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Mo2 FeB2 is a good boron based cermet material with high temperature resistance, wear resistance and high strength. It has broad application in the field of mould. The structural stability, elastic properties, hardness and electronic structure of Mo2 FeB2 with Nb alloying were investigated by using first-principles calculations. The calculated cohesive energy and formation enthalpy showed that Nb prefers to occupy the Fe site of Mo2 FeB2, and the Nb at Fe site of Mo2 FeB2 possesses better mechanical properties compared with that at Mo site. Moreover, the calculated results showed that Nb doping could increase the shear modulus, Young’s modulus, bulk modulus and hardness, but slightly decrease the ductility. The suitable doping concentration should be 2.5 at. %. The calculated electronic structure indicated that the increase of mechanical properties is attributed to the formation of Nb-B covalent bonds. [ABSTRACT FROM AUTHOR]

The dynamic change of water level in a hydrological year can keep riverbank soil in the state of alternating dry and wet. The variety of water content of riverbank soil can change the mechanical properties of soil to a certain extent, which can affect riverbank stability. In order to investigate quantitatively the influence of dry-wet alternation condition on mechanical properties of riverbank clay soil, a field observation and sampling were first conducted at eight typical riverbanks in upper and lower Jingjiang Reach, which the clay soil of the typical riverbanks in Jingjiang Reach of the Yangtze River was taken as the study object. Through a comprehensive analysis of measured data, indoor soil tests and BSTEM simulation, the composition and mechanical properties of these samples were obtained, which indicated that the vertical soil composition of riverbank was characterized by a typical composite structure of non-cohesive lower bank and cohesive upper bank. The indoor soil test results revealed the quantitative change of soil mechanics with dry-wet alternation condition, and a close relationship between water content and shear strength indicators was obtained. With an increase of water content, the cohesion first increased and then decreased, with the peak values of 21 kPa and 34 kPa for the critical water content of 16.0% and 22.8% at Jing 61 and Beimenkou sections, and eventually reached a constant, while internal friction angel decreased significantly. Considering the dry-wet alternation condition of riverbank soil and the change of river water level in a hydrological year, the degrees of riverbank stability at Jing 61 and Beimenkou sections were analyzed during four different water level periods using BSTEM, and the process of bank failure of two sections were simulated in 2013. The results indicated that: the model-predicted results of the total bank retreat width were in close agreement with the measured data with the relative errors 1.69% and 3.74%, respectively. At the same time, the safety factors under different dry and wet conditions were calculated based on the BSTEM simulated results of two typical sections. The relationship between safety factor and water content was obtained, which indicated the safety factor first increased and then decreased with an increase of water content. It was consistent with the relationship between soil cohesive and water content which proved that the soil cohesive has an important influence on the stability of river bank. Quantitative relationships between safety factors and cohesive and internal friction angle of two typical sections were identified, respectively, and the correlation coefficients were 0.980 and 0.876 for Jing 61 section, and 0.992 and 0.986 for Beimenkou section, respectively. The relationships between them were linear function from which the safety factors increased with the increase of the cohesive and internal friction angle, respectively. Thus, a conclusion can be drawn that the safety factor was mainly affected by soil cohesive under different dry and wet conditions. For actual project, when water content of the riverbank soil was obtained, the cohesive and internal friction angle of soil can be calculated by proposed formulas, thereby the safety factor of riverbank can be calculated and the stability of river bank can be identified. [ABSTRACT FROM AUTHOR]

