Soft magnetic composites (SMCs) can be described as soft magnetic powders covered by electrically insulating layers. In this work, iron powders with high purity and organic-silicon epoxy resin were chosen for good magnetic properties, thermal stability, and mechanical properties, respectively. The effect of amount of resin, different annealing temperatures on the microstructure, and performance of SMCs was investigated. Results show that organic-silicon epoxy resin has excellent properties as dielectric coating materials for coating iron powders and maximum heat-resistant temperature is about 400 ℃. According to magnetic properties and flexural strength analysis, the optimum annealing temperature of organic-silicon epoxy resin-coated composite is 200 ℃. Furthermore, the finite element analysis indicates that the strength of the whole composites is related to the adhesion of resin and iron and the strength of resin itself.

A trunnion joint is modeled as a circular plate with two types of outer boundary conditions. One is clamped supported and the other is simply supported. Symmetrical bending deflection is produced when an external force acts on the inner side of the circular plate. The governing equations of the circular plate with these two kinds of boundary conditions are solved by using finite difference method, and the axial stiffness of the circular plate is obtained according to the relationship between the external force and the bending deflection of the circular plate. In order to verify the accuracy of the finite difference method, a finite element method was also given. The effects of rotational speed and the ratio of inner radius to outer radius of the circular plate on the axial stiffness are studied. It is shown that the rotational speed can significantly affect the axial stiffness of the trunnion joint for these two cases, especially for a lower ratio of inner radius to outer radius of the circular plate. The axial stiffness increases monotonically with the increase in rotational speed. More specifically, for a lower ratio of inner radius to outer radius of the circular plate, the axial stiffness with the simply supported boundary condition at high rotational speed is more than twice as much as the case without considering the rotational speed. Correspondingly, it is more than one and a half times for the clamped supported boundary condition.

To analyze the influence of the component size ratio(matrix/inclusion) on the densification and magnetic property, the equivalent model of SMCs at particle scale was used for static case. The relation of porosity, density against the component size ratio δ is deduced. To calculate the effective permeability of the model, the equivalent magnetic circuit method and magnetic energy method are proposed and compared. The results show that the densification and effective permeability are dependent on the component size ratio. The effect of porosity is even more pronounced for the effective permeability. In addition, the results of this model are consistent with the experimental results.

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Abstract. Bolted joint is one of the most widely used connections because of relatively simple structure, reliability, easy disassembly and maintenance. However, self-loosening of bolted joints under cyclic external loading is still an unsolved issue and need to make a further research. As is known to all, the self-loosening process can be divided into two distinguishable stages under cyclic transverse loading. The first stage is featured by a short and sharp clamping force reduction with no relative rotation between the nut and the bolt. The loss of the clamping force is due to the accumulation of local cyclic plastic deformation at the root of the engaged thread, which is account for no more than 10-15%. Therefore, the second stage is the primary cause of self-loosening. In this study, a further research on the second stage self-loosening of bolted joints is presented by the ways of combining theoretical analysis with the three-dimensional finite element simulation. The nature of the second stage self-loosening of bolted joints lies in: 1) the variation of the contact pressure between the engaging thread surfaces, 2) lateral micro-slip between the engaging thread surfaces. Both of them result in an apparent slip between the engaging thread surfaces of bolt and nut which finally leads to the self-loosening of bolted joints. In addition, the effects of preload, amplitude of cyclic transverse loading and the friction coefficient of engaging surfaces on self-loosening are studied by the finite element simulation. Moreover, a reasonable explanation of the trend about the self-loosening of bolted joints is given. The corresponding results are very important for the bolted design. It can be concluded that reasonable preload may improve the ability of bolted joints resisting to self-loosening.