Influence of different corn ear position and orientation and water content on fracture mechanics of corn peduncle

There are many problems exsist in the harvesting process of corn head. Firstly, kernels are likely to shed and broken because of the collision and friction between corn head and corn ears. Secondly, the working principle of the existing corn head is to snap corn ears by stretching, which needs a large amount of power consumption. Thirdly, most husks are remained around the corn ears, as the fracture point are mostly located at the growing point of the peduncle, which aggravates the difficulty of dehusking of corn ears and cleaning of corn kernels. However, the mentioned problems above could be avoided effectively when people picking corn ears with their two hands. People apply bending moment with the loading hand and hold peduncle and stalk together tightly with the supporting hand at the same time. Corn peduncles are subjected to tensile forces by the corn ear and tensile force by the stalk. Besides, a bending moment is applied on the peduncle by corn ear, as corn ear are subjected to lever action by people's hand. A fracture model of corn peduncle was refined in the progress of picking corn ear by people's hands in this research. The fracture behavior of corn peduncle could be altered by changing the position and orientation of corn ears. Through the fracture model, a design idea for corn ear snapping was proposed based on the existing corn heads. It worked with the principle of applying lateral force to corn ear when it got in collision with the deck plates. Researches were made to explore the fracture behavior of peduncle at different position and orientation under a range of moisture content and deflection angle. The test material were corn ears with the kernels moisture contents of 34.8%, 30.2%, 25.1% and 20.3%. The fracture force of peduncles, the stretching amount when peduncle fracture and the removal rate of husks were taken as the test indices. The first series of randomized block experiments were carried out on corn ears fixed with a deflection angle relative to the corn stalk. The deflection angle included six treatment from 0° to 75° with an incremental interval of 15°. The sceond series of randomized block experiments were conducted with the deflection angle of 50° and 55° as data jumped greatly between 45°and 60 °. The results showed that there were critical angles of peduncles with the kernels moisture of 34.8%, 30.2%, 25.1% and 20.3%. The critical angles were 50° to 55°, 50° to 55°, 45° to 50° and 45° to 50° corresponding to the moisture contents above. As the deflection angle of corn ears increased to the critical angle, the average fracture force of peduncles decreased from 717.18, 676.49, 611.23 and 462.86 N to 139.98, 94.70, 97.72 and 90.54 N, with the decreasing ratio of 80%, 86%, 84%, and 80%, corresponding to kernels moisture of 34.8%, 30.2%, 25.1% and 20.3%. Also, the stretching amount when peduncle fracture increased with the ratio of 72%, 70%, 93% and 84%, while the removal rate of husks increased by 41%, 34%, 32% and 36%. The Logistic function was the optimal approximation function for the fitting of fracture force of peduncles and the stretching amount when peduncle fracture, while a cubic functions of one variable was optimal for the removal rate of husks. By analysing the "load-displacement" curves of corn peduncles with the deflection angle of 45° and 60° at the moisture content of 25.1%, it showed that the acute change of data was attributed to the change of peduncle fracture mechanism. When the deflection angle was less than the critical angle, the peduncle fractured instantly after crack formation on the surface. The reason for the formation of crack was tensile stress getting higher than the stress limit. Otherwise, the peduncle fractured slowly after crack formation, with the formation reason of crack was bending normal stress getting higher than the stress limit. As an instructive conclusion, the bionic corn ear snapping device could be implemented by applying lateral force on corn ears to change their position and orientation. This study provides not only theory basis but also support data for the design and improvement of bionic corn snapping mechanism.