VIBRATION PROPERTIES OF WOOD

Rani Kaba

Bachelor of Engineering with Honours

(Mechanical Engineering and Manufacturing Systems)

2006

Faculty of Engineering

i

VIBRATION PROPERTIES OF WOOD

RANI ANAK KABA

This project is submitted in partial fulfillment of

the requirements for the degree of Bachelor of Engineering with Honours

(Mechanical Engineering and Manufacturing System)

2006

ii

Specially Dedicated to My Marvelous Family

UNIVERSITY MALAYSIA SARAWAK

BORANG PENGESAHAN STATUS TESIS

Judul VIBRATION PROPERTIES OF WOOD

SESI PENGAJIAN: 2005/2006

Saya, RANI ANAK KABA

(HURUF BESAR)

mengaku membenarkan tesis * ini disimpan di Pusat Khidmat Maklumat Akademik, Universiti

Malaysia Sarawak dengan syarat-syarat kegunaan seperti berikut:

1. Tesis adalah hakmilik Universiti Malaysia Sarawak.

2. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat

salinan untuk tujuan pengajian sahaja.

3. Membuat pendigitan untuk membanguankan Pangkalan Data Kandungan Tempatan.

4. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat

salinan tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi.

5. ** Sila tandakan ( √ ) di kotak yang berkenaan.

SULIT (Mengandungi maklumat yand berdarjah keselamatan atau

kepentingan Malaysia seperti yang termaktub di dalam AKTA

RAHSIA RASMI 1972).

TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan Oleh

organisasi/badan di mana penyelidikan dijalankan).

TIDAK TERHAD

Disahkan oleh

(TANDATANGAN PENULIS) (TANDATANGAN PENYELIA)

Alamat tetap 76, Kampung Merdang Lumut Prof. Madya Dr. Sinin Bin Hamdan

Jln. Dato’ Mohd. Musa Nama Penyelia

94300 Kota Samrahan, Sarawak

Tarikh: Tarikh:

CATATAN * Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah, Sarjana dan Sarjana Muda

** Jika tesis ini SULIT dan TERHAD, sila lampirkan surat daripada pihak

berkuasa/organiasis berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini

perlu dikelaskan sebagai SULIT dan TERHAD

√

APPROVAL SHEET

This project report attached here to, entitle “VIBRATION PROPERTIES

OF WOOD” was prepared and submitted by Rani Anak Kaba as partial fulfilment of

the requirement for the degree of Bachelor of Engineering with Honours in

Mechanical Engineering and Manufacturing System is hereby read and approve by:

_________________________ __________________

Assoc. Prof. Dr. Sinin Bin Hamdan Date

Supervisor

Faculty of Engineering

University Malaysia Sarawak

iii

ACKNOWLEDGEMENTS

First and foremost, the author would like to give thanks to God for the blessing in

making this project successful. A sincere gratitude and appreciations to the project

supervisor, Associate Professor Dr. Sinin Hamdan for his guidance and expert advices in

conducting the experiment and writing the report.

The author also would like to express thanks to Dr. Mohd. Shahril Osman for his

assistance in the experiment hardware as well as be the coordinator for the Final Year

Project. Additionally, thanks also to Mr. Yahya Sedik for his opinion and

recommendations in the project. Not forgetting to the laboratory assistants and other

technical staffs who kindly sacrificing their time and their aid during the experiment.

Throughout the project, the author received an endless support and

encouragement from her beloved family, Kenny Adams Ajang, and colleagues that

always have faith on her for the best outcomes for this project. Nothing words can be

expressed for appreciation to all the people who have involved direct or indirectly in the

project. Lastly, thank you everyone.

iv

ABSTRACT

The potential of local wood such as Alan Bunga, Selangan Batu, Belian, Damar

Minyak, and White Meranti for musical instruments were investigated. Their physical

and mechanical properties were determined in order to obtain their characteristics. The

density ρ, specific gravity γ, Modulus of Elasticity E, and internal friction tan δ of each

wood were attained from the Free-free Beams Forced Vibration Method. Furthermore,

the correlation between E/γ and γ as well as between tan δ and E/γ were plotted to verify

the suitability of wood for the musical instruments. Damar Minyak has proved its usage

as a guitar where the wood showed the highest E/γ and the lowest tan δ. Alan Bunga and

