Study of the Physical and Mechanical Properties of Edible Sunflower at Harvest

The optimized design of key components in harvesting equipment is significantly impeded by the significant grain loss from the header and high energy consumption during stalk cutting that result from the lack of physical and mechanical parameters regarding the plant-flower head system during the mechanized harvesting of edible sunflowers. To furnish the design of mechanized harvesting equipment for palatable sunflowers with theoretical support and foundational data, physical parameters measured included geometrical properties, critical bending angle, coefficient of static friction, moisture content, and head seed collision loss rate. Mechanical parameters—radial elastic modulus, shear modulus, and shear strength—were obtained from stalk compression and shear tests using a universal testing machine. Stem-head detachment force was quantified with a universal testing machine fitted with bespoke fixtures, and orthogonal experiments were conducted with tensile speed, head-picking plate spacing, and tensile angle as factors to establish the significance hierarchy and optimal configuration. Considerable heterogeneity was observed: mean plant height, head diameter, and head thickness were (1733 ± 153) mm, (275 ± 28) mm, and (93 ± 19) mm, respectively. The critical bending angle decreased with height, whereas stalk moisture content increased from base to apex. Mean stalk and head moisture contents were 65% and 61.4%. The coefficient of static friction varied from 0.24 to 0.63 depending on contact material. A critical impact velocity of 2–3 m/s induced mechanical damage and seed cracking. The stalk radial elastic modulus was (1.12 ± 0.27) MPa; shear modulus and shear strength increased with decreasing sampling height, with basal stalks exhibiting a mean shear modulus of 2.47 MPa and shear strength of 1.87 MPa. Sampling position significantly influenced shear modulus (p < 0.05). The factor significance for stem-head detachment force was head-picking plate spacing > tensile angle > tensile speed. The optimal combination (tensile speed 500 mm/min, head-picking plate spacing 50 mm, tensile angle 10°) yielded a detachment force of (202.3 ± 9.5) N, with a relative error below 5% compared to prior detachment force measurements, confirming the reliability of the optimised results. These data provide essential foundations for developing stalk cutting, head inserting, and combine harvesting equipment.