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In order to clarify the rheological mechanical properties of millet grain group during mechanical harvesting and processing, this paper studied the effects of different varieties and different moisture contents on the creep characteristics of millet grain group. In this experiment, different varieties (Jingu 21, Zhangza 10), and different moisture contents (12.10%, 16.05%, 20.00%) of millet grain group were selected as creep experimental factors. The creep characteristics (instantaneous elastic modulus, delayed elastic modulus, relaxation time and viscosity coefficient) of millet seed group were used as experimental indicators, and one-way analysis of variance and multi-factor analysis of variance were performed. Based on the original contents of millet seed group, the target moisture contents of the millet grain group were formulated to be 12.10%, 16.05%, 20.00%. The experiment was conducted on the CMT-6104 universal testing machine, and the special fixture for testing the creep characteristics of millet grain group was designed. Combining the Burgers model, nonlinear programming method was used to optimize search regression parameters, and creep parameters of millet grain group were obtained. The creep curve of millet grain group of different varieties showed that, as time going on, the amount of deformation caused by creep tended to be constant, which reaching the strain saturation. There were differences in the millet grain group creep characteristic curves of the different varieties. The significance test standard was 0.05, and the variance analysis was performed. The results showed that the creep characteristics of millet grain group could be described by the four-element Burgers model, and the creep parameters of millet grain group with different moisture content and different varieties were different. The variety had a significant effect on the delayed elastic modulus of the millet grain group. The delayed elastic modulus of the Jingu 21 millet grain group was higher than that of Zhangza 10. The moisture content had significant effects on the instantaneous elastic modulus, delayed elastic modulus and viscosity coefficient of the millet grain group, which was decreasing while the moisture increasing. The instantaneous elastic modulus of the millet grain group with the water content of 12.10% was significantly higher than the water content of 16.05% and 20.00%. The delayed elastic modulus of the millet grain group with the moisture content of 12.10% was significantly higher than the water content of 20.00%. The instantaneous elastic modulus and the delayed elastic modulus represented elasticity and hardness of the millet grain group, respectively. With the increasing of the moisture content of the millet grain group, the instantaneous elastic modulus and the delayed elastic modulus of millet grain group decreased, resulting in a high increasing of the creep curve. The strain in the screw conveyor of combine harvester was correspondingly larger. In this paper, the creep properties of millet grain group with different varieties and different moisture contents were studied experimentally, which provided theoretical support for low-loss harvesting, processing and storage and parameter optimization of millet. There are many factors affecting the mechanical properties of the material, in addition to the influence of moisture contents and varieties, it is also related to many factors such as temperature, internal molecular structure and chemical composition of the material, et al. The rheological properties of agricultural materials need to be further studied in conjunction with the principles of life sciences. [ABSTRACT FROM AUTHOR]

The silo has the advantages of small area, good sealing conditions, low circulation costs, low cost and etc. It is currently the leading warehouse type of grain storage in China. Most silos still use gravity-based discharging methods, however, arches often form during silo discharging, it causes the pressure that should have been taken from the bottom of the warehouse to the wall of the warehouse. As a result, cracks may form in the silo walls causing serious damage. In addition, when there are workers above the grain surface or when the arch is manually broken, the collapse of the arch will not only result in personal injury or death of the grain surface staff, but also may damage the warehouse structure and facilities in the warehouse. In recent years, with the development of building technology, the silo volume has been continuously increasing, the diameter and height of the silo have also become larger and larger, and the related accidents caused by unloading and arching silos have also become more frequent Silo arch accidents in Daqing 2013, Lanxi 2015, in Heilongjiang province, and in Jing County in 2016 in Anhui province, for example, have resulted in the destruction of some silo facilities and casualties. Existing studies have shown that silo unloading and arching are closely related to the internal and external friction of grain. However, in those studies, a single circular particle is used in the current discrete element simulation. The real contact area of simulated grain is much smaller. As such, the simulation cannot objectively reflect the grain of the unloading process. The frictional situation is also more difficult to restore the mesoscopic dynamic process of unloading grain arching. In this paper, based on the existing PFC3D discrete element program, the micro particle simulation dust with larger viscosity coefficient was added to create an improved particle for the defect that the internal friction force of the circular particle in the discrete element simulation was smaller than that in the real grain. We used geometric methods in the structural mechanics model to determine the contact between the circular particles and derives the force-displacement relationship between the basic units. Based on typical accident cases and laboratory test results, the established particle structure mechanics model was used to simulate the force-displacement relationship between circular large particles and between small round particles and walls in the dynamic process of unloading grain and arching. The displacement map of shear stress and its stress characteristic curve were basically consistent with the experimental results. By using this model, the dynamic meso-mechanism of unloading and arching silos can be objectively reflected. The improved particle structure mechanics model proposed in this paper can not only be used to simulate the unloading and arching mechanism simulation, but also has certain reference value for the simulation of the characteristics of loose particles flow and the mechanism of the interaction between the bulk and the silo wall. [ABSTRACT FROM AUTHOR]

