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적층 복합재료의 내부감쇠와 복소탄성계수 측정에 관한 연구
이재혁,박세만,김형삼,Lee, Jae-Hyeok,Park, Se-Man,Kim, Hyeong-Sam 한국재료학회 1998 한국재료학회지 Vol.8 No.10
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. 감쇠란 주기적인 변형하에 에너지를 소산시킬 수 있는 시스템이나 재료의성질을 말하며, 이로서 공진에서 진폭을 감소시키며 아울러 전달하는 파의 빠른 감소를 유발한다. 이것은 진동을 일으키는 응력을 감소시키게 되는데 결국은 피고 수명을 연장시키는 결과를 가져오게 된다. 본 연구에서는 적층된 복합재료의 내부감쇠와 복소탄성 계수를 실험적으로 측정하였다. 실험은 충격 기법을 사용하였으며 비교적 간단한 모델러서 외팔보의 휨진동을 측정하였다. 복소 탄성계수는 공진법을 이용하여 공진주파수를 측정 storage modulus를 계산하고 이를 통해 loss modulus를 구한 다음 계산하였고, 내부감쇠는 bandwidth technique과 전달함수의 실부부분 이용방법에 의해 각각 구하였다.
이재혁,송진규,양홍석,최미선,Lee, Jae-Hyeok,Song, Jin-Kyu,Yang, Hong-Suk,Choi, Mi-Sun 대한건축학회 2011 대한건축학회논문집 Vol.27 No.2
The flat plate system is an undefined seismic resistance system in the design code. In general, it is designed as a building frame system or dual system with shear wall, which has not yet been verified. In this study, we investigated the system level seismic capacity for 45 shear-reinforced flat plate systems using a nonlinear pushover analysis. Overstrength factor and a effective response modification factor are used to major parameters to define seismic capacity of the system, both of which are design factors of the seismic resistance system in the KBC2009 as an index. Analysis results showed that the effective response modification factor had exceeded the value presented in the KBC2009 in most cases. But, in some cases, the overstrength factor failed to meet the value presented in the KBC2009. Therefore, the flat plate system cannot be generally defined as a dual system with shear wall. But, plat plate system reinforced with shear band showed the efficiency of RC intermediate moment resistance frame except for 5-story case.
공진주파수, 오일러 티모센코 빔 방정식을 이용한 복합재료의 동적탄성계수 측정에 관한 연구
이재혁,박세만,김형삼,Lee, Jae-Hyeok,Park, Se-Man,Kim, Hyeong-Sam 한국재료학회 1999 한국재료학회지 Vol.9 No.7
탄성계수의 정밀측정은 과학적인 관점과 공학적인 관점 모두 중요하다. 과학적인 관점에서 본다면 탄성계수를 측정함으로써 원자와 원자사이, 이온과 이온 사이의 bending에 관한 해석 및 이해중진의 중요한 도구가 되며 공학적인 측면에서 본다면 공학적인 기계설비에 반드시 고려해야 할 설계기준 중의 하나이다. 본 연구에서는 보다 정확한 탄성계수 측정을 위해 두 가지의 동적 진동실험(음향 공진법과 충격가진 방법)을 비교해 보았으며, 이 두 실험적으로 얻은 공진수파수는 Euler 빔 방정식과 Timoshenko 빔 방정식에 각각 적용하여 그 차이를 비교해 보았다. Accurate measurements of elastic constants are important from the view points of both science and engineering. The measurement can be viewed from scientific principle as a service tools for analyzing and improving the understanding of the nature of bondings between atoms and between ions. Also, from engineering perspective it would became an important factor to be definitely considered for the design of machinery equipments. In this investigation, two dynamic experimental methods of vibrations (acoustic method and Impulse technique method) are utilized and the results from the both methods are compared to obtain elastic constants data with a high degree of accuracy. The resonance frequencies obtained from the two methods are applied to both Euler and Timoshenko beam equations respectively, to determine the sources for possible differences.