MECHANICAL STRENGTH PROPERTIES OF MANGIFERA INDICA IN AXIAL DIRECTION AT DIFFERENT MOISTURE REGIMES

* Aleru K. K. and David-Sarogoro N. Department of Forestry and Environment, Rivers State University of Science and Technology, NkpoluOroworukwo, Port Harcourt, Rivers State, Nigeria. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

This study assessed the Modulus of Rupture (MOR), Modulus of elasticity (MOE) and Impact strength (IM) of Mangifera indica woods in axial direction. The dimensions of wood samples were determined in accordance to British Standard (BS) 373(1957) and samples were subjected to the oven dry method for moisture content(MC) determination at Green state (90%) and Dry basis (12% MC). The result showed that there was significant difference (P<0.05) between MOR in the green and dry bases and along axial heights. The axial variations on wet basis shows that, MOR was highest at the base with 42.30Nmm 2 followed by the middle with 42.16 Nmm 2 and least at the top with 19.64 Nmm 2 while at 12% MC, MOR was highest at the middle with 48.59 Nmm 2 followed by the top with 43.18 Nmm 2 and lowest at the bottom with 43.14 Nmm 2 . There was significant difference (P<0.05) between the Modulus of Elasticity (MOE) in the wet and dry bases. Conversely, at their axial heights there was no significant difference (P>0.05) between stands.MOE at the wet bases along axial heights was highest at the middle (10272.3Nmm 2 ) followed by base (8202.06 Nmm 2 ) and least at the top (5137.71Nmm 2 ) whereon the dry basis, MOE was highest at the base (52112.80 Nmm 2 ) followed by middle (14070.38 Nmm 2 ) and least at the top (9386.40 Nmm 2 ). There was no significant difference (P>0.05) of the Impact Strength (IM) in their different moisture regimes (wet and dry bases).IM strength at the wet and dry bases was highest at the middle (1.86; 2.16 Nmm 2 ) followed by the base (1.85; 2.51Nmm 2 ) and least at the top (1.48; 1.52Nmm 2 ). A comparison with other species indicates that Mangifera indica serve other utilitarian purpose apart from its fruit benefits.

…………………………………………………………………………………………………….... Introduction:-
Mangifera indica Linn (Mango) is a hard wood species that belongs to the Anacardiaceae family and genus Mangifera. .It is an evergreen tree that attains a height of 15-30m and when cultivated can attain a height of 3-10m (More, 2004; Bally, 2006). It develops a girth of over 4m with a dense and umbrella shaped crown (Keay et al, 1964;Bally, 2006). The specie is a native of Asia-specifically India where it has spread to other parts of the world. The existence of Mango in Nigeria dates back to the 20 th century through the travels of merchant missionaries and colonist which has resulted to an indigenous species in the cropping systems (Aiyelaagbe, 2002;Niyishir, 2004).

ISSN: 2320-5407
Int. J. Adv. Res. 4 (11), 1520-1526 1521 Wood as a substance of great complexities more than other engineering materials (Aguda, et al, 2012) which calls for a degree of scientific, engineering and technological understanding. Thus, wood is a heterogeneous conglomeration of large number of cells which are hollow, spindle shaped and parallel to each other exhibiting hydroscopic and anisotropic tendencies. Suffice to say, wood has varying modes of behavior in relation to their moisture content and elastic properties which in turn affect their strength properties.
Modulus of rupture is a measure of the specimens' strength before rupture (Meier, 2008). It reflects the maximum load carrying capacity of a member in bending and is proportional to a maximum borne by the specimen (Green, et al, 1999).The Modulus of elasticity is a measure of resistance to bending (Kwaku et al, 2014) while the impact strength is the ability of the wood to resist suddenly applied load (Nwisuator and Emerhi, 2014). Thus, mechanical properties emphasises the ability of members to resist applied and/or external force. The fruit tree Mangifera indica has been known before now for its food purpose and medical value to man. This study is however imperative to unravel its strength property, MOR to bring it to fore to serve for other utilitarian purposes.

Materials and Method:-Study Area:-
The woods were obtained from Rivers State University of Science and Technology, Nkpolu-Oroworukwo, Port Harcourt, River state Nigeria. Mature standing trees of Mangifera indica were randomly selected and felled.

