VIBRATION AND ACOUSTICAL PROPERTIES OF SANDWICH COMPOSITE MATERIALS Except ...

203 Pages·2005·1.95 MB·English

by  Yan Du

VIBRATION AND ACOUSTICAL PROPERTIES OF SANDWICH COMPOSITE
MATERIALS

Except where reference is made to the work of others, the work described in this
dissertation is my own or was done in collaboration with my advisory committee.
This dissertation does not include proprietary or classified information.

_________________
Zhuang Li

Certificate of approval:

___________________ __________________________
Subhash C. Sinha Malcolm J. Crocker, Chair
Professor Distinguished University Professor
Mechanical Engineering Mechanical Engineering

____________________ ___________________________
George T. Flowers A. Scottedward Hodel
Professor Associate Professor
Mechanical Engineering Electrical Engineering

___________________________
Stephen L. McFarland
Acting Dean
Graduate School
VIBRATION AND ACOUSTICAL PROPERTIES OF SANDWICH COMPOSITE
MATERIALS

Zhuang Li

A Dissertation

Submitted to

the Graduate Faculty of

Auburn University

in Partial Fulfillment of the

Requirements for the

Degree of

Doctor of Philosophy

Auburn, Alabama
May 11, 2006
VIBRATION AND ACOUSTICAL PROPERTIES OF SANDWICH COMPOSITE
MATERIALS

Zhuang Li

Permission is granted to Auburn University to make copies of this dissertation at its
discretion, upon request of individuals or institutions and at their expense.
The author reserves all publication rights.

______________________________
Signature of Author

______________________________
Date of Graduation

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VITA

Zhuang Li, son of Shouan Li and Shuxian Hao, was born on September 4, 1975, in
Shijiazhuang, Hebei Province, China. He graduated from the Middle School Attached to
Hebei Normal University in 1994. He entered Tianjin University, Tianjin, China in
September 1994, and graduated with two Bachelor of Engineering degrees in Precision
Instrument Engineering and Industrial Engineering in July 1998. He continued his study
in Tianjin University in September 1998, and obtained Master of Engineering degree in
Precision Instruments and Machinery in March 2001. He entered Graduate School,
Auburn University, in August 2001. He married to Yan Du, daughter of Xingrun Du and
Fengqin Liu, on December 25, 2002.
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DISSERTATION ABSTRACT
VIBRATION AND ACOUSTICAL PROPERTIES OF SANDWICH COMPOSITE
MATERIALS
Zhuang Li
Doctor of Philosophy, May 11, 2006
(M.E., Tianjin University, 2001)
(B.E., Tianjin University, 1998)

203 Typed Pages

Directed by Malcolm J. Crocker

In applications where the use of lightweight structures is important, the introduction
of a viscoelastic core layer, which has high inherent damping, between two face sheets,
can produce a sandwich structure with high damping. Composite sandwich structures
have several advantages, such as their high strength-to-weight ratio, excellent thermal
insulation, and good performance as water and vapor barriers. So in recent years, such
structures have become used increasingly in transportation vehicles. However their
fatigue, vibration and acoustic properties are known less. This is a problem since such
composite materials tend to be more brittle than metals because of the possibility of
delamination and fiber breakage. Structures excited into resonant vibration exhibit very
high amplitude displacements which are inversely proportional to their passive damping.
The transmission loss of such composite panels is also poor at coincidence. Their passive
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damping properties and attempts to improve their damping at the design stage are
important, because the damping properties affect their sound transmission loss, especially
in the critical frequency range, and also their vibration response to excitation.
The research objects in this dissertation are polyurethane foam-filled honeycomb
sandwich structures. The foam-filled honeycomb cores demonstrate advantages of
mechanical properties over pure honeycomb and pure foam cores. Previous work
including theoretical models, finite element models, and experimental techniques for
passive damping in composite sandwich structures was reviewed. The general dynamic
behavior of sandwich structures was discussed. The effects of thickness and delamination
on damping in sandwich structures were analyzed. Measurements on foam-filled
honeycomb sandwich beams with different configurations and thicknesses have been
performed and the results were compared with the theoretical predictions. A new modal
testing method using the Gabor analysis was proposed. A wavelet analysis-based noise
reduction technique is presented for frequency response function analysis. Sound
transmission through sandwich panels was studied using the statistical energy analysis
(SEA). Modal density, critical frequency, and the radiation efficiency of sandwich panels
were analyzed. The sound transmission properties of sandwich panels were simulated
using AutoSEA software. Finite element models were developed using ANSYS for the
analysis of the honeycomb cell size effects. The effects of cell size on both the Young’s
modulus and the shear modulus of the foam-filled honeycomb core were studied in this
research. Polyurethane foam may produce a negative Poisson’s ratio by the use of a
special microstructure design. The influence of Poisson’s ratio on the material properties
was also studied using a finite element model.
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ACKNOWLEDGMENTS

