http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
엔진 커넥팅로드의 좌굴평가를 위한 유한요소법 및 실험방법 연구
이문규(Moon Kyu Lee),이영민(Young Min Lee),맹준수(Junsoo Maeng),이형일(Hyungyil Lee),이태수(Tae Soo Lee),신성원(Sung Won Shin),장훈(Hun Chang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
To reduce the weight of the connecting rod of a vehicle's engine, the accurate buckling estimation is used as a major valuation basis. This study improves the previous efforts, based on finite element analysis, to include experimental results and accurate geometrical conditions. The critical buckling stresses of connecting rods which were cut off shank portion with various slenderness ratios, were estimated using the rig device which was made in this lab. Also the finite element model was improved by addition to the geometrical contact condition on the basis of experimental results. Hence this result indicates that the buckling prediction through FEA is more effective method than the classical formula.
엔진 커넥팅로드 Shank 부의 경량화를 위한 좌굴 민감도 분석
이영민(Young Min Lee),이문규(Moon Kyu Lee),문희욱(Hee Wook Moon),신성원(Sung Won Shin),장훈(Hoon Jang),이형일(Hyungyil Lee),이태수(Tae Soo Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Connecting rod under incessant dynamic motion has a major effect on the engine performance according to its lightweight degree. In engine parts design, the effect of buckling has been considered less than static load and fatigue, and there were limited studies that compared the effect of those three factors. The purpose of this study is to analyze the sensitivity of buckling by comparing the safety factors for static stress, fatigue and buckling with respected to the change of section area of the connecting rod shank. Static stress, fatigue and buckling analysis are performed by FE model which has width and thickness as design variables, and buckling sensitivity with the change of the cross sectional area in shank is analyzed by comparing the safety factor decreasing ratio. Sensitivity analysis demonstrated that the effect of buckling needs to be considered in designing the connecting rod, and reducing the width can be more profitable than reducing the thickness of the shank.
J and CTOD Estimation for Homogeneous and Bi-Material Fracture Toughness Testing Specimens
Lee, Hyungyil,Kim, Yun-Jae The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.8
This paper proposes J and CTOD estimation schemes applied to fracture toughness testing, covering typical homogeneous and bi-material specimens. Recommendations are based on the plastic limit analysis (either slip line field or finite element limit analyses), assuming the rigid plastic material behavior. The main outcome of the present study is that the J and CTOD estimation schemes (both codified and non-codified), recommended for homogeneous specimens, can be equally used for bi-material specimens with interface cracks. The effect of yield strength mismatch in bi-material specimens on the J-integral CTOD is discussed.
Scratch-tip-size effect and change of friction coefficient in nano / micro scratch tests using XFEM
Lee, Kwangmin,Marimuthu, Karuppasamy Pandian,Kim, Chang-Lae,Lee, Hyungyil Elsevier 2018 Tribology international Vol.120 No.-
<P><B>Abstract</B></P> <P>Compared to the experimental studies, numerical studies on scratch test have been limited due to the difficulty of numerical modeling. Here, we experimentally investigate the scratch-tip-size effect (STSE) based on coefficient of friction (COF) change to make extended finite element (XFE) models considering STSE, COF change, failure modes, yielding strength, shear strength, elastic recovery and pile-up. XFE models are then validated through nano/micro scratch tests on soda-lime glass. Finally, components of COF are extracted and then effects of tensile cracks and parameters of Drucker-Prager model on COF are investigated. We expect that proposed XFE models contribute to the understanding of damage characteristics during the scratch test.</P> <P><B>Highlights</B></P> <P> <UL> <LI> FE models for nano/micro scratch test on soda-lime glass are proposed. </LI> <LI> Scratch-tips of different size cause various failure modes. </LI> <LI> Scratch-tip size effect significantly influences friction coefficient change. </LI> <LI> Drucker-Prager model of material is calibrated considering indentation size effect. </LI> <LI> Components of coefficient of friction are extracted from experiment by using FEM. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Overload failure curve and fatigue behavior of spot-welded specimens
Lee, Hyungyil,Kim, Nahmho,Lee, Tae Soo Elsevier 2005 Engineering fracture mechanics Vol.72 No.8
