• Composites Research
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• v.33 no.5
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• pp.262-267
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• 2020

With increasing demands for high-speed machining and lightweight design of machine tools, increasing likeliness of generation of machine tool spindle vibrations has become an important issue. Spindle vibration has a significant impact on the surface finish of the workpiece in ultra-precision machining. It is necessary to resolve the machine tool spindle vibration in various machining processes to improve machining accuracy. In this paper, a TiC-SKH51 metal-matrix composite was used to suppress the vibration of the machine tool spindle. To confirm the dynamic characteristic of the TiC-SKH51 composite, impact hammer tests were conducted. After verifying the reliability of a finite element analysis (FEA) by comparing the results of the impact hammer test with the modal analysis using FEA, the analysis of the machine tool spindle model was performed. The FEA results show that the TiC-SKH51 composite applied machine tool spindle can be utilized to suppress the vibration generation.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.166-166
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• 2011

한국건설기술연구원내에 세계 최초로 UHPC(초고성능 콘크리트)를 활용한 보도사장교를 설계 및 시공하여 공용중이다. 초고성능 콘크리트(UHPC, Ultra High Performance Concrete)는 기존의 콘크리트의 단점을 극복하기 위하여 강섬유 및 혼화재료를 사용하여 고강도화와 더불어 인장강도, 휨강도, 균열에 대한 저항성, 전단강도 및 내충격성을 대폭 개선시켜서 구조부재의 연성 및 강도를 확보하기 위해 개발된 것으로서 한국건설기술연구원이 독자적 연구를 바탕으로 UHPC를 개발하였고, KICT-UHPC의 특성을 충분히 반영한 보도사장교를 한국건설기술원내에 실구조물로 시공하였다. 한국건설기술연구원내 본관 1, 2동 연결 보도사장교(SUPER BRIDGE 1)의 진동실험을 통해 UHPC 보도사장교의 동특성(고유진동수 및 모드형상)을 평가하였다. 대상교량에는 보도사장교의 캔틸레버 구조 특성에 의해 발생하는 진동을 제어하기 위한 질량 264kg의 난간형 수직진동제어장치(TMD) 4대가 설치되어 있으며, 부가질량의 운동을 기계적으로 구속하거나 구속을 해제하여 TMD의 작동을 켜거나 끌 수 있도록 되어있다. TMD의 가동 및 정지시 동특성을 비교하는 정밀한 검증 실험을 통하여 TMD 설치에 의한 동특성의 변화도 평가하였다. 가진망치에 의한 충격실험으로부터 획득한 가속도 시간이력 데이터와 가진망치의 가진력 시간이력 데이터를 사용하여 주파수응답함수(FRF, frequency response function)를 계산하고, 이로부터 Super Bridge I의 동적모드형상과 고유진동수를 추출하였다. 1차 모드의 고유진동수는 TMD 정지시 2.2949 Hz, TMD 작동시 2.0996 Hz로서 8%정도 감소하였다. 충격해머에 의한 가진 실험을 통해 세계 최초로 시공한 UHPC 보도사장교의 진동특성과 관련한 신뢰성 있는 자료를 확보할 수 있었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1069-1074
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• 2014

In this study, the piezoelectric characteristics of a piezoelectric paint sensor were investigated in relation to the poling time. This piezoelectric paint sensor was composed of PNN-PZT powder and epoxy resin with a 1:1 weight ratio. The dimensions of the paint specimen were $40{\times}10{\times}1mm^3$, and the top and bottom sides were both coated with a silver paste to create electrodes. During the poling treatment, the poling time was controlled to examine the effect of the piezoelectric properties, while the poling temperature was fixed at room temperature and the electric field was set to 4 kV/mm. The piezoelectric properties were measured by comparing the output voltage from the paint sensor to the force signal from an impact hammer when the impact hammer hit the specimen. In conclusion, the optimal poling conditions were found to be an electric field of 4 kV/mm and a poling time of around 30 min at room temperature.

• Composites Research
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• v.28 no.4
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• pp.155-161
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• 2015

A composite structure was fabricated with embedded impact detection capabilities for applications in Structural Health Monitoring (SHM). By embedding sensor functionality in the composite, the structure can successfully perform impact localization in real time. Smart resin, composed of $Pb(Ni_{1/3}Nb_{2/3})O_3-Pb(Zr,\;Ti)O_2$ (PNN-PZT) powder and epoxy resin with 1:30 wt%, was used instead of conventional epoxy resin in order to activate the sensor function in the composite structure. The embedded impact sensor in the composite was fabricated using Hand Lay-up and Vacuum Assisted Resin Transfer Molding(VARTM) methods to inject the smart resin into the glass-fiber fabric. The electrodes were fabricated using silver paste on both the upper and bottom sides of the specimen, then poling treatment was conducted to activate the sensor function using a high voltage amplifier at 4 kV/mm for 30 min at room temperature. The composite's piezoelectric sensitivity was measured to be 35.13 mV/N by comparing the impact force signals from an impact hammer with the corresponding output voltage from the sensor. Because impact sensor functionality was successfully embedded in the composite structure, various applications of this technique in the SHM industry are anticipated. In particular, impact localization on large-scale composite structures with complex geometries is feasible using this composite embedded impact sensor.

