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미소 시험편 기술의 응용을 통한 소재의 기계적 물성 평가
이윤희(Y.-H. Lee),안정훈(J.-H. Ahn),최열(Y. Choi),주장복(J.-B. Ju),권동일(D. Kwon) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
The evaluation of mechanical properties is necessary for maintaining the reliability of structural components. However, the applications of conventional mechanical tests have some problems such as complex preparation of macro-sized standard specimen and time consuming test procedures. Therefore, a simple, nearly nondestructive mechanical test using small specimen is needed. Local indentation and small punch, which use small specimen, satisfied these needs. Recently, nanoindentation test, which obtains indentation load-depth curve from the load and indenter displacement during indentation, is developed. The mechanical properties including yield strength, work-hardening index of soft film are predicted by the analysis of indentation load-depth curve and stress field under the indenter. And, the mechanical strength and microphase identification are characterized using the nanoindentation technique combined with atomic force microscope. The effect of residual stress to mechanical indentation is also verified using a novel stress-generating gadget. The fracture toughness of structural steel was evaluated using a revised small punch test. The revised technique is based on the fracture mechanics by adopting a sharp notch in the center of plate specimen. The fracture toughness in lower shelf brittle region is consistent with the conventional results.
압입변형의 응력의존성 분석을 통한 소재의 표면 잔류응력 평가
이윤희(Y.-H. Lee),지원재(W.-j. Ji),장재일(J.-i. Jang),권동일(D. Kwon) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.3
Apparent mechanical properties in structural components are changed from the initially designed values due to the formation of the residual stress in metal forming and welded joints. Tensile residual stress has problems of lower resistances to deformation, crack initiation and fatigue fracture. Therefore, the evaluation of residual stress is very important in the reliability diagnosis of structural components. For that reason, a non-destructive automated indentation technique is proposed to evaluate various strength concerning mechanical properties from the analysis of load-depth curve induced from the indentation deformation of materials by a rigid indenter. In this study, quantitative residual stress estimation by analyzing the variations of indentation loading curve by residual stress through a theoretical model. and comparison with residual stress from strain gage are performed.
전용원(Y.W.Jeon),김규찬(G.C.Kim),이상호(S.H.Lee),이윤희(Y.H.Lee),김철수(C.S.Kim),장주섭(J.S.Jang),배흥용(H.Y.Bae),이충호(C.H.Lee) 한국자동차공학회 1995 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1995 No.11_1
A System for reducing vehicle body roll by active control is developed. The stabilizer bar with hydraulic rotary actuator produces anti-roll moment which suppresses roll tendency. This reduction of roll improves the driving safety as well as the ride comfort. Vehicle test data shows considerable reduction of roll angle during steady-state turning. Also improvement of ride comfort is achieved by making the actuator freely rotatable. i. e. by connecting all chambers of actuator in normal driving conditions. A control algorithm using steering wheel angle and vehicle speed signal as input value is applied.<br/>