Shear Strength of Stem and Picking Force for Saffron Flowers

The shear strength and shear energy per unit area, as well as the force and energy required for picking flowers, are important parameters in the design and development of harvesting mechanisms. In this study, shear strength and shear energy per unit area of saffron (Crocus sativus L.) stems were determined at different bevel angles and shear velocities. The force and energy required for picking of saffron flowers were determined as a function of picking velocity and age of plant. The experiments were conducted usinga universal testing machine on samples selected from the farms of Kashmar in eastern Iran. The data was statistically analyzed using a completely randomized design. The results showed that the bevel angle of the cutting blade and shear velocity had a significant effect on shear strength and shear energy per unit stem area, but their interaction was not significant. With an increase in bevel angle from 17° to 24°, the shear strength increased from 0.130 to 0.190 MPa and shear energy per stem area increased from 0.305 to 0.443 mJ/mm2. Increasing shear velocity from 20 to 200 mm/min decreased the average shear strength significantly from 0.179 to 0.158 MPa and shear energy per stem area significantly from 0.467 to 0.340 mJ/mm2. Further increase in shear velocity (from 200 to 500 mm/min) did not decrease shear strength andshear energy significantly. Thus, the cutting blade at a bevel angle of 17° and shear velocity of 200 mm/min is recommended for cutting saffron stems. The results showed that increasing picking velocity from 50 to 500 mm/min increased the average picking force, tensile strength and energy per unit area from 0.339 to 0.459 N, 0.169 to 0.229 MPa and 0.473 to 1.914 mJ/mm2, respectively. The age of the plants had no significant effect on picking force and energy and tensile strength. The data gathered can be useful for the design and development of saffron harvesting mechanisms.