Abstract:
The Effect of Slope of Grain on Modulus of Rupture (MOR) and Modulus of Elasticity (MOE) of sunt (Acacia nilotica) Wood Grown in Blue Nile State
This investigation delt with the effect of grain angle on modulus of rupture (MOR) and modulus of elasticity (MOE) of sunt wood grown in Blue Nile State. Static bending test was carried out for samples with five different grain angles including zero angle i.e. clear wood with straight grain. The slopes used included 1in 16, 1in 12, 1in 8, and 1in 6. From test results modulus of rupture and modulus of elasticity were calculated for each slope of grain. Four grades were selected arbitrarily and suitable strength ratios were assigned to these grades. From the test results and using the strength ratios the MOR was calculated for each grade. Analysis of variance and Duncan’s Multiple Range test were carried out, looking for the level of significance of the variations in MOR and MOE between the different grain angles. Regression analysis was also carried out for establishing relationships between each of MOR and MOE as dependent variables and grain angles as independent variables for estimating grain angles for different grades. The relationship between grain angle and MOR was established for short duration ultimate stress. The values of MOR for each grade (MORg) were substituted in the model relating MOR to slope of grain to find the slope of grain for each grade. Highly significant differences were found between MOR for the different slopes of grain (P < 0.0001). Significant differences were also obtained between MOE for the different slopes of grain (p = 0.0086). This p–value shows that MOE is not as sensitive to changes in slope of grain as MOR.
Regression analysis resulted in a model for estimating MOR from the slope of grain or vice versa. The model is as follows:
MOR = 1986-3697.6×SG .Where: SG= slope of grain,
The model for MOE was as follows:
MOE = 173580 – 189299 × SG
The slopes of grain obtained for the different grades were as follows:
Grade First Second Third Fourth
Slope of grain 1 in 10 1 in 6 1 in4 1 in 3
It appeared from the results that the variability of wood as a natural material affected the relationship between MOR and MOE on one side and slope of grain on the other by reducing R² values. The small size of the samples used also contributed to the same above effect.
