Study On The Physical And Mechanical Properties Of Frozen Maize Grains

Owing to the vast area of maize plantation in the northeast region of China,large amounts of maize are not harvested before early frost occurs because of the short harvesting period.The physical and mechanical properties of frozen maize grains are the bas ic data for the design and improvement of threshing and cleaning device of maize combine harvester.Because of the irregular shape of maize grains,it is difficult to obtain accurate values of some physical and mechanical properties based on existing measuring methods.With the development of computer simulation technology,more and more scholars at home and abroad use numerical simulation method to study maize threshing and cleaning.The accuracy of physical and mechanical propertie s of grains is one of the main reasons that affect the simulation results.In this paper,some physical and mechanical properties of frozen maize grains were studied with the project of National Natural Science Foundation of China(51475090),Heilongjiang Science Foundation(E2017004),the National Key Research and Development Program(2018YFD0300103)and the Key Laboratory of Heilongjiang Province for Modern Agricultural Equipment in Northern Cold Areas.The main research contents are as follows:(1)The moisture content,density,1000 grains weight and shape size of Jidan No.1 frozen maize grains were measured.According to the shapes of frozen maize grains,the frozen maize grains were divided into round,quadrate and wedged grains.The outlines of the grain and embryo were obtained by image processing and fitted into different functions.Three-dimensional models were established by using the built-in functions available in Solid Works software.The grain centroid was determined based on the densities of different parts of the frozen maize grain by using Solid Works software.(2)The coefficients of static friction of different shapes of frozen maize grains were determined based on the platform for coefficient of static friction testing.Using MATLAB image processing technology,the accumulation angle of frozen corn grain on galvanized sheet and grain layer was extracted.The hardness and elastic modulus of different parts of th e frozen maize grain were determined by texture analyzer.(3)The existing formulas of coefficient of restitution are sorted out,the calculation models of coefficient of restitution were determined by using a function derived based on the grain velocities in the direction of the contact force.(4)The existing platform for testing the coefficient of restitution will make particles bound by external force during collision.An automatic control platform was designed and constructed to realize the particle-particle collision without external interference and measure the coefficient of restitution.The regulating angle mechanism was used to adjust the impact angle.The air pressure at the outlet of conduit from the air pump was controlled by the throttle.The grains can be controlled by air suction.The design of the glass track can realize the precise collision between particles and improve the collision probability.The grain mechanical behavior of the frozen maize grain was traced by using a high-speed digital camera.Then the velocity of grain after collision could be obtained.(5)The coefficients of restitution of particle-wall and particle-particle collision were determined based on the platform for testing the coefficient of restitution.The effects of the moisture content,impact velocity,impact angle and impact position on the coefficient of restitution of the particle-wall and particle-particle collision were investigated.The moisture content of the frozen maize grains has slight effect on the coefficient of restitution of particle-wall collision and particle-particle collision as the moisture content increases from 15.7% to 18.6%.The coefficients of restitution of the particle-wall and particle-particle collision decrease as the impact velocity increases from 0.9 m/s to 1.9 m/s.The coefficient of restitution of the particle-wall collision decreases as the impact angle increases from 35 ° to 60°.The coefficient of restitution of the particle-particle collision decreases as the impact angle increases from 35° to 40°.However,the coefficient of restitution increases as the impact angle increases from 40 ° to 60°.When the impact angle and impact velocity are constant,the coefficient of restitution of the particle-particle collision decreases with an increases in the rotation angle of the grain.The results of this study can lay a foundation for the design and improvement of threshing and cleaning device of frozen maize and the simulation study of discrete element movement of frozen maize grains,and provide a reference for the measurement coefficient of restitution,which is the basic physical characteristic parameter of irregular shape in agricultural materials.