Abstract:
Abstract: The corn threshing without cob fracture can greatly simplify cleaning link. The rupture of corn ear can directly affect the effect of the core threshing without cob fracture. In order to study the anti-pressing properties and rupture laws of corn ear and explore the effect of water content on anti-pressing properties, the static compress experiments were carried out on the electronic universal testing machine. The analysis of the biological characteristics of corn ear showed that the wooden ring form had compact structure and its strength was big. And the core pulp and the glume shell had loose structure and small strength. The corn varieties selected by experiment were Zhongdan 868 and Zhenghuangnuo No. 2. The water content of each variety was treated as 5 criteria. Four tests were done for each test level. The corn variety and the water content of corn cob were used as test factors. The maximum load and the maximum stress of corn ear were used as the test indices. The experimental data were analyzed by MATLAB software and the function relation between water content of corn cob and test indices was obtained. The relationship between water content of corn cob and fracture strain of corn ear indicated that the plasticity of corn ear was firstly enhanced and then declined with the increase of the water content of corn cob. Through the analysis of the fitting curves between the water content of corn cob and the test indices, it was known that the water content of corn cob had a tremendous effect on the anti-pressing properties of corn ear. When the water content was below 13%, with the decrease of water content, the plasticity of corn ear decreased and the compressive strength increased slowly, which resulted in a slow enhancement of the anti-pressing ability of corn ear. When the range of water content was 13%-25%, with the increase of water content, the plasticity and the compressive strength of corn ear both increased, which resulted in the enhancement of the anti-pressing ability. When the water content was higher than 25%, the plasticity of corn ear was weakened and the compressive strength decreased with the increase of water content, which resulted in a sharp decline of the anti-pressing ability. To observe the internal fracture process of corn ear, samples were cut in radial direction and then the cut samples were put on the test bench to do experiment. Using the radial section of corn ear as the observation window, the whole process of corn ear compression test was recorded by camera. Through the analysis of the photos of corn ear in the process of compression, it was known that the core pulp firstly ruptured and the crack was extended in vertical direction. Then the crack gradually approached to the wooden ring form. Finally, the wooden ring form ruptured and corn ear presented obvious deformation. The analysis of the strain-stress curves indicated that stress gradually increased and corn ear showed plastic deformation with the increase of strain. Stress began to decline after peak. Curves showed jagged wave and the yield stage was entered. The rupture of the wooden ring form led to the decline of stress curves. So the wooden ring form was the main anti-pressing part of corn ear. In the process of compression, corn ear showed the phenomenon of grains falling. The radial balance equations of grain were established by force analysis. Analysis indicated that pressure would be transmitted to the grains in the circumferential distribution. The increase of the pressure between grains would destroy the radial force balance of grains, resulting in the fracture of the carpopodium. Test results showed that the anti-pressing ability of corn ear was the strongest when the water content of corn cob was 25%, and this water content of corn cob was the most suitable for the corn threshing without cob fracture. The rupture of corn ear was a gradual rupture process by the inside-out. Applying pressure less than 610 N to corn ear could not only prevent the fracture of corn ear but facilitate threshing. The research results can provide data reference and theoretical support for the further research of the corn threshing without cob fracture.