Research On The Compression Mechanism And Optimisation Of Compression Processing Parameters Of Chopped Corn Stalk Based On The Discrete Element Method

Corn stalk is an important biomass resource,which can be used for feed,fuel and fertilizer.In order to facilitate storage and subsequent use,the straw needs to be crushed and compressed.Straw compression is a complex process,and it is difficult to intuitively analyze the changes in mechanical properties caused by local changes of straw during the compression process through bench tests,and the rheological mechanism of compression cannot be accurately proved.The numerical simulation of discrete element method（DEM）shows unique advantages in developing agricultural machinery and equipment,revealing the interaction mechanism between agricultural machinery and granular materials,and provides new ideas and methods for studying the evolution of force chains in the compression process of broken corn stalk.Therefore,this paper conducts the determination of the basic parameters required for the simulation compression process of chopped corn stalk,establishes a discrete element model of chopped corn stalk,and uses the Edinburgh Elasto-Plastic Adhesion（EEPA）contact model to calibrate the parameters required for the straw DEM simulation.The discrete element method is used to simulate and analyze the straw compression molding mechanism,and then optimize the compression process parameters.The main research results are as follows:（1）Determination of physical and mechanical parameters and contact parameters of chopped stalks.The lengths of chopped corn stalks are 6 types（≤20 mm,20～40 mm,40～60 mm,60～80 mm,80～100 mm,100～120 mm）,and the mass proportions of various stalks are 8.4%,18.5%,26.6%,20.7%,17.6%,8.2%;the average density is about 0.42 g/cm³,the elastic modulus and shear modulus are 14.22 MPa and 5.08 MPa,respectively;the static friction coefficients between straw and steel plate,straw and straw are 0.53,0.3～0.9,respectively,straw and steel plate,straw The collision recovery coefficients between stalks and stalks were 0.21 and 0.1-0.5,respectively.（2）Calibration of simulation parameters in the compression process of chopped corn straw.The static friction coefficient（X₁）,recovery coefficient（X₃）,surface energy（X₄）and contact plasticity ratio（X₅）between straw particles have obvious effects on the compression displacement through the screening of Plackett-Burman test.The order of influence is X₅>X₁>X₃>X₄;the regression model between the compression displacement and the four parameters are established based on the Box-Behnken test,and the optimal combination of the four parameters are obtained by the multi-objective optimization method as follows:X₁=0.63,X₃=0.13,X₄=5.8 J,X₅=0.56.The two-sample t-test was carried out on the simulated compression test data and the physical compression test data,and the results showed that there was no obvious difference between the two groups of test data,which further verified the reliability and authenticity of the simulated compression test.（3）Research on the compressor theory of chopped corn stalks.By analyzing the influence of the feeding amount on the stress-strain during the compression process,it is concluded that when the compression conditions are consistent and the strain is the same,the stress is positively correlated with the feeding amount,that is,the larger the feeding amount,the greater the stress;under the same feeding amount,the stress growth rate gradually increases from slow to faster.By analyzing the influence of the cross-section size on the force-strain,it is concluded that when the compression conditions are consistent and the strain is the same,the stress is negatively correlated with the cross-section size,that is,the smaller the cross-section size,the greater the stress;under the same cross-section size,the stress growth rate also gradually increases from slow to faster.By analyzing the influence of the feed amount on the pressure-compression density in the simulated compression process,it is concluded that when the compression conditions are consistent and the pressure is the same,the compression density is negatively correlated with the feed amount,that is,the larger the feed amount,the smaller the compression density;under the same feed amount,the growth rate of compression density gradually slows down from fast.By analyzing the influence of section size on pressure-compression density,it is concluded that when the compression conditions are consistent and the pressure is the same,the compression density is positively correlated with the section size,that is,the larger the section size,the greater the compression density;under the same section size,the growth rate of compression density also gradually slows down from fast.The mathematical models of stress-strain and pressure-compression density are established by using the power exponential function as follows:σ=aε^b+c、ρ=a F^b+c.（4）Research on optimization of compression process parameters of chopped corn stalks.Taking the feeding amount,compressive section size and maximum compressive stress as the test factors,and compressive density and specific energy consumption as the evaluation indicators,a second-order response surface model between the factors and the indicators was established based on the response surface method,and the factors were analyzed.The influence of the index is obtained through parameter optimization.The maximum compressive stress is 4 kg,the maximum compressive stress is 378 mm×400 mm,the maximum compressive stress is 77 k Pa,the maximum compressive density is 141.32 kg/m³,and the compression ratio The minimum energy consumption is 274.55 J/kg.Using this parameter combination to carry out the bench verification test,the compressive density and specific energy consumption values are 147.41 kg/m³ and 280.15J/kg,respectively,and the relative errors with the predicted value are 4.3%and 2.04%,respectively,none of which exceed 5%.It shows that the second-order response model of compression density and specific energy consumption is relatively reliable.