玉米秸秆揉丝破碎过程力学特性仿真与试验.

As a large agricultural country, China has abundant straw resources, and the annual output of corn stalks is 3 billion tons. Corn straw could be used as silage after mechanized processing, it could effectively alleviate the current shortage problem of animal feed. At present, the research on kneading and crushing of corn straw mainly focused on physical experiment, but less on numerical simulation. Therefore, the lack of effective numerical simulation method in the crushing process of corn straw and the improvement efficiency for the structure of processing equipment is reduced to some extent. Based on the above background, in this paper, a discrete element model for bimodal distribution of corn straw was established based on discrete element method, which was originally applied to the field of geotechnical mechanics. This process included setting particle size, filling geometric model, obtaining particle group coordinate information and so on. All of the numerical simulations were carried out in EDEM 2018 version, and users were allowed to customize the settings. Then the parameters calibration for the bonded particle contact model of corn straw was carried out that combined with physical experiment and virtual experiment. The mechanical parameters were obtained through compressing and shearing experiments of corn stalk samples. This parameter could provide basis for theoretical calculation of bonded particle model parameters of corn stalks. The mechanical properties of bonded particle model were determined by 5 parameters: normal stiffness coefficient, tangential stiffness coefficient, normal critical stress, shear critical stress and bonded radius which could be obtained through theoretical formula calculation. In the virtual experiment, the corn stalk model was subjected to axial compression experiment and radial shear experiment, respectively. The final BPM (bonded particle model) parameters were determined by the phenomenological simulation method which was compared physical experiment and virtual experiment. Finally, the discrete element model of corn straw was simulated and verified by physical experiment. This process involved the kneading and crushing simulation of corn straw model, classifying the types of materials and weighing the mass of materials, and using API plug-in to realize particle replacement and adding bonded particle model in the simulation process. After the simulation was completed, the change of bonded number and the shape classification of broken materials were analyzed. The whole research results showed that the maximum critical loads were 2,260 N and 110 N, respectively when the straw was compressed and sheared at a loading rate of 5 mm/min; After calibrating the parameters of bonded particle model, it was found that the normal stiffness coefficient, tangential stiffness coefficient, critical normal stress, critical tangential stress and bonded radius were 9.60×106 N/m, 6.80×106 N/m, 8.72 MPa, 7.5 MPa and 2 mm, respectively. At this time, the mechanical properties of the discrete element model were close to the harvested corn straw that had a moisture content of 87.8%. After the simulation, material could be divided into four types: short type, standard type, long type and incomplete crushing type. At the same time, the simulation mass of 4 materials were 5.2, 5.8, 8.2 and 8 g, respectively. After the physical experiment, the mass of different types of materials were respectively 4.8, 5.3, 7.6 and 9.1 g. The deviation of the mass for different materials were 8.3%, 9.4%, 7.8% and 7.7%, respectively. The mass deviation for different types of materials between the physical experiment and virtual experiment was kept within 10%. This research could not only prove that it was feasible to establish corn straw model by discrete element method and simulate the kneading and crushing process, but also provide guidance for kneading other straws. [ABSTRACT FROM AUTHOR]