| The milling process of sugarcane is a very complicated non-linear process,which involves the elastic-plastic deformation of sugarcane,the solid-liquid coupling between sugarcane fibers and juice,and the friction among pressing rollers and sugarcane fibers.Because of the complexity of the process,these problems have not been effectively solved by the existing theory and methods of sugarcane pressing.At present,Chinese sugar industry is facing tremendous pressure of upgrading and transformation,but the design skill for the corresponding equipment is still poor.Therefore,sugarcane was employed as research object,starting from the mechanical properties of sugarcane,and using material performance experiments,mathematical models and simulation experiments,sugarcane constitutive model,elastic-plastic coupling model,solid-liquid coupling model,three-dimensional simulation method of sugarcane pressing and optimization of the design method of sugarcane roller structure were investigated.These works can clarify the above problems and improve the existing theory and method of sugarcane pressing and are very important for understanding sugarcane pressing process,improving the pressing technology and optimizing the design of the pressing roller.Also,these can help enterprises to improve their technology and achieve good economic and social benefitsThe parameters of sugarcane are the basis for accurately establishing the constitutive model of sugarcane.Because the parameters change constantly during the process of sugarcane pressing,scholars generally used the average values of material parameters to make models,which were inaccurate.Therefore,the stress and compression ratio curves of sugarcane were obtained by uniaxial compression test.The Young’s modulus,compression index and swelling index of sugarcane fiber were gotten by loading-unloading test.The relationship between confining pressure and Poisson’s ratio of sugarcane was gained using consolidated-drained test.The shear properties of sugarcane were obtained by direct shear test.The experimental analysis shows that the axial and lateral compression laws are similar in compression process.First,sugarcane undergoes elastic deformation,then plastic deformation,and then plastic hardening,but ultimately is not yield.During the loading-unloading process,the sugarcane changed from over-consolidated to under-consolidated state,had poor rebound resilience and good plasticity.The volume strain of sugarcane changed greatly under hydrostatic pressure.The shear failure of sugarcane obeys Mohr-Coulomb law.The elastic-plastic coupling of sugarcane and solid-liquid coupling of sugarcane fiber and juice is the key of the process of sugarcane juice extractionIn the paper,the constitutive model of sugarcane was expressed by elastic and plastic characteristics.The plastic characteristics are mainly similar to the critical state of clay.The modified Cam Clay model and the modified DPC model of clay were analyzed and compared,and the constitutive model of sugarcane was established.The evolution of void ratio with Young’s modulus,Poisson’s ratio and Cap parameter of sugarcane respectively,as well as the evolution of hydrostatic yield pressure and plastic volumetric strain were fitted using multivariate spline interpolation,and the elastic-plastic model of sugarcane was established.It was found that the Young’s modulus and Poisson’s ratio of sugarcane decreased with increasing void ratio,and the decreasing trend became more obvious.The smaller the cap parameter is,the larger the void ratio is,and the hydrostatic yield pressure increases with increasing plastic volume strain.A solid-liquid coupling model of sugarcane was established by Biot effective stress principle.Quasi-static and dynamic compression experiments of sugarcane were simulated by Abaqus software,and verified by experiments.The simulation results show that the simulation results of the non-elastic-plastic coupling model are smaller than those of the compression experiment,and the simulation results of the elastic-plastic coupling model are close to those of the quasi-static compression experiment at a larger compression ratio,which indicates that the results of the quasi-static compression experiment can be more accurately predicted;the axial pressure of the dynamic compression experiment is much larger than that of the quasi-static compression experiment at a larger compression ratio.The axial forces from dynamic compression experiments are similar to those from the simulation experiments,especially when the compression ratio is between 1.5 and 3.5,the error is less than 5%.It shows that the solid-liquid coupling model of sugarcane fiber can effectively predict the load of sugarcane juice extraction.The coupling model is suitable for the simulation of sugarcane pressing and can well reflect the mechanical phenomena of sugarcane fiber and fluid during sugarcane pressing process.Using the dynamic compression simulation experiment of 500mm/min.the stress distribution rule and the relationship between the stress and the compression ratio of sugarcane fiber were foundSugarcane juice discharged from the front roller are more than 60%of the total,so it is particularly important to study the stress variation of sugarcane material in the area from the front and back rollers to the neutral plane.Based on the solid-liquid coupling model ofsugarcane fiber with evolutionary parameters,the process of juice extraction by two-roll pressing was simulated by three dimensional modeling and finite element method.The laws of stress-strain,juice flow and pore pressure of sugarcane fiber,and the effects of compression ratio,surface speed of rollers,blanket thickness and diameter of rollers on roll load and torque were analyzedIn the milling process of sugarcane,how to ensure low energy consumption and high extraction rate has always been a hot issue in sugar industry,so the structure design of sugarcane pressing roller is particularly significant.In this paper,the advantages and disadvantages of traditional method and finite element method for design of sugarcane pressing roller are analyzed and compared.The advantages and disadvantages of traditional method and finite element method for the design of sugarcane press roll weare analyzed and compared.The uniform design method is used to design the experiment of four-factor,i.e.tooth spacing,tooth angle,tooth width and radius,and eleven-level.The sample space for the structural parameters of the pressing roller,the maximum pore pressure of sugarcane and roll torque were acquired by using three-dimensional simulation of sugarcane pressing process.The R2FI model in response surface methodology was employed to establish the mathematical regression model between the strmctural parameters of the pressing roller and the maximum pore pressure of sugarcane and roll torque.By saliency analysis of the model and parameters,it was found that the model had good predictive ability and the effects of the interaction between tooth angle and tooth width on the maximum pore pressure of sugarcane and roll torque were investigate.By many iterations,the muti-objective particle swarm optimization algorithm,which used the fitness function ofthe approximate model by response surface method and the boundary of sample space of the range of structural parameters,was employed to calculate multiple optimal combinations among the structure parameters of the pressing roller,roll torque and the maximum pore pressure of sugarcane.The results were examined by verification tests,and the relative errors of the results from the muti-objective particle swarm optimization algorithm were very small.The design method can be used to optimize the structure of the pressing roller and to predict the related parameters such as roll torque and the maximum pore pressure. |
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