Mechanical Properties Of Rice Grain And Threshing Injury Based On The Energy Conservation

By international standards, imperfect rice rate is one of the important factors affecting the quality of rice, besides color, impurity content etc. Because broken rice rate is on the high side, our country's rice is difficulty to get into the international market, especially into the Europe and America market. With the living conditions of the people being improved, an even higher demand on imperfect rice rate has been set. Besides internal and external stress, injury to rice grain is concerned with mechanical properties. In this study, the physical behaviors of rice grain were determined. The force -deformation curve of rice grains was measured by the compression test. Some phenomena that occurred in the compression test were described. Compression failure force and compression failure energy are two important indexes to the injury of rice grains. The computing methods of compression failure force and compression failure energy were given. The effects of different varieties, harvest time and after ripening action on mechanical properties of rice grain were determined. The differences of mechanical properties between rice grains (with hull) and brown rice (without hull) were put forward. The significant effects of hull on reducing the injury to rice grain were shown. The bending and shearing mechanical properties of rice grain were also studied by experiments. The mechanical properties of rice grain can offer the base for optimization design of relevant devices. On self-designed test equipment, the experiment of effect of different varieties, harvest time and after ripening action on threshing broken rate of rice grain were conducted for paddy rice. The relationship between mechanical properties of rice grain and threshing broken rate was brought forward.The relationship between internal structure and mechanical properties of rice grain was analyzed. Based on the injury definition of engineering material, the injury definition of rice grain was given. The injury characteristics of rice grain under compressing, bending and shearing load were analyzed. Energy conservation law is used in studied the injury to rice grain. That the injury (crack propagation) degree of rice grain is proportional to the energy absorption was testified by experiments, when the injury is fracture. The hysteresis energy consuming behavior of rice grain was studied by means of experiments. The energy absorption by rice grain on one loading cycle was obtained. An investigation on the principle of grain injury under static load was made. The effects of different varieties, harvest time and after-ripening action on the energy absorption of rice grain were determined.During harvesting, handling, and transporting, injury of rice grain is due not only to size of the force acting on it but also to number of the loading cycles. An investigation on the principle of grain injury under repeated loads was made. The multiply element quadratic model between the maximum of pressure, number of the load cycles and the injury percentage of rice grain was developed. Statistical value F was made in order to prove the correctness of the multiply element quadratic model. The relationship between the maximum of pressure and number of the load cycles was obtained when injury percentage of rice grain is equal to 1%. One development way to compute the maximum impact frequency of threshing tooth against rice grain was given. The effect of grasp chain velocity on threshing broken rate of rice grain and the axial distribution of the threshing broken rate (for semi feed condition and for whole feed condition) are studied by means of threshing experiments.Threshing is the key working operation in combine-harvesting of rice. Though threshing machine had been using for over two centuries, fewer theoretical analyses were made on threshing process because the interactions between threshing tooth and rice grain are difficult to describe. Up to now, all the studies have been concentrated on developed the mathematical model between threshing performance and the structural, motion parameters of threshing unit by means of experiments, which only show the superficial laws, can not find the inherent laws of threshing process. In this study, the relative motion of rice grain with threshing tooth was analyzed. Using the principles of impulse and relative motion, the changes of rice grain relative velocity and kinetic during impact between threshing tooth and rice grain were given. Based on the energy conservation law, surface energy absorbed by rice grain was obtained. The quantity of threshing injury to rice grain was calculated. Round and rectangular section threshing tooth were compared. Based on the theoretical analysis of interpretation between single, multiple rice grains and threshing tooth, the mathematical model between threshing tooth velocities and threshing broken rate was developed. On self-designed test equipment, the experiment of relationship between threshing tooth velocities and threshing broken rate was conducted for paddy rice. The unknown coefficients in the mathematical model were determined based on the experiments. The correctness of the mathematical model was proved. The mathematical model not only provides a theoretical base for designs and optimizations of rice threshing machine, but also enlightens us on studying the mechanical injury to other agriculture materials, such as corn peanut and soybean. It has broad prospect for application.