The silo has the advantages of small area, good sealing conditions, low circulation costs, low cost and etc. It is currently the leading warehouse type of grain storage in China. Most silos still use gravity-based discharging methods, however, arches often form during silo discharging, it causes the pressure that should have been taken from the bottom of the warehouse to the wall of the warehouse. As a result, cracks may form in the silo walls causing serious damage. In addition, when there are workers above the grain surface or when the arch is manually broken, the collapse of the arch will not only result in personal injury or death of the grain surface staff, but also may damage the warehouse structure and facilities in the warehouse. In recent years, with the development of building technology, the silo volume has been continuously increasing, the diameter and height of the silo have also become larger and larger, and the related accidents caused by unloading and arching silos have also become more frequent Silo arch accidents in Daqing 2013, Lanxi 2015, in Heilongjiang province, and in Jing County in 2016 in Anhui province, for example, have resulted in the destruction of some silo facilities and casualties. Existing studies have shown that silo unloading and arching are closely related to the internal and external friction of grain. However, in those studies, a single circular particle is used in the current discrete element simulation. The real contact area of simulated grain is much smaller. As such, the simulation cannot objectively reflect the grain of the unloading process. The frictional situation is also more difficult to restore the mesoscopic dynamic process of unloading grain arching. In this paper, based on the existing PFC3D discrete element program, the micro particle simulation dust with larger viscosity coefficient was added to create an improved particle for the defect that the internal friction force of the circular particle in the discrete element simulation was smaller than that in the real grain. We used geometric methods in the structural mechanics model to determine the contact between the circular particles and derives the force-displacement relationship between the basic units. Based on typical accident cases and laboratory test results, the established particle structure mechanics model was used to simulate the force-displacement relationship between circular large particles and between small round particles and walls in the dynamic process of unloading grain and arching. The displacement map of shear stress and its stress characteristic curve were basically consistent with the experimental results. By using this model, the dynamic meso-mechanism of unloading and arching silos can be objectively reflected. The improved particle structure mechanics model proposed in this paper can not only be used to simulate the unloading and arching mechanism simulation, but also has certain reference value for the simulation of the characteristics of loose particles flow and the mechanism of the interaction between the bulk and the silo wall. [ABSTRACT FROM AUTHOR]

The silo has the advantages of small area, good sealing conditions, low circulation costs, low cost and etc. It is currently the leading warehouse type of grain storage in China. Most silos still use gravity-based discharging methods, however, arches often form during silo discharging, it causes the pressure that should have been taken from the bottom of the warehouse to the wall of the warehouse. As a result, cracks may form in the silo walls causing serious damage. In addition, when there are workers above the grain surface or when the arch is manually broken, the collapse of the arch will not only result in personal injury or death of the grain surface staff, but also may damage the warehouse structure and facilities in the warehouse. In recent years, with the development of building technology, the silo volume has been continuously increasing, the diameter and height of the silo have also become larger and larger, and the related accidents caused by unloading and arching silos have also become more frequent Silo arch accidents in Daqing 2013, Lanxi 2015, in Heilongjiang province, and in Jing County in 2016 in Anhui province, for example, have resulted in the destruction of some silo facilities and casualties. Existing studies have shown that silo unloading and arching are closely related to the internal and external friction of grain. However, in those studies, a single circular particle is used in the current discrete element simulation. The real contact area of simulated grain is much smaller. As such, the simulation cannot objectively reflect the grain of the unloading process. The frictional situation is also more difficult to restore the mesoscopic dynamic process of unloading grain arching. In this paper, based on the existing PFC3D discrete element program, the micro particle simulation dust with larger viscosity coefficient was added to create an improved particle for the defect that the internal friction force of the circular particle in the discrete element