The Acoustics of Wood (1995)

301 Pages·1995·73.485 MB·\301

by  Voichita Bucur (Author)

ACOUSTICS
O f
WOOD
Voichita Bucur
Institut National de la Recherche Agronomique
Centre de Recherches Forestières
Nancy, France
First published 1995 by CRC Press
Taylor & Francis Group
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Reissued 2018 by CRC Press
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CONTENTS
Foreword .................................................................................. ix
Preface ........................................................................................................................................................... x
Chapter 1
Introduction
1.1. General Remarks on Wood Material.................................................................................................. 1
1.2. Outline of the Book .......................................................................................................................... 4
References ...................................................................................................................................................... 4
PART I ENVIRONMENTAL ACOUSTICS
Chapter 2
Acoustics of Forests and Acoustic Quality Control of Some Forest Products
2.1. Acoustics of Forests and Forest Products....................................................................................... 9
2.2. Ultrasound for the Germinability Detection of Acorns ............................................................... 13
References ...................................................................................................................................................... 17
Chapter 3
Wood and Wood-Based Materials in Architectural Acoustics
3.1. Influence of Anatomical Structure of Wood on Sound Absorption Characteristics ................ 19
3.2. Wood Materials as Acoustic Insulators......................................................................................... 20
3.3. Wood and the Acoustics of Concert Halls .................................................................................... 24
References ...................................................................................................................................................... 31
PART II MATERIAL CHARACTERIZATION
Chapter 4
Theory and Experimental Methods for the Acoustic Characterization of Wood
4.1. Elastic Symmetry of Propagation Media ...................................................................................... 35
4.1.1. Isotropic Solids...................................................................................................................... 36
4.1.2. Anisotropic Solids ................................................................................................................ 36
4.2. Wave Propagation in Anisotropic Media ........................................................................................ 42
4.2.1. Ultrasonic Bulk Wave Propagation in Orthotropic Media ............................................. 44
4.2.1.1. Velocities and Stiffnesses. The Eigenvalues of Christoffel’s
Equations ............................................................................................................... 44
4.2.1.2. The Eigenvectors of Christoffel’s Equations ................................................... 49
4.2.2. Mechanical Vibrations in the Acoustic Frequency Range ............................................. 51
4.2.2.1. Resonance Vibration Modes in Rods and Plates ............................................. 51
4.2.2.2. Engineering Constants ......................................................................................... 52
4.3. Velocity of Ultrasonic Waves in Wood........................................................................................... 58
4.3.1. Measurement System ........................................................................................................... 59
4.3.1.1. Devices ................................................................................................................... 59
4.3.1.2. Transducers............................................................................................................ 60
4.3.2. Specimens for Ultrasonic Testing ....................................................................................... 60
4.3.2.1. Preparation of Samples ........................................................................................ 62
4.3.2.2. Coupling Media..................................................................................................... 65
4.3.2.3. Specimens of Finite Dimensions ........................................................................... 66
4.3.2.4. Influence of the Physical Properties of Wood on Measurement
of Ultrasonic Velocity .......................................................................................... 70
4.4. Attenuation of Ultrasonic Waves ..................................................................................................... 73
4.4.1. Theoretical Considerations................................................................................................. 74
4.4.2. Measurement Technique .................................................................................................... 74
4.4.3. Factors Affecting Attenuation Measurements ................................................................ 74
4.4.3.1. Geometry of the Specimen ............................................................................... 74
4.4.3.2. Characteristics of the Materials ........................................................................ 76
4.5. Internal Friction in Wood in the Audible Frequency Range .................................................... 79
4.5.1. Typical Damping Coefficient Values ............................................................................... 80
4.5.2. Damping Coefficients as Indicators of Microstructural Modifications
Induced by Different Factors ............................................................................................ 81
4.5.2.1. Temperature and Moisture Content ................................................................. 81
4.5.2.2. Chemical Treatment ........................................................................................... 82
4.5.2.3. Dynamic Loading ............................................................................................... 83
References .................................................................................................................................................... 84
Chapter 5
Elastic Constants of Wood Material
5.1. Global Characterization ................................................................................................................... 91
5.1.1. Optimization Criteria for Off-Diagonal Terms of the Stiffness Matrix Determined
Using Bulk Waves.............................................................................................................. 91
5.1.2. Stiffnesses and Mode Conversion Phenomena from Bulk to Surface
Waves .................................................................................................................................... 101
