Studies On Mechanism Of Corn Threshing Damage And Threshing Device For Corn Grain Harvest

Corn is the largest food crop in China,harvesting is the most labor-intensive procedure of its production process.Corn grain harvest,which means picking,peeling,threshing and obtaining corn kernels directly at the time during its field harvesting,its advantages of labor and time saving have made it an inevitable trend.However,mechanical damage such as grain breakage and stress cracking is readily caused when the corn is threshed,which seriously affects the quality of the corn.Therefore,to understand the mechanism of threshing damage and design threshing devices for grain harvest,in this stuy,the mechanical properties of corn kernel tissue were evaluated,corn kernel and its tissues models were reconstructed,based on which threshing impact damage were simulated and predicted.A threshing device for corn grain harvest was designed,made and tested.The main conclusions are as follows:(1)Mechanical properties of three main corn tissues(horny endosperm,floury endosperm and germ)in three varieties(Jinyu818,Zhengdan958 and Dafeng30)with five stages of moisture contents(11.78?34.73%w.b.)were evaluated.Results showed that there was no or weak significant difference between varieties,while significant moisture and tissue material effects were observed.Higher rupture force,ultimate strength,rupture energy,modulus of elastic,bioyeiled force,bioyeiled strength values were obtained for horny endosperm of maize kernel at lower stage of moisture contents comparing with floury endosperm and germ at higher moisture contents,while for rupture deformation values were obtained as higher at inner layer with higher moisture content.Microstructral observation showed that the tissues' mechanical properties are closely related to its microstructure.(2)? Simulation results showed that the impact process can be roughly divided into three stages:pre-impact,impacting and post-impact.During the impact,the largest Von mises stress was found at the center of the contact area,and the stress spreaded along the surround and gradually decreased.The kinetic energy and the internal energy were transformed into each other,and part of the initial kinetic energy of the grain was converted into interfacial slip energy.Kernel damage occured during the impact,and the damaged area might be the stress concentration area of the contact.In the simulation,the hourglass energy only accounted for 4.67%of the total energy,which verified the reliability of the finite element model.? Corn kernel model based on image and NURBS loft reconstruction technology had high precision.The finite element analysis of threshing impact damage based on this model could predict the threshing damage of the tissues.The crack was firstly occurred in the floury endosperm,and then developed into the horny endosperm as the load increased,and the last damaged tissue was the germ.By establishing linear regression models,the critical damage velocities of horny endosperm,floury endosperm and germ were predicted as 13.58,9.66 and 17.23 m/s at a moisture content of 11.78%,respectively,and 15.92,11.29 and 18.44 m/s at a moisture content of 17.64%,respectively.At 23.45%,they were 19.50,13.80 and 21.52 m/s,respectively,21.64,14.37 and 22.74 m/s at a moisture content of 29,31%and 23,98,16.72 and 24.40 m/s at a mositure content of 34.73%,respectively.(3)? A threshing device for corn grain harvest was designed and made.3D virtual prototypes were drawn using UG NX 8.5 software and the key components were drawn using CAD software,based on which a test bench was made.? Threshing test was carried out based on the corn grain harvest threshing test bench,the effects of threshing gap,drum rotation speed,moisture content and feed amount on corn threshing performance were studied.Drum rotation speed,threshing gap,feeding amount and moisture content were slelected as the influencing factors,and impurity rate,damage rate and loss rate were responses,orthogonal test was carried out and experimental data was analyzed.Regression models for responses were established.Multi-objective optimization was used to optimize the parameters,the combination of the optimized parameters were verificated using the test bench.This study not only provides a new method and device for the threshing process of corn grain harvest,but also contributes to improve the key technologies of corn kernel harvesting and harvesting machinery in China.