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권동일(Dongil Kwon),이경우(Kyung Woo Lee),김성훈(Sung-Hoon Kim),김주영(Ju-Young Kim),이윤희(Yun-Hee Lee) 한국정밀공학회 2005 한국정밀공학회 학술발표대회 논문집 Vol.2005 No.10월
The nanoindentation technique is widely used to investigate the mechanical properties of nano-microscale materials. The nanoindentation method for assessing mechanical properties at low loads and shallow depths is already well established for the characterization of thin films as well as bulk materials. In this study, we evaluated residual stress in DLC and Au thin films usign nanoindentation technique with a new stress-relaxation model. Moreover, We suggest a composite hardness equation and quantify the magnitude of hardness increase by using an equation based on the interface hardness and the interface thickness, derived by comparing results derived from this equation and those determined in nanoindentation tests. Finally, We present an indentation size effect (ISE) model that extends the available contact depth for ISE application down to several tens of nanometers by considering the tip bluntness effect.
이윤희 ( Yun Hee Lee ),김주영 ( Ju Young Kim ),김용일 ( Yong Il Kim ),남승훈 ( Seung Hoon Nahm ),권동일 ( Dong Il Kwon ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 대한금속·재료학회지 Vol.44 No.7
The material pile-up around indenter/surface contact region can make the conventional Oliver and Pharr`s analysis of the nanoindentation curve inaccurate. We suggests a novel methodology for characterizing pile-up incorporated contact properties by adopting the Matlab(R)visualization tool in this study. Based on our approximation of contact boundary as peak of the pile-up region, radial indentation surface profiles observed with an atomic force microscope are differentiated with the distance from the indent center and a closed contact boundary is formed by connecting special differentiated points having their values as zero. The calculated load-off hardness was nearly consistent with the result of nanoindentation curve analysis for pileup free material such as fused quartz. This experimental result supports validity of the newly proposed method, However, the load-off hardness of metallic solids such as (100) tungsten monocrystal and pure copper showed that the nanoindentation curve analysis could overestimate the hardness more than 50% in the cases of severe pile-up.
이윤희 ( Yun Hee Lee ),김국환 ( Kuk Hwan Kim ),남승훈 ( Seung Hoon Nahm ),권동일 ( Dong Il Kwon ) 대한금속재료학회 ( 구 대한금속학회 ) 2009 대한금속·재료학회지 Vol.47 No.7
Approaches for analyzing indentation hardness are still controversial, although the instrumented indentation technique has been generalized as one powerful method that can record surface deformation behaviors. Material pile-ups around the indenter/surface contact region make the conventional Oliver and Pharr`s analysis on the instrumented indentation curve inaccurate. Thus, in order to prove the validity of the hardness analyses, five approaches were applied to the experimental data obtained from fused quartz and (100) monocrystalline tungsten specimens; an elastic recovery analysis on instrumented indentation curves, three indentation work analyses on the unit plastic volume, and a differentiation analysis on remnant indentation morphologies were tried. Five kinds of indentation hardness overlapped on one result plot showed the validity of each analysis. The modified indentation work approach based on a new definition of plastic volume showed consistent results with those from the Oliver-Pharr`s and image differentiation methods. In the case of pile-up accompanying deformation, the Oliver-Pharr`s and image differentiation methods showed the upper and lower limits of indentation hardness, respectively.
나노 압입곡선의 이론적 분석을 통한 박막의 잔류응력 평가
이윤희,장재일,권동일,Lee, Yun-Hee,Jang, Jae-Il,Kwon, Dong-Il 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.7
Residual stress is a dominant obstacle to efficient production and safe usage of device by deteriorating the mechanical strength and failure properties. Therefore, we proposed a new thin film stress-analyzing technique using a nanoindentation method. For this aim, the shape change in the indentation load-depth curve during the stress-relief in film was theoretically modeled. The change in indentation depth by load-controlled stress relaxation process was related to the increase or decrease in the applied load using the elastic flat punch theory. Finally, the residual stress in thin film was calculated from the changed applied load based on the equivalent stress interaction model. The evaluated stresses for diamond-like carbon films from this nanoindentation analysis were consistent with the results from the conventional curvature method.
연속압입 시험기법을 이용한 석유화학설비 경년손상의 새로운 평가변수 고찰
장재일,최열,손동일,이윤희,권동일,김정태,Jang, Jae-Il,Choi, Yeol,Son, Dongil,Lee, Yun-Hee,Kwon, Dongil,Kim, Jeoung-Tae 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.5
Newly developed continuous indentation technique has made nondestructive assessment of tensile properties possible. The present study was undertaken to determine new parameters for indicating time-dependent material degradation of petro-chemical plant. Continuous indentation tests were performed for Cr-Ni steel and Cr-Mo steel which are widely used as facilities of petro-chemical plant. From the results, it was found that yield strength and tensile strength cannot be used as general degradation parameters because the changes in the strengths with aging time didn't show any tendency. On the other hand, work hardening exponent and yield ratio showed consistent tendency with increasing aging time. Therefore, nam attention of this work was paid on them as new degradation parameters, and the in-field applicability of the parameters was evaluated and discussed.
나노압입시험을 이용한 마이크로/나노 소재의 물성 특성화 및 응용
김주영 ( Ju Young Kim ),이윤희 ( Yun Hee Lee ),장재일 ( Jae Il Jang ),권동일 ( Dong Il Kwon ) 대한금속재료학회 ( 구 대한금속학회 ) 2006 ELECTRONIC MATERIALS LETTERS Vol.2 No.2
Over the last two decades, nanoindentation has been widely used for evaluating mechanical properties of micro/nano materials. Principles to measure mechanical properties, basically hardness and elastic modulus, using nanoindentation were introduced and its applications are also presented. We explain and introduce main nanoindentation topics in detail as follows: contact depth determination to take surface roughness into account, indentation size effect models, quantitative evaluation of residual stress, materials phenomena such as yielding and phase transformation.