Study On Characteristics Of Crushing Mechanics And Crack Variation Of Brown Rice

Considering that rice is one of the most crucial crops in China,its production is absolutely related to national food security.Nevertheless,the subsequent processing and machining causes most losses,especially the problems of broken rice damaged by milling machine.In addition to affecting the processing quality of rice,this problem also causes serious food waste,thus restricting the development of national rice production severely.As a consequence,solving the problem of broken rice in the milling process becomes particularly important,which is of great significance to improve food security in China.As for the key to solve this problem,it is to reveal the characteristics of broken brown rice,while the study on characteristics of crushing mechanics of brown rice and crack growth retardation of brown rice is the key to understand the characteristics of broken brown rice.However,most of the current studies on the characteristics of broken rice are based on Hertz contact theory,while relevant studies on the damage of grain from energy conservation lack systematical considering about the diversity of movement and stress modes of grain in the whitening room,as well as the influence of mechanical properties of grain.Aiming at the problem of damage of rice in milling machines,this paper first established a testing platform of mechanical properties of brown rice based on relevant theories of material mechanics to test the mechanical properties of brown rice.Secondly,a numerical simulation of damage and failure process of brown rice was carried out by combining the cohesion damage model with finite element technology.Finally,the simulation results were compared and verified with the testing results of mechanical properties.This research can not only provide guidance for the structural optimization of rice milling machine,but also provide reference for other mechanical characteristics of similar biomaterials.Based on the above,this paper focuses on the following three aspects and obtains the following conclusions:(1)Study on breaking characteristics and crack propagation of brown rice under frontal loading.During the milling process,the brown rice will rotate with the roller with ribs,during which it will be crushed by extrusion,bending,shearing and other loads.Therefore,three mechanical tests of extrusion,shearing and three-point bending were carried out on the front part of the brown rice,and the internal crack propagation of the brown rice after being loaded was observed,The mechanical properties of brown rice under different stress were compared and analyzed.The results showed that the ability of resisting extrusion deformation of brown rice was the largest,the ability of resisting three-point bending deformation was the second,and the ability of resisting shear deformation was the smallest;Compared with extrusion load,the breaking strength and breaking energy of brown rice under three-point bending and shear load are smaller,which can better reflect the breaking characteristics of brown rice in the rice mill;Under the action of extrusion load,brown rice mainly produces two cracks with a certain angle and approximately symmetrical distribution in the short axis direction,and a transverse crack in the long half axis direction.Under the action of bending and shear load,brown rice mainly produces longitudinal cracks along the short axis direction,and the cracks propagate from the supporting end to the stressed end.(2)Study on breaking characteristics and crack propagation of brown rice under stress on abdomen and back.Based on the test of mechanical properties of brown rice,three-point bending and shear tests were carried out on the abdomen and back of brown rice,and the propagation of internal cracks was observed and explored after the abdomen and back of brown rice were loaded.Secondly,the crushing characteristic index of brown rice was calculated.Finally,combined with the crushing force distribution of brown rice under bending and shear loads,the front and back of brown rice were compared and analyzed The difference of crushing characteristics between abdomen and back.The results showed that the distribution of bending breaking force at abdomen and back of brown rice was different,but there was no significant difference in shear breaking force;Under the three-point bending and shear force,the cracks on the belly and back of brown rice always start to propagate from the supporting end;The breaking force,breaking strength and elastic modulus of brown rice under abdominal stress are greater than those under back stress,while the breaking deformation and breaking energy under abdominal stress are less than those under back stress,which is consistent with the conclusion that the abdominal tissue strength of brown rice is less than that of back;No matter under bending load or shear load,the breaking resistance of brown rice in front is stronger than that in abdomen and back,while that in abdomen is stronger than that in back.(3)Numerical analysis of the crushing characteristics and crack propagation of brown rice.Based on cohesive damage mechanics model,the crack propagation of brown rice grain model under the action of extrusion,three-point bending and shear load was simulated by finite element method,in order to obtain the relationship between stress and strain change and crack growth of brown rice grain model under various loads.The results show that the crushing stress of brown rice under extrusion load is the largest,the second is under three-point bending load,and the minimum under shear load;The crack of brown rice grows from the center to the outside under the action of extrusion load,while under the action of three-point bending and shear load,the brown rice crack mainly occurs near the support end.The rapid growth of the crack causes the grain fracture.The overall change trend of the grain model force and displacement and the change rule of crack expansion are basically consistent with the test results,The feasibility of the mechanical property test method and the accuracy of the results are verified.