Influence of moisture content on the axial resistance and modulus of elasticity of clonal eucalyptus wood

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ScienceDirect Materials Today: Proceedings 13 (2019) 562–568

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ICMES 2018

Influence of moisture content on the axial resistance and modulus of elasticity of clonal eucalyptus wood M. Amera*, B. Kabouchia, M. Rahoutib, A. Famiric, A. Fidahc, and S. El Alamia a

Laboratory of Condensed Matter and Interdisciplinary Sciences, Faculty of Sciences, Mohammed V University in Rabat, 4 Avenue Ibn Battouta B.P. 1014 RP, Morocco b Center of Plant and Microbial Biotechnologies, Biodiversity and Environment, Faculty of Sciences, Mohammed V University in Rabat, 4 Avenue Ibn Battouta B.P. 1014 RP, Morocco c Laboratory of Physics and Mechanics of Wood, Centre de Recherche Forestière, Rabat, Charia Omar Ibn Al Khattab. B.P, 763 Agdal-Rabat 10050 Morocco

Abstract The mechanical and physical properties of wood are important factors used to determining the suitability and application of wood material. Modulus of elasticity and resistance values of wood which is changed according to the factors such as, temperature, moisture content, and density. Obtained results in this study show that the modulus of elasticity and the axial resistance for studied clones woods increase when the wood moisture decreases. According to the stress of rupture, both woods are classified within the range of weak stress. In addition, these results show that Eucalyptus grandis clone 3758 has a high modulus of elasticity in compression and low axial resistance compared to E. camaldulensis clone 579. © 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the International Conference on Materials and Environmental Science, ICMES 2018. Keywords: Clonal eucalyptus; Wood; Axial resistance; Modulus of elasticity; Moisture.

2214-7853 © 2019 Elsevier Ltd. All rights reserved. Peer-review under responsibility of the scientific committee of the International Conference on Materials and Environmental Science, ICMES 2018.

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Nomenclature σC F t,r E L Lo SMOE ρ CV h ε R2 FSP

Stress of rupture in axial compression Maximum load Dimensions of the cross section of specimen modulus of elasticity in axial compression Final length of samples Primary length of samples Specific modulus of elasticity Density of wood samples Coefficients of variation Humidity of wood samples Deformation of wood specimens Coefficients of determination Fibers saturation point

(kg/cm2) (N) (mm) (MPa) (mm) (mm) (MPa/kgm-3) (kgm-3) (%) (%)

1. Introduction In Morocco, Eucalyptus plantations occupy a very important area and play an important socioeconomic roles, they provide firewood, logs and pulp production [1-4]. Selected material of clonal and hybrids plants, adapted to various bioclimatic conditions in order to satisfy the imperative needs for pulpwood, were developed by national program of improvement eucalyptus plantations initiated in Morocco in 1987 [5]. The physical and mechanical properties of wood are important factors used to determining the suitability and application of wood material, these characteristics depend on the wood specie, age of material, its moisture content and density of wood [6-14]. The change in humidity affects the elasticity of wood, especially when the wood moisture content is in the hygroscopic range; the upper limit of this domain are the fibers saturation point (FSP), which varies according to the species of wood and the temperature [15- 21], these properties vary significantly with the moisture content below FSP. Above this point most mechanical properties are almost constant with the changes of wood moisture content [22]. Knowledge of mechanical properties of clonal Eucalyptus wood is essential for any attempt to develop and valorization this type of wood. It will allow the identification of the conditions of its uses. Thus, constitute a basis for a technical and economic argument for its development in the local market. This study aims to determine the resistance and modulus of elasticity in axial compression at different wood moisture levels at ambient temperature. 2. Material and Methods 2.1. Material Vegetal material used for this study consists of two trees having good straightness and free from defects and carried the minimum branches. One tree of Eucalyptus grandis clone (3758) and another of Eucalyptus camaldulensis clone (579) originated from 9-year-old plantation established in Maâmora forest Heights and circumferences of trees are respectively: 20 m and 91 cm for clone 3758; 18 m and 73 cm for clone 579. 2.2. Experimental The axial compression resistance test was performed according to the French standard NF B 51-007 [23] on 240 specimens for clones (3758 and 579) of dimension (20x20x60) mm3 in the RTL directions. These samples divided

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into six groups, each group contains 20 samples, and tests were done at different wood moisture levels (100, 80, 60, 40, 20 and 12)% at ambient temperature. The apparatus used for this test is an Universal hydraulic press brand "Testwell" having a maximum load cell equal to 12 tons and set at an average progressive load displacement speed of approximately 5 mm / min to obtain the values of the displacements and the appropriate breaking load was shown in Fig. 1. The transverse dimensions and lengths of samples were previously measured by a Mitutoyo comparator.