The Author would like to express his sincere appreciation and thanks to his advisor
Professor Malcolm J. Crocker for his guidance during the studies. All the committee
members provided considerable assistance for which I am grateful. My appreciation also
goes to my friends and colleagues at Auburn University. Last and not least, I want to
express my special thanks to my parents Shouan Li and Shuxian Hao, and my wife Yan
Du, for their support and love.

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Journal used: Journal of Sound and Vibration

Computer software used: Microsoft Word 2002

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TABLE OF CONTENTS

LIST OF TABLES . . . . . . . . xii
LIST OF FIGURES . . . . . . . . xiii
CHAPTER 1 INTRODUCTION. . . . . . . 1
1.1 Sandwich Composite Materials . . . . . 1
1.2 Motivation for Research . . . . . . 4
1.3 Organization of Dissertation . . . . . 6
CHAPTER 2 LITERATURE OVERVIEW . . . . . 12
2.1 Overview of Damping . . . . . . 12
2.1.1 Damping mechanisms . . . . . 13
2.1.2 Measures of damping . . . . . 15
2.1.3 Measurement methods . . . . . 16
2.2 Damping in Sandwich Structures . . . . . 17
2.2.1 Analytical models . . . . . 18
2.2.2 Damping and damage . . . . . 26
2.2.3 Finite element models . . . . . 27
2.2.4 Statistical energy analysis method . . . 29
CHAPTER 3 ANALYSIS OF DAMPING IN SANDWICH MATERIALS . 40
3.1 Equation of Motion . . . . . . 41
3.2 Effects of Thickness . . . . . . 46
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3.3 Effects of Delamination . . . . . . 51
3.4 Damping Improvement using Multi-layer Sandwich Structures . 51
3.5 Experiments . . . . . . . 55
3.5.1 Experimental setup . . . . . 55
3.5.2 Experimental results . . . . . 56
3.5.3 Discussion . . . . . . 57
CHAPTER 4 DAMPING CALCULATION AND MODAL TESTING . 74
USING WAVELET AND GABOR ANALYSES
4.1 Wavelet and Gabor Analyses . . . . . 75
4.2 Modal Extraction using Wavelet Analysis . . . 79
4.3 Damping Calculation using Gabor Analysis . . . 82
4.3.1 Decouple modes using Gabor analysis . . . 83
4.3.1 Damping calculation . . . . . 85
4.3.2 Simulations . . . . . . 86
4.3.3 Comparison with FFT-based technique . . . 88
4.4 Modal Testing using Gabor Transform . . . . 89
4.5 Experiments . . . . . . . 92
4.5.1 Experimental setup . . . . . 92
4.5.2 Natural frequency and mode shape . . . 93
4.5.3 Damping ratio . . . . . . 93
CHAPTER 5 ANALYSIS OF SOUND TRANSMISSION THTROUGH . 110
SANDWICH PANELS
5.1 Review of the Sound Transmission Loss of Sandwich Panels . 111
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