5.1.3. Young’s Moduli, Shear Moduli, and Poisson’s Ratios from Dynamic
(Ultrasonic and Resonance) Testsa nd Static Tests ........................................................ 105
5.2. Local Characterization ..................................................................................................................... 107
5.2.1. Acoustic Microscopy ........................................................................................................ 108
5.2.1.1. Operating Principle ........................................................................................... 110
5.2.1.2. Acoustic Images ................................................................................................ Ill
5.2.2. Photoacoustics in Wood Science .................................................................................... 112
5.2.2.1. Principles ............................................................................................................ 113
5.2.2.2. Instrumentation ................................................................................................... 113
5.2.2.3. Applications......................................................................................................... 114
References .................................................................................................................................................... 114
Chapter 6
Structural Anisotropy and Ultrasonic Parameters of Wood
6.1. Filtering Action Induced by the Anatomic Structure of Wood ................................................ 119
6.2. Estimation of Anisotropy by Velocities of Longitudinal and Transverse Bulk
Waves ................................................................................................................................................. 120
6.3. Estimation of Anisotropy by Invariants ........................................................................................ 124
6.3.1. Acoustic Invariants ............................................................................................................. 125
6.3.2. Elastic Invariants ................................................................................................................. 129
References .................................................................................................................................................... 131
PART III QUALITY ASSESSMENT
Chapter 7
Wood Species for Musical Instruments
7.1. Acoustic Properties of Wood Species ............................................................................................ 135
7.1.1. Acoustic Properties of Resonance Wood for Violins .................................................... 135
7.1.1.1. Spruce ................................................................................................................... 136
7.1.1.2. Curly Maple ........................................................................................................ 140
7.1.1.3. Wood for the Bow ............................................................................................ 141
7.1.1.4. Wood for Other Components........................................................................... 141
7.1.2. Acoustic Properties of Wood for Guitars ......................................................................... 141
7.1.3. Acoustic Properties of Wood for Woodwind Instruments ............................................. 142
7.1.4. Acoustic Properties of Wood for Percussion Instruments ............................................. 143
7.1.5. Acoustic Properties of Wood for Keyboard Instruments: The Piano ......................... 143
7.1.6. Relationships between Elastic Properties of Resonance Wood and
Its Typical Structural Characteristics............................................................................... 145
7.1.6.1. Macroscopic Structural Parameters ................................................................. 145
7.1.6.1.1. Growth Ring Pattern ....................................................................... 147
7.1.6.1.2. Densitometric Pattern of the Annual Ring in Resonance Wood 150
7.1.6.2. Microscopic and Submicroscopic Structural Parameters.............................. 151
7.1.7. Tonal Quality of Musical Instruments and Wood Properties ...................................... 153
7.1.8. Conclusion ........................................................................................................................... 154
7.2. Factors Affecting Acoustic Properties of Wood for Musical Instruments ............................... 155
7.2.1. Influence of Natural Aging on Resonance Wood ........................................................... 155
7.2.2. Influence of Environmental Conditions ........................................................................... 158
7.2.3. Influence of Long-Term Loading ..................................................................................... 159
7.2.4. Influence of Varnishing ...................................................................................................... 161
7.3. Chemical Treatments for Improving the Acoustic Properties of Common Solid
Wood Used for Mass-Produced Instruments ............................................................................... 163
7.4. Composites as Substitutes for Resonance Wood ......................................................................... 165
Appendix ...................................................................................................................................................... 168
References .................................................................................................................................................... 170
Chapter 8
Ultrasound as a Complementary Nondestructive Tool for Wood Quality
Assessment
8.1. Ultrasound and Wood Quality ........................................................................................................ 177
8.2. Ultrasonic methods for Trees, Timber, and Wood Composites ................................................ 177
8.2.1. Ultrasound and Trees ......................................................................................................... 177
8.2.1.1. Detection of the Slope of the Grain ................................................................ 177
8.2.1.2. Detection of Reaction Wood .................................................................. 179
8.2.1.3. Detection of Pruning Trees............................................................................. 181
8.2.1.4. Detection of Curly Figures in Trees ............................................................... 183
8.2.2. Ultrasound and Lumber Grading ...................................................................................... 185
8.2.2.1. Ultrasonic Velocity Method for Grading Timber and Round Wood .......... 186
8.2.2.2. Stress-Wave Grading Technique for Testing Timber and Wood
Composites .......................................................................................................... 190
