Contact stiffness is an important parameter for describing the contact behavior of rough surfaces. In this study, to more accurately describe the contact stiffness between grinding surfaces of steel materials, a novel microcontact stiffness model is proposed. In this model, the novel cosine curve-shaped asperity and the conventional Gauss distribution are used to develop a simulated rough surface. Based on this simulated rough surface, the analytical expression of the microcontact stiffness model is obtained using contact mechanics theory and statistical theory. Finally, an experimental study of the contact stiffness of rough surfaces was conducted on different steel materials of various levels of roughness. The comparison results reveal that the prediction results of the present model show the same trend as that of the experimental results; the contact stiffness increases with increasing contact pressure. Under the same contact pressure, the present model is closer to the experimental results than the already existing elastic–plastic contact (CEB) and finite-element microcontact stiffness (KE) models, whose hypothesis of a single asperity is hemispherical. In addition, under the same contact pressure, the contact stiffness of the same steel material decreases with increasing roughness, whereas the contact stiffness values of different steel materials under the same roughness show only small differences. The correctness and accuracy of the present model can be demonstrated by analyzing the measured asperity geometry of steel materials and experimental results.

Springs are critical components in mining vibrating screen elastic supports. However, long-term alternating loads are likely to lead to spring failures, likely resulting in structural damages to the vibrating screen and resulting in a lower separation efficiency. Proper dynamic models provide a basis for spring failure diagnosis. In this paper, a six-degree-of-freedom theoretical rigid body model of a mining vibrating screen is proposed, and a dynamic equation is established in order to explore the dynamic characteristics. Numerical simulations, based on the Newmark-β algorithm, are carried out, and the results indicate that the model proposed is suitable for revealing the dynamic characteristics of the mining vibrating screen. Meanwhile, the mining vibrating screen amplitudes change with the spring failures. Therefore, six types of spring failure are selected for simulations, and the results indicate that the spring failures lead to an amplitude change for the four elastic support points in the x, y, and z directions, where the changes depend on certain spring failures. Hence, the key to spring failure diagnosis lies in obtaining the amplitude change rules, which can reveal particular spring failures. The conclusions provide a theoretical basis for further study and experiments in spring failure diagnosis for a mining vibrating screen.

Permanent magnet coupling is extensively studied owing to its economic efficiency and stability. In this study, a computational model for cylindrical permanent magnet coupling (CPMC) was designed using the magnetic field division method to divide an air gap magnetic field. An equivalent magnetic circuit model was also designed based on the equivalent magnetic circuit method. The novelty of this study is that both the skin effect and the working point of the permanent magnet are taken into consideration to obtain the magnetic circuit and induce eddy current characteristics of permanent magnet coupling. Furthermore, a computational model was obtained for the transmission torque of the CPMC based on the principles of Faraday’s and Ampere’s laws. Additionally, the accuracy of the model was verified using a finite element simulation model and a test bench.

：By fitting the measured topography data of a single asperity on the plane grinding surface, a method of using the semi-periodic cosine curve rotating body equivalent asperity is proposed. The method of calculating the dimension parameters of a single asperity topography is obtained by marking the peak and valley of the measured surface topography. Combining with the Gauss distribution, the simulated surface which can more accurately characterize the actual surface morphology is established. Based on the simulated surface, the critical interference of the asperities in the elastic-plastic deformation region is re-calculated by using contact mechanics theory and statistical theory. The analytical relationship between contact parameters and contact pressure at different deformation stages are obtained. Then, a micro-contact model of rough surface in plane grinding is established. Finally, the statistical parameters of the measured grinding surface are taken as the initial values for the data simulation. The prediction results of average distance and real contact area are compared among present model, CEB model and KE model. The results show that under the same contact pressure, the average distance and the real contact area predicted by the present model are larger than those obtained by CEB model and KE model, and the difference between the three models increases with the increase of contact pressure. According to the fitting results of measured topography data by different asperity topography assumptions, the prediction results of contact parameters of surface grinding in present model are more accurate and reasonable.

Permanent-magnet couplers are widely used in various industrial applications due to their high functionality and economy. The magnetic field of the magnetic circuit of a permanent-magnet coupler is divided by the segmentation method, by which the magnetoresistance of each area can be calculated. The magnetic resistance of the magnetic flux and the permanent-magnet coupler characteristics outside the magnetic circuit are obtained using the equivalent magnetic circuit model of permanent-magnet couplers. The working point of the permanent magnet is analyzed, and the skin effect is found to be equivalent to a conductor plate with an increase in its resistivity. According to the principle of electromagnetic induction, the ampere force received by each part is calculated. Finally, the theoretical calculation model of the transmitted torque of the permanent-magnet coupler is obtained, and its accuracy is verified by finite element simulation and experiments. This can significantly guide the design and engineering applications of permanent-magnet couplers.