Discrete Element Simulation Of Strength And Deformation Characteristics Of Wheat From Triaxial Tests

Grain is related to human survival and development and national economy and people’s livelihood.It is also an important material for China’s strategic reserve.The safe storage of grain is an important guarantee of food security,and the safety and reliability of granary is the basic guarantee of grain safety storage.The mechanical characteristics of grain stored in the granary are the key parameters for the structural design of granary.The conventional triaxial test can simulate the different stress states under various grain storage conditions in the storage bin.The simulation of triaxial test with discrete element method can conveniently analyze the strength and deformation development process of triaxial specimen from the micro perspective,which provides the basis for the mechanism analysis later.In this paper,wheat is selected as the research object,and the ellipsoid model generated by PFC3D is used to simulate wheat particles,and the numerical model of wheat triaxial test with different lateral boundaries is established.The numerical test results are fitted with the indoor triaxial test results to calibrate the meso parameters of the model.On this basis,the stress-strain characteristics and volume strain characteristics of wheat were studied by parameter analysis,and the grain movement trend of triaxial specimen during shear process was analyzed from the micro perspective.The main research contents are as follows:(1)The ellipsoid model of wheat particles was established by using the three-dimensional discrete element software PFC3D,and the three-axis numerical model of the wheat with different lateral boundaries(rigid and flexible membrane boundaries)was established.The mesoscopic parameters of the numerical model are calibrated by the conventional triaxial test.Comparing the numerical results with the results of conventional triaxial tests,it is found that the flexible membrane test can better reproduce the drum deformation characteristics of indoor test samples.The stress softening degree of the stress-strain curve obtained by the flexible membrane test is weaker than that of the rigid membrane test,and its overall trend is more in line with the indoor triaxial test curve.The feasibility and rationality of wheat triaxial test numerical model were verified.(2)Considering different lateral boundary conditions,triaxial tests of wheat under different confining pressures and initial porosity were carried out.the result shows:Under different lateral boundary conditions,the initial elastic modulus and peak strength of wheat increased with the increase of confining pressure.With the increase of initial porosity,the peak strength and initial elastic modulus of wheat decreased.The peak strength and initial elastic modulus of rigid film test were greater than that of flexible film test.In terms of strength parameters,the peak internal friction angle and dilatancy angle decrease with the increase of initial porosity,while the dilatancy angle decreases with the increase of confining pressure.The internal friction angle and dilatancy angle obtained from the rigid boundary numerical test are greater than those from the flexible boundary test.(3)In the numerical model with different lateral boundaries,the force chain diagram,displacement field diagram and velocity field diagram of numerical samples under different confining pressures were analyzed.The coordination number,porosity and vertical stress in the measurement circle at different positions inside the specimen were monitored.At the same time,the movement trend of particles in the specimen with different lateral boundaries is discussed,and the deformation development of the sample was analyzed.