Effects of moisture content and level in the crop on the engineering properties of alfalfa stems

Some physical and mechanical properties of alfalfa stems are presented. The experiments were conducted at four moisture content levels from 10% w.b. to 80% w.b. and at three levels up the stem. At all levels along the stem, moisture contents less than 40% w.b. did not significantly influence major and minor diameters, thickness, cross-sectional area, second moment and polar moment of area. At the different moisture contents studied, the values of the tensile strength were within the ranges 9.24-26.35 MPa, 16.31-32.74 MPa, and 28.88-43.82 MPa for the upper, middle and lower levels in the crop, respectively. The maximum shear strength and shearing energy were 28.16 MPa and 345.80 mJ, respectively. The value of the bending stress obtained at the lowest moisture content was approximately 3 times greater than at the highest moisture content. The average Young's modulus ranged from 0.79 GPa to 3.99 GPa. The maximum and minimum of torsional stresses were found to be 4725 kPa and 465 kPa, respectively. The fact that a greater shearing energy was obtained at the lower levels in the crop could be due to the accumulation of more mature fibres in the stem. It was concluded that an increase in moisture content of stem leads to a decrease in the tensile strength, bending stress, Young's modulus, torsional stress, modulus of rigidity and to an increase in shear strength and shearing energy. (C) 2008 IAgrE. Published by Elsevier Ltd. All rights reserved.