Preparation of Sample:-
Tree samples were collected from the Top, Middle, and Base of merchantable height (Mitchell and Dane, 1997). The species were immediately covered with a black nylon bag to prevent moisture loss. Specimens from the different positions were trimmed to 20x20x300mm in accordance to British Standard(BS) 373( 1957) for Modulus of Rupture, Modulus of elasticity and Impact Strength. Test samples were taken to the Forestry Research Institute of Nigeria (FRIN), Ibadan for assessment. The wood specimens were oven dried at 105 0 C and conditioned to have a stabilised moisture content of 12% for comparism with the moist wood at 90% MC.

Determination of Modulus of Rupture (MOR):-
The Modulus of rupture (MOR) was determined using specimen size of 20x20x300mm in accordance to BS 373(1957) from the three positions (Mitchell and Dane, 1997). The load was applied at the rate of 0.1m/sec using a Housfield Tensometer at the Forestry Product Development and Utilization Department of FRIN. The maximum load was noted. Values were substituted into the MOR formula; Where; P=Breaking Load/ Maximum Load at Failure (N) L=Distance between Knife edge/Span (mm) B=Sample Depth/Thickness (mm)  =Deflection at bean centre at proportional load.

Determination of Impact Strength Parallel to Grain:-
The Impact strength test was done using the Hatt-Tuner impact tester in accordance to BS373 (1957) with a standard test samples of 20x20x300mm supported over a span of 240mm on a support radius of 15mm with spring restricted yokes fitted to arrest rebounce. The test samples were subjected to a repeated blow from a weight of 1.5kg at increasing height initially from 50.8mm, and then every 25.4mm until complete failure occurred. The height at which failure occurred was recorded in meter as the height of maximum hammer drop (Ogunsanwo and Omole, 2010).

Experimental Design and Data Analysis:-
Completely Randomized Design with three treatments replicated thrice and a descriptive statistics and a one-way analysis of variance (ANOVA) were used to analyze the data Results:-   (Fig.1).  Aguda et al (2012) in that defects such as knots affects bending properties of trees and this in turn affects the affinity between MOR and sampling height. The reports also suggest that variability could be due to changing influences such as moisture, soil conditions, growing space etc (Green et al, 1999).

Modulus of elasticity:-
Modulus of elasticity is a measure of resistance to bending (Kwaku et al, 2014); this implies that deformations produced by low stress are completely recoverable after loads are removed (Green et al, 1999). In simplest term MOE measures the woods stiffness and is a good indicator of wood strength (Meier, 2008). The variations between the moisture regimes of the wood stands at their wet and dry basis is due to the fact that moisture lowers the stiffness (MOE) and strength of wood -it softens the wood cell walls, thus the cellulose micro fibrils are longer strongly bonded to each other making it easier to untangle and hence stretch the fibers (Yee, 2013 and University of Cambridge, 2004). This report also corroborates with the assertions of Cave, (1978), Green et al, (1999), Kretschmann and Green, (1996), Wang and Wang, (1999), Kojima and Yamamoto, (2004), that virtually all mechanical properties of wood decreases with increase in MC below the fiber saturation point. Temperature also played a salient role in relation to the MC of wood -as wood is cooled below normal temperature its mechanical properties (MOE) tends to increase. Conversely, when wood is heated its mechanical properties decreases. The magnitude of this change is dependent on the MC of the wood and when wood is heated on the duration of  (Cave, 1968). Walker and Butterfield (1995) and Lichtenegger et al (1999) opined that woods with higher microfibril angle (MFA) has low MOE which supports the standards of (TEDB, 1994) on its classification on the modulus of elasticity of wood at 12% moisture content. Although with the TEDB (1994) standard the wood is classified as a heavy wood at the dry bases but not very heavy due to slight variation in values.   (Wikipedia, 2016) which the results fulfilled. The mean impact strength ranges from 1.49-2.15Nmm 2 and 1.89-2.21Nmm 2 at the wet and dry basis respectively. This increase across the axial plan agrees with the findings of Ogunsanwo (2000), Aguda (2012), Adejoba (2008) and Adedipe (2004) in Triplochiton scleroxylon, Fiscus mucuso and Gmelina arborea.

Conclusion:-
From the study, Mangifera indica has shown an outstanding strength property when compared with other wood species. However, it is primal to state that moisture, site, location and individual characteristics influenced the variability between the stands. More so, with the strength values it can be deduced that the species is highly dense which is as a result of high density of the heartwood to sap wood .The species can be recommended for some engineering works like furniture making, aesthetics etc and other utilitarian purposes. However further research is also recommended for further strength properties.