ANISOTROPIC BEHAVIOUR OF NATURAL WOOD PALMYRA (BORASSUS AETHIOPUM MART) OF CHAD

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International Journal of Mechanical Engineering and Technology (IJMET)

Volume 6, Issue 9, Sep 2015, pp. 102-111, Article ID: IJMET_06_09_010

Available online at

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ISSN Print: 0976-6340 and ISSN Online: 0976-6359

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ANISOTROPIC BEHAVIOUR OF NATURAL

WOOD PALMYRA (BORASSUS

AETHIOPUM MART) OF CHAD

NGARGUEUDEDJIM K and ANNOUAR D. M.

LERTI: Laboratoire d’Etude et de Recherche en Techniques Industrielles, Faculté

des Sciences Exactes et Appliquées (FSEA), Université de N’Djaména, BP 1027,

Tchad.

G.E. NTAMACK

GMMA: Groupe de Mécanique, Matériaux et Acoustique, Département de Physique,

Faculté des Sciences, Université de Ngaoundéré B.P. 454 Ngaoundéré, Cameroun

S. CHARIF D’OUAZZANE

LMTM: Laboratoire de Mécanique, Thermique et Matériaux, Ecole Nationale de

l’Industrie Minérale (ENIM), B.P. 753 Rabat, Maroc

BIANPAMBE H. W.

LERTI: Laboratoire d’Etude et de Recherche en Techniques Industrielles, Faculté

des Sciences Exactes et Appliquées (FSEA), Université de N’Djaména, BP 1027,

Tchad.

GMMA: Groupe de Mécanique, Matériaux et Acoustique, Département de Physique,

Faculté des Sciences, Université de Ngaoundéré B.P. 454 Ngaoundéré, Cameroun

ABSTRACT

The Palmyra (Borassus aethiopum Mart.) is a plant with great size none

forked which produces lumber used in the domain of construction, housing

and in textiles. Its anatomical structure brings up the naked eye in both

directions of fiber orientation: one is parallel along the axis of growth of the

trunk and the other is inclined relatively to this axis. It should be noted that in

Chad we know very little about their scientific characteristics. This work

concerns the determination of elastic constants of the wood of an individual

aged of about 30 years. The mechanical tests performed in this study using the

method of six specimens were used to determine its:

- Young's modulus in the longitudinal GL, radial GR and tangential ET.

- Poissons coefficient TL, TR, LR, LT, RT, RL.

- Coulombs modulus GRL, GLT and GRT.

The values of the elastic constants confirm the anisotropic nature of the

wood.

Anisotropic Behaviour of Natural wood Palmyra (Borassus Aethiopum Mart) of Chad


Key words: Borassus Aethiopum Mart, Wood, Anisotropic Material, Fiber,

Natural Composite.

Cite this Article: Ngargueudedjim K, Annouar D. M, G.E. Ntamack, S.

Charif D’ouazzane and Bianpambe H. W. Anisotropic Behaviour of Natural

wood Palmyra (Borassus Aethiopum Mart) of Chad, International Journal of

Mechanical Engineering and Technology, 6(9), 2015, pp. 102-111.

http://www.iaeme.com/currentissue.asp?JType=IJMET&VType=6&IType=9

1. INTRODUCTION

The Palmyra is an angiosperm spermatophyte plant (class of monocotyledons) in the

class of palm. It grows in the African savannah [1]. He develops a trunk from 15m to