White Meranti resulted in a moderate E/γ and tan δ values that had a potential as a new

species for musical instruments. The usage of Belian and Selangan Batu as a material

used in construction is undeniable because the outcomes showed the woods had the

lowest E/γ and the highest tan δ compared to other woods.

v

ABSTRAK

Potensi kayu tempatan seperti Alan Bunga, Selangan Batu, Belian, Damar

Minyak, dan Meranti Putih untuk alat muzik dikaji. Sifat-sifat fizikal dan mekanikal

dikenalpasti untuk memperolehi ciri-ciri setiap kayu tersebut. Ketumpatan ρ, graviti

specifik γ, modulus elastik E, dan geseran dalaman tan δ untuk setiap kayu diperolehi

daripada eksperimen “Free-free Beams Forced Vibration Method”. Selain daripada itu,

kaitan di antara tan δ dengan E/γ dan E/γ dengan γ diplotkan bagi memastikan kesesuaian

kayu untuk membuat alat muzik. Damar Minyak dibuktikan penggunaannya sesuai

sebagai gitar di mana kayu tersebut menunjukkan E/γ yang paling tinggi dan tan δ yang

paling rendah. Alan Bunga dan Meranti Putih menunjukkan nilai E/γ dan tan δ yang

sederhana yang boleh diambil kira sebagai spesis baru untuk alat muzik. Penggunaan

Belian dan Selangan Batu sebagai bahan di dalam pembinaan memang tidak dapat

dinafikan kerana hasil experimen menunjukkan kayu-kayu tersebut mempunyai E/γ yang

paling rendah dan tan δ yang paling tinggi berbanding dengan kayu-kayu yang lain.

