Mechanical properties of seven types of wood in laos

5.1.2.5 Strength in static bending 57 5.2 Comparison of wood strengths 58 Chapter 6 Conclusion 73 References 75 Appendix A Graphs for static bending test 79 Appendix B Graphs for tens

Abstract

This study deals with the mechanical and physical properties of seven types of wood in Laos These woods are naturally-grown tree which grow in the middle part of the country Seven types of woods are selected and classified into two groups: hardwoods and

softwoods; hardwoods are May Deng, May Tai, May Dou, and May Khen Hine whereas softwoods are May Nhang, May Khen Heua, and May Khe Foy In this project, the focus is

on test to determine the various strengths as well as modulus of elasticity and weight density, and specific gravity according to ASTM standard D143 Eight tests were performed in this study such as tension parallel and perpendicular to grain, compression parallel and perpendicular to grain, shear parallel to grain, hardness, static bending and specific gravity Finally, the test results have compared the strength values obtained in this study with some popular woods in US such as Locus(western), Hickory(pecan), Maple(sugar), Oak(swamp white), Larch(western), Douglas fir(coast), and Pine(longleaf) The results found that some wood strengths obtained in the present experiment and some wood strengths in USA are identical and some slight differences

Keywords: Seven types of wood; Four hardwoods; Three softwoods; Wood testing;

Mechanical and physical properties

Acknowledgements

This graduate study program was supported to the funds from ASEAN University Network/Southeast Asia Engineering Education Development Network (AUN/SEED-Net) Japan International Cooperation Agency(JICA) I deeply thank the AUN/SEED-Net for supporting the budget during my study at NUS

My sincere appreciation goes to Assoc Prof F S Chau and Assoc Prof S L Toh for all their help and advice in this research project

Thanks to the National University of Singapore for giving me chance to study here Also, thanks for providing my research project with funding for expenses on the wood specimens and other resources

Finally, I thank Mr Cheong and the laboratory technicians in the experimental mechanics laboratory for their assistance in the experimental work

Table of contents

Summary i

Acknowledgements iii

Table of contents iv

List of figures vii

List of tables xv

Chapter 1 Introduction 01

1.1 General 01

1.2 Objectives of the project 02

Chapter 2 Literature review 04

2.1 Literature review on work done on wood tests 04

2.2 Literature review on the test methods 08

Chapter 3 Laotian wood-characteristics and its applications 11

3.1 Kinds of wood 11

3.2 Features of wood 12

3.3 Wood applications and the purpose of strength tests 13

Chapter 4 Experimental work 22

4.1 Method 22

4.2 Selection of materials 22

4.3 Preparation of the specimens 23

4.4 Test methods 24

4.4.1 Tension parallel to grain test 25

4.4.2 Tension perpendicular to grain test 27

4.4.3 Compression parallel to grain test 28

4.4.4 Compression perpendicular to grain test 29

4.4.5 Shear parallel to grain test 30

4.4.6 Hardness test 31

4.4.7 Specific gravity and density 32

4.4.8 Static bending test 34

Chapter 5 Results and discussion 51

5.1 The results of physical characteristics and mechanical properties of wood 51

5.1.1 Physical characteristics 51

5.1.2 Mechanical properties 53

5.1.2.1 Strength in tension 53

5.1.2.2 Strength in compression 54

5.1.2.3 Strength in shear 55

5.1.2.5 Strength in static bending 57

5.2 Comparison of wood strengths 58

Chapter 6 Conclusion 73

References 75

Appendix A Graphs for static bending test 79

Appendix B Graphs for tension parallel to grain 108

Appendix C Graphs for tension perpendicular to grain test 137

Appendix D Graphs for compression parallel to grain test 152

Appendix E Graphs for compression perpendicular to grain test 167

Appendix F Graphs for shear parallel to grain test 182

Appendix G Graphs for hardness test 197

Appendix H Manner of the failure specimens 212

Appendix I The results of wood properties in eight tests 239

List of figures

Figure 3.3 Schematic diagram of softwood, illustrating the relative appearance of

Figure 3.4 Schematic diagram of hardwood, illustrating the relative appearance of

vessels and tracheids (vascular cells) 20 Figure 3.5 Cross section of tree trunk: A = outer bark (dry dead tissue), B = inner

bark (living tissue), C = cambium, D = sapwood, E = heartwood,

Figure 3.6 Diagrammatic illustration of the principal structural features 21 Figure 4.1 Methods of sawing logs for lumber or beam: flat-sawn and quarter-sawn 39 Figure 4.2 Method of flat (or plain) sawing wood in Laos 40 Figure 4.3 The samples of the flat-cut woods in different dimensions 40 Figure 4.4 Rectangular pieces for making wood specimens 41 Figure 4.5 Wood specimen and its dimension, and direction of applied force for

tension parallel to grain test (dimension in mm) 41 Figure 4.6 Wood specimen and its dimension, and direction of applied force

for tension perpendicular to grain test ( dimension in mm ) 42 Figure 4.7 Wood specimen and its dimension and direction of applied force

for compression parallel to grain test (dimension in mm) 42 Figure 4.8 Wood specimen and its dimension and direction of applied force

for compression perpendicular to grain test (dimension in mm) 43 Figure 4.9 Wood specimen and its dimension and direction of applied force for static