8.3. Ultrasonic Control of Wood-Based Composites ........................................................................... 190
8.4. Other Nondestructive Techniques for the Detection of Defects in Wood ............................... 192
References .................................................................................................................................................... 193
Chapter 9
Environmental Modifiers of the Structural Parameters of Wood Detected With
Ultrasounic Waves
9.1. Dependence of Ultrasonic Velocities and Related Mechanical Parameters of Wood
on Moisture Content and Temperature ......................................................................................... 197
9.1.1. Influence of Moisture Content on Solid Wood................................................................... 197
9.1.2. Influence of Temperature on Solid Wood ......................................................................... 201
9.1.3. Influence of the Hygrothermal Treatment on the Quality of Wood
Composites .......................................................................................................................... 206
9.2. Ultrasonic Parameters and Biological Deterioration .................................................................. 207
9.2.1. Bacterial Attack ................................................................................................................... 207
9.2.2. Fungal attack ....................................................................................................................... 209
9.2.3. Wood-Boring Agents ....................................................................................................... 213
9.2.4. Archeological Wood ........................................................................................................... 214
References .................................................................................................................................................... 217
Chapter 10
Acoustic Emission
10.1. Principles and Instrumentation ....................................................................................................... 221
10.1.1. Principles .............................................................................................................................. 221
10.1.2. Instrumentation .................................................................................................................... 223
10.1.2.1. Systems................................................................................................................. 223
10.1.2.2. Material Conditioning ........................................................................................ 224
10.1.2.3. Transducers........................................................................................................... 225
10.1.2.4. Amplifiers and Signal Processors..................................................................... 225
10.1.2.5. Signal Processing ................................................................................................ 225
10.1.2.6. Factors Affecting Acoustic Emission Responses from
Wooden Materials ............................................................................................... 226
10.2. Acoustic Emission for the Structural Evaluation of Trees, Solid Wood,
Particleboard, and Other Wood-Based Composites ..................................................................... 227
10.2.1. Cavitation ............................................................................................................................. 227
10.2.2. Detecting the Activity of Biological Agents................................................................... 229
10.2.3. Acoustic Emission and Fracture Mechanics ................................................................... 230
10.2.3.1. In Solid Wood ..................................................................................................... 232
10.2.3.2. In Wood Composites .......................................................................................... 235
10.3. Acoustic Emission for Monitoring Technological Processes ..................................................... 236
10.3.1. Adhesive Curing and Adhesive Strength ........................................................................ 236
10.3.2. For Controlling Drying of Lumber .................................................................................. 238
10.3.3. As a Strength Predictor in Timber and Large Wood Structures .................................. 241
10.3.4. Signals in Wood Machining .............................................................................................. 247
References .................................................................................................................................................... 249
Chapter 11
High-Energy Ultrasonic Treatment for Wood Processing
ILL Modifications Induced in Anatomic Structure by high-Energy Ultrasonic Waves ................ 257
11.2. High-Energy Ultrasonic Treatment, A Tool for Wood Processing ........................................... 257
11.2.1. Drying ................................................................................................................................... 257
11.2.2. Defibering ............................................................................................................................. 257
11.2.3. Cutting .................................................................................................................................. 261
11.2.4. Plasticizing Effect ............................................................................................................... 261
11.2.5. Regeneration Effect on Aged Glue Resins ..................................................................... 262
11.3. Improving Wood Preservation Using Ultrasound ........................................................................ 263
References .................................................................................................................................................... 265
Appendix: List of Wood Species Cited in this Book ........................................................................... 267
Index 271
FOREWORD
The Hooke’s law of elasticity
I0 #] = [CijkliiZ-ki]
appears in its general forms as Equation 4.1 at the beginning of this book, as it usually does in many
texts of elasticity or acoustics. In order to thoroughly appreciate the spirit that inspired the author in
writing the “Acoustics of Wood”, one should have seen the very same formula projected by the same
author on the screen of one of the Erice lecture halls during the presentation of an advanced research
lecture, as the author herself quotes in the Preface to this volume, few, elegantly handwritten letters
“[o-y] = [Qu][€*J” filled the whole screen in a symphony of pastel colours. The attention of the audience
was gently captured. Science and art were locked together within a simple formula, as science and art
link together in the author’s life, as science and art frequently share common fate in wood history.
