Mechanical properties of seven types of wood in laos

Chapter 5

Results and discussion

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.

1


Chapter 5

Results and discussion

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.

2


Chapter 5

Results and discussion

Table of contents

Summary

i

Acknowledgements

iii

Table of contents

iv

List of figures

vii

List of tables

xv

Chapter 1

Chapter 2

Chapter 3

Introduction

01

1.1 General

01

1.2 Objectives of the project

02

Literature review

04

2.1 Literature review on work done on wood tests

04

2.2 Literature review on the test methods

08

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

3


Chapter 5

Chapter 4

Chapter 5

Results and discussion

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

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

5.1.2.4 Hardness

56
4


Chapter 5

Chapter 6

Results and discussion

5.1.2.5 Strength in static bending

57

5.2 Comparison of wood strengths

58

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

239

The results of wood properties in eight tests

5


Chapter 5

Results and discussion

List of figures

Figure 3.1

The hardwood tree

19

Figure 3.2

The softwood tree

19

Figure 3.3

Schematic diagram of softwood, illustrating the relative appearance of
tracheids

20

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,
F = pith, G = wood rays.

21

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

Wood specimen and its dimension, and direction of applied force
for tension perpendicular to grain test. ( dimension in mm )

42

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

42

Wood specimen and its dimension and direction of applied force
for compression perpendicular to grain test. (dimension in mm)

43

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Wood specimen and its dimension and direction of applied force for static
bending test (dimension in mm)
43

Figure 4.10

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

parallel to grain test. (dimension in mm)
44

6


Chapter 5

Results and discussion

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

7


Chapter 5

Results and discussion

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
(May Deng)

110

Figure B.1.2b1-b6

Load vs displacement in tension parallel to grain test
(May Tai)

112

Figure B.1.3c1-c6

Load vs displacement in tension parallel to grain test
(May Dou)

114

Figure B.1.4d1-d6

Load vs displacement in tension parallel to grain test
(May Nhang)

116

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

Load vs displacement in tension parallel to grain test
(May Tai)

126

Load vs displacement in tension parallel to grain test
(May Dou)

128

Load vs displacement in tension parallel to grain test
(May Nhang)

130

Figure B.2.2b1-b6

Figure B.2.3c1-c6

Figure B.2.4d1-d6

8


Chapter 5

Results and discussion

Figure B.2.5e1-e6

Load vs displacement in tension parallel to grain test
(May Khen Heua)

132

Figure B.2.6f1-f6

Load vs displacement in tension parallel to grain test (May Khen
Hine)
134

Figure B.2.7g1-g6

Load vs displacement in tension parallel to grain test (May Khe
Foy)
136

Figure C.1.a1-a6

Load vs displacement in tension perpendicular to grain
(May Deng)

139

Load vs displacement in tension perpendicular to grain
(May Tai)

141

Load vs displacement in tension perpendicular to grain
(May Dou)

143

Load vs displacement in tension perpendicular to grain ( May
Nhang)

145

Load vs displacement in tension perpendicular to grain
(May Khen Heua)

147

Load vs displacement in tension perpendicular to grain
(May Khen Hine)

149

Load vs displacement in tension perpendicular to grain
(May Khe Foy)

151

Load vs displacement in compression parallel to grain
(May Deng)

154

Load vs displacement in compression parallel to grain
(May Tai)

156

Load vs displacement in compression parallel to grain
(May Dou)

158

Load vs displacement in compression parallel to grain
(May Nhang)

160

Load vs displacement in compression parallel to grain
(May Khen Heua)

162

Load vs displacement in compression parallel to grain
(May Khen Hine)

164

Figure C.2.b1-b6

Figure C.3.c1-c6

Figure C.4.d1-d6

Figure C.5.e1-e6

Figure C.6.f1-f6

Figure C.7.g1-g6

Figure D.1.a1-a6

Figure D.2.b1-b6

Figure D.3.c1-c6

Figure D.4.d1-d6

Figure D.5.e1-e6

Figure D.6.f1-f6

9


Chapter 5

Results and discussion

Figure D.7.g1-g6
Figure E.1.a1-a6

Load vs displacement in compression parallel to grain
(May Khe Foy)
166
Load vs displacement in compression perpendicular to grain test

