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압입하중-변위곡선의 정량적 해석을 통한 가공경화지수의 평가
全銀埰,安政勳,權東一 대한금속재료학회 2001 대한금속·재료학회지 Vol.39 No.12
Continuous indentation test with ball indenter has been studied for years because of its convenience and simpleness. Especially, the test is expected to supersede tensile test. Among tensile properties work-hardening exponents of various steels were evaluated by the test. We newly defined true stress and true strain with contact depth and indentation load. Finite element analysis shows that the contact depth is affected by elastic deflection and pile-up/sink-in. Therefore, the contact depth was calculated with taken both elastic deflection and pile-up/sink-in into account. The work-hardening exponents derived in this study show good agreement to those from tensile test.
전은채,박주승,권동일 대한금속재료학회 2002 대한금속·재료학회지 Vol.41 No.2
The continuous indentation test, which measures indentation depth with applied load, has been used to evaluate the tensile properties whose accuracy can vary depending on such experimental conditions as maximum depth ratio, indenter radius, number of unloadings and unloading ratio. In this study, Taguchi method, one of the designs of experiment, was applied to quantify the effects of the experimental conditions effectively. Using a signal-to-noise ratio calculated from the error in the indentation tensile properties, the optimum values of the experimental conditions were presented. The indentation tensile properties from the load-depth curves with the optimum conditions showed better accuracy than those with existing conditions.
전은채,백민경,김성훈,박주승,권동일 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.12
Continuous indentation test is getting more used to derive indentation flow curve. The overall deriving algorithm is relatively well-established, the details of the algorithm are, however, still argued. One of the arguments is the definition of true strain which constitutes the indentation flow curve. In this study, work-hardening exponent was adopted for determining what definition is appropriate to obtain accurate indentation flow curve since work-hardening exponent is affected by only the definition of true strain not by other constants. The effect of calibrating contact depth was eliminated using finite element analysis. Finally, the definition based on tangent function was determined to be proper for deriving the indentation flow curve. (Received September 8, 2004)
Jeon, Eun Chae,Baik, Min Kyung,Kim, Sung Hoon,Lee, Baik Woo,Kwon, Dong Il Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.297 No.-
<P>A new method [1] to evaluate indentation flow curves using an instrumented indentation test has been applied to many materials for several years. Though the method produces relatively good results compared to uniaxial tensile tests, a few parameters had not been verified by theoretical or numerical methods. In this study, proportional constants of representative strain and representative stress were verified using finite element analysis and proven to be unaffected by the elastic property and strain level. The constants were generally dependent on the plastic property; however, one combination of the constants is independent of all properties. The values of this combination are consistent with early research and produced overlapping indentation flow curves with uniaxial curves. </P>
Optimum definition of true strain beneath a spherical indenter for deriving indentation flow curves
Jeon, Eun-chae,Kim, Ju-Young,Baik, Min-Kyung,Kim, Sung-Hoon,Park, Joo-Seung,Kwon, Dongil Elsevier 2006 Materials science & engineering. properties, micro Vol.419 No.1
<P><B>Abstract</B></P><P>Several methods have been suggested for deriving indentation flow curves using the instrumented indentation technique, in which true stress and true strain are defined with indentation parameters. The definition of true stress is nearly the same in all methods, but the definitions of true strain fall into two categories, sine function and tangent function. We adopted the work-hardening exponent to determine the definition appropriate in obtaining accurate indentation flow curves. The work-hardening exponent was proven to be affected only by the definition of true strain and not by other parameters when the effect of real contact depth was eliminated using finite element analysis. The sine function yields too large work-hardening behaviors for materials that obey power-law work-hardening, but the tangent function evaluates them accurately. The definition based on the tangent function was thus determined to be more appropriate in deriving the indentation flow curve.</P>
Jeon, Eun-Chae,Lee, Je-Ryung,Je, Tae-Jin,Choi, Doo-Sun,Ham, Young-Bog,Lee, Eung-Sug,Choi, Sang-Kyu,Kim, Hwi Korean Society for Precision Engineering 2014 International Journal of Precision Engineering and Vol.15 No.11
A COB(chip-on-board) LED(light emitting diode) system has advantages such as low cost and good heat dissipation. LED chips are bonded on PCB(printed circuit board) directly without packaging process in case of COB LED systems. Dome lenses made of polymeric resin are generally covered on the bonded LED chips by air dispensing for preventing mechanical damage and making white light. However, it is hard to control the shape of dome lenses precisely due to viscosity of the polymeric resin. We analyzed the relationship of the shape of dome lenses and experimental conditions of the air dispensing in this study. We introduced a new parameter, air pressure * dispensing time, whose physical meaning is impulse per unit area, and obtained much clear relationship of dispensing parameters and shape parameters of the dome lens. This relationship was similar to viscoelastic behavior. The aspect ratio (height over diameter) was increased as the new parameter increased, and was converged to a certain value. The maximum aspect ratio could be calculated by Young's equation of contact angle.