• Journal of Biomedical Engineering Research
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• v.16 no.4
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• pp.457-462
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• 1995

Unlike the usual bone plate and screw fracture fixation, an improved plate fixation method, which can transfer gradually physiological load to bones, is described. The key feature of the present method is to use washers between the plate and the screw. Bio-absorbable materials or non-ferrous materials with good damping characteristics are used to manufacture the washers. The purpose of this paper is to discuss potential advantages of the proposed method, and to show experimentally its improved impact-absorbing characteristics. Vibration experiments are carried out for pig femurs and cow tibias with and without the proposed washers. This experiments show that the washers can drop the first peak value suite substantially in the FRF plots. Although in-vivo experiments have not been conducted, the present fixation method appears to be a simple and effective alternative to the presently used method.

• Composites Research
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• v.27 no.4
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• pp.146-151
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• 2014

In this study, the experimental study has been performed by varying the polarization of the electric field and impact force to check the piezoelectric characteristics of piezoelectric paint sensor. Piezoelectric paint sensor used in this study is composed of epoxy resin with a hardener and PNN-PZT powder in 1:1 weight ratio. The dimensions of the paint sensor specimen are $40{\times}40{\times}1mm^3$ and regular specimens were made using a mold. The voids are removed from the specimen in the vacuum desiccator. Both upper side and bottom side of the paint sensor were coated with silver paste for making an electrode and then dried at room temperature for a day. The poling treatment has been carried out under controlled conditions of the electric field in order to check the effect of piezoelectric sensitivities, while the poling temperature was fixed at room temperature and the poling time was set to 30 min. The piezoelectric sensitivities have been measured by comparing output voltage from paint sensor with output force from impact hammer when the impact hammer hits the paint sensor. In result, the effect of the electric field has been evaluated for the sensitivity and describe the result.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.1
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• pp.104-117
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• 1999

The Composite materials has been used in the field of high technology industry because of high specific stiffness and high specific strength. Specially, the composite materials has been widely applied to the field of the aircraft and the transportation by the effectiveness of light weight due to low specific weight and reduction of the parts due to bonding, molding and so on. These advantages about the composite have led to study and apply in the transmission shaft for the aircraft and the drive shaft for the automobile. The composite material propeller shaft with the high vibrational stability was designed and analyzed. In order to verify the analysis, two types of experimental test which are the FFT analyzer with impact hammer and the rotational equipment were applied.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.18 no.2
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• pp.162-169
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• 2009

This paper describes a study on dynamic characteristics analysis and dynamic compliance evaluation of a 5-axis multi-tasking machine tool of ram-head type. Structural dynamics analysis and evaluation are necessary to machine tool design and development to secure good machine tool performance against tough and harsh machining conditions. In this study, natural frequencies and corresponding vibration modes of the machine tool structure were analyzed by using both F.E.M. modal analysis and impulse hammer test. Furthermore, dynamic compliance of the machine tool was analyzed by using F.E.M. and also measured by using a hydraulic exciter test. Both the theoretical analysis and experimental test results showed good agreement with each other.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.102-106
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• 2003

An experimental modal analysis and dynamic stiffness evaluation of a moving body structure of a high speed machining center are presented in this paper. The natural frequencies and corresponding modes, and dynamic compliance of a moving body structure of high speed machining center are investigated by using F.E.M., hydraulic exciter test, and impulse hammer test. The lowest three natural frequencies were found to be 56.6 Hz, 112.7 Hz, and 142.7 Hz by FEA respectively, while those were 55 Hz, 112 Hz, 131 Hz by experimental analysis. Furthermore, both computed and measured absolute dynamic compliances of the moving body structure in iso-direction showed good agreement especially at the first two mode frequencies. With our experimental data, the dynamic characteristics of the machining center can be exploited to get a new development of structural dynamic design and modification.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.1
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• pp.1-6
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• 2011

The accurate results of finite element analysis are directly related to reliability FE model which is exactly describing dynamic characteristics of target structure. So, a model updating is necessary to establish reliable FE(Finite Element) model with a lot of experience and effort using modal testing. A large structure is too difficult to obtain the dynamic characteristics owing to its weight and size. In this work, using main gun firing test, modal testing was performed to obtain dynamic characteristics of large naval vessel, which is difficult to tap the general modal testing method. The result of experiment was considered its possibility and future plans.