Figure 4.10 Wood specimen and its dimension and direction of applied force for shear

parallel to grain test (dimension in mm) 44

Figure 4.11 Tension parallel to grain test (May Khen Heua e1) 44

Figure 4.12 Graph for calculating the modulus of elasticity in axial tension (May Khe Foy g6) 45

Figure 4.13 Tension perpendicular to grain (May Nhang d6) 45

Figure 4.14 Compression parallel to grain test (May Khen Heua e1) 46

Figure 4.15 Compression perpendicular to rain test (May Dou c1) 47

Figure 4.16 Shear parallel to grain test (May Khe Foy g5) 47

Figure 4.17 Hardness test (May Khe Heua e2) 48

Figure 4.18 The performance of wood specimens in a conventional oven 49

Figure 4.19 Static bending test (May Khen Heua e1) 50

Figure 4.20 Load vs deflection under the proportional limit in static bending (May Deng) 50

Figure 5.1 Static bending strengths of woods in comparison with some US woods 69

Figure 5.2 Compressive strength of woods in comparison with some US woods 70

Figure 5.3 Shearing strengths of woods in comparison with some US woods 71

Figure 5.4 Hardness of woods in comparison with some US woods 72

Figure A.1.1.a1-a6 Load vs displacement in static bending for May Deng 81

Figure A.1.2.b1-b6 Load vs displacement in static bending for May Tai 83

Figure A.1.3.c1-c6 Load vs displacement in static bending for May Dou 85

Figure A.1.4.d1-d6 Load vs displacement in static bending for May Nhang 87

Figure A.1.5.e1-e6 Load vs displacement in static bending for May Khen Heua 89

Figure A.1.6.f1-f6 Load vs displacement in static bending for May Khen Hine 91

Figure A.1.7.g1-g6 Load vs displacement in static bending for May Khe Foy 93

Figure A.2.a1-a6 Load vs displacement in static bending for May Deng 95

Figure A.2.b1-b6 Load vs displacement in static bending for May Tai 97

Figure A.2.3.c1-c6 Load vs displacement in static bending for May Dou 99

Figure A.2.4.d1-d6 Load vs displacement in static bending for May Nhang 101

Figure A.2.5.e1-e6 Load vs displacement in static bending for May Khen Heua 103

Figure A.2.6.f1-f6 Load vs displacement in static bending for May Khen Hine 105

Figure A.2.7.g1-g6 Load vs displacement in static bending for May Khe Foy 107

Figure B.1.1a1-a6 Load vs displacement in tension parallel to grain test 110

(May Deng) Figure B.1.2b1-b6 Load vs displacement in tension parallel to grain test 112

(May Tai) Figure B.1.3c1-c6 Load vs displacement in tension parallel to grain test 114

(May Dou) Figure B.1.4d1-d6 Load vs displacement in tension parallel to grain test 116

(May Nhang) Figure B.1.5e1-e6 Load vs displacement in tension parallel to grain test (May Khen heua) 118

Figure B.1.6f1-f6 Load vs displacement in tension parallel to grain test ( May Khen Hine ) 120

Figure B.1.7g1-g6 Load vs displacement in tension parallel to grain test (May Khe Foy) 122

Figure B.2.1a1-a6 Load vs displacement in tension parallel to grain test (May Deng) 124

Figure B.2.2b1-b6 Load vs displacement in tension parallel to grain test (May Tai) 126

Figure B.2.3c1-c6 Load vs displacement in tension parallel to grain test (May Dou) 128

Figure B.2.4d1-d6 Load vs displacement in tension parallel to grain test (May Nhang) 130

Figure B.2.5e1-e6 Load vs displacement in tension parallel to grain test

Figure B.2.6f1-f6 Load vs displacement in tension parallel to grain test (May Khen

Figure C.5.e1-e6 Load vs displacement in tension perpendicular to grain

Figure C.6.f1-f6 Load vs displacement in tension perpendicular to grain

Figure C.7.g1-g6 Load vs displacement in tension perpendicular to grain

Figure D.1.a1-a6 Load vs displacement in compression parallel to grain

Figure D.5.e1-e6 Load vs displacement in compression parallel to grain

Figure D.6.f1-f6 Load vs displacement in compression parallel to grain

Figure D.7.g1-g6 Load vs displacement in compression parallel to grain

Figure E.1.a1-a6 Load vs displacement in compression perpendicular to grain test

Figure E.5.e1-e6 Load vs displacement in compression perpendicular to grain test

Figure E.6.f1-f6 Load vs displacement in compression perpendicular to grain test

Figure E.7.g1-g6 Load vs displacement in compression perpendicular to grain test

Figure F.1.a1-a6 Load vs displacement in shear parallel to grain test

Figure F.2.b1-b6 Load vs displacement in shear parallel to grain test (May Tai) 186

Figure F.3.c1-c6 Load vs displacement in shear parallel to grain test (May Dou) 188

Figure F.4.d1-d6 Load vs displacement in shear parallel to grain test 190

(May Nhang)

Figure F.5.e1-e6 Load vs displacement in shear parallel to grain test 192

(May Khen Heua)