Mechanical harvesting technology of cotton has been increasing in modern agriculture in China, particularly for cotton serving as an important strategic reserve material. In mechanized harvesting of cotton, mechanical properties of machine-harvested cottons have become the key factors to cotton harvesting, even to the design of harvesting machinery. The machine-harvested cotton can fall off early in a bad weather after maturity, due mainly to the physical parameters of boll shell, resulting in the loss of pre-harvest cotton. Sometimes the cotton cannot be completely harvested, but the cotton can be knocked off when mechanized harvesting, resulting in the losses during harvest. The physical parameters of boll shell can be closely related to the mechanical effect of working parts, when the cotton is mechanically harvested, with emphasis on the separation force between the boll shell and cotton. Therefore, it is necessary to reveal the effect of physical parameters of boll shell on mechanical properties of machine-harvested cotton, particularly when designing cotton harvesting machinery. In this study, 3 kinds of representative machine-harvested cottons were selected as the research objects, including Xinluzao 45, Xinluzao 66, and Xinluzao 83, collected from the Shihezi area of Xinjiang, China. A laboratory tensile separation test was used to assess the mass fraction of boll shell, carpel angle, and lock angle for the 3 kinds of machine-harvested cottons under the same growth conditions. The experimental results showed that the separation force between cotton and boll shell were 0.155-0.980 N, 0.275-0.967 N, 0.258-0.667 N, for the Xinluzao 45, 66, and 83 machine-harvested cottons, respectively. Three stage can be divided for the machine-harvested cottons, including the elastic-like stage, yield-like stage, and separation stage, in the laboratory tensile separation tests. In the yield-like stage, the tensile separation curve of cotton showed the zigzag fluctuation with the multiple peaks. It inferred that there were concurrently elastic and plastic deformation of cotton fiber with the dominance of plastic deformation. The internal interlaced and intertwined fiber of cotton tissue can produce local dislocation, when the external load of cotton flower reached a critical value. The mass fraction of boll shell, carpel angle, and lock angle in the machine-harvested cottons have a significant effect on the separation force of cotton from boll shell (P<0.01). A power function relationship can be found between the separation force of cotton boll shells and the carpel angle, as well as the mass fraction of boll shell (P<0.001). The separation force of cotton and boll shell gradually decreased, with the increase in carpel angle and mass fraction of boll shell. There was a significantly negative correlation between the lock angle and the separation force, indicating that the separation force of cotton and boll shell gradually decreased with the increase of lock angle. A recommendation was made that a relatively small weight ratio of shell and a uniform locking angle can be selected, when breeding cotton crops for machine harvesting. The cotton can be timely harvested after maturity, in order to avoid the losses before harvest, when choosing the harvesting time. The finding can provide a sound theoretical and practical guidance for the cultivation of new harvesting cotton, as well as for the design and optimization for the harvesting machinery of cotton. [ABSTRACT FROM AUTHOR]

Mechanical harvesting technology of cotton has been increasing in modern agriculture in China, particularly for cotton serving as an important strategic reserve material. In mechanized harvesting of cotton, mechanical properties of machine-harvested cottons have become the key factors to cotton harvesting, even to the design of harvesting machinery. The machine-harvested cotton can fall off early in a bad weather after maturity, due mainly to the physical parameters of boll shell, resulting in the loss of pre-harvest cotton. Sometimes the cotton cannot be completely harvested, but the cotton can be knocked off when mechanized harvesting, resulting in the losses during harvest. The physical parameters of boll shell can be closely related to the mechanical effect of working parts, when the cotton is mechanically harvested, with emphasis on the separation force between the boll shell and cotton. Therefore, it is necessary to reveal the effect of physical parameters of boll shell on mechanical properties of machine-harvested cotton, particularly when designing cotton harvesting machinery. In this study, 3 kinds of representative machine-harvested cottons were selected as the research objects, including Xinluzao 45, Xinluzao 66, and Xinluzao 83, collected from the Shihezi area of Xinjiang, China. A laboratory tensile separation test was used to assess the mass fraction of boll shell, carpel angle, and lock angle for the 3 kinds of machine-harvested cottons under the same growth conditions. The experimental results showed that the separation force between cotton and boll shell were 0.155-0.980 N, 0.275-0.967 N, 0.258-0.667 N, for the Xinluzao 45, 66, and 83 machine-harvested cottons, respectively. Three stage can be divided for the machine-harvested cottons, including the elastic-like stage, yield-like stage, and separation stage, in the laboratory tensile separation tests. In the yield-like stage, the tensile separation curve of cotton showed the zigzag fluctuation with the multiple peaks. It inferred that there were concurrently elastic and plastic deformation of cotton fiber with the dominance of plastic deformation. The internal interlaced and intertwined fiber of cotton tissue can produce local dislocation, when the external load of cotton flower reached a critical value. The mass fraction of boll shell, carpel angle, and lock angle in the machine-harvested cottons have a significant effect on the separation force of cotton from boll shell (P<0.01). A power function relationship can be found between the separation force of cotton boll shells and the carpel angle, as well as the mass fraction of boll shell (P<0.001). The separation force of cotton and boll shell gradually decreased, with the increase in carpel angle and mass fraction of boll shell. There was a significantly negative correlation between the lock angle and the separation force, indicating that the separation force of cotton and boll shell gradually decreased with the increase of lock angle. A recommendation was made that a relatively small weight ratio of shell and a uniform locking angle can be selected, when breeding cotton crops for machine harvesting. The cotton can be timely harvested after maturity, in order to avoid the losses before harvest, when choosing the harvesting time. The finding can provide a sound theoretical and practical guidance for the cultivation of new harvesting cotton, as well as for the design and optimization for the harvesting machinery of cotton. [ABSTRACT FROM AUTHOR]