PHYSICAL-MECHANICAL CHARACTERIZATION OF Eucalyptus urophylla WOOD

Eucalyptus urophylla consists in a wood-producing species, which offers a natural multiple raw material of good quality for applications in rural and civil constructions. However, Eucalyptus urophylla still has a small utilization as building parts and elements, resulting from the possible ignorance and low diffusion of its structural possibilities. Thereby, the present research aims to measure the main thirteen mechanical properties of Eucalyptus urophylla wood for two different moisture contents, 12% and 30% (green wood). Furthermore, in these two conditions of moisture content evaluation, volumetric mass densities were also evaluated. At the end of this evaluation, which included 2688 determinations, all the obtained results were statistically treated with t-test at a 5% of significance level in order to evaluate the influence of moisture content in the evaluated properties. Twelve mechanical properties were significantly affected by moisture content, and the behavior pattern consisted in increasing the values of the properties with the reduction of the moisture content.


INTRODUCTION
The increasing consumption of wood products raises the use of wood from native forests. Therefore, the implantation of planted forests constitutes a viable alternative for reducing the pressure exerted on native forests (Paiva et al., 2013). Eucalyptus wood has a greater applicability (Wallis, 1970), since each day Eucalyptus wood has been consolidating as an important raw material for different industrial applications (Plaster et al., 2012).
It is native to the Myrtaceae family (Sein & Mitlöhner, 2011;Lorenzi et al., 2003); the Timor White Gum is a species of Eucalyptus (Wiersema & León, 2016) whose scientific name is Eucalyptus urophylla S.T. Blake (Corbasson, 1986;Boland et al., 2006). This species is also found in Indonesia (Vieira & Bucsan, 1980;Scanavaca Jr & Garcia, 2003a;Martins-Corder et al., 1996), Ivory Coast (Wencelius, 1983, Corbasson, 1986, Cameroon, Gabon, Guyana, Madagascar (Corbasson, 1986), Congo (Corbasson, 1986;Gouma 1998), Vietnam (Sein & Mitlöhner, 2011), Malaysia, Papua New Guinea (Soerianegara & Lemmens, 1993, among others. In addition, Eucalyptus urophylla is present in Brazil (FAO, 1981;Gonçalves & Passos, 2000;Oliveira et al., 2005;Andrade et al., 2010;Guimarães JR. et al., 2012) from its introduction during the 1970s, through seeds harvested in several islands belonging to Indonesia (Rocha et al., 2006). Perennial, Eucalyptus urophylla can reach heights of 45 to 55 m, however, in unfavorable environments this tree develops as a twisted bush (Sein & Mitlöhner, 2011). Of great size and fast growth, this species constitutes in a perennial tree with straight and cylindrical trunk, covered by a thick bark endowed with fine longitudinal cracks of gray-dark color (Lorenzi et al., 2003). Due to the supply of dark forests, this species offers great utility as protection for livestock breeding in hot and humid climates (FAO, 1981). The wood of the Eucalyptus urophylla has a texture between moderately thick to thick. The color of its core is reddish brown or dark reddish brown, while its sapwood is white, cream or light pink (Soerianegara & Lemmens, 1993). This species is a moderately quality wood-producing tree, although its slender architecture makes it possible to direct it to landscaping (Lorenzi et al., 2003).
Due to the potential of Eucalyptus urophylla wood for the construction, Valle et al. (2013) have shown that this species presents easy treatment and penetration of chemicals preservation.
Despite the great potentiality, Eucalyptus urophylla wood still has low levels of use in civil construction (Christoforo et al., 2014), which is also justified by the lack of knowledge of its physical and mechanical properties, especially in the absence of characteristics such as age or region source. Due to the problem raised, this research aimed to present the main physical and mechanical properties of the Eucalyptus urophylla species as well as to investigate the effect of the moisture content (12%, 30% -saturated) in the properties evaluated, reinforcing the wide possibility of use timber as structural elements.