Figure F.6.f1-f6 Load vs displacement in shear parallel to grain test

Figure F.7.g1-g6 Load vs displacement in shear parallel to grain test

Figure G.1.a1-a6 Load vs displacement in hardness test (May Deng) 199 Figure G.2.b1-b6 Load vs displacement in hardness test (May Tai) 201

Figure G.3.c1-c6 Load vs displacement in hardness test (May Dou) 203 Figure G.4.d1-d6 Load vs displacement in hardness test (May Nhang) 205 Figure G.5.e1-e6 Load vs displacement in hardness test (May Khen Heua) 207

Figure G.6.f1-f6 Load vs displacement in hardness test (May Khen Hine) 209

Figure G.7.g1-g6 Load vs displacement in hardness test (May Khe Foy) 211

Figure H.1.1 The broken specimens of May Deng under tension parallel to grain 213 Figure H.1.2 The broken specimens of May Tai under tension parallel to grain 213 Figure H.1.3 The broken specimens of May Dou under tension parallel to grain 214 Figure H.1.4 The broken specimens of May Nhang under tension parallel to grain 214 Figure H.1.5 The broken specimens of May Khen Heua under tension parallel to 215

grain

Figure H.1.6 The broken specimens of May Khen Hine under tension parallel to 215

grain

Figure H.1.7 The broken specimens of May Khe Foy under tension parallel to grain 216

Figure H 2.1 Types of broken specimens of May Deng under tension perpendicular to

Figure H 2.5 Types of broken specimens of May Khen Heua under tension

Figure H 2.6 Types of broken specimens of May Khen Hine under tension

Figure H 2.7 Types of broken specimens of May Khe Foy under tension

Figure H 3.1 The failure specimens of May Deng under compression parallel

Figure H 4.1 The failure specimens of May Deng under shear parallel to grain test 228

Figure H 4.2 The failure specimens of May Tai under shear parallel to grain test 229

Figure H 4.3 The failure specimens of May Dou under shear parallel to grain test 230 Figure H 4.4 The failure specimens of May Nhang under shear parallel to grain test 231

Figure H 4.5 The failure specimens of May Khen Heua under shear parallel to 232

Figure H 5.1 The failure specimens of May Deng under static bending test 235

Figure H 5.2 The failure specimens of May Tai under static bending test 235

Figure H 5.3 The failure specimens of May Dou under static bending test 236

Figure H 5.4 The failure specimens of May Nhang under static bending test 236

Figure H 5.5 The failure specimens of May Khen Heua under static bending test 237 Figure H 5.6 The failure specimens of May Khen Hine under static bending test 237 Figure H 5.7 The failure specimens of May Khe Foy under static bending test 238

List of Tables

Table 3.1 Application and cost of Laos wood (December, 2002) 18

Table 4.1 General information on the sample trees 39

Table 5.1 The specific gravity, the moisture content and weight density of the seven types of wood 62

Table 5.2 Typical mechanical properties of seven types of wood 63

Table 5.3 Typical mechanical properties of seven types of wood 64

Table 5.4 Strength and stiffness of hardwoods in relation to weight density 65

Table 5.5 Strength and stiffness of softwoods in relation to weight density 66

Table 5.6 Comparison of mechanical properties of Laos woods and some US woods 67

Table 5.7 Comparison of mechanical properties of Laos woods and some US woods 68

Table I.1.1 The results of tension parallel to grain test (May Deng) 240

Table I.1.2 The results of tension parallel to grain test (May Tai) 240

Table I.1.3 The results of tension parallel to grain test (May Dou) 241

Table I.1.4 The results of tension parallel to grain test (May Nhang) 241

Table I.1.5 The results of tension parallel to grain test (May Khen Heua) 242

Table I.1.6 The results of tension parallel to grain test (May Khen Hine) 242

Table I.1.7 The results of tension parallel to grain test (May Khe Foy) 243

Table I.1.8 The final results of tension parallel to grain test (Seven types of wood) (T.S – Tensile strength); STDV – Standard deviation 243

Table I.2.1 The results of tension perpendicular to grain test (May Deng) 244

Table I.2.2 The results of tension perpendicular to grain test (May Tai) 244

Table I.2.3 The results of tension perpendicular to grain test (May Dou) 245

Table I.2.4 The results of tension perpendicular to grain test (May Nhang) 245 Table I.2.5 The results of tension perpendicular to grain test (May Khen Heua) 246

Table I.2.6 The results of tension perpendicular to grain test (May Khen Hine) 246

Table I.2.7 The results of tension perpendicular to grain test (May Khe Foy) 247

Table I.2.8 The final results of tension perpendicular to grain test 247

(Seven types of wood) Table I.3.1 The results of compression parallel to grain test (May Deng) 248 Table I.3.2 The results of compression parallel to grain test (May Tai) 248 Table I.3.3 The results of compression parallel to grain test (May Dou) 249 Table I.3.4 The results of compression parallel to grain test (May Nhang) 249 Table I.3.5 The results of compression parallel to grain test (May Khen Heua) 250

Table I.3.6 The results of compression parallel to grain test (May Khen Hine) 250

Table I.3.7 The results of compression parallel to grain test (May Khe Foy) 251 Table I.3.8 The final results of compression perpendicular to grain test 251

(Seven types of wood) Table I.4.1 The results of compression perpendicular to grain test (May Deng) 252

