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김길수(K. S. KIM),박세만(S. M. BAHK),박명균(M. K. PARK) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.11_1
This investigation determines dynamic crack initiation roughnesses(K_id, J_id) of metallic materials such as SM20C and STD 11. Dynamic fracture toughnesses were was evaluated by conducting instrumented charpy impact tests. Specially, in this study, signals obtained from the strain gage implanted in the impact tup is transformed to Load-Time data by digital signal processings. To obtain appropriate data, the data were critically reviewed and tested against three criteria; inertia effects, limited frequency responses and energy levels. Initiation energy was determined using the method of compliance changing rate and was corrected to take into account of energy which was absorbed by inertia force.<br/>
계장화 샤피충격시험기를 이용한 재료의 동적파괴특성에 관한 연구
김길수(K. S. KIM),김기동(K. D. KIM),박세만(S. M. BAHK),박명균(M. K. PARK) 한국자동차공학회 1996 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1996 No.6_1
This investigation determines dynamic fracture characteristics of metals such as SM45C, SM20C and SS41. One of the dynamic' characteristics, dynamic fracture toughness, was evaluated by conducting instrumented charpy impact tests. Specially, in this study, signals obtained from the strain gage implanted in the impact tup is transformed to Load-Time data by digital signal processing. To obtain appropriate dynamic fracture toughness, the Load-Time data is critically reviewed and tested based on three criteria; inertia effect, limited frequency response and energy levels. This procedure ensures the reliability of the data. The data is, then, examined in view of topological aspects of fractured surfaces of the metals to reveal dynamic natures of materials failure.<br/> <br/>
4행정 가솔린 기관의 배기계 맥동압력 전달특성에 대한 주파수 해석
이준서(J.S.Lee),정광국(K.K.Chung),박종남(J.N.Park),유병구(B.K.Yoo),박세만(S.M.Bahk),차경옥(K.D.Cha) 한국자동차공학회 1994 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Pulsating pressure of exhaust system is generated by pulsating gas flow due to working of exhaust valve. The pulsating gas flow is closely<br/> concerned to engine power loss according to back pressure and exhaust noise. However, because of nonlinear effect due to large amplitude of pulsating pressure. it is difficult to exactly calculate pulsating pressure propagation in exhaust system of typical engine, Moreover, in case of estimating exhaust system performance, conventional prediction method which is based on linear theory, gives many restrictions and overestimate.<br/> As the first step for solving this problem, this paper contains experimental model to measure pulsating pressure propagation and shows power spectrum density, frequency response function, coherence in frequency domain for characterize pulsating pressure propagation in exhaust system of typical engine.<br/>
공진주파수 측정을 통한 복합재료의 탄성계수 측정과 이론식과의 비교 평가
김형삼(H.S.Kim),박세만(S.M.Bahk),박명균(M.K.Park),이재혁(C.H.Yi),최흥섭(H.S.Choi) 한국자동차공학회 1997 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1997 No.11_2
The need to develop and use light-weight structural components in the design of aircraft and automotive vehicles has brought increasing applications of composite materials. To evaluate elastic constants which are one of important mechanical properties of composite materials a method of experimentation is conceived and an experimental set-up is constructed to evaluate elastic constants of composites. The experimental method utilizes resonance phenomenon which occurs when natural frequencies of materials match externally applied frequencies. Flexural resonance frequencies are determined to evaluate Young's moduli E} and E2 which torsional resonance frequencies are measured to evaluate shear moduli G_13 and G_23. The experimentally determined values of elastic constants are compared with those values computed from theoretical considerations utilizing the rule of mixtures to establish the extent of agreement between the experimental and theoretical methods.
공진법에 의한 Carbon-Epoxy 복합재료의 탄성계수 평가
김형삼(H.S.Kim),박세만(S.M.Bahk),박명균(M.K.Park),이재혁(C.H.Yi),최홍섭(H.S.Choi) 한국자동차공학회 1997 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1997 No.6_2
Carbon/epoxy is a well known composite material for its outstanding performance in structural applications. A method of experimentation is conceived and an experimental set-up is constructed to evaluate elastic constants of carbon/epoxy composites. The frequencies are measured for three different modes: torsional, flexural and longitudinal vibrations.<br/> There has existed a formula expressing an explicit relationship between resonance frequencies and elastic constants. However the formula is valid only for a isotropic media. Area moments of inertia for composite materials are computed from measured frequencies of both longitudinal and flexural vibrations. The computed moments of inertia are utilized to determine elastic constants of carbon/epoxy composites. Which are then compared with elastic constants obtained from the formula developed for isotropic materials. Also. Variations of elastic constants at different temperatures are investigated with applications of the modified formula that has corrected values of area moment of inertia.<br/>
[재료부문] 열피로가 부가된 Carbon-Epoxy 복합재료의 탄성계수 변화에 관한 연구
이동식(D.S.Lee),박세만(S.M.Bahk) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-
Applications of composite materials have been increased in automotive and aircraft industries prompting active researches. The carbon-epoxy composite one of widely accepted composite materials. is selected to study its thermal characteristics. During thermal fatigue processes composed of repeated cooling and heating variations of elastic constants are investigated to understand thermal effects on the carbon-epoxy composite. In this investigation values of E show amount of increases depending on number of cycles of the thermal fatigue processes whereas values of G do not indicate noticeable changes. Also in cases of E and G their values decrease to a certain extend in initial stages after applications of thermal fatigue processes. However. the number of cycles of the applied thermal fatigue processes does not seem to affect their values.
[재료] 열충격이 부가된 Carbon-Epoxy 복합재료의 탄성계수 변화에 관한 연구
이동식(D.S.Lee),박세만(S.M.Bahk) 한국자동차공학회 1999 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1999 No.11_2
Composite materials have been recognized for continuing increase in their usages and applications in automotive and aircraft industries. This trend inevitably calls for extensive researches in the materials. Carbon-epoxy' composites. one of the foremost composites are selected for investigate ions to determine their thermal characteristics. Being subjected to thermal shocks consisting of repeated heatings and coolings the carbon-epoxy composites show variations in elastic constants revealing the thermal nature of the composites. In this study the values of E₁are observed to increase and the values of G13 are observed to decrease as thermal shocks are applied. However the values of E₁, E₂and G12 another elastic constant. G23 exhibits very different behavior with increasing temperatures.