Bending and Shearing Characteristics of Alfalfa Stems

Bending stress, young’s modulus, shearing stress and shearing energy were determined for Alfalfa (Medicago Sativa L.) stem. The bending forces were measured at different moisture contents and the bending stress and the young’s modulus were calculated from these data. For measuring the shearing forces, the stem specimens were severed by using a computer aided cutting apparatus. The shearing energy was calculated by using the area under the shearing force versus displacement curve. The experiments were conducted at a moisture content of 10%, 20%, 40% and 80% w.b. The bending stress decreased as the moisture content increased. The value of the bending stress at low moisture content was obtained approximately 3 times higher than at high moisture content. The average bending stress value varied from 9.71 to 47.49 MPa. The young’s modulus in bending also decreased as the moisture content and diameter of stalks increased. The average young’s modulus ranged from 0.79 to 3.99GPa. The results showed that the shearing stress and the shearing energy increased as the moisture content increased. The maximum shear strength and shearing energy were found to be 28.16 MPa and 345.80 mJ, respectively. Both the shearing stress and the specific shearing energy were found to be higher in the lower region of the stalk due to structural heterogeneity

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A b s t r a c t. The objective of this research was to determine the effects of moisture content and stalk region on some physical and mechanical properties of safflower stalks. The experiments were conducted at four moisture contents of 9.98, 17.85, 26.37 and 38.75% w.b. and at the bottom, middle and top regions of stalk. The values of the stalk physical properties increased with increasing moisture content. Their values also increased towards the bottom region. The bending stress and Young modulus in bending decreased with increase in the moisture content and increased towards the top regions. The average bending stress values and Young modulus in bending varied between 47.71 and 25.9 MPa and between 2.52 and 1.28 GPa, respectively. The shearing stress and the specific shearing energy increased with increasing moisture content. Their values also increased towards the bottom region of the stalk. The maximum shear stress and specific shearing energy were found to be 7.66 MPa and 33.05 mJ mm -2 , respectively, and both occurred at the bottom region with the moisture content of 38.75% w.b. K e y w o r d s: safflower stalk, bending stress, Young modulus, shearing stress, specific shearing energ