Table I.4.2 The results of compression perpendicular to grain test (May Tai) 252 Table I.4.3 The results of compression perpendicular to grain test (May Dou) 253

Table I.4.4 The results of compression perpendicular to grain test (May Nhang) 253

Table I.4.5 The results of compression perpendicular to grain test 254

(May Khen Heua)

Table I.4.6 The results of compression perpendicular to grain test 254

(May Khen Hine)

Table I.4.7 The results of compression perpendicular to grain test (May Khe Foy) 255

Table I.4.8 The final results of compression perpendicular to grain test 255

(Seven types of wood) Table I.5.1 The results of shear parallel to grain test (May Deng) 256 Table I.5.2 The results of shear parallel to grain test (May Tai) 256 Table I.5.3 The results of shear parallel to grain test (May Dou) 257 Table I.5.4 The results of shear parallel to grain test (May Nhang) 257 Table I.5.5 The results of shear parallel to grain test (May Khen Heua) 258 Table I.5.6 The results of shear parallel to grain test (May Khen Hine) 258 Table I.5.7 The results of shear parallel to grain test (May Khe Foy) 259 Table I.5.8 The final results of shear parallel to grain test (Seven types of wood) 259 Table I.6.1 The results of measuring load on hardness test (May Deng) 260 Table I.6.2 The results of measuring load on hardness test (May Tai) 260 Table I.6.3 The results of measuring load on hardness test (May Dou) 261 Table I.6.4 The results of measuring load on hardness test (May Nhang) 261 Table I.6.5 The results of measuring load on hardness test (May Khen Heua) 262

Table I.6.6 The results of measuring load on hardness test (May Khen Hine) 262 Table I.6.7 The results of measuring load on hardness test (May Khe Foy) 263

Table I.6.8 The final results of measuring load on hardness test 263

(Seven types of wood) Table I.7.1 The results for measuring specific gravity (May Deng) 264 Table I.7.2 The results for measuring weight density (May Deng) 264 Table I.7.3 The results for measuring specific gravity (May Tai) 265 Table I.7.4 The results for measuring weight density (May Tai) 265 Table I.7.5 The results for measuring specific gravity (May Dou) 266

Table I.7.7 The results for measuring specific gravity (May Nhang) 267

Table I.7.8 The results for measuring weight density (May Nhang) 267

Table I.7.9 The results for measuring specific gravity (May Khen Heua) 268

Table I.7.10 The results for measuring weight density (May Khen Heua) 268

Table I.7.11 The results for measuring specific gravity (May Khen Hine) 269

Table I.7.12 The results for measuring weight density (May Khen Hine) 269

Table I.7.13 The results for measuring specific gravity (May Khe Foy) 270

Table I.7.14 The results for measuring weight density (May Khe Foy) 270

Table I.7.15 The final values of the weight density and specific gravity 271

(Seven types of wood) Table I.8.1 The results for static bending test (Mau Deng) 272

Table I.8.2 The results for static bending test (May Tai) 272

Table I.8.3 The results for static bending test (May Dou) 273

Table I.8.4 The results for static bending test (May Nhang) 273

Table I.8.5 The results for static bending test (May Khen Heua) 274

Table I.8.6 The results for static bending test (May Khen Hine) 274

Table I.8.7 The results for static bending test (May Khe Foy) 275

Table I.8.8 The final values of static bending test (Seven types of wood) 275

Chapter 1 Introduction

1.1 General

Wood is a natural, renewable, organic substance with a number of purposes and uses Wood is widely used in construction for low buildings and short span bridges, flooring, fence posts, and many other products In fact, wood is a cheap and easy to work with, and easy to repair Therefore, many people still use wood for their construction such

as houses and any other products

Wood is an anisotropic material, which means that its strength properties are different, depending on whether the forces are applied parallel or perpendicular to the direction of the wood fibers Generally, wood is strongest along the grain and weakest at right angles to it Also, because of different growing conditions, the properties vary with some different factors such as type of soil, amount of sun and rain[1] So, the different strengths in both directions is not so important for its resistance to external forces The resistance of wood to such forces depends on the manner of loading and the purposes of use of the product This project is related to analysis of the wood strength in eight tests on seven types of wood from Laos Woods which were used for this project are derived from

a region of warm climate in the middle part of the country (Vientiane province) Wood in other parts will be tested in the future for comparison with the values obtained in this study

At the present time, wood from natural forests has declined considerably and undergone significant changes because of the increasing number of uses of wood for

construction and for other purposes The annual consumption of wood in Laos currently exceeds the annual growth Therefore, the amount wood cutting from the forests has been limited by Laos’ government policy Some of hardwoods are allowed to be cut only after trees had died or fallen, whereas softwoods must have grown to a sufficient height with diameter large enough (at least 60 cm) to be allowed to be cut In addition, in the past many houses have been built with woods that are familiar to the local population Today, many house types are modeled with increasing quantities of wood used in construction, and with the advent of new timbers of unknown strengths, it has became necessary to carry out precise tests to find out just how strong they are So the mechanical properties and specific gravity data of individual wood play a very important role under selecting them for construction and to conserve the tree population Also, the strength properties can be used for architects and wood engineers to be able to calculate exactly the optimum dimensions for different structural members and stiffness, thus bringing about economic benefits

