Research On The Discrete Element Modeling Method Of Corn Stalk's Mechanical Characteristics

As a kind of important biomass resources,people gradually pay attention to the corn straw in the resource shortage economy era.Because of the corn straw's complicated internal structure,so as to it has unique differences and different mechanical properties,all of these will directly affect its use.It can provide the basis of theoretical basis on its depth comprehensive utilization and the designing of pretreatment processing machinery by studying the mechanical properties of various components and their differences,establishing the corresponding mechanical model,and discussing the change law of load displacement under external loading.For the relatively difficult problems of the corn straw's mechanical characteristics theoretical analysis and mathematical modeling,the corn straw's discrete element mechanics model was established on the basis of discrete element method in the study of biological physical and mechanical characteristics of corn straws.The corn straw's discrete element mechanical model includes: the shear,tensile mechanical properties of discrete element model of the corn stalk's skin and inside part;the compression,bending mechanical properties of discrete element model of the whole corn stalk stem and the discrete element model of baling mechanical properties of corn stalk collection and so on.Centre on the corn straw's discrete element mechanics model,the corn stalk's physical and mechanical properties were studied in this paper.The main research results as follows:(1)The basic material properties parameters of corn stalk are tested.The average diameter of corn stalks is 16.14±4.05 mm,the average cortical thickness of corn stalks is 0.9 mm,the average density of corn stalk's scarfskin,inner and whole stem is respectively 1.12?0.66 and1g/cm3;At the same time,the corn straw stalk fiber cross section size is 0.15 mm by using image processing methods;the moisture content of fresh corn stalk is 80% and the moisture content of air drying corn stalk is 8% measured by the drying method.(2)The discrete element model on the axial shear mechanical property of the corn stalk rind was set up in this paper and the axial shear test simulation were conducted.The resultsshowed that the average shear strength of the skin t was 3.00 MPa,and the average elastic modulus was 0.23 GPa.Axial rind shear strength and elastic modulus decreased with internode position,but the moisture content and variety had no impact on mechanical properties.The simulation results show that the mechanical properties of the discrete element model on the rind axial shear after load was consistent with the actual test mechanical properties;force-displacement curve in the damaging process of simulation sample was consistent with the results in the laboratory;at the same time,the discrete element model parameters between the vascular bundles were obtained,s-bond and kn were 0.14-0.32 N and1×106-1.2×107 N·m-1 respectively.(3)The tensile mechanical properties of discrete element model of corn stalk rind and inner pith were established.The tensile test and discrete element simulation were conducted about the corn stalk's rind and inner pith.The results showed that the straw rind tensile had the characteristics of the plastic material.In fresh status,the tensile strength was 131.1?48MPa and modulus of elasticity was 22.93 ? 13GPa;while in the air-dry condition,the tensile strength was 113.42?40MPa and modulus of elasticity was 15.71?6GPa.In addition,the inner of corn stalk had the characteristics of brittle material.In fresh state,the tensile strength was1.09?0.27 MPa and modulus of elasticity was 0.06?0.02GPa;while in the air-dry condition,the tensile strength was0.86?0.67 MPa and modulus of elasticity was 0.12?0.07 GPa.Besides,the corn stalk's tensile strength and modulus of elasticity decreased with internode position but increased with increasing moisture content;at the same time,the tensile strength was affected by varieties but the tensile elastic modulus was not affected by varieties.For the inner pith of corn stalk,the tensile strength of the fresh state is greater than the air-dry stalk and the tensile modulus of elasticity of ari-dry stralk is greater than the fresh state;and the internode position and variety would be no obvious effect on the tensile strength and elastic modulus.The discrete element model simulation results show that discrete element model of axial tensile mechanical characteristic curve of corn stalk's skin and inside organization and phenomenon of destruction would be similar to the measured characteristics;the axial discrete element parameters of the skin and inner pith of corn stalk were obtained.(4)The radial compression mechanical properties discrete element model of a whole corn stalk(skin and inner)was established and the radial compression test and discrete element simulation were conducted about a whole corn stalk.The simulation results showed that the virtual load-displacement curve including the elastic stage,failure and strengthening phase,and analyzing the virtual compression failure phenomena and the microscopic mechanical response during the process of compression;the experimental results showed that the average compressive strength and elastic modulus were 0.26 MPa and 279.27 MPa.The radial compressive strength increased with the increase of moisture content and the radial compressive strength with nodal position was greater than without nodal position;the radial compression elastic modulus decreased with the increase of moisture content and the radial compression elastic modulus with nodal position was greater than without nodal position.Comparing test results with simulation results,the discrete element model matched with the actual material and the combined with internal mechanism of the corn stalk was gotten through the model analysis during stress.(5)The bending mechanical properties of discrete element model of the whole corn stalk pole was established and the bending test and discrete element simulation were conducted about a whole corn stalk.The experimental results showed that the average bending strength and the elasticity modulus were 6.66 MPa and 46.14 MPa and the average bending strength and the elasticity modulus increased with the decrease of moisture content;the average bending strength and the elasticity modulus of the air drying corn stalk increased with the rising of internode position.The simulation results showed that the bending mechanical characteristic curve and the bending stress map were similar to the test results and the internal structure change of the corn stalk bending failure was obtained by model analysis.(6)The discrete element model of the bundling mechanical characteristics of the corn stalk was established and the experimental testing results and the virtual bundling were conducted about the corn stalks bundle.The degree of baling tightness and baling density was the quadratic curve relationship from the baling test;the rope tension of straw baling and the strapping diameter was Index function relation.The virtual bundling simulation results showed that the virtual baling mechanics performance curve was similar to the test curve;the virtual baling simulated load and the radius of round bundle was Index function relation.The same trend between the test results and the model simulation showed that the discrete element model could be used in the material mechanical properties simulation during the design of corn stalk processing machinery.