The making of violins, cellos, or pianos or other musical instruments has been an art long before
being an object of scientific investigation. Architectural wood structures are artists’ representations
that rely on advanced achievements of mechanics. The scientific knowledge of wood properties and
characteristics is a necessary step toward its best use in artistic representations. This might really be a
rather personal interpretation of the reading of the book, but it could be really one of the ways to
approach the reading.
Acoustics of wood deals with wood in all aspects that are of concern to acoustics: from sound
barriers produced by forests and trees, to the use of wood in acoustical panels; from the crystallographic
symmetry classes of different woods, to the surface wave propagation in wood structures; from the
influence of aging and moisture in the elastic propagation in wood, to the chemical methods for
improving acoustic properties; from the counting of the average ring width in violin tops, to the high Q
properties of guitar wood for sustaining “sing” modes; from acoustic micrographs of acoustic microscopy
techniques, to the acoustic emissions characteristics of different wood species.
Acoustics of wood, however, preliminarily needs information about wood, from seed germination
to forest growth, through moisture, aging and anatomical properties. The intrinsic coordinate system
of wood is a cylindrical system, that follows the axial direction of growth of the stem, the azimuthal
and radial directions, the commonest case of wood materials presents an orthotropic symmetry, where
three mutually perpendicular mirror planes of symmetry exist, related to the directions of growth.
Velocity of ultrasonic waves present a wide spread of values, from 6000 m/s for longitudinal waves
along the fiber direction to 400 m/s for shear waves in the radial-tangential plane.
An interesting general review of wave equations and solutions accompanies Part I devoted to material
characterization, where elastic constant relations to technical constants is duely reviewed together with
Christoffel equations and eigenvalue properties of the wave equation. That is the science part, as we
said at the beginning, that matches with the technical part reported as the last section of the book,
where probing of materials and common techniques of testing are also reviewed. And all is treated
with meticulous care as to completeness and with careful attention to biographical sources, that are
listed by subject at the end of each chapter. But art and style are blended with science, and that is
materially achieved with a series of color plates properly selected to show grain and fiber structure in
different samples.
Wood is technically studied because of its importance in the manufacture of musical instruments:
what are the characteristics of a guitar plate or of a harp soundbox or a violin bow and what are the
wood species to be used? Names with exotic charm like Manilkara, Mauritius ebony or Pernambuco
wood, alternate with those of cultural Latin origin, like Picea abies or Acer pseudoplatanus and so on.
And they are of interest because of their Young’s modulus or Poisson ratio or high quality factor.
What was known about quality factor or Poisson ratio by the handcraft masters of the past? Why
is wood the best material for many musical instruments, still not overtaken by the ubiquitous power
of plastics? Perhaps Nature is science and art at the same time and we usually follow different routes
to get to the target, only to discover at the end that it could have been achieved through either route.
Adriano Alippi
Istituto di Acustica “O. M. Corbino”
Rome, Italy