1.2 Objectives of the project

In this project, the focus is on tests with six specimens taken from each of seven different species of wood to determine their mechanical properties and physical properties

Seven types of wood are: May Deng, May Tai, May Dou, May Nhang, May Khen Heua, May Khen Hine and May Khe Foy A total of 336 specimens (dry condition) have been

tested for seven strength and two physical properties In this project, the specimens of each wood were made from only one piece of timber The eight tests conducted are tension parallel to grain, tension perpendicular to grain, compression parallel to grain,

compression perpendicular to grain, shear parallel to grain, hardness, static bending, and specific gravity according to the ASTM D143-94 (Re approved 2000), “Standard Method

of Testing Small Clear Specimens of Timber” The purpose of the research is to use the test method of wood testing to define a range of the Laos wood strength values when compared with other wood in other countries In the past, the strength properties of Laos wood have not been reported and provided yet In addition, this information may help us

to determine the value and use of the wood in a variety of construction or in markets This project will also be of benefit to the researcher’s faculty or country for carrying on with testing of wood in other areas of the country when the project had been accepted

The main important purpose of this project is an analysis of the test results of mechanical properties for wood application, the manner in which the specimens break and the comparison of wood strengths with some popular woods of USA such as hardwoods:

Locus (black), Hickory (pecan), Maple (sugar), and Oak (swamp white); softwoods: Larch (western), Douglas fir (coast), and Pine (longleaf) The mechanical properties sought are

tensile strength, compressive strength, bending strength, shear strength, hardness and modulus of elasticity Next, the manner of the broken specimens i.e different appearance

of cracks will indicate the mode of failure The details of comparison are discussed in results and discussion sections

Chapter 2 Literature review

Investigations into the properties of wood have been conducted by a number of researchers around the world It is well-known that the mechanical properties of the wood play an important role in their use for construction and many other purposes They help the wood engineers or architect to determine the correct sizes of lumber, beams, trusses, etc and which wood can be used to resist the exterior forces This chapter aims to show what researchers have done in the area of wood testing and the test methods for evaluation wood properties The two parts of this review are shown in the following sections

2.1 Literature review on work done on wood testing

Bao et al [2] conducted experiments to study the intrinsic differences in various

wood properties between juvenile wood and mature wood in China They also considered the differences in wood properties between plantation-grown juvenile and mature wood, and between naturally-grown juvenile wood and mature wood Different tests, such as static bending for determining modulus of elasticity, as well as modulus of rupture, compression parallel to grain, tension parallel to grain, shear parallel to grain, cleavage parallel to grain and toughness were conducted in this study Their test results compare for juvenile wood and mature wood in both plantation-and naturally-grown trees

Kopac et al [3] studied the machining of wood by cutting, which is a demanding

technological process because of wood’s specific structure Next, this study focused on the structural and mechanical properties of wood with outcome of the cutting process Finally,

their work was intended to show the experimental results as regard to the wood strength in two different directions of wood cutting The first is the differences between the modulus

of elasticity and the strength characteristic on the grain orientation (three strengths: compression, bending and tension) The second is that the hardness of wood had a major influence on the wood density and moisture content in three typical direction of wood tissue

Oloyede et al [4] measured the mechanical properties of wood in tension parallel

to grain by for specimens prepared using three drying methods, ie air-drying at ambient temperature, a conventional oven at two elevated temperatures and a microwave oven at two different power settings Then, the results of the mechanical tests were compared for the various drying methods The findings showed that microwave drying had reduced the strength of the dried timber compared with the strength when air-dried or dried in a conventional oven

Edwin et al [5] reported more than 3500 tests (green and drying condition)

performed for seven strength and two physical properties The wood samples (western juniper) were selected from 42 trees, and specimens were tested according to ASTM standard D-143-94 This work tried to explain the testing processes of static bending, compression, tension, shear, and hardness test and their application purpose The strength values obtained for green and drying condition were compared with other wood from other areas, eg Incense cedar, eastern and western red cedar, ponderosa pine and Douglas fir

The strength properties of some commercially important woods grown in the United States are given in the Handbook-wood [6] The strength values of sixty seven hardwoods and twenty nine softwoods, in static bending, impact bending, compression parallel to grain, compression perpendicular to grain, shear parallel to grain, tension perpendicular to grain and side hardness are recorded in this handbook These values also indicate that some softwoods had greater strength than some hardwoods

Josepf et al.[7] measured the strengths of some wood adhesives used in Cameroon

This work carried out block shear tests to determine the shear strength of various types of adhesives selected in the Cameroonian market, according to ASTM standard D905-94 The shear tests had been performed in four species of wood blocks such as Sadar glue, Ponal glue, Ebycoll glue and Bostik glue The findings found that Sadar glue was more resistant than other three species

Morrell et al [8] focused on the testing of Norway spruce dried by two methods

microwave drying and conventional air-drying Their work was conducted to determine the strength of wood by using the three-point bending test Wood specimens with a moisture content of 12% were tested The findings found that the strength of wood had changed between specimens of the same species because of different structures for different purposes for its life In addition, what affects wood strength was changeable such

as moisture content, density, weight, width and thickness Finally, the results showed the values of modulus of elasticity lie between 8.3 to 13 GPa and for modulus of rupture between 66 to 84 MPa

