined by the diamond tools of two different shape, the deformation and generation of burr were investigated.