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An Evaluation of Loss Factor of Damping Treatment Materials for Panels of Railway Vehicles

철도차량용 패널 감쇠처리재의 감쇠계수 평가

  • Received : 2019.01.11
  • Accepted : 2019.04.05
  • Published : 2019.04.30

Abstract

This paper is a study on the evaluation of loss factor of damping treatment materials to reduce the noise and vibration for panels of railway vehicles and automobiles. In order to determine the modal parameters of damping materials, beam excitation tests were carried out using different type PVC coated aluminum and steel base beam specimens. The specimens were excited from 10 Hz to 1000 Hz frequency range using sinusoidal force, and transfer mobility data were measured by using an accelerometer. The loss factors were determined by using integrated program, based on theories of Half Power Method, Minimum Tangent Error Method, Minimum Angle Error Method and Phase Change Method, which enable to evaluate the parameters using modal circle fit and least squares error method. In the case of lower loss factor and data of linear characteristics, any method could be applied for evaluation of parameters, however the case of higher loss factor or data including non-linear characteristics, the minimum angle error method could reduce the loss factor evaluation. The obtained dynamic properties of the coating material could be used for application of Finite Element Method analyzing the noise control effects of complex structures such as carbody or under-floor boxes of rolling stock. The damping material will be very useful to control the structural noise, because the obtained modal loss factors of each mode show very good effect on over $2^{nd}$ mode frequency range.

본 논문은 철도차량 및 자동차용 패널의 진동 및 소음억제용으로 사용되는 감쇠 처리재의 감쇠특성 평가에 관한 연구이다. 감쇠재의 모드별 매개변수들을 구하기 위해 다른 종류의 PVC를 알루미늄과 철계 빔위에 도포한 시편을 제작하여 가진시험을 수행하였다. 시편은 10 Hz부터 1,000 Hz까지의 주파수 대역을 조화력으로 가진하여 가속도계로 전달 모빌리티값을 측정하였다. 감쇠계수는 몇 가지 이론인 반력법, 최소 탄젠트오차법 및 최소 각오차법 조합법과 위상변화법을 모드 원호곡선 맞춤과 최소자승오차법을 사용하여 작성한 통합 프로그램을 이용하여 평가하였다. 감쇠값이 비교적 낮고 측정값이 선형인 경우는 어느 방법을 사용해도 되나, 감쇠값이 높거나 측정값에 비선형특성이 있는 경우에는 최소 각오차법이 감쇠계수 측정오차를 줄일 수 있다. 도포 감쇠재의 동적특성 평가로부터 구한 재료의 물성값은 차체나 철도차량 하부 기기함과 같이 복잡한 구조물의 소음해석을 위한 유한요소법에 사용할 수 있다. 빔 시험에서 수행한 모드별 감쇠계수의 특성 평가 결과 2차 이상 모드의 주파수 대역에서 감쇠 효과가 크기 때문에 구조소음억제에 유용할 것으로 사료된다.

Keywords

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Fig. 1. Damping material coated beam specimens

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Fig. 2. Coated beam tests: (a) boundary excitation,(b) environmental chamber tests

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Fig. 3. Frequency response plot by transfer mobility of beam tests: aluminium base specimen

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Fig. 4. Curve fit HPM(Al 1.0 mm, mode 3, 1 Hz resolution)

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Fig. 5. Close modes(damping treated AL 1.6mm based beam, mode 3, 0.25 Hz resolution), (a) frequency response plot (b) 3D Nyquist plot

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Fig. 6. Modal circle fit for close modes(damping treated AL beam, mode 3, 0.25 Hz resolution)

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Fig. 7. Flowchart of loss factor evaluation(HPM,Combination of MTEM & MAEM & PCM)

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Fig. 8. Loss factor comparisons to evaluate the coating mass effect of material

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Fig. 9. Loss factor comparisons to evaluate the coating thickness effect of material

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Fig. 10. Loss factor comparisons to evaluate the base metal effect and frequency dependency of material

Table 1. Test specimens for the coated beam test

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Table 2. Input frequency bandwidth dependency of modal parameters of combination of MTEM & MAEM (Fig. 5. coated AL beam, mode 3, 0.25 Hz resolution)

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Table 2. Dynamic parameter determination: coating material properties

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