20m of length and 0.5m to 1.2m of diameter [2]. Its characteristics vary from one

region to another. Its wood has a woody tight structure, typical of palm trees, with

significant internal tensions [3, 4]. Unlike other woods whose heartwood (wood very

old and hard) is in the heart of the stem, Palmyras heartwood is located between

sapwood and bark. This wood rots hardly, even in water, and resistant to salinity. It is

not attacked by termites, marine borers and mushroom. It is an excellent lumber

which was widely used in civil engineering for the construction of bridges, wharves,

warehouses of infirmaries and in ports. Its fibrous structure and strength makes it a

material of choice carpentry and plastering. Finally, we note the recent use of this

wood in joinery and cabinet for manufacturing modern living rooms furniture, trunks

etc [1, 5, 6]. In Chad, we found plenty in the Sudano-Sahelian zone [7, 8]. In some

rapidly growing cities, It constitutes the frame of houses (walls supports, frames, door

and window frames, window frames). In rural areas, it is also widely used in

construction and as palisades support poles, in addition to many other domestic

purposes (manufacture beehives, seats, and shelters for domestic animals). Given its

importance in the construction work, knowledge of scientific data is essential to

define a strategy for the rational use. The work carried out concerning the extent of its

elastic constants as an orthotropic anisotropic material (natural composite).

Specifically, it is to determine its mechanical parameters which are the Young's

modulus, Poisson’s coefficients and shear modulus by using the 6 test method.

2. PLANT MATERIAL TESTING

The plant material is taken from a trunk of a male Palmyra tree aged of about 30

years. Its average height and bead diameter in the middle of the useful length (8m of

height) are respectively 16m and 34cm. The trunk is cut into pieces of 1.20m. The

piece of the base circumference of 1.46m is used for these experimental tests. The

sampling site is in the village Malfana at south of N'Djamena – Chad, located at

15°15.113 east longitude and 11°11.771 north latitude (figure 1).

Figure 1: Localization of Palmyra groves of the village Malfana.

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Ngargueudedjim K, Annouar D. M, G.E. Ntamack, S. Charif D’ouazzane And Bianpambe H. W


The average values of its chemical composition are 65.66% of cellulose, 23.66%

of lignin, 9.33% of hemicellulose and 1.35% of extractives. The density at 12% humidity is

823.22kg/m3 [9].

3. METHODOLOGY

3.1. Theoretical reminders

3.1.1. Anisotropy wood material

Wood is a natural composite material which is heterogeneous, porous anisotropic. It

has several levels of well organized cellulars structures and is made with 3 natural

biopolymers including:

- 2 amorphous polymers, lignin and hemicellulose which constitute the matrix,

- 1 crystalline polymer, cellulose which contributes to strengthening [10].

With the anisotropic material, the main directions of strain are not necessarily those

stress. In the case of a parallel or perpendicular effort to the direction of the fiber, the

two main directions are the same. It is possible to determine the Young’s modulus in

this direction and the corresponding Poisson's ratio with one strain gauge placed along

one of the two directions. If the force is neither parallel nor perpendicular to the fiber

direction the main directions of the strain are different from those of the stress and

those of the material. It takes this time a diagonal rosette (3 gauges at 45°) or Delta

rosette (3 gauges at 60°) for measuring strain. For an orthotropic material in plane

stresses or in the presence of an isotropic plane, it must necessarily the following five

parameters to calculate the stresses:

- Poisson’s coefficient III, Young’s modulus EI, EII and Coulomb’s modulus GI II,

which are independent,

- Poisson’s coefficient II I = I II * EII / EI if the material properties are the same in

tension and compression.

3.1.2. Linear orthotropic elasticity of wood

It is assumed that wood is a continuous, elastic, homogeneous orthotropic medium

admitting a cylindrical symmetry hardware [11, 12]. Then, we adopt the system of

orthogonal axes (R, T, L) for this study (figure 2).

(a) (b)

Figure 2: (a) System of cylindrical symmetry coordinates, (b): Test tube oriented along the

symmetry axes [12].