vi

TABLE OF CONTENTS

DESCRIPTION PAGE

ACKNOWLEDGEMENTS iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENTS vi

LIST OF FIGURES ix

LIST OF TABLES xi

LIST OF APPENDIXES xii

CHAPTER 1: INTRODUCTION

1.1 Wood 1

1.1.1 Acoustical Properties of Wood 3

1.1.2 Wood for Musical Instruments 4

1.2 Vibration 8

1.2.1 Fundamental of Vibration 9

1.2.1.1 Free Vibration 11

1.2.1.2 Forced Vibration 11

1.3 Objectives 12

vii

CHAPTER 2: LITERARTURE REVIEW

2.1 Sharpness of Resonance 13

2.2 Axes of the Wood 15

2.3 Modes of Vibration 16

2.4 Physical Properties of Wood 18

2.4.1 Density 18

2.4.2 Specific Gravity 19

2.5 Mechanical Properties of Wood 20

2.5.1 Modulus of Elasticity 20

2.5.2 Internal Friction 22

CHAPTER 3: METHODOLOGY

3.1 Principle of Free-Free Beams Forced Vibration Method 25

3.2 PicoScope Software 30

3.2.1 Real Voltage and Time 30

3.2.2 Frequency Spectrum 31

3.2.3 PicoScope Advantages 32

3.3 Wood Specimens 35

CHAPTER 4: RESULTS AND DISCUSSIONS

4.1 Introduction 37

4.2 Experimental Data

4.2.1 Density 38

viii

4.2.2 Specific Gravity 40

4.2.3 Modulus of Elasticity 42

4.2.4 Internal Friction 44

4.3 Discussions 46

CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 51

5.2 Recommendations 53

BIBLIOGRAPHY 54

APPENDICES 58

ix

LIST OF FIGURES

DESCRIPTION PAGE

CHAPTER 1: INTRODUCTION

Figure 1.1 : Types of Color and Grain Pattern of the Wood 3

Figure1.1.2 : Bending Process of the Shape Side of the Guitar 5

Figure 1.2.1a : Periodic Vibration 10

Figure 1.2.1b : Random Vibration 10

CHAPTER 2: LITERARTURE REVIEW

Figure 2.1 : Response Curve 15

Figure 2.2 : The Three Principal Axes of Wood with Respect

to Grain Direction and Growth Rings 16

Figure 2.3 : Modes of vibration: (a) first mode, (b) second mode,

(c) third mode 17

Figure 2.4.2 : Response Curve of the Amplitude-Frequency Relationship 23

CHAPTER 3: METHODOLOGY

Figure 3.1a : Schematic Diagram of Free- free Beams Forced

Vibration Method 26

Figure 3.1b : The Position of Microphone and Speaker 26

x

Figure 3.1c : Function Generator 27

Figure 3.1d : Fine Tuning 27

Figure 3.1e : Amplifier 28

Figure 3.1f : Sound Level Meter 28

Figure 3.1g : Oscilloscope (Type ADC 216) 29

Figure 3.1h : Free-free Beams Forced Vibration Method Set-up 29

Figure 3.2.1a : Real Voltage and Time Display 33

Figure 3.2.1b : Two Channels of the Real Voltage and Time Display 33

Figure 3.2.2a : Frequency Spectrum Display 34

Figure 3.2.2b : Two Channels of the Frequency Spectrum Display 34

CHAPTER 4: RESULTS AND DISCUSSIONS

Figure 4.2.1 : The Density of the Five Experimented Woods

and Their Standard Value 39

Figure 4.2.2 : The Specific Gravity of the Five Experimented Woods 41

Figure 4.2.3 : The Modulus of Elasticity of Five Experimented Woods 43

Figure 4.2.4 : The Internal Friction of Five Experimented Woods 45

Figure 4.3a : Relationship between E/γ and Specific Gravity, γ 49

Figure 4.3b : Relationship between tan δ and E/γ 50

xi

LIST OF TABLES

DESCRIPTION PAGE

CHAPTER 1: INTRODUCTION

Table 1.1.2 : Several Types of Imported Woods Used for Making

Musical Instruments 6

CHAPTER 2: LITERARTURE REVIEW

Table 2.4.1 : The Density of Several Wood Species 19

Table 2.5.1 : Elastic Ratios for Various Wood Species 21

Table 2.5.2 : The Internal Friction of Several Wood Species 24

CHAPTER 3: METHODOLOGY

Table 3.3 : List of Wood Specimens 36

CHAPTER 4: RESULTS AND DISCUSSIONS

Table 4.2.1 : The Density of the Five Experimented Woods 38

Table 4.2.2 : The Specific Gravity of the Five Experimented Woods 40

Table 4.2.3 : The Modulus of Elasticity and Frequency Resonance

of Five Experimented Woods 42

Table 4.2.4 : The Internal Friction of Five Experimented Woods 44

xii

LIST OF APPENDICES

DESCRIPTION PAGE

APPENDIX A : Frequency Spectrum of Alan Bunga 58

APPENDIX B : Frequency Spectrum of Selangan Batu 62

APPENDIX C : Frequency Spectrum of Belian 66

APPENDIX D : Frequency Spectrum of Damar Minyak 70

APPENDIX E : Frequency Spectrum of White Meranti 74

1

CHAPTER 1

INTRODUCTION

1.1 WOOD

Wood is much known as a preference for making musical instruments. Musical

instruments such as guitar, piano, and violin are mainly made from wood. Apart from

its attractive color and the beautiful texture of the wood itself, wood is a suitable

material to transmit sound when vibrations or resonance occur in the wood.

In order to obtain the essential mechanical properties of the wood for producing

the musical instrument, the wood specimen should undergo the vibration test. The

vibration test to be used is Free-free Beams Forced Vibration Method, a type of

nondestructive testing (NDT) techniques as an alternative method to measure the wave

pattern traveling in the wood specimen. The resonance frequency that resulted from the

method is employed in predicting the wood properties.

2

Wood is a natural material that had been used in most structures through ages

even before the era of metals. Wood product is greatly established in the furniture,

flooring, tools, vehicles, decorative objects, and musical instruments. Generally, the

main factor for selecting wood in producing a product is the pleasant in appearance in

term of its grain pattern and color (see Figure 1.1). Some of the wood also has a

pleasant odor for a long time after it is removed from the forest.

Wood can be categorized into hardwoods and softwoods. Hardwoods are the

deciduous trees that have broad leaves and usually shedding in the fall. Meanwhile, the

conifers are called softwoods that have needles and cones containing seeds.