<P><B>Abstract</B></P><P>The mechanical behavior of a spot-welded specimen is generally approached in angles of overload and fatigue failures. The primary issue in an overload failure is to establish an overload failure criterion. Fatigue failure of spot-welded specimens can be dealt with a fracture parameter, since a spot-weld forms a singular geometry of external crack type. In this work, we express the limit loads in terms of base metal yield strength and specimen geometries. We then present a master overload failure curve for a single spot-welded specimen in a mixed-mode load domain. The coordinates of the domain are normalized by the limit loads of single spot-welded specimens. Recasting the load vs. fatigue life relations experimentally obtained, we attempt to predict the fatigue life of various spot-weld specimens with a single parameter denoting the equivalent stress intensity factor. This crack driving parameter is demonstrated to successfully describe the effects of specimen geometry and load type in an inclusive manner. The suggested fatigue life formula for a single spot-weld can be used in the assessment of spot-welded panel structures as the fatigue strength of multi-spots is eventually determined by that of each single spot-weld.</P>
Lee, Jin Haeng,Lee, Hyungyil,Hyun, Hong Chul,Kim, Minsoo Cambridge University Press (Materials Research Soc 2010 Journal of materials research Vol.25 No.11
<P>Conical indentation methods to determine residual stress are proposed by examining the finite element solutions based on the incremental plasticity theory. We first note that hardness depends on the magnitude and sign of residual stress and material properties and can change by up to 20% over a specific range of elastic tensile and compressive residual stress, although some prior indentation studies reported that hardness is hardly affected by residual stress. By analyzing the characteristics of conical indentation, we then select some normalized indentation parameters, which are free from the effect of indenter tip rounding. Adopting dimensional analysis, we present practical conical indentation methods for the evaluation of elastic/plastic equi- and nonequi-biaxial residual stresses. The validity of developed approaches is confirmed by applying them to the experimental evaluation of four-point bending stress.</P>
A numerical approach to evaluation of elastic modulus using conical indenter with finite tip radius
Lee, Jin Haeng,Lee, Hyungyil,Kim, Deok Hoon Cambridge University Press (Materials Research Soc 2008 Journal of materials research Vol.23 No.9
<P>Geometrical self-similarity is a feature of mathematically sharp indenters such as conical and Berkovich indenters. However, self-similarity is considered inappropriate for practical use because of inevitable indenter tip blunting. In this study, we analyze the load-depth curves of conical indenters with various tip radii via finite element analyses. Based on the numerical data, we propose a method of restoring the Kick’s law coefficient <I>C</I> of finite tip-radius indenter to that of zero tip-radius indenter, thereby retaining the self-similarity of the sharp indenter. We then regress the unloading slope for the evaluation of elastic modulus in several ways. Finally, we establish a method to evaluate elastic modulus, which successfully provides the value of the elastic modulus with a maximum error of less than 5%, regardless of tip radius and material properties of both indenter and specimen.</P>
이형일(Hyungyil Lee),이진행(Jin Haeng Lee) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
In this work, effects of hyper-elastic rubber material properties on the indentation load-deflection curve and subindenter deformation are first examined via finite element (FE) analyses. An optimal data acquisition spot is selected, which features maximum strain energy density and negligible frictional effect. We then contrive two normalized functions, which map an indentation load vs. deflection curve into a strain energy density vs, first invariant curve. From the strain energy density vs. first invariant curve, we can extract the rubber material properties. This new spherical indentation approach produces the rubber material properties in a manner more effective than the common uniaxial tensile/compression tests. The indentation approach successfully measures the rubber material properties and the corresponding nominal stress-strain curve with an average error less than 3%.
이형일(Hyungyil Lee),이진행(Jin Haeng Lee) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.10
The present work reviews the methods to evaluate elastic-plastic material characteristics by indentation tests. Especially the representative stress and strain values used in some papers are critically analyzed. The values should not only represent the load-depth curve, but also represent the whole of deformed material around the impression. We briefly introduce other indentation techniques to evaluate residual stresses, creep properties, and fracture toughness. We also review some technical problems that are related to the accuracy issues in indentation tests.