Experimental Study On The Mechanical Properties Of Millet And Buckwheat Kernels And Discrete Element Simulation Analysis

Millet and buckwheat were defined as small grain grains with small grain size and small planting area.In mechanical equipment such as seeder and combine harvester,grain will be damaged and broken by external load of related parts.Therefore,it is necessary to master the mechanical characteristics of grain groups of millet and buckwheat under external load.Based on the actual situation of millet and buckwheat seeds in the process of mechanized sowing,harvesting and transportation,the basic physical parameters and grain group mechanical characteristics of millet and buckwheat seeds were studied.(1)First,the basic physical properties parameters of millet and buckwheat grains were measured,including the external dimensions,thousand-grain weight,grain density,bulk density,recovery coefficient,etc.The results of the data show that the moisture content has a very significant effect on the grain size,thousand kernel weight,and bulk density(p<0.05),while the moisture content has no significant effect on the collision recovery coefficient.The millet grains are ellipsoidal,and the shape of the millet varieties varies little.There are two types of buckwheat: tartary buckwheat and sweet buckwheat.The appearance of different types of buckwheat is quite different.The outer surface of tartary buckwheat is rough,but the outer surface of sweet buckwheat is relatively smooth and smooth.(2)Through the self-made test equipment,the grain characteristics(sliding friction coefficient,angle of repose)of different millet and buckwheat grain groups with different water content and different varieties were tested.The test results show that: the sliding friction coefficient of the Jigu and Qinzhou yellow grain groups is between 0.182 and 0.203;the sliding friction coefficient of the Heifeng No.1 buckwheat grain group is between 0.367 and 0.533;the sliding of the Yuba No.4 buckwheat grain group The coefficient of friction is between 0.332 and 0.468.The range of repose angle of millet grain group is 24.98°~25.85°;the range of repose angle of buckwheat grain group is 27.98°~35.73°.Using SAS software to carry out a significant analysis of the test results,it is concluded that the moisture content has a very significant effect on the sliding friction coefficient and angle of repose of millet and buckwheat grain groups(p<0.05).The higher the water content,the greater the sliding friction coefficient and angle of repose of the grain group.For buckwheat,the sliding friction coefficient and angle of repose of different varieties of grain groups are obviously different.Under the same water content,the sliding friction coefficient and angle of repose of Heifeng No.1 are greater than that of Yuqiao No.4.(3)When the millet grain group is subjected to different static and dynamic loads,the damage degree of the grain can be clearly observed using the stereo microscope,and the damage rate of the millet grain group can be statistically analyzed.When the moisture content of the millet grain group was 15.2% and the static load was 4000 N,the damage rate of the millet grain group was the highest,reaching 76.67%.When the drop height of the weight is 100 cm,the breakage rate of the millet grain group is the highest,reaching87.78%.At the same time,the shell of the millet was severely damaged,and the seeds were also broken.It can be observed under the microscope that each damaged millet grain starts with a crack starting from the sharp crown of the grain.It shows that the sharp crown of millet grain has poor performance to withstand external force.(4)The discrete element simulation software EDEM was used to construct the grain model of millet and buckwheat grains,and the relevant model parameters were determined by referring to relevant literature and testing.Simulate the angle of repose formed by the grain group when the millet and buckwheat grain groups are naturally piled up and the sliding friction angle when the grain group just slides relative to each other on the slope.By comparing simulation and actual test results,the error of millet grain group is about5%,while the error of buckwheat grain group is about 10%.It shows that it is feasible to use the software EDEM to simulate the mechanical properties related to millet and buckwheat grains.For buckwheat grains,it is necessary to establish a simulation model more in line with its shape and characteristics.