Fig. 1. Testwell compression machine

The effective moisture of the specimens was controlled gravimetrically by drying oven. 20 specimens of each clone having the same dimensions as the samples used in experiment, were placed in a basin of water for three days until they saturated with water, and then placed in a drying oven at a temperature 80C, the masses were measured during ranges time by an electronic balance of 1mg precision. Fig. 2 shows drying curves were obtained by measuring the masse of samples for different times. By these curves, the required time has been determined for the samples to reach the specific value of moisture which the test is conducted. For ensuring stability of humidity of samples at the specific level, Fig. 3 oven drying samples are put in the desiccator until use.

Fig. 2. Evolution of moisture content of wood clones by oven drying.

Fig.3. Enclosure reproducing the hygroscopic conditions.

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2.3. Mathematical expression The stress of rupture in axial compression (C) is given by the following relation:

C 

F tr

(1)

The modulus of elasticity in axial compression (E) is calculated using the formula:

E

C 

(2)

The deformation of wood specimens during axial compression (ε), calculated from the following equation:



L  Lo L

(3)

Specific modulus of elasticity is determined by the following equation [24]: E SMOE 

(4)



3. Results and Discussion Result of mechanical characteristics obtained for six levels of moisture, Table 1 shows that the modulus of elasticity and stress of rupture in axial compression and applied force on both woods are increasing by decreasing the wood moisture. Significant increase is obtained when the humidity is less than 40% (saturation point of the fibers). At all levels of humidity, the wood of clone 3758 has the largest change in the modulus of elasticity value. While, the wood clone 579 has the largest values of stress of rupture. Also the density of wood varies according moisture levels, and it decreases for low moisture contents. At different levels moisture, the average of wood density for clone 579 is greater than for clone 3758, while the specific modulus is lower than for clone 3758. Table. 1 Mechanical characteristics in axial compression of two clonal woods. CV Fmax CV h ρave max Clone (%) (kg/m3) (N) (%) (%) (kg/cm2) 100 973 2 8402 12 201 80 820 7 9463 9 204 60 763 4 10228 14 234 3758 40 628 7 10825 7 251 20 623 5 15119 20 386 12 582 10 16654 10 423 100 975 2 8575 10 202 80 880 3 8790 10 215 60 768 4 10621 12 251 579 40 711 6 10999 13 267 20 668 4 15132 15 388 12 628 10 17877 13 454

CV (%) 8 10 13 9 19 9 11 11 13 12 15 13

Eave (MPa) 1161 1197 1246 1294 1745 2240 939 1116 1176 1300 1693 1807

CV (%) 22 19 15 13 22 19 19 23 18 21 16 22

E/ρ (MPa/Kg m-3) 1.19 1.46 1,63 2.06 2.80 3.85 0.96 1.27 1.53 1.83 2.70 2.71

CV (%) 22 18 15 13 22 19 19 22 18 21 16 22

Humidity of wood (h), Density (ρave), Maximum applied force (Fmax), Axial stress of rupture (max), Modulus of elasticity in compression ( Eave), Specific modulus of elasticity (E/ρ), and their coefficients of variation (CV%). The modulus of elasticity (Eave) and stress of rupture in axial compression (max) varies in a significant way as a function of the wood moisture for the two clones (Figs. 4 and 5), which implies that the moisture is a main parameter which influences these mechanical characteristics. The results indicate a strong linear negative correlation between wood moisture, modulus of elasticity, and stress of rupture. According to coefficients of determination (R2), it is clear that the correlation between both the modulus of elasticity and the stress of rupture with moisture content for wood of clone 579 is greater than those of which for clone 3758.

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Fig. 4. Modulus of elasticity as a function in wood moisture of clones 3758 and 579.

Fig. 5. Stress of rupture as a function of wood moisture for clones 3758 and 579.

A strong positive linear correlation is also found between modulus of elasticity an stress of rupture in axial compression for both wood (Fig. 6). This correlation is much greater for clone 579 wood according its determination coefficient value (R2).

Fig. 6. Relationship between modulus of elasticity and stress of rupture for clones 3758 and 579.

According to the relationship between the stress of rupture in axial compression and force applied on both wood at different levels of wood moisture content, determined by regression analysis, it was found that there a great correlation positive between applied force and stress of rupture (Fig. 7).

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Fig.7. Relationship between stress of rupture and force applied for clones 3758 and 579.

The relationship between the wood density at different levels of moisture and both modulus of elasticity (Eave) and Specific modulus of elasticity (SMOE) was determined by regression analysis (Figs 8 and 9). The relationship between wood density ( ρave) and both modulus of elasticity (Eave) and specific modulus can be fitted by negative linear regression.

Fig. 8. Relationship between modulus of elasticity and wood density for two clones.

Fig. 9. Relationship between specific modulus of elasticity and moisture for two clones.