Hardwoods are commonly harder than softwoods however some hardwoods are

softer than softwoods. For example, from the United States, the softwoods such as

longleaf pine and Douglas-fir produce wood that is typically harder than the hardwoods

basswoods and aspen [1]. Hardwoods are majority used in construction for flooring,

architectural woodwork, trim, furniture, pallets, containers, and paneling. Softwoods on

the other hands are used in constructions for framing, cabinets, scaffoldings, doors, and

musical instruments.

3

Figure 1.1: Types of color and grain pattern of the wood [22]

1.1.1 ACOUSTICAL PROPERTIES OF WOOD

Wood has good insulating properties against sound. The cellular structure of

wood turns sound energy into heat energy due to frictional resistance of the minute

interlocking pores. Wood has a higher damping capacity than most materials because of

this feature; wood is a preferred material for building structures when sound damping is

required. Wood also reduces the magnitude of resonant vibrations, so wood is used

extensively where good acoustics are required, for example concert venues, music

suites, halls, and meeting rooms.

4

Although wood has a good sound attenuation property which tends to absorb and

dissipate vibrations, yet wood is still an incomparable material for such musical

instruments such as violins, guitars, and pianos.

1.1.2 WOOD FOR MUSICAL INSTRUMENTS

In musical instrument, low damping due to internal friction and high damping

due to sound radiation is desirable. For such cases, wood meet the requirement which

provides high damping due to sound radiation and low internal friction.

Moreover, wood is easier to bend according to the shapes rather than the metal,

whereas the bending process of the wood do not require such a technology like the

bending process of the metal (see Figure 1.1.2). However, each type of wood bends

differently. They have unique responses to water, heat and the severity of the curve

being bent. The easiest woods to be bent are Plain Indian Rosewood and Plain Maple.

Rosewood has resins that make it pliable, and maple is tough. On the other hand, Plain

Mahogany and Walnut are quite difficult to be bent. These woods are brittle and resist

bending if the conditions are not right. The hardest woods to bend are Figured woods.

Figured Curly Koa is particularly tricky to bend. Curly Maple and Figured Rosewood

(particularly Brazilian rosewood) bend just a little bit easier than Curly Koa [2].

5

Diverse species of wood have different reactions to sound and it is a vital

consideration while selecting species for musical instruments [3]. Local wood such as

Bintangor or its scientific name Calophyllum spp., Kayu Hitam or Diospyros celebica

Bakh., and Merbau or Intsia bijuga are among the woods selected for making musical

instruments.

Unfortunately, most of the musical instruments are made from the imported

woods such as Eastern spruce and Sitka spruce (see Table 1.1.2). This project aims to

identify for a new source from the local woods as to replace the role of imported woods.

The important characteristics in the woods for making the musical instruments are used

for a guideline to decide the new suitable woods.

Figure 1.1.2: Bending Process of the Shape Side of the Guitar [2]

6

Table 1.1.2: Several Types of Imported Woods Used for Making Musical

Instruments

Ref: [1], [23], and [24]

Common

Name Scientific Name Origin Uses

Asanfona

Ref: [23]

Aningeria spp.

Africa

Musical instruments, heavy

construction, marine, furniture,

flooring

Beech

ibid

Fagus spp. UK, Europe,

North America

Furniture, flooring, musical

instruments

Blackwood,

African

ibid

Dalbergia

melanoxylon Africa

Musical instruments, craft

products

Boxwood,

European

ibid

Buxus

sempervirens Europe

Turnery, craftwork, sports goods,

musical instruments

Cherry,

European

ibid

Prunus spp. UK, Europe,

North America

Specialized crafted furniture and

decorative work, musical

instruments

Ebony

ibid

Diospyros spp. Africa, Asia Cutlery handles, musical

instruments, craftwork.

Hornbeam

ibid

Carpinus betulus UK, Europe Minor items, musical instruments

Jacareuba

ibid

Calophyllum

spp.