MATERIAL AND METHODS
Eucalyptus urophylla wood logs from eight Brazilian cities (Table 1) were duly housed in the Wood and Wood Structures Laboratory (LaMEM), in São Carlos Engineering School (EESC), at São Paulo University (USP). It should be emphasized that the tests also occurred in the dependence of the LaMEM, and that the determination of the physical and mechanical properties for the wood in the two moisture contents (12%, 30%) followed the Brazilian standard ABNT NBR 7190 (ABNT, 1997). The physical properties evaluated consisted of the basic and apparent densities. Strength values were obtained in the normal and parallel compression, parallel and normal traction, in the static bending test, shear and spinning, and the stiffness values were calculated in the normal and parallel compressions, parallel traction and static bending, being also determined the hardness in the parallel and normal directions. It is noteworthy that 2654 determinations (number of values obtained from physical and mechanical properties) were obtained involving wood in both moisture content (12%, 30%). The number of determinations (n) of each property and for each moisture content is explained in Tables 2 to 5.
After the physical-mechanical tests (15 properties), the results were evaluated by means of the t test analysis at a level of significance of 5% (P-value <0.05), with the objective of investigating the influence of the moisture contents in the physical and mechanical properties of the woods. By the formulation of the hypotheses, P-value higher than the level of significance implies accepting the null hypothesis (the means of the two groups are equivalent), and rejecting it otherwise (means of the two groups are not equivalent). Table 2 shows the number of determinations (n), mean values (MD), standard deviations (sd) and the P-value (Probability P) of the test t concerning wood densities for the two moisture contents. From the t test (Table 2), the volumetric mass density was not significantly affected by the moisture content variation. Table 3 shows the results of the descriptive statistics and the t test for the strength values of the wood evaluated at the two moisture contents.  (Table 3 ). The analysis of the t test indicated that the properties of parallel and normal compression, normal traction and static bending were significantly influenced by the reduction in the moisture content of the wood (P-value <0.05), as discussed in the research developed by Logsdon & Clil JR (2002), it was not observed in the parallel traction, that did not undergo significant variations influenced by the difference of the moisture content (P-value> 0.05). Table 4 shows the results of the descriptive statistics and the t test for the values of the elasticity modulus for the wood evaluated in the two moisture contents. Similarly, the evaluated elasticity modulus also indicated increases in all its properties, such as: 10.62% (1422.4 MPa) in parallel compression, 11.27% (1732.9 MPa) in the parallel traction, 15.73% (100.8 MPa) in normal compression and 15.06% (2020.8 MPa) in static bending (Table 4). The analysis of the t test indicated that in the four properties (parallel and normal compressions, parallel traction and static bending), the values of the elasticity modulus had a significant influence (P-value <0.05) on their means when the moisture content was reduced from 30 to 12% (Logsdon & Clil JR, 2002). Table 5 shows the results of the descriptive statistics and the t test for the values of shear strength, crack strength and hardness in the normal and parallel directions for the wood evaluated in the two moisture contents. In addition to the strength properties evaluated, the normal and parallel hardness and the shear and cracking increased with the reduction of the moisture content in the order of 18.35% (1.18 kN), 13.96% (0.8 kN), 23.74% (3.3 MPa) and 26.44% (0.23 MPa), respectively ( Table 5). The t test indicated that the four properties were influenced in their means by the reduction in the moisture content of the wood (Table 5).

CONCLUSIONS
Based on the results, with the reduction of the moisture content of 30% to the value (12%) pre-established by the Brazilian standard ABNT NBR 7190 (ABNT, 1997), it can be concluded that: -The volumetric mass density was not affected significantly by the variation of the moisture content; -The following mechanical properties of Eucalyptus urophylla presented significant increases: shear strength in parallel and normal compressions, normal traction and static bending; elasticity modulus in parallel and normal compressions, parallel traction, static bending; shearing; cracking and hardness in the parallel and normal directions to the fibers; Considering the increments obtained for twelve mechanical properties evaluated, it was verified that the wood of the Eucalyptus urophylla presented higher strength and stiffness values for the moisture content of 12%, which may stimulate a greater use of this species in structural elements and components under such conditions.