4. Conclusion In view of obtained results about the influence of wood moisture content on modulus of elasticity in axial compression of clonal eucalyptus wood, we can conclude that:  The modulus of elasticity, stress of rupture and density for wood two clonal eucalyptus varies with the changes of wood moisture;

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 According to the values of modulus of elasticity, the wood of clone 3758 has a rigidity greater than of clone 579;  Modulus of elasticity and stress of rupture increase in approximately a linear way with drying from 100% to 40%, after that, their values increase significantly with decrease of moisture content; and values of the modulus of elasticity and stress of rupture varies with the changes wood density of both clones. The differences between some specific mechanical properties such as modulus of elasticity and stress of rupture of both woods can be attributed to the presence of tension wood, juvenile wood with the combination of silvicultural factors. These results can give precise knowledge for artificial drying tests of this type of wood. Acknowledgements This work is supported by the Forest Research Center in Rabat (High Commission for Waters, Forests and Fight against Desertification) in collaboration with Faculty of Sciences in Rabat (Mohammed V University), Morocco. References [1] L. Messoudi, L. Rohi, Y. Ouguas, Bulletin de l’Institut Scientifique, Rabat, Section Sciences de la Vie. 36(2014) 49-56. [2] A. Famiri, B. Kabouchi, A. Hakam, J. Gril, Fofest Sci. Bulgaria. 1/2(2001) 45-50. [3] M. Amer, B. Kabouchi, M. Rahouti, A. famiri, A. Fidah, J. Indian Acad. Wood Sci. 14(2017) 91-98. [4] B. Barcha, Caractérisation papetière des nouveaux clones d'eucalyptus Maroc par le procédé kraft. PhD Thesis, Université Mohammed V Rabat (2014). [5] I. Loulidi, A. Famiri, M, Chergui, M. Ghorba, Int. J. of Engineering and Sci. 1(2012) 1-7. [6] M. Kiaei, Middle-East J. of Sci. Research, 9(2011) 279-284. [7] P.C. Raposo, J.A.F.O. Correia, D. Sousa, M.E. Salavessa, C. Reis, C. Oliveira, A. De Jesus, Sci. Direct Procedia structural integrity. 5(2017) 1097-1101. [8] G.Y. Jamala, S.O. Olubunmi, D.A. Mada, P. Abraham, J. of Agriculture and Veterinary Sci. 5(2013) 29-33. [9] M.P. Lima Jr., J.C. Biazzon, V.A. De Araujo, R.A. Munis, J.C. Martins, J. Cortez-Barbosa, M. Gava, I.D. Valarelli, E.A.M. Mechanical, BioResources, 13(2018) 3377-3385. [10] A. Burgers, Caractérisations physico-mécaniques de bois ”sans défauts” pour la conception mécanique: application aux pins de la région méditerranéenne française. PhD Thesis, Université de Montpellier (2016). [11] F.S. Ferro, F.H. Icimoto, D.H. De Almeida, A.L. Christoforo, F.A.R. Lahr, Int. J. of Agriculture and Forestry, 3(2013) 66-70. [12] E. Güntekin, T. Yılmaz -Aydın, P. Niemz, General Technical Report FPL-GTR-239 Proceedings: 19th Int. Nondestructive Testing and Evaluation of Wood Symposium, (2015) 7-14. [13] B.C. Bal, I. Bektas, Ormancılık Dergisi, 9(2013) 71-76. [14] A.R. Awan, M.I. Chughtai, M.Y. Ashraf, K. Mahmood, M. Rizwan, M. Akhtar, M.T. Siddiqui, R.A. Khan, Pak. J. Bot. 44(2012) 2067-2070. [15] W. Molinski, E. Roszyk, A. Jablonki, J. Puszynski, Maderas-Cienc Tecnol. 20(2018) 1-16. [16] D.F. Llana, G. Iniguez-Gonzalez, F. Arriaga, P. Niemz, Wood Research, 59(2014) 769-780. [17] Wood as an engineering material, Wood handbook, Centennial Ed., General Technical Report FPL-GTR-190. Madison, WI: U.S. Department of Agriculture, Forest Service, 2010. [18] D.A.L. Silva, F.A.R. Lahr, O.B. De Faria, E. Chahud, Materials Research, 15(2012) 300-304. [19] M. Ekevad, A. Axelsson, BioResources, 7(2012) 4730-4743. [20] P.K. Poonia, S. Tripathi, J. of Tropical Forest Sci. 28(2016) 153-158. [21] H.C. Spatz, J. Pfisterer, Arboriculture & Urban Forestry, 39(2013) 218-225. [22] E. Güntekin, T.Y. Aydın, Int. Caucasian Forestry Symposium, (2013) 878-883. [23] P. Sallenave, Propriétés Physiques et Mécaniques des bois tropicaux de l'union Française. Centre Technique Forestier Tropical, BelleGabrielle, Nogent-sur-Marne (Seine), France, 1955. [24] P. Kral, P. Klimek, P.K. Mishra, R. Wimmer, D. Decky, Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis 63(2015) 433-438.