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Low carbon alloy steel 20CrNiMo is a kind of high strength surface hardening material which was commonly used as high-quality gears. After surface nitriding, carburizing or carbonitriding quenching treatment, it has good tooth surface hardness and tooth root toughness. According to the relevant national standards, a number of material test bars had been designed and carried out, the tensile strength and tensile fatigue strength date of material had been obtained. The lognormal distribution and two parameters Weibull distribution were used to fit and test the testing data, and the R-S-N curves of materials with the different confidence levels were obtained by calculating the probability distribution function. The fatigue life data of the material was more suitable for the lognormal distribution.

According to the space meshing theory, the mathematics model of conjugate surfaces is constructed. Based on the coordinate transformation of this model, the mathematical solution of the wheel and pinion tooth surfaces is obtained. On the basis of surface synthesis, the construction method of gradient surface (Ease-off) for tooth modification is given. Taking the rotating projection plane of the tooth surface as the coordinate plane, the normal deviation of the modified tooth surface from the conjugate tooth surfaces for pinions is calculated, and the Ease-off surface of the spiral bevel gear is obtained. Based on analysis of the Ease-off surface, the complete contact morphological characteristics of tooth surface are obtained: the contact line-off, contact path, transmission error, etc., which are highly consistent with the actual contact pattern of the tooth surface. The above findings provide an accurate and feasible method for the topology design and meshing simulation of complex tooth surfaces.

A model for calculating the topological deviation of the actual tooth surface based on the coordinates of the detected cylindrical gear tooth surface points is established. The 3D tooth surface topological deviation map is constructed,and tooth profile deviation curve and helix deviation curve at different positions are obtained by slicing along the direction of tooth length and tooth height. The extraction method of tooth profile deviation and helix deviation is established. The experimental test and analysis results are compared with the report of Gleason 650GMS Gear Measurement Center to verify the accuracy of the method and provide a theoretical basis for the comprehensive evaluation and digital control of tooth surface accuracy.

Recent studies on microencapsulated self-healing cementitious materials have primarily focused on the particle size and preparation methods of the microcapsules. However, there has been limited attention paid to the microscopic aspects, such as the selection of curing agents and the curing duration of these materials. In this study, urea-formaldehyde resin/epoxy resin E-51 microcapsules were synthesized through in situ polymerization. This research investigates the feasibility of self-healing from a molecular mechanism perspective and evaluates the repair performance of microencapsulated self-healing cement mortar with varying microcapsule concentrations, curing agent types, and curing ages. The findings demonstrate that the microcapsule shells bond effectively with the cementitious matrix, with radial distribution function peaks all located within 3.5 Å. The incorporation of microcapsules enhanced the tensile strength of the modified cement mortar by 116.83% and increased the failure strain by 110%, indicating improved adhesion and mechanical properties. The restorative agent released from the microcapsule core provided greater strength after curing compared to the uncured state. Although the overall strength of the microencapsulated self-healing cement mortar decreased with higher microcapsule concentrations, the repair efficiency improved. The strength recovery rate of 28-day aged modified cement mortar had a significant improvement with the addition of X and Y curing agents, respectively. [ABSTRACT FROM AUTHOR]

In order to analyze the bearing capacity and transmission performance of equal base circle bevel gear under actual working conditions, the tooth contact analysis （TCA）is performed to simulate the tooth surface contact pattern and transmission error. Without errors of installing，the modification of tooth line and tooth profile of bevel gear is carried out, the influence of modification parameters of tooth line and tooth profile on transmission error of bevel gear and change of contact area of tooth surface are analyzed. By adjusting the modification parameters to improve the meshing characteristics of the gears，realize better lubricating performance and transmission stability. By machining and rolling a pair of modified equal base bevel gears，the correctness of TCA modification program is verified. The theoretical and experimental basis for the meshing performance analysis of gear is provided.

Accurately evaluating particle surface micro-texture levels and distribution at different wavelength scales of granular material is critical to optimise service stability of granular material under long-term dynamic loads. Firstly, generalised regression neural network (GRNN) and empirical mode decomposition (EMD) were adopted to impute missing data points and remove the arc-shaped tendency of granular materials' particle wear raw surface profile. Then, granular materials' particle surface micro-texture levels and their distribution within constant bandwidth narrow band spectrum and octave/fractional octave band spectrum were obtained with spectral analysis method, which could characterise granular materials' particle surface properties at different wavelength scales. Fourteen types of parent rocks of granular materials were tested with a modified micro tribological experiment simulating tribological behaviour among particle contact interfaces under dynamic loads. A contrastive analysis with traditionally used surface mean roughness was performed. The results indicate that the micro-texture levels and their distribution obtained in this study can detect the level of the exact texture scales (i.e. 32 and 2 μm wavelengths) significantly influencing the kinetic friction coefficient of granular materials, while surface mean roughness can only represent the global surface property. A high correlation was found between normalised micro-texture level (i.e. 32 μm) and Moh's hardness and coefficient of friction. [ABSTRACT FROM AUTHOR]

On the consideration of the existing tooth surface modification technology of spiral bevel gear limited to special milling tooth machine,a kind of tooth surface modification method based on the machining center is put forward. Based on the forming machining method of spiral bevel gear,the pinion tooth surface equation is derived by using the conjugate principle,and the amount of modification is added to discrete points by applying the differential curved surface equation. The digital gear tooth surface of the pinion is obtained by the NURBS surface meshing,which is analyzed with the theoretical tooth surface of the gear. The cutting experiment on machining center is performed on the machining center,and the rolling test experiments show that the tooth contact area and the simulation results mainly agreed. The feasibility of the modification method proposed is verified,which provides the technical support for the spiral bevel gear tooth being processed on machining center and the control of the meshing quality.