simulation was smaller than that in the real grain. We used geometric methods in the structural mechanics model to determine the contact between the circular particles and derives the force-displacement relationship between the basic units. Based on typical accident cases and laboratory test results, the established particle structure mechanics model was used to simulate the force-displacement relationship between circular large particles and between small round particles and walls in the dynamic process of unloading grain and arching. The displacement map of shear stress and its stress characteristic curve were basically consistent with the experimental results. By using this model, the dynamic meso-mechanism of unloading and arching silos can be objectively reflected. The improved particle structure mechanics model proposed in this paper can not only be used to simulate the unloading and arching mechanism simulation, but also has certain reference value for the simulation of the characteristics of loose particles flow and the mechanism of the interaction between the bulk and the silo wall. [ABSTRACT FROM AUTHOR]

The silo has the advantages of small area, good sealing conditions, low circulation costs, low cost and etc. It is currently the leading warehouse type of grain storage in China. Most silos still use gravity-based discharging methods, however, arches often form during silo discharging, it causes the pressure that should have been taken from the bottom of the warehouse to the wall of the warehouse. As a result, cracks may form in the silo walls causing serious damage. In addition, when there are workers above the grain surface or when the arch is manually broken, the collapse of the arch will not only result in personal injury or death of the grain surface staff, but also may damage the warehouse structure and facilities in the warehouse. In recent years, with the development of building technology, the silo volume has been continuously increasing, the diameter and height of the silo have also become larger and larger, and the related accidents caused by unloading and arching silos have also become more frequent Silo arch accidents in Daqing 2013, Lanxi 2015, in Heilongjiang province, and in Jing County in 2016 in Anhui province, for example, have resulted in the destruction of some silo facilities and casualties. Existing studies have shown that silo unloading and arching are closely related to the internal and external friction of grain. However, in those studies, a single circular particle is used in the current discrete element simulation. The real contact area of simulated grain is much smaller. As such, the simulation cannot objectively reflect the grain of the unloading process. The frictional situation is also more difficult to restore the mesoscopic dynamic process of unloading grain arching. In this paper, based on the existing PFC3D discrete element program, the micro particle simulation dust with larger viscosity coefficient was added to create an improved particle for the defect that the internal friction force of the circular particle in the discrete element simulation was smaller than that in the real grain. We used geometric methods in the structural mechanics model to determine the contact between the circular particles and derives the force-displacement relationship between the basic units. Based on typical accident cases and laboratory test results, the established particle structure mechanics model was used to simulate the force-displacement relationship between circular large particles and between small round particles and walls in the dynamic process of unloading grain and arching. The displacement map of shear stress and its stress characteristic curve were basically consistent with the experimental results. By using this model, the dynamic meso-mechanism of unloading and arching silos can be objectively reflected. The improved particle structure mechanics model proposed in this paper can not only be used to simulate the unloading and arching mechanism simulation, but also has certain reference value for the simulation of the characteristics of loose particles flow and the mechanism of the interaction between the bulk and the silo wall. [ABSTRACT FROM AUTHOR]

The silo has the advantages of small area, good sealing conditions, low circulation costs, low cost and etc. It is currently the leading warehouse type of grain storage in China. Most silos still use gravity-based discharging methods, however, arches often form during silo discharging, it causes the pressure that should have been taken from the bottom of the warehouse to the wall of the warehouse. As a result, cracks may form in the silo walls causing serious damage. In addition, when there are workers above the grain surface or when the arch is manually broken, the collapse of the arch will not only result in personal injury or death of the grain surface staff, but also may damage the warehouse structure and facilities in the warehouse. In recent years, with the development of building technology, the silo volume has been continuously increasing, the diameter and height of the silo have also become larger and larger, and the related accidents caused by unloading and arching silos have also become more frequent Silo arch accidents in Daqing 2013, Lanxi 2015, in Heilongjiang province, and in Jing County in 2016 in Anhui province, for example, have resulted in the destruction of some silo facilities and casualties. Existing studies have shown that silo unloading and arching are closely related to the internal and external friction of grain. However, in those studies, a single circular particle is used in the current discrete element simulation. The real contact area of simulated grain is much smaller. As such, the simulation cannot objectively reflect the grain of the unloading process. The frictional situation is also more difficult to restore the mesoscopic dynamic process of unloading grain arching. In this