(May Deng)
169

Figure E.2.b1-b6

Load vs displacement in compression perpendicular to grain test
(May Tai)
171

Figure E.3.c1-c6

Load vs displacement in compression perpendicular to grain test
(May Dou)
173

Figure E.4.d1-d6

Load vs displacement in compression perpendicular to grain test
(May Nhang)
175

Figure E.5.e1-e6

Load vs displacement in compression perpendicular to grain test
(May Khen Heua)
177

Figure E.6.f1-f6

Load vs displacement in compression perpendicular to grain test

(May Khen Hine)
179

Figure E.7.g1-g6

Load vs displacement in compression perpendicular to grain test
(May Khe Foy)
181

Figure F.1.a1-a6

Load vs displacement in shear parallel to grain test
(May Deng)

184

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
(May Nhang)

190

Figure F.5.e1-e6

Load vs displacement in shear parallel to grain test
(May Khen Heua)

192

Figure F.6.f1-f6

Load vs displacement in shear parallel to grain test
(May Khen Hine)

194

Load vs displacement in shear parallel to grain test
(May Khe Foy)

196

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 F.7.g1-g6

10


Chapter 5

Results and discussion

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
grain

215

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

215

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
rain test
217
Figure H 2.2 Types of broken specimens of May Tai under tension perpendicular to
grain test
218
Figure H 2.3 Types of broken specimens of May Dou under tension perpendicular
to grain test

219

Figure H 2.4 Types of broken specimens of May Nhang under tension perpendicular
to grain test
220
Figure H 2.5 Types of broken specimens of May Khen Heua under tension
perpendicular to grain test

221

Figure H 2.6 Types of broken specimens of May Khen Hine under tension
perpendicular to grain test

222

Figure H 2.7 Types of broken specimens of May Khe Foy under tension
perpendicular to grain test

223

11


Chapter 5

Results and discussion

Figure H 3.1 The failure specimens of May Deng under compression parallel
to grain
Figure H 3.2 The failure specimens of May Tai under compression parallel to
Grain test

224
224

Figure H 3.3 The failure specimens of May Dou under compression parallel to
grain test

225

Figure H 3.4 The failure specimens of May Nhang under compression parallel to
grain test

225

Figure H 3.5 The failure specimens of May Khen Heua under compression parallel to
grain test
226
Figure H 3.6 The failure specimens of May Khen Hine under compression parallel to
grain test
226
Figure H 3.7 The failure specimens of May Khe Foy under compression parallel to
grain test

227

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
grain test

232

Figure H 4.6 The failure specimens of May Khen Hine under shear parallel to
grain test

233

Figure H 4.7 The failure specimens of May Khe Foy under shear parallel to
grain test

234

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

12

Chapter 5

Results and discussion

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

13


Chapter 5

Results and discussion

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

Comparison of mechanical properties of Laos woods and
some US woods

68

Table 5.7

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

14


Chapter 5

Results and discussion

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
(Seven types of wood)

247

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
(Seven types of wood)

251

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
(May Khen Heua)

254

Table I.4.6

The results of compression perpendicular to grain test
(May Khen Hine)

254

Table I.4.7

The results of compression perpendicular to grain test (May Khe Foy) 255

15


Chapter 5

Results and discussion

Table I.4.8

The final results of compression perpendicular to grain test
(Seven types of wood)

255

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
(Seven types of wood)

263

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.7.6

The results for measuring weight density (May Dou)

266
16


Chapter 5

Results and discussion

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

(Seven types of wood)

271

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

17


Chapter 5

Chapter 1

Results and discussion

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

18


Chapter 5

Results and discussion

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,
19


Chapter 5

Results and discussion

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.

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Chapter 5

Chapter 2

Results and discussion

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,

21

Chapter 5

Results and discussion

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.

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Chapter 5

Results and discussion

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.

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Chapter 5

Results and discussion

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.

24

Chapter 5

Results and discussion

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.

25