In the base (1, 2, 3), the elastic behaviour of the material is characterized by the

tensor of the compliances (Sij) which links the strain tensor (ij) to the stress (ij)

tensor:

TR

LRLT

L (3)

T (2)

R (1)

R

L

T

TR

LRLT

L (3)

T (2)

R (1)

TR

LRLT

L (3)

T (2)

R (1)

R

L

TR

L

T



12

31

23

3

2

1

66

55

44

333231

232221

131211

12

31

23

3

2

1

S00000

0S0000

00S000

000SSS

000SSS

000SSS

2

2

2 (1)

In the basic (R, T, L), equation (1) becomes:

RT

LR

TL

L

T

R

RT

LR

TL

LT

TL

R

RL

L

LT

TR

RT

L

LR

T

TR

R

RT

LR

TL

L

T

R

G

100000

0G

10000

00G

1000

000E

1

EE

000EE

1

E

000EEE

1

(2)

Modulus EL, ER and ET in the directions L, R and T, respectively, are defined by:

11R

S

1E ,

22T

S

1E ,

33L

S

1E (3)

The coefficients of Poisson RT RL, TR, LT, LR, and TL are given by the following

relationships:

11

31RL

33

23LT

22

12TR

33

13LR

22

32TL

11

21RT

S

S,

S

S,

S

S

S

S,

S

S,

S

S

(4)

The shear modulus GLR, GLT and GRT in the planes LR, LT and RT, respectively, are

defined for a rosette orthogonal by:

TLTLTLTLT2L

2LTTL

66RT

RLRLRLRLR2L

2LRRL

55LR

RTTRTRTRR2T

2TRTR

44LT

EEE2EE4E

EEE

S

1G

EEE2EE4E

EEE

S

1G

EEE2EE4E

EEE

S

1G

(5)

The components Cijkl of elastic stiffness tensor allow calculating the components kl

of stress tensor according the components ij of strain:

klijklij C (6)



3.2. Testing equipment

3.2.1. The strain gauge rosettes used

The rosette used comprises 3 gauges type CEA-06-240UZ-120 arranged at 45°. Its

dimensions are 16x10 mm. The active length of the gate of the gauge is 5mm (upper

3mm minimum recommended value in literature) it is sufficient to integrate the

macroscopic effect of the deformations of the material. The gauge dimensions are also

sufficient to allow for the dissipation of heat, therefore, to ensure greater compatibility

with a correct answer of the dynamic phenomena and gradients stress. Their

resistance and factor are R=120 and K=2.055, respectively.

3.2.2. Device tests

The test device (Figure 3) comprises

- 2 bridges strain type P3 of VSHAY Micromesures Firm. They have 4

independent channels and a dial LCD display. This bridge provides a facility for

setting the resistance, the gauge factor, the type of mounting of the bridge and the unit

of measurement.

- 1 bending and twisting machine designed and manufactured in the Exact and

Applied Sciences Faculty of University of N’Djamena-Chad. It is equipped with a

hydraulic system ENERPAC brand louse weight bearing. The maximum pressure of

the pump of the hydraulic system is 70bars. The piston of the hydraulic system is set

down in a vertical position for the occasion. Its diameter and maximum stroke are

25.3mm and 25mm respectively.

Figure 3 Device testing and specimens in position of test compression

3.3. Preparation of test specimens and conducting trials

The six specimens for the adopted method of characterization are collected from the

base of palmyra at 1m from the ground, especially in the part of the heartwood after

wood splitting into 4 parts (Figure 4) as follows:

- 3 specimens in main directions R, T and L,

- 3 specimens in tangential directions at 45° in the plans RT, RL and TL.

After their machining milling to dimensions 25x25x40mm, the two adjacent side

surfaces to receive the rosettes were polished to P800 sandpaper. The alignment pins

of the gauges on the surfaces have been drawn in pencil hard lead. These surfaces

have been degreased, cleaned and dried in the open air under the sun. The gauges are

cleaned resin solvent and neutralized before being glued with the M200 cyanoacrylate

Piston

Specimen

Bridge strain P3

Hydraulic pump



superglue. Next, the connecting wires are welded on each gauge in quarter (1/4) of the

Wheatstone bridge mounting (figure 5).

Figure 4: Specimens for the six pieces method.

Figure 5 Test specimen with 2 diagonal rosettes (3 gauges at 45°).