paper, based on the existing PFC3D discrete element program, the micro particle simulation dust with larger viscosity coefficient was added to create an improved particle for the defect that the internal friction force of the circular particle in the discrete element simulation was smaller than that in the real grain. We used geometric methods in the structural mechanics model to determine the contact between the circular particles and derives the force-displacement relationship between the basic units. Based on typical accident cases and laboratory test results, the established particle structure mechanics model was used to simulate the force-displacement relationship between circular large particles and between small round particles and walls in the dynamic process of unloading grain and arching. The displacement map of shear stress and its stress characteristic curve were basically consistent with the experimental results. By using this model, the dynamic meso-mechanism of unloading and arching silos can be objectively reflected. The improved particle structure mechanics model proposed in this paper can not only be used to simulate the unloading and arching mechanism simulation, but also has certain reference value for the simulation of the characteristics of loose particles flow and the mechanism of the interaction between the bulk and the silo wall. [ABSTRACT FROM AUTHOR]

In this paper, an innovative compression technology is developed to study and analyze the mechanical properties of lotus seed kernel with regard to elastic modulus, compression strength and ultimate load when the whole lotus seed kernel is under the pressure. The objectives of this paper are to study the damage and crushing characteristics of lotus seed kernel under the condition of squeezing the load and reducing the crushing rate in the processing and transportation. Firstly, the universal testing machine is utilized to implement tests of elastic modulus and compression strength for lotus seed kernel samples. A series of the mechanical properties are measured for the lotus seed kernel with varied moisture content (5.52%, 7.78%, 10.29%, 12.47%, and 15.06%) in terms of vertical elastic modulus, horizontal elastic modulus, longitudinal compression strength and transverse compression strength. The corresponding transverse stress-strain curve and longitudinal stress-strain curve are figured out. The measurement results indicate the vertical and horizontal elastic modulus and compression strength of lotus seed kernel decrease with the increase of moisture content. The longitudinal values are higher than transverse values as to samples with same level of moisture content. Therefore, lotus seed kernel belongs to a kind of anisotropic material. It is much easier to cause lotus seed kernel broken when it suffers horizontal compression. When the moisture content is relatively low (5.52%, 7.78%, 10.29%), there is a linear relationship between stress and strain. Lotus seed kernel shows brittleness. If the moisture content is much higher (12.47%, 15.06%), strain becomes larger, which means lotus seed kernel has great toughness. The regression equation is established for the sake of carrying out regression analysis based on test results of elastic modulus and compression strength. It is obtained that the minimum compression strength and minimum elastic modulus of qualified lotus seed kernel with moisture content smaller than 11% are 5.12 and 37.12 MPa respectively. Furthermore, the crack caused by compression is also discussed on the basis of varied moisture contents and different compression methods. It is measured that the ultimate loads under the flat pressure for 5 experimental samples are 103.92, 89.87, 72.21, 59.60 and 51.73 N, respectively. Similarly, the ultimate loads under the side pressure are 88.19, 72.78, 57.80, 45.58 and 39.16 N, respectively. From the measurement data, the moisture content and compression method of lotus seed kernel have great influence on ultimate loads. The ultimate loads increase with the decrease of moisture content, no matter it suffers side pressure or flat pressure. Furthermore, the ultimate load of side pressure is less than that of flat pressure in terms of same level of moisture content. Therefore, side pressure is much easier to make the lotus seed kernel broken. The first crack positions are the load position, parting surface and area around the drilled hole in flat pressure test. As to the side pressure test, the first crack positions are on the both sides of parting surface. Based on the test results of ultimate loads of lotus seed kernels, a regression model of ultimate loads and moisture content is established. It is calculated that the maximum compression load of the qualified lotus seed kernel (moisture content is less than 11%) should be less than 53.60 N. In practical cases, the compression load should be less than this limit value. Lastly, a dynamic model of lotus seed kernel compression is developed with the finite element method. The stress distribution of pressure states of lotus seed kernel is figured out. The analysis results demonstrate the stress at load position, parting surface and area around the drilled hole is larger in flat and side pressure tests. The parting surface is the weak part of lotus seed kernel. It expresses that the simulation results well fit the crack position and direction in the compression test, which identifies the correctness of measurement parameters. The study results provide a reliable evidence for determining process parameters of processing and conveying equipment in the lotus seed kernel production. [ABSTRACT FROM AUTHOR]