Douglas et al [9] focused on experimental shear strength research with three types

of wood (green condition) and two other types of wood (air-drying condition) Experiments were performed to determine their shear strengths A three-point bending support investigated the effects of splits on shear strength and a five-point setup investigated the effects of drying on beam shear Additional tests conducted on seasoned Douglas Fir and Southern Pine gave mixed results on the effects of splits The test results showed that shear strengths ranged from 3.9 to 8.5 MPa for green condition and 7.4 to 12.7 MPa for air-drying condition

Mattson et al [10] focused on determining of wood properties related to drying

methods of wood seasoning such as air drying method and kiln drying method Seventy four types of wood were conducted to measure the specific gravity and shrinkage in volume, and seasoning characteristics The woods used for the tests were not classified under hardwoods and softwood; instead, only local and family names were specified

The above works attempt to describe the experimental test processes of wood for a number of different tests In this research, the author will use the same test method and present the test results for seven species of Laotian wood This research aims to conduct a similar study as the above-mentioned works in which only mechanical properties and physical characteristics were considered

2.2 Literature review on the test methods

It is well-known that ASTM D-143-94 (2000) [11] is one of the most commonly used standard method for testing of wood in the world This method is meant for testing small clear specimens, and cover the two test methods, The primary and secondary methods The primary methods provide for specimens of 50 by 50 mm cross-section These methods have been used for the mechanical tests as in the following experiments: static bending, compression parallel to grain, compression perpendicular to grain, hardness, shear parallel to grain, tension parallel to grain, tension perpendicular to grain test and specific gravity

Static bending test: The strength properties that can be determined from a three-point

bending test in which a load is applied at a constant slow rate of 2.5 mm/min at the center

of the beams which are 50x50x760 mm, are modulus of rupture and modulus of elasticity The modulus of rupture can be computed using the bending moment caused by the ultimate load The modulus of elasticity can be computed using the straight-line portion of the load-deflection curve

Compression parallel to grain test: In this test, the load is applied to the end grain

surface of a specimen 50x50x200 mm in size at the rate 0.5 mm/min It is ensured that the ends of a specimen are parallel to each other and at right angles to the longitudinal axis Longitudinal load is applied, increasing until the specimen fails From the loads and displacements measured during the test, a load-displacement curve plotted

Compression perpendicular to grain test: In this test, the load is applied through a metal

bearing plate placed across the upper surface of the specimen at equal distances from the ends and at right angles to the length The specimens, 50x50x150 mm, are tested at a constant slow rate of 0.305 mm/min Load-compression curves are taken for all specimens

up to 2.5 mm compression

Hardness test: The hardness tests (resistance to indentation) are measured by driving a

specially-hardened steel tool ball 10 mm in diameter (having a projected area of 100 mm2)

to a depth to half its diameter The test is carried out on the side of the test piece with dimension of 50x50x150 mm

Shear parallel to grain test: Shear tests are made on 50x50x63 mm specimens notched

to produce failure on the 50x50 mm surface The load is applied through out the test at a rate of motion of 0.6 mm/min In the ASTM test for shear strength, there is no gradual yielding; instead, failure is sudden and only the ultimate load is observed

Tension parallel to grain test: This test is made on specimens of the size and shape in

accordance with ASTM D-143 [11] Tensile strength is measured by pulling the specimens at a rate of 1 mm/min until the failure point Modulus of elasticity is determined by fastening the specimens in special grips with the gage length set at 50 mm and by taking load-extension readings until the proportional limit is passed

Tension perpendicular to grain test: Tensile strength is measured by applying the load

at a rate of 2.5 mm/min on specimens with a size and shape in accordance with ASTM D-143 [11] The load-displacement curve for this test shows a definite ultimate load

Specific gravity: This test is made on specimens of size 50x50x150 mm which are dried

at 103±2°C in a conventional oven until approximately constant mass is reached After oven drying, the specimens are weighted and still warm, immersed in a paraffin bath, taking care to remove them quickly to ensure a thin coating

This section describes the test procedures in various experiments and methods of seasoning the specimens before the tests Also, this section gives the author a clear understanding of how the tests are conducted and how to apply the data obtained to the desired material properties

Chapter 3 Laotian wood-characteristics and applications

Wood is a product of nature and is renewable through natural processes and reforestation programs Therefore, wood characteristics are dependent on many factors, such as species, growing condition, wood quality and the region from which the wood came In this study, tests have been carried out on wood harvested from the middle part of Laos in the Vientiane province

example in pine (May Pek, May Nhang, etc.) The softwood tree is illustrated in Figure

3.2 Some hardwoods are truly hard whereas others can be softer than softwoods

Figure 3.3 and Figure 3.4 show the differences in internal structure between softwood and hardwood and the variation in properties in different directions The structure of softwood (Figure 3.3), is composed of long, tube-like cells running in the longitudinal direction with some other cells normal to this direction (radial) A new layer

of longitudinal cells (tracheids) is grown each year from the cambium The structure of

hardwood (Figure 3.4) is similar in several ways to that of softwood The cells of

hardwood have long dimensions parallel to the longitudinal axis of the tree, and early wood and late wood are present, giving growing rings These longitudinal cells are called fibers Resin ducts are not present [11-13]