To prevent the erosion of borders and ensure the proper distribution and alignment

of the load, a square steel plate side 30mm and 5mm thick is placed on each of the

two charging tips of the specimen. Each specimen is tested at 351.90 N (7 bars) of

magnitude compressive force tree times. The average values of deformations recorded

manually permits the calculation of the components of the tensor of the strain’s

coefficients.

4. RESULT AND DISCUSSIONS

The values of the observed deformations were used to calculate the tensor

components of the elastic compliances (table 1).

Rosettes

Connecting

wires



Table 1 Elastic compliances of Palmyra

S11 S22 S33 S12 S21 S13

-5,21.10-4 -6,15.10-4 - 2,0.10-4 8,28.10-4 -2,89.10-4 8,69.10-5

S31 S23 S32 S44 S55 S66

5,42.10-5 -3,34.10-5 -6,05.10-5 1,20.10-3 5,97.10-3 1,29.10-3

The Young's modulus (table 2), the Poisson's ratios (table 3) and the Coulomb’s

modulus (table 4) are calculated by using the values of the compliance.

Table 2 Young’s modulus of Palmyra

EL (MPa) ER (MPa) ET (MPa)

5005.68 1918.17 1630

Table 3 Poisson’s coefficient of Palmyra

RT LT LR TR RL TL

0,55 0,43 0,16 0,13 0,10 0,09

Tableau 4 Coulomb’s modulus of Palmyra

GLR (MPa) GTL (MPa) GRT (MPa)

834.51 775.88 167

It is observed from Table 2 that the longitudinal Young's modulus EL has a higher

value than the radial and tangential modulus. Indeed, fibers are reinforcing elements

along the major axis; they are coated by a softer matrix consisting of the common

lamella. Thus, since the majority of fibers will be oriented along the axis of the trunk,

this will give a fibrous reinforcement in the longitudinal direction and consequently a

higher Young's modulus. Woody rays constitute reinforcement along the radial axis

and that is why the ER value is greater than that of ET. The cells constituting the

woody radius induce a strengthening in the radial direction relative to the tangential

direction. Under a tangential force, the longitudinal fibers and woody radius are

charged perpendicularly to the long axes of the cells, which give a low tangential

modulus [10]. The shear modulus GLT in the longitudinal plane-tangential is very high

because this plane contains the longitudinal fibers and woody radius which improves

on the shear strength. In the radial-tangential plane, the crystalline polymers

(cellulose) and amorphous polymers (lignin and hemicellulose) are cut, which makes

easier shearing.

Table 4 Young's modulus of Palmyras heartwoods on 2 different areas in Chad

Origin of Chadian

Palmyra

Longitudinal elastic modulus (Young’s modulus)

(MPa)

EL ER ET

Malfana 5005.68 1918.17 1630

Houndouman [12] 6400 199.83

Table 4 shows the effect of the maturity of the tree on the mechanical properties

of the wood. Indeed, the Palmyra of Houndouman (at 15°04.47 east longitude and

11°51.33 North latitude) is oldest (40 years) than that of Malfana (30 years) standed at



15°15.113 east longitude and 11°11.771 north latitude. Its heartwood is more resistant

(EL = 6400 MPa) than Malfana’s one (EL = 5005.68 MPa).

Tables 2, 3 and 5 highlight anisotropic nature of palmyra wood. Indeed, the

anisotropy of the wood results in the following order relationships:

- EL >> ER > ET for Young's modulus [12],

- GLR > GTL > GRT for shear modulus and RT > LT >> LR > TR > RL > TL for

the Poisson's ratios [10].

Table 5 Poisson's coefficients at 12% moisture content of the wood Palmyra with other

species [10].

