Research On Oil Tree Peony Stem Cutting Properties And Mechanism

Mechanized harvesting of oil tree peony fruit is an important condition for the industrialization of oil peony.It is of great significance to improve the self-sufficiency of edible oil and solve the contradiction between supply and demand of edible oil.However,the existing oil tree peony fruit harverster can only partly meet the needs of mechanized operation,but the cutting mechanism of the stem and cutting tool parameters is still lack of sufficient theoretical research,and the optimal design of the fruit harvester has not been realized.Therefore,this paper considered the oil tree peony stem as the research object,and carries out experimental research on the macro cutting mechanism,microstructure difference and shear deformation characteristics of the stem.Based on this,a stem cutting constitutive equation is established,and the key parameters of the cutting tool are optimized through the finite element simulation method,which provides a theoretical basis and technical support for the design of oil tree peony fruit harvester.The main research results are discribed as follows:1.A stem cutting test device for oil tree peony was built up in this study.The discrepancy of growth stages,cutting tool angle and cutting speed were considered as the experiment factors,and the stem cutting experiment was set up.The results showed that there were significant differences in the stem cutting properties of oil tree peony stems in different growth stages.The average cutting strength of the stems in the fructescence stage was the lowest,which was conducive to fruit harvest.The effect of blade angle and sliding-cutting angle was carried out in this test,and the mechanism is analyzed based on sliding-cutting theory.The result also shows that cutting speed had significant effects on the stem cutting properties,and the cutting force and energy were increased with the increase of cutting speed,which indicates that there is an obvious strain rate effect in the process of stem cutting.2.According to the difference of stem cutting properties of oil tree peony stems in different growth stages,the microstructure of stem in different growth stages was determined by scanning electron microscope,and the average moisture content of stem in each growth stage was also determined.Futher more,the cutting experiment of oli tree peony stem in different growth stages was carried out,and the effects of microstructure and moisture content on the shear strength of stem were studied.Based on the method of multiple regression analysis,a regression equation was established with the shear strength as the dependent variable,Sclerenchyma tissue content,vascular bundle,moisture content,the interaction between vascular bundle content and moisture content as the independent variable.The accuracy of the equation was verified by experiments,and the cross-scale relationship between stem cutting properties and its microstructure and moisture content was established department.3.Based on two-dimensional digital image correlation(2D-DIC)mehtod,according to the basic principle of camera imaging,an off-plane displacement error correction algorithm was proposed,and the calculation method of displacement field and strain field of stem cutting process was realized.Based on this algorithm,a stem cutting deformation test system was set up to measure the deformation and strain of oil tree peony stem cutting process.The calculation of three-dimensional displacement field and strain field on the stem surface including off-plane displacement information was realized.The characteristics of oil tree peony stem cutting deformation were studied,which found that the deformation and strain of the moving blade side of the stem was more concentration during the shear deformation process.And the reduction of cutting tool blade angle can produce more obvious strain concentration to reduce cutting resistance.The research shows that an effective measurement system and method of stem shear deformation are established.4.According to the mechanism of stem shear and shear deformation of oil peony,the finite element method is proposed to simulate the stem cutting.According to the obvious strain rate effect in the cutting process of oil peony stem,a constitutive model of stem cutting was established based on the Plastic Kinematic model by introducing a self-defined adjustment coefficient reflecting the performance difference of stem in different growth stages.Based on the physical meaning of the constitutive parameters of the model,the quasi-static and dynamic tensile test methods are proposed,the constitutive parameters are measured,the finite element simulation is carried out by using the model,and the simulation results are verified by the stem shear test.The results show that the self-defined constitutive model can effectively reflect the stress-strain characteristics of oil peony stem in the plastic deformation stage during the cutting process and the influence of stem growth period difference on the shear properties.5.Based on the stem cutting constitutive model established in this study,combined with the needs of the cutting tool design of the fruit harvester,three key parameters including the blade angle,sliding-cutting angle and the cutting speed were optimized.By using the finite element simulation method,according to the requirements of orthogonal experiment,the multi factor simulation research is carried out,and the horizontal combination of cutting blade angle,sliding cutting angle and cutting speed is optimized.The reliability of the simulation results is verified by building a cutting test bench.The results show that the most labor-saving parameter combination is 15 ° cutting blade angle,10 °sliding-cutting angle and 0.2m/s cutting speed,which is the best design parameter of the cutter.