Different Scale Compression Mechanics Of Lingwu Long Jujube Based On Finite Element Method Model Establishment And Analysis

As a unique fresh food jujube variety in Lingwu District,Lingwu Long Jujube has attractive color,unique taste,sweet taste,crispy and refreshing pulp,and contains rich nutrients,known as"king of fruits",and is favored by consumers.With the gradual expansion of industry scale and market,brand influence is increasing,Lingwu Long Jujube plays an important role in the development of Ningxia Agricultural Economy and farmers’ income.However,due to the high water content of jujube,it is easy to lose water and shrink after harvest,soften the pulp,browning,rot and liquification,which leads to the short period of fresh sale,and thus the centralized listing is in a hurry to sell.The quality of jujube is crisp and tender,which is easy to be damaged by machinery in the process of picking,transportation,processing and storage,and difficult to be sold far away,which has caused the market value of fresh jujube to shrink seriously.Therefore,it is necessary to improve the storage and preservation technology of Lingwu Long Jujube while ensuring its quality,to quickly predict its internal mechanical behavior under the action of external forces,and to take appropriate measures to reduce mechanical damage and prolong the preservation period.The stress-strain reflects the damage degree of jujube.In order to analyze the response law of stress and strain in the inner of Lingwu Long Jujube to extrusion,the paper used the universal mechanical testing machine to compress the whole fruit horizontally and vertically under the five different extrusion rates of 15,20,25,30 and 35mm/min,and then fit the force deformation curve to obtain the rigidity and fracture force of the jujube during compression and fracture,The finite element model was established to verify the accuracy of the model,and the distribution of stress and strain in the extrusion process of Lingwu Long Jujube was analyzed.The results showed that the mechanical properties of Lingwu Long Jujube were anisotropic when it was squeezed,and the transverse compressive resistance was stronger.The stress and strain at the stress point were greatest in the pulp and extend along the equator towards the core and decrease gradually,making it most vulnerable to damage caused by compression.The deviation between the simulated value and the experimental value of the finite element model with the compression rate of 15mm/min was 14.98%,and that of the finite element model with the compression rate of 35mm/min was 11.06%.It was feasible to use the finite element method to simulate the extrusion of Lingwu Long Jujube,which can quickly predict the internal mechanical response of Lingwu Long Jujube unnder a certain extrusion rate.In order to further study the compressive mechanical properties of the pulp of Lingwu Long Jujube,to explore the micro mechanism of the mechanical behavior of the tissue under certain compression conditions,and to predict the response of internal stress and strain to extrusion,the pulp tissues of Lingwu Long Jujube at the storage time of 0d,2d,4d,6d,8d and 12d were compressed at different rates of 15mm/min and 35mm/min at room temperature.Scanning electron microscopy(SEM)was used to observe the pulp tissues at the 0d and 12d after 15mm/min and 35mm/min compression,and the comparison was made with the uncompressed flesh tissues.The flesh tissues at the 0d and 12d compression rates of 15mm/min and 35mm/min were analyzed by finite element method(FEM).A nonlinear finite element model of pulp tissue was established to analyze the distribution of stress and strain during extrusion.The results showed that the compressive strength of the pulp tissue of Lingwu Long Jujube decreased and the elastic modulus increased during storage.There was no significant difference in compressive strength and elastic modulus between 15mm/min and 35mm/min compression rates.The compressive strength and elastic modulus of pulp were affected by cell size and space.When subjected to external force,the deformation of Lingwu Long Jujube pulp tissue decreased from top to bottom,and the decreasing speed at the edge was less than that at the inner center.The maximum deformation was at the top surface and the minimum was at the bottom center.The stress,elastic strain and plastic strain values decreased along the edge of the hexahedron and the diagonal of each surface to the center of the top surface.The maximum error between the model and the experimental force-deformation was 20.91%.The model can be used to study the mechanical behavior of the pulp tissue.The study of mechanical behavior at cell level is an organic link of biomechanics research at both macroscopic and microscopic levels.The number and arrangement of cells in the pulp of Lingwu Long Jujube are closely related to its mechanical properties.A three-dimensional columnar geometry model was used to establish a finite element model of Lingwu Long Jujube pulp cells.The mesh division was optimized and the quality of mesh was evaluated.The compression finite element simulation of different number and arrangement of Lingwu Long Jujube cells was carried out at the rates of 15mm/min and 35mm/min.The results showed that the hexagonal cylindrical three-dimensional mechanical model of long jujube flesh cells with 29.2 side length could be divided into a hexahedral mesh with 2.92 size,and the mesh quality was better.In the transverse arrangement,the stress strain decreased with the increase of the number of longitudinal cells.In the longitudinal arrangement,the number of transverse cells remained unchanged,and the greater the number of longitudinal cells,the smaller the stress and strain.The transverse arrangement had greater stress and strain than the vertical arrangement.When the compression time and number of cells were the same,the compression rate of 35mm/min was larger than the maximum stress and strain of 15mm/min.The distribution of danger spots was greatly affected by the number of vertical cells in both horizontal and vertical arrangement.The results provided theoretical basis for further study on the micromechanical properties of Lingwu Long Jujube,establishment of micromechanical model and storage and transportation technology.