Essence (kg/m3) RT LT LR TR RL TL

Douglas 650 0.52 0.47 0.17 0.21 0.05 0.02

Spruce 450 0.42 0.40 0.34 0.38

Pine 490 0.45 0.44 0.39 0.39

Oak 560 0.6 0.57 0.39 0.18 0.04 0.02

Palmyra 823.22 0.55 0.43 0.16 0.13 0.10 0.09

Compared to other woods (table 5), the Palmyra wood has a low coefficient of

shrinkage in LR TR and LR plans. This can be explained by its consistency due to its

high lignin content (23.66%). His withdrawal coefficients in the RT plans, LT and LR

are close to the timber Douglas. Table 6 shows that the wood Palmyra is stronger than

spruce and Douglas in the shear plan RS and RT. Their shear modulus is similar to

those of pine and oak in the LR and LT plans. Its radial and tangential Young's

modulus are much higher than those of spruce, pine, Douglas and oak. Paradoxically,

the longitudinal Young's modulus of Palmyra is 10 times lower than those of other

timber. Palmyra Heartwood of Houndouman tested has given the longitudinal

Young's modulus of 6400 MPa in compression and 15044 MPa in flexure [13]. In

reality, flexural strength of high quality wood often exceeds the compressive strength

[12]. But this enormous gap values requires careful thought because the only

anisotropic character is not enough. Its anatomical structure which is heavily

composed of coarse fibers (figure 5) seems one explanation of this comportment. Like

other wood, Palmyra has Young’s modulus and Coulomb’s modulus well below those

of monvingui.

Table 6 Coulomb's modulus of Palmyra with other species to 12% of wood humidity

Essence Palmyra Douglas [10] Spruce

[14] Pine [10] Oak [10] Monvingui [14]

(kg/m3) 823.22 470 390 490 560 760

EL (MPa) 5005.68 16872 11800 16015 15248 16000

ER (MPa) 1918.17 949 920 1182 1182 2490

ET (MPa) 1630 934 510 616 616 1730

GLR (MPa) 834.51 749 760 828 828 1410

GLT (MPa) 775.88 802 730 688 688 1230

GRT (MPa) 167 114 40 320 320 550



Table 7 Poisson's coefficients of Palmyra with Broad-leaved tree and resinous to 12% of

wood humidity

Essence (kg/m3) RT LT LR TR RL TL

Broad-leaved

tree [10] 650 0.67 0.46 0.39 0.38 0.048 0.033

Resinous [10] 450 0.51 0.43 0.39 0.31 0.03 0.02

Palmyra 823.22 0.55 0.43 0.16 0.13 0.10 0.09

Table 8: Coulomb's coefficients of Palmyra with Broad-leaved tree and resinous to 12% of

wood humidity.

(kg/m3) GTL

(MPa)

GLR

(MPa)

GTR

(MPa) EL/ER GLR/GTR GTL/GTR

Broad-leaved

tree [10] 650 971 1260 366 12,1 à 62 3,4 2,6

Resinous [10] 450 745 862 83,6 40,6 à 182 10,3 8,9

Palmyra 823.22 775.85 834.51 167 5,0 4,6

Tables 7 and 8 show that Palmyra is a special wood whose mechanical

characteristics are similar to those of resinous.

5. CONCLUSION

The objective of this work is was to characterize the mechanical wood Palmyra of

Chad. The study has identified its elastic compliances, its elastic constants (Young's

modulus, Coulomb’s modulus and Poisson's ratios) using the method of six

specimens. The test results of this study corresponds to what is reported in the

literature. In the same test conditions, the Young's modulus in the longitudinal

direction is much higher than the radial and tangential modulus. The values of

different elastic constants found confirm the anisotropic nature of Palmyra wood. The

comparison on the elastic constants of 2 individuals of different ages (30 and 45

years) showed that the Young's modulus of the Palmyra heartwood depends strongly

of the maturity of the tree. Compared to other species, wood Palmyra seems very

durable and has mechanical characteristics similar to those of oak wood. The results

of our tests give a longitudinal Young’s modulus well below those of other species;

this enormous gap values requires careful thought. The results of this work will

undoubtedly contribute to a better understanding of the mechanical behaviour of

Palmyra wood of Chad.

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ANISOTROPIC BEHAVIOUR OF NATURAL WOOD PALMYRA (BORASSUS AETHIOPUM MART) OF CHAD