Mechanical properties of sorghum stalk in relation to quasi-static deformation

Shear, compression and bending properties of sorghum (S. bicolor) stalks were determined at the forage stage and seed stage using a universal testing machine. The stalk specimens were deformed in a quasi-static process using flat knives with 30-70 degrees bevel angles at a rate of loading from 10 to 100 mm/min. The maximum shear strength increased from 3.74 to 8.18 MPa at the forage stage and from 4.68 to 9.02 MPa at the seed stage when the bevel angle was increased from 30 to 70 degrees at a 10 mm/min rate of loading. As the rate of loading was increased from 10 to 100 mm/min at a 30 degrees knife bevel angle, the maximum shear strength decreased from 3.74 to 1.94 MPa at the forage stage and from 4.68 to 2.20 MPa at the seed stage. The specific cutting energy increased from 34.1 to 101.1 mJ/mm(2) at the forage stage and from 36.5 to 142.7 mJ/mm(2) at the seed stage when the bevel angle was increased from 30 to 70 degrees at a 10 mm/min rate of loading. As the quasi-static rate of loading was increased from 10 to 100 mm/min with a 30 degrees knife bevel angle, the specific cutting energy requirement decreased from 34.1 to 12.2 mJ/mm(2) at the forage stage and from 36.5 to 17.6 mJ/mm(2) at the seed stage. The compressive strength and the energy absorbed in compression increased as the bevel angle was increased and both decreased as the rate of loading was increased from 10 to 100 mm/min. The bending strength and the energy absorbed in bending, however, did not vary significantly with the rate of loading and knife bevel angle. (C) 1999 Silsoe Research Institute.