South America

General purpose timber, musical

instruments

Maple

ibid

Acer spp. North America Flooring, musical instruments

Persimmon

ibid

Diospyros

virginiana

North America

Decorative ware, musical

instruments, turnery

Rosewood

ibid

Dalbergia spp. Africa, South

America, India

Furniture, musical instruments

7

Common

Name

Scientific

Name Origin Uses

Sitka spruce

[1]

Picea

sitchensis

North America,

Alaska

Furniture, millworks, sash, doors,

blinds, boats, sounding boards for

pianos

Eastern

spruce

ibid

Picea

Rubens (red)

Picea Glauca

(white)

Picea

Mariana (

black)

New England

Lake States

Lake States

Framing material, general millwork,

boxes and crates, piano sounding boards

Spanish-

cedar

Ref: [24]

Cedrela spp.

Mexico and

Argentina

Millwork, cabinets, fine furniture,

musical instruments, boat building,

patterns, sliced- and rotary-cut veneer,

decorative and utility plywood, cigar

wrappers, and cigar boxes

Brazilian

Rosewood

ibid

Dalbergia

nigra

South America

(Brazil)

Decorative veneers, fine furniture and

cabinets, parts of musical instruments,

brush backs, knife and other handles,

fancy turnery, piano cases, marquetry

Cocobolo

ibid

Dalbergia

retusa

Central

America

(Mexico)

Highly favored in the cutlery trade for

handles, inlay work, brush backs,

musical and scientific instruments,

jewelry boxes, chessmen, and other

specialty items

Honduras

Rosewood

ibid

Dalbergia

stevensonii

Belize(British

Honduras)

Parts of musical instruments including

percussion bars of xylophones, veneers

for fine furniture and cabinets, brush

backs, knife handles, fine turnery, many

specialty items

8

1.2 VIBRATION

Vibration is the study of the repetitive motion of objects relative to a stationary

frame of reference or nominal position where usually at equilibrium state [4]. The

swinging of a pendulum or playing a guitar is typical example of vibration applications.

The applications of vibration effect tremendously in the engineering field. To

prevent devastation by the vibration problems in most mechanical works, the engineer

tries to design the machine or engines to minimize the unbalance caused by the

vibration.

Common

Name

Scientific

Name Origin Uses

Alerce

[24]

Fitzroya

cupressoides

Central part of Chile,

Province of Chubut in

Southern Argentina

Shakes and shingles, general

construction, pencil slats,

musical instruments, vats and

tanks, lumber cores, and

furniture components

Trebol

Macawood

ibid

Platymiscium

spp.

Continental tropical

America from

Southern Mexico to

the Brazilian Amazon

region, and Trinidad

Fine furniture and cabinet work,

decorative veneers, musical

instruments, turnery, joinery,

specialty items (violin bows,

billiard cues)

Honduras

Mahogany

ibid

Swietenia

macrophylla

Southern Mexico

southward to

Colombia, Venezuela

Fine furniture and

cabinetmaking, interior trim,

paneling, fancy veneers,

musical instruments, boat

building, patternmaking,

turnery, and carving

9

The vibration that occurs in the wood specimen can provide information about

mechanical properties of the wood including the elastic properties, damping properties,

and energy dissipation from the wood. Elasticity implies that deformations produced by

low stress are completely recoverable after loads are removed [5]. Plastic deformation or

failure occurs when the specimen are being loaded to a higher stress levels. Damping

properties occurs when the driving force is removed; the successive amplitudes of

vibration will decrease. The energy dissipation is defined as energy dissipated partly by

radiation of sound and partly in the form of heat by internal friction [6]. The internal

friction is a complex function of temperature and moisture content.

Vibration can be destructive and should be avoided, or else it also can be greatly

useful and desired. In this paper, the usage of vibration principles is extremely

applicable as to achieve the desirable outcome.

1.2.1 FUNDAMENTAL OF VIBRATION

Basically vibration occurs in two categories that are periodic vibration and

random vibration. Periodic vibration is a motion occurring at equal intervals of time.

Harmonic motion is an example of periodic vibration (see Figure 1.2.1a). The motion is

represented by force functions where the time variation is a sine or cosine function.

Random vibration on the other hand is a nondeterministic vibration (see Figure

1.2.1b). The motion is unpredictable in terms of time and amplitude explaining that the

earthquake motion, blast, and wind gust are classified as random excitations.