3.2 Features of wood

Trees grow in three directions: They grow upward as trunks and limbs, they grow downward through roots, and they grow in diameter Trees grow in diameter by adding material to their grown layer (cambium layer) Figure 3.5 shows the cross-section of a typical tree: The cambium layer is inside of the inner bark and forms wood and bark cells The cambium layer is nearly invisible in a tree’s cross-section; it is a sticky film that exists

on the outer portion of the sapwood The inner bark which is moist and soft, and nearest the cambium, is alive and provides protection around the tree and carries prepared food from leaves to all growing parts of the trees The outer bark layer is composed of dry dead tissues The bark gives general protection against external injures such as insects and diseases

Sapwood is the outer layer of growth which contains the only living elements It is

a light-colored wood lying beneath the bark and carries sap from roots to leaves Heartwood is the inner portion of the tree which is no longer living It gives the tree strength and can be resistant to decay and attack from fungi and insects Pith locates in the central core of tree (see Figure 3.6) It is the soft tissue about which the first wood growth takes place in the newly-formed twigs The pith has no particular use in construction or manufacturing Wood rays connect to the various layers from pith to the bark for storage [12] [14] [15] [16]

Wood is made up of small fibers which are hollow The length of the fibers is not a criterion in determining the strength of a wood Wood tends to be strongest longitudinally (or along the grain) Strength in the other directions is lower In tension, the fiber do not generally separate from one another but rather, they rupture

3.3 Wood applications and the purpose of strength tests

Wood is a most versatile material, it has been used for many purposes, such as lumber, beams, doors, windows, light framing, siding, exterior finish, interior finish, frames, roofing, flooring, sub-flooring, parquet, furniture, fencing, packaging The principal woods used in this study and their cost are shown in Table 3.1

Softwoods are commonly used for construction, because they are cheaper and easier to work with Some hardwoods are used for non-construction products such as furniture, parquet, doors, windows, because they have good appearance, are durable but are more expensive than softwoods

At the present time, which wood is used as constructional or non-constructional materials is dependent on a customer’s or user’s familiarity with wood and cost in Laos The price of wood is usually not considered together with the strength and weight This present study may help architects and engineers when designing a structure and choosing wood and wood qualities such as strength, stability, and availability in required sizes Therefore, the mechanical properties of wood become very significant factors for wood applications, hence the purposes of strength tests [16] [17] [18] [19] which are: tension

compression perpendicular to grain, shear parallel to grain, hardness test, static bending test, specific, and density

Tension parallel to grain test:

Tensile strength is particularly necessary for woods that are to be bent into curved shapes after steaming For defect-free wood, tensile strength parallel to the grain is higher than compressive strength in the same direction Clear, straight-grained used has the highest strength This test can also be used for determining modulus of elasticity

Tension perpendicular to grain test:

This test measured the resistance of wood to forces acting across the grain that tend to split a member This property is useful for wood to be used for purposes such as walls (lumber), boxes, and packing cases They should be able to take nails without splitting In this test, the specimens usually fail in splitting, which is similar to the cleavage test

Compression parallel to grain test:

High strength in this direction is required of wood used as columns, props, chair legs, ie structures that have to bear loads imposed on them parallel to the grain of the wood The long length of specimens in relation to their cross-sectional areas may cause buckling at high stresses and failure is from bending rather than true compression

Compression perpendicular to grain test:

Resistance to compression is an important property for wood used for example, as railway sleepers, rollers, wedges, bearing blocks and bolted wood These woods are high

in density and have high compression strength across the grain

Shear parallel to grain test:

This test indicates the ability to resist internal slipping of one part upon another along the grain This is the most important property for wood used in joints The area surrounding the bolt hole or the mortise should be able to resist high longitudinal shear stresses Shear strength parallel to grain is less than in any other direction Failure of specimens in this test is sudden and only the ultimate load is observed

Hardness test:

Hardness is an important property for various uses, such as floors, decking, mallets, rollers, bearing blocks, furniture, sport items, etc Some woods are relatively soft, others have a medium hardness and some are hard Hardness is related to the strength of wood in resisting abrasion and scratching with various objects

Static bending test:

Bending strength is important in wood used for floor, ceiling joists, roof truss members, table tops and chair bottoms which must resist the high bending loads Also, static bending is a measure of the strength of a material as a beam In the resting position, the upper half of a beam is in compression and the lower half in tension Stiffness (modulus of elasticity) is the ability of a material to resist bending It is an important property in joists and beams involving high bending stresses, otherwise the ceiling beneath them would crack if the floor above flexed too much under load

Specific gravity provides the relative weight of wood compared to an equal

volume of water For many engineering applications, the basis for specific gravity is generally the oven dry weight and volume at a 12% moisture content (MC) Specific gravity is used as a standard basis to compare species A larger number indicates a heavier material

Density is the weight of wood per cubic cm at a specified MC Density is

important to indicate strength in wood and may predict certain characteristics such as hardness, ease of machining and nailing resistance A larger number indicates a stronger wood

