Impact Technique을 이용한 적층복합재료의 내부감쇠특성과 복소탄성계수 측정에 관한 연구

이재혁(C.H.Yi),박세만(S.M.Bahk),김형삼(H.S.Kim) 한국자동차공학회 1998 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1998 No.11_2

Damping is a property for materials and systems to dissipate energy during periodic deformations. Generally, damping causes stiff decrease in amplitudes and shifts in phases. Also, even at resonance, amplitudes are substantially attenuated. This phenomenon of damping helps in reducing stresses developed during vibrations and consequently improves fatigue lives of materials. In this work internal damping and complex moduli are experimentally determined. An impulse technique is utilized in experiments and cantilever beams are selected as test subjects for the measurements of flextural vibrations since the beams lend themselves easily as simplistic ideal models. A resonance method is employed to determine resonance frequencies which are utilized to compute storage moduli. Also, loss moduli are evaluated from damping capacities and storage moduli. The storage and loss moduli combined yield complex moduli. Finally internal damping is evaluated from bandwidth technique, the real component of the transfer function.<br/>

Carbon-Epoxy 복합재료의 열피로 거동에 관한 연구

이동식(D.S.Lee),박세만(S.M.Bark),이재혁(C.H.Yi),김형삼(H.S.Kim) 한국자동차공학회 1998 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1998 No.11_2

An experimental apparatus is contrived and constructed for measurements of resonance frequencies to determine dynamic elastic constants of composite materials. Materials selected for testing are carbon/epoxy composites that are well accepted in automotive and aerospace industries. Specimens prepared from the composites are subjected to thermal fatigue cyclings that are composed of repeatedly exposing specimens alternately between room temperature and desired elevated temperatures. The cycling temperatures are systematically raised with an increment of 20°C up to 200°C at which physical changes in the specimens are visible. The heat-treated specimens are tested to measure resonance frequencies for torsional and flexural vibrations, respectively which are subsequently utilized to evaluate the elastic constants E₁, E₂, G_23, and G_13 of the composites at elevated temperatures. Also, investigations are conducted to discern any effects on the elastic constants of the composites due to the thermal fatigue cyclings. The elastic constants E₁ exhibits maximum around 100°C and continuously decrease afterwards whereas E₂ does not show a consistent pattern of behavior or variations in its measured values.<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/>

유한요소법을 이용한 구보용 2024-T3 재료의 동적 물성치 평가

이재혁,김형삼,이동식,박세만 명지대학교 대학원 1999 대학원논문집 Vol.3 No.-

There are two types of beam theories: the first one is the traditional Euler-Bernoulli theory while the second one is Timoshenko beam theory that considers additional effects of shear deformations and rotary inertia. In this investigation, the both theories are utilized to evaluate elastic constants. leading to direct comparisons of the two theories. Also, for a numerical analysis the commercial FEM program. ANSYS 5.3 is employed to conduct modelling of test specimens for a modal analysis, enhancing the understanding of the nature of the FEM analysis and allowing comparisons with experimental results.

적층 복합재료의 내부감쇠와 복소탄성계수 측정에 관한 연구

이재혁,박세만,김형삼 명지대학교 대학원 1998 대학원논문집 Vol.2 No.-

Damping is a property for materials and systems to dissipate energy during periodic deformations. Generally damping causes stiff decrease in amplitudes and shifts in phases. Also, even at resonance, amplitudes are substantially attenuated. This phenomenon of damping helps in reducing stresses developed during vibration and consequently improves fatigue lives of materials. In this work internal damping and complex moduli are experimentally determined. An impulse technique is utilized in experiments and cantilever beams are selected as test subjects for the measurements of flextural vibrations since the beams lend themselves easily as simplistic ideal models. A resonance method is employed to determine resonance frequencies which are utilized to compute storage moduli. Also, loss moduli are evaluated from damping capacities and storage moduli. The storage and loss moduli combined yield complex moduli. Finally internal damping is evaluated from bandwidth technique, the real component of the transfer function.

Graphite-Epoxy 복합재료의 온도변화에 따른 탄성계수 측정

김형삼,박세만,박명균,이재혁 明知大學校 産業技術硏究所 1998 産業技術硏究所論文集 Vol.17 No.-

Composites find wide applications as structural materials for automobiles and aircrafts owing to their superior mechanical prosperities. Among the mechanical properties of composites it is the dynamic elastic modulus thatrequires special attentions since its accurate measurements and careful assessments are important sep to find further applications of the composits. Therefore, in this work dynamic modulus of Graphite / Epoxy composites are measured and also temperature effects are examined with each temperature increment of 10 degrees in the range of 20℃~100℃.

티모센코 보방정식에 의한 카본-에폭시 복합재료의 탄성계수 변화에 관한 연구

김형삼,이재혁,이동식,박세만 명지대학교 대학원 1999 대학원논문집 Vol.3 No.-

Usages of composite materials have been steadily on the rise in the industries of automobiles, air crafts, shipbuilding and other structures for transportations. Commonly required in those industries are light weight and high strength of the structures. Consequently, serious efforts in research have been focused on searching for light materials and on developments and characterization of advanced substitutes including various kinds of composite materials. In this investigation, transversely isotropic composite materials are chosen and formed into two kinds of beams: Euler-Bernoulli beam(thin beam) and Timoshenko beam(thick beam) for determinations of elastic constants. As an experimental technique Acoustic Resonance Method is utilized to measure resonance frequencies of the beams of the composite materials in vibration tests. Elastic constants are evaluated from measured resonance frequencies for the two types of beams to observe and establish possible existence of effects of rotary inertia and shear deformations.