A Novel Technique to Extract the Modal Damping Properties of a Thin Blade

Composite materials are widely used for their peculiar combination of excellent structural, mechanical, and damping properties. This work presents an experimental study on the dissipation properties of disk-shaped composite specimens exploiting vibration tests. Two different polymer matrix composites with the same number of identical laminae, but characterized by different stacking sequences, namely unidirectional and quasi-isotropic configurations, have been evaluated. An ad-hoc steel structure was designed and developed to reproduce an in-plane torsional excitation on the specimen. The main idea of the proposed approach relies on deriving the damping properties of the disks by focusing on the modal damping of the overall vibrating structure and, in particular, using just the first in-plane torsional deformation mode. Experimental torsional damping evaluations were conducted by performing vibrational hammer excitation on the presented setup. Two methods were proposed and compared, both relying on a single-degree-of-freedom (SDOF) approximation of the measured frequency response function (FRF).

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Effect of an Interleave Natural Viscoelastic Layer on the Dynamic Behaviour of a Bio-Based Composite

Advanced Composites Letters ◽

10.1177/096369351702600601 ◽

2017 ◽

Vol 26 (6) ◽

pp. 096369351702600

Author(s):

H. Daoud ◽

J.-L. Rebiere ◽

A. El Mahi ◽

M. Taktak ◽

M. Haddar

Keyword(s):

Natural Rubber ◽

Dynamic Behaviour ◽

Natural Frequencies ◽

Viscoelastic Layer ◽

Damping Properties ◽

Beam Test ◽

Modal Damping ◽

Present Letter ◽

Vibration Tests ◽

Stiffness And Damping

The purpose of the present letter is to analyse the damping properties of a bio-based composite with flax fibre. Damping parameters were investigated using beam test specimens and an impulse technique. Through a series of resonance vibration tests, the natural frequencies and modal damping were evaluated. The second part of the work was to investigate the effect of an interleave viscoelastic layer made of natural rubber on the dynamic behaviour of the composite. A comparison of the different results was performed; it shows that the viscoelastic layer had a significant influence on vibration behaviour, bending stiffness and damping factors.

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Modeling method of element Rayleigh damping for the seismic analysis of a 3D FEM model with multiple damping properties

Journal of Vibration and Control ◽

10.1177/1077546317718969 ◽

2017 ◽

Vol 24 (17) ◽

pp. 4065-4077 ◽

Cited By ~ 1

Author(s):

Shohei Onitsuka ◽

Yuichi Ushio ◽

Naoki Ojima ◽

Tadashi Iijima

Keyword(s):

Least Squares Method ◽

Seismic Analysis ◽

Weighted Least Squares ◽

Damping Properties ◽

Lumped Mass ◽

3D Fem ◽

Mass Model ◽

Weighted Least Squares Method ◽

Rayleigh Damping ◽

Modal Damping

Damping modeling is important for the accurate evaluation of the seismic response of structures. Our group previously reported a damping modeling method using element Rayleigh damping and evaluated the effectiveness using a simple lumped-mass model with multiple damping properties; however, the effectiveness of the method was not evaluated for three-dimensional (3D) finite element method (FEM) models with multiple damping properties. Moreover, further studies showed that the method needed to be improved to be applied to 3D FEM models. Therefore, the method has been improved to enable application to the seismic analysis of 3D FEM models, and the effectiveness of the method has been evaluated. The proposed method uses a weighted least-squares method to automatically determine the coefficients of element Rayleigh damping. The weighted least-squares method minimizes the differences between the modal damping ratios to be modeled and those given by element Rayleigh damping. Although all modal damping ratios in a simple lumped-mass model were used for damping modeling in our previous study, obtaining them for 3D FEM models is impractical because these models have more natural modes than simple lumped-mass models. Therefore, we used modal damping ratios below a cut-off frequency. The effectiveness of the proposed method was evaluated by comparing it with conventional methods in terms of the modeling errors related to the modal damping ratios and the maximum absolute acceleration. The proposed method tended to have lower errors than the conventional methods and is concluded to be more effective for the seismic analysis of 3D FEM models with multiple damping properties. The proposed method can automatically determine the coefficients of element Rayleigh damping and can more accurately model the damping properties of analysis models, indicating that the proposed method is a powerful tool for the seismic analysis of 3D FEM models with multiple damping properties.

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