Jeon, Eun-Chae,Je, Tae-Jin,Lee, Eung-Sug,Park, Eun-Suk,Lee, Je-Ryung,Choi, Hwanjin,Chang, Seonghwan,Choi, Sang-Kyu Korean Society for Precision Engineering 2013 International Journal of Precision Engineering and Vol.14 No.6
A new concept, 'hybrid LED package system (HLP system)', is proposed as a simpler LED manufacturing process that unifies two steps of the process, the package step and the module step. Moreover, the HLP system can increase optical efficiency by virtue of its integrated optical pattern. A square pyramidal pattern was selected as the basic shape of the pattern of the HLP system. Four shape parameters of the HLP system were selected for optimizing the system. Nine cases of optical simulations organized according to the Taguchi method were performed using LightTools, and the optimum values of the parameters were determined by an SN ratio analysis. Using the optimum values, 28% higher illuminance and 32% higher luminance were predicted simultaneosly compared to the values without the integrated optical pattern. The optimum square pyramidal pattern was machined on a metal mold using an ultra-fine planer and a 90 degree angle diamond tool which would be used as a mold for manufacturing the optimized integrated optical pattern of the HLP system. The exact shape of the square pyramidal pattern with a height of <TEX>$25{\mu}m$</TEX> and a 90 degree angle was obtained. This study verified that the micro machined mold for manufacturing an optimized integrated optical pattern could be machined accurately, and finally the HLP system with the integrated optical pattern had higher uniform and brighter light distribution.
Analysis of Size Effect of Nano Scale Machining Based on Normal Stress and Indentation Theories
Eun-chae Jeon(전은채),Yun-Hee Lee(이윤희),Tae-Jin Je(제태진) 한국기계가공학회 2018 한국기계가공학회지 Vol.17 No.6
Recently nano meter size pattern (sub-micro scale) can be machined mechanically using a diamond tool. Many studies have found a ‘size effect’ which referred to a specific cutting energy increase with the decrease in the uncut chip thickness at micro scale machining. A new analysis method was suggested in order to observe ‘size effect’ in nano scale machining and to verify the cause of the ‘size effect’ in this study. The diamond tool was indented to a vertical depth of 1,000nm depth in order to simplify the stress state and the normal force was measured continuously. The tip rounding was measured quantitatively by AFM. Based on the measurements and theoretical analysis, it was verified that the main cause of the ‘size effect’ in nano scale machining is geometrically necessary dislocations, one of the intrinsic material characteristics. st before tool failure.
전은채(Jeon Eun-chae),권동일(Kwon Dongil),박주승(Park Joo-Seung) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
Ithasbeenshownthatadvancedindentationtechniquecanevaluatetensilepropertiesfromtheload-depth<br/> curveswithoutopticalobservationbymanyresearches.Whentheexperimentsareperformed,itis,however,<br/> verydifficulttodeterminethevaluesofvariousexperimentalvariations.Theireffectsontheresultswere<br/> seldomstudied.Amongthevariations,themaximumdepthratio,theindenterradius,thenumberofunloads<br/> andtheunloadingratioareveryimportant.UsingTaguchimethod,whichisoneoftheDOE(designof<br/> experiment),westudiedtheireffectsquantitatively.Theload-depthcurveswereanalyzedbythemethod<br/> toderivetensileproperties.Todeterminetheoptimumvaluesofthevariations,theSN(signal-to-noise)values<br/> werecalculated.ForeachparameterthevaluewhoseSNvalueismaximumisdeterminedastheoptimum<br/> one.Thetensilepropertiesfromtheload-depthcurveswiththeoptimumvaluesshowedbetterconsistency<br/> thanoneswithothervalues.
패턴 주변의 소성변형현상을 제거한 고품위 불연속패턴 가공기술 개발
전은채(Eun-chae Jeon),제태진(Tae-Jin Je),장성환(Sunghwan Chang) 한국기계가공학회 2010 한국기계가공학회지 Vol.9 No.6
Patterned optical components are widely used for optical products such as LCD and lighting. Since CCFL was used as a light source in the products, prism films having linear continuous optical patterns were widely used. However, LED which is a dot light source is popular recently, therefore, the optical products need new optical components having non-continuous optical patterns. Indentation machining method is a powerful method for machining of non-continuous pattern. When a copper mold and a brass mold were machined by this method, severe plastic deformation called pile-up was observed around the patterns. Since pile-up has negative relationship to ductility, this deformation can be eliminated by annealing treatment which makes the materials ductile. No plastic deformation occurred when machined after annealing at 600℃ and 575℃ for copper and brass, respectively. Finally, non-continuous optical patterns with high quality were machined on a copper mold and a brass mold successively.