Study On The Compression Damage And Mechanical Damage Assessment Of Citrus Reticulata Blanco

In order to solve the damage problem of Citrus Reticulata Blanco under static load compression,the Mechanical properties and static load compression creep characteristics of Citrus Reticulata Blanco were researched in this paper.And based on the CAD/CAE technology,the finite element models of Citrus Reticulata Blanco were established to simulate the citrus under the linear elastic compression and compressive creep.The mechanical damage of Citrus Reticulata Blanco under different load conditions,such as compression and dropping were studied.The differences in performance change of the mass and hardness of citrus fruits during storage period were analyzed.Combining experimental data and mathematical modeling,a method for evaluating the mechanical damage of citrus was initially established.The degrees of mechanical damage of citrus fruits were quantitatively estimated.And the main damage factors of citrus fruits were analyzed.Based on relevant mathematical physical models,the damaged citrus fruits were qualitatively evaluated and predicted.And the method was used to compare the protective effects of different cushioning materials under compression and dropping.This research was used to Provide a theoretical reference for predicting citrus mechanical damage and optimizing the design of low damage citrus picking,storage and transportation machinery.The main contents and conclusions of this paper are as follows:?1?The mechanical properties such as mass,hardness,elastic modulus,rupture limit force,and total deformation rupture energy of citrus fruits were measured.The Change of the mechanical properties with storage time was explored.With the increase of storage time,the mass loss of citrus fruits increased,the hardness decreased gradually,but the other mechanical properties such as elastic modulus,rupture limit force,and total deformation rupture energy generally increased first and then decreased,which were significant.?2?The test data fit and verified that the static creep deformation curves of the whole fruit,pulp,and pericarp of Citrus Reticulata Blanco during the loading stage were compliance with the Burgers model,and the fitting coefficients were all greater than 0.97.The test results show that the storing time T is highly positively correlated to the creep compliance J(3T_rel).The creep compliance J(3T_rel)is highly negatively correlated to the instantaneous stiffness coefficient?₀,the retardation stiffness coefficient?₁,and the viscosity coefficient n₂,but positively correlated to the delay time T_rel.The creep compliance J(3T_rel)can be a more comprehensive representation of the creep characteristics of citrus fruits.Controlling the same level of other factors for citrus fruit,the larger the constant compression load,the greater the creep deformation was;the larger the loading rate,the larger and more visibly the creep deformation was;the creep deformation of the equatorial part was the larger and more visibly than the top of citrus fruits;the longer the storing time is,the smaller the hardness is,and the larger the creep deformation was.It can be concluded that the critical strain failure theory can be used to explain the damage caused by the static creep of citrus fruits.When the whole citrus was loaded,the load was larger,or the loading time was continuously increased,the creep deformation was larger.And the deformation exceeded a certain critical value.At the threshold,the citrus produced mechanical damage and rupture?except for"strain saturation"?.?3?The quasi-static compressive creep parameters of citrus were deduced and calculated after certain ideal hypotheses.The required viscoelastic parameters of the Prony series expansion of three-dimensional relaxation shear modulus were obtained.Two types of finite element models of citrus fruits were established.The linear elastic compression of the citrus fruits were simulated.Compared with the results of the experimental test,the goodness of fit was 0.8838 for the single-layer whole fruit model,and the goodness of fit for the double-layer pericarp-flesh model was 0.8902.Both of these models were reasonable and feasible.The quasi-static compression creep of the citrus fruits were simulated.Compared with the results of the experimental test,the goodness-of-fit for the single-layer whole fruit model was 0.9610,which is reasonable and feasible,and for the double-peel-carcass model,the goodness of fit was 0.5718.The stress distribution of the citrus fruits under compressive loading was studied and it was found that compressing the top of citrus fruits,whether it is displacement load or constant force load,the citrus fruits were ruptured due to the tensile stress of the peel.the ruptured section of the citrus appears consistent with the direction of compression.?4?A method for evaluating the mechanical damage of citrus fruits was initially established.Based on the mass loss of citrus and fruit softening,the degree of mechanical damage of citrus fruits were quantitatively estimated.Using the k-nearest neighbor classification in machine learning problems,a two-category model of mechanical damage of citrus fruits were established to predict qualitatively the"damaged"citrus fruits under load conditions such as compression and dropping.Combined with the degree of the mechanical damage of citrus fruits,the prediction results showed that the maximum compressive force of citrus should not exceed 20 N without protective measures,and it should be less than 10 N.Dropping height of citrus fruits should not exceed 90 cm,preferably less than 60 cm.?5?The protective effects of different cushioning materials under different Loading conditions such as compression and dropping were compared.Evaluating from the degree of damage and the forecasting model of citrus fruits,it can be seen that the corrugated board has the best damage reduction effect in a single static compression test,followed by the EPE board,and rubber plate was the worst;In a single vertical drop test.the EPE board had the best effect followed by the rubber plate,and corrugated board was the worst.