The purpose of the tests as mentioned above is related to the strength properties of wood which differ greatly according to the direction of the grain in relation the stress

applied Wood has different strengths in the longitudinal grain or transverse grain and therefore, the differences in the two directions of the grain wood are dependent on how it

is to be used In this research, the testing of seven types of wood was performed as for the same purposes for wood application as mentioned above

For hardwoods, eg May Khen Hine is widely used to make tables, chairs, windows

and door frames and is usually cut into the different sizes of beams (see Table 3.1) Others

such as May Deng, May Tai, and May Dou are most popular for making parquet flooring

and furniture because they have fine-colored grain, as well as being hard Therefore, hardness and compression perpendicular to grain test are more suitable means of testing for them; whereas other tests are less important Wood for making parquet floors and furniture must have hard surfaces which can resist the applied load without scratching and cracking Moisture content is an important factor in considering the wood that a member can safely use in flooring without warping and shrinkage Normally, wood that is to be used for this purpose must have a moisture content of approximately 12%

Softwoods, eg May Nhang, May Khen Heua ,and May Khe Foy are commonly

used to make beams and lumber for use in construction and buildings These woods are sold in many shops in Vientiane in different sizes (as shown in Table 3.1) For them, the static bending test, shear test, compression parallel to grain test are the most important tests

Table 3.1 Applications and cost of Laos wood (December, 2002)

60 x 120 mm

1 May Deng Interior of the house, window

and door, furniture, parquet 400-600 1.9 – 2.80 US/LPm

2 May Tai Interior of the house, window

and door, furniture, parquet

400-600 1.9 – 2.80 US/LPm

3 May Dou Interior of the house, window

and door, furniture, parquet, framing, tool handles

400-600 1.9 – 2.80 US/LPm

4 May Nhang Beam with different sizes

Lumber, table, chair etc

100-200 0.52 – 0.63US/LPm

5 May Khen Heua Beam with different sizes

Lumber, table, chair etc

100-200 0.63 – 0.72 US/LPm

6 May Khen Hine Beam with different sizes

Lumber, table, chair, framing

150-300 0.63 – 0.72 US/LPm

7 May Khe foy Beam with different sizes

Lumber, table, chair etc

150-300 0.63 – 0.72 US/LPm

Data from five sawmills: Ban Mai km47, Ban Elay km21, Ban Sikai No1, Ban Sikai No2, and Ban Dongsavath 40x80mm, 50x100mm, and 60x120mm is a size of cross section LPm = Length per meter (Length of beam is 2-6 meters)

Figure 3.6 Diagrammatic illustration of the principal structural features (from reference [16])

Figure 3.5 Cross-section of a tree trunk: A = outer bark (dry dead tissue),

B = inner bark (living tissue), C = cambium, D = sapwood, E = heartwood,

F = pith, G = wood rays (from reference [12])

pith

Chapter 4 Experimental work

4.1 Method

In December 2002, a survey was conducted by using a questionnaire form in five sawmills in Laos The questionnaire asked about the cutting, cost, applications and location of wood, as well as the wood drying that there are the main purpose of the survey From the survey, we found that the woods were taken from the middle part of the country (Vientiane province) In this region, the environment is a warm climatic condition Next, timber from the forest was dried in air in the field for several months to reduce the moisture content Then, logs were cut into boards of different sizes by using a flat cut method The boards were dried in air in the sawmill to a moisture content of about 16-20% Also, we found that the wood cutting in the sawmills has a different purpose for their applications Some sawmills cut wood for making parquets and some for boards or lumbers (some data are shown in Table 3.1 and Table 4.1)

4.2 Selection of materials

Lumber or board is the main sawn wood The appearance of sawn wood may vary depending on the way in which the wood is cut from the logs and on the part of the tree from which the wood is taken Normally, logs are cut into lumber using two

principal methods: Flat (or plain) sawing wood and quarter-sawn wood as shown in Figure 4.1 which is from reference [12] Flat sawing wood is cut generally tangential to the rings

of the log Also, flat-cut lumber requires less labour and wastage (Figure.4.2) sawn wood is produced by cutting longitudinally and radially toward the center of a log

Quarter-In this study, a round log is cut along its length into rectangular pieces of varying sizes (see Figure 4.3) Then the rectangular pieces were cut into small boards by using flat-cut, because this method of cutting is less costly and wasteful Then, after cutting, these pieces were dried in air for 2 to 6 months dependent on the type of wood In this project, seven types of wood from two sawmills were selected for making the test specimens (Ban Sikai’ and Ban dongsavath’s sawmill) Four hardwoods were selected, ie

May Deng, May Tai, May Dou, and May Khen Hine and the other three were softwoods May Nhang, May Khen Heua, and May Khe Foy The wood samples selected for this

research were taken from each of the thick boards (Figure 4.3) General information of trees used in this study are shown in Table 4.1

4.3 Preparation of the specimens

The wood specimens were selected from the dry rectangular pieces shown in

Figure 4.3 which shows one of the woods (May Dou) selected and used for this study

Most of them were cut and machined into small clear specimen, and then surfaced into standard sizes according to ASTM standard D143 The configuration and dimensions of wood specimens for the various tests are shown in Figures 4.5 to 4.10 Three types of the specimens were made the same size (as shown in Figure 4.8) for the compression perpendicular to grain test, hardness test and specific gravity For this project, for each test, six specimens were made from each type of wood at the workshop of National