Some sandy sediment in the coasts in Hainan province is rich in organic matters and the sand particles might be coated and disseminated by organic carbon. This could alter the surface of the sand and thus compromises the mechanical strength of the concrete made using such sands as aggregates. This paper experimentally investigated how organic-disseminated sand particles impact the mechanical properties and constitutive equation of the associated concrete. The sample species were prepared by mixing 20% (w/w) and 7.5% of lime with water at water: cement ratio of 0.45; they were then further mixed with sand particles disseminated by organic carbon coating. Concrete using standard sands served as the control. The mechanical properties and constitutive equation of the specimens were measured using the unconfined and uniaxial compressive tests. The unconfined compression test was to measure the compressive strength at curing time of 7d, 14d, 21dand 28d, respectively, and their failure mode. The uniaxial compression test was to measure the stress-strain curve, the stiffness variation rule and the modified Duncan-Zhang constitutive equation. The results show that 1) the failure mode of the concrete with organic-disseminated sands was plastic shear failure and brittle shear failure, while the failure mode of the specimens with standard sand at the same curing time was brittle shear failure. 2) The compressive strength of the concrete with organic- disseminated sands was significantly smaller than that with standard sands at early stage of the curing, although both increased exponentially with the curing time. The compressive strength of each specimen reached asymptotically to a constant after 14 days of curing. 3) The stiffness of the concrete with organic- disseminated sands increased with curing time. After the loading was applied, its shear modulus increased with the axial strain initially, but when the strain reached about 2%, the shear modulus started to decrease with a further increase in strain. In terms of plasticity, the former is known as stiffness hardened and the latter is known as stiffness softening. The stiffness of the concrete with organic-disseminated sands increased with curing time, and the peaked shear modulus at Day 28 is 4.36 times that at Day 7. 4) The stress-strain curve of the concrete with organic-disseminated sands was a interplay of various deformation processes under uniaxial load, and can be divided into two stages: plastic stage and softening stage. 5) The modified Duncan-Zhang model was obtained to describe the full stress-strain curve. Comparison with measured data showed that the model adequately described the stress-strain of the concrete with organic-disseminated sand particles. [ABSTRACT FROM AUTHOR]

In order to effectively solve the problem of the motor's power margin too adequate to ensure the stable operation of the equipment which widely exists in the current mechanical transmission system, a kind of squirrel cage asynchronous magnetic coupler (SCAMC) is proposed based on the principle of three-phase asynchronous motor. The SCAMC has the advantages of the simplicity of mechanical structure, high reliability in successive operation, simple maintenance, weak skin effect of the squirrel cage rotor and adjustable slip ratio and so on. According to the specific characteristics of the SCAMC structure, the mathematical model of air gap magnetic flux density is established by using the scalar magnetic potential method and two-dimensional field boundary conditions. The air gap magnetic flux density generated by the permanent magnet in SCAMC can be decomposed into radial component and tangential component, and it is only the former one that cuts the cage bar and generates induction current and electromagnetic torque. As a consequence, the effect of tangential air gap flux density can be ignored when studying the operating characteristics of SCAMC; only the radial air gap magnetic flux density needs analysis. The time variable is introduced into the expression of radial air gap flux density, and thus the expression of induced current changing over time is deduced and the transformation rule of induced current with space phase and electrical angle is revealed. Based on the current's superposition characteristics, the current of the cage bar is converted onto the rotor surface and the Lorentz force produced by induced current is integrated along the circumference, and thus the electromagnetic torque model is established. On the base of the above theoretical and technological foundation, a 37 kW SCAMC experimental prototype is designed and produced. After installing the prototype on a 37 kW, 6-pole drive motor, the theoretical calculation, simulation verification and experiment measurement on its mechanical behavior are performed. The results show that the simulation value, experimental value and theoretical value of the electromagnetic torque and the slip ratio of SCAMC are all consistent, and the prototype possesses fine overload characteristics. On condition of identical slip ratio, the error rate between simulation and experimental data and theoretical value is less than 5%. In the process of the load torque increasing from 0 to the rated torque of drive motor (366 N·m), the change of slip ratio of SCAMC is 0-4.8%, which can meet the need of a relative fixed output speed during common machinery producing. However, under the rated load, the maximum slip ratio of the 37 kW, 6-pole drive motor is 2%, while the ratio of SCAMC is 4.8%, about 2.5 times that of the former. That is to say, the mechanical characteristic of SCAMC is softer than the asynchronous motor, which means its impact on the motor can be released when the load is changed. When loaded to the maximum experimental torque, which is corresponding to the drive motor overloading by 10%, the slip ratio of SCAMA is 5.7%, which is increased by 9% compared with that under the rated load, but the operation still falls in the linear area, proving the strong overload capability of SCAMC. The simulation and experimental results verify the validity of the model established in this paper, and provide the theoretical and technological reference for the use of magnetic coupler in machineries with large inertia, difficult starting and frequent overload. [ABSTRACT FROM AUTHOR]