The main types of carbides in M50 bearing steel are MC, M₂C and M₂₃C₆. Under the scanning electron microscopy (SEM), they exhibit significant differences in the shape, size, and distribution. Some carbides have larger sizes and uneven distribution. They become areas of stress concentration under loading，which has a negative impact on the bearing fatigue performance. So an improved mask region-based convolutional neural network (Mask R-CNN) model was proposed which can batch identify the types of three kinds of carbides in SEM pictures, the diameters of carbides were measured, and the distribution of carbides was showed. The output images and histogram results show that the size of M₂C carbide in M50 bearing steel is large and unevenly distributed, but the distribution of MC carbide with the largest size and M₂₃C₆ with the smallest size is reasonably uniform.

Metro gearbox is a key component for torque transmission in vehicles, and its failure will directly affect the safety of train operation. The vibration characteristics of tooth breakage faults in metro gearbox were studied by combining dynamic simulation and vibration test. Firstly, based on the dynamic relationships and constraint characteristics between various components of metro gearbox, a rigid-flexible coupling dynamic model of metro gearbox with tooth breakage faults was established through the impact function method, Coulomb friction model, bearing modeling, flexible body of the housing and gear system dynamics theory. The dynamic response of the gearbox under different types of tooth breakage faults was studied, and the influence of operating parameters on the vibration characteristics of tooth breakage was analyzed. Then,through vibration test, the dynamic response of metro gearbox under normal state and broken tooth fault was obtained,verifying the accuracy of the dynamic simulation model. The results indicate that the rigid-flexible coupling dynamic model can effectively calculate the acceleration response of gearbox in different operating states, provide diagnostic basis for the prediction and identification of tooth breakage faults in the gearbox.

To investigate the mechanical properties of woven composite hybrid bonded/bolted joints, a mechanical failure model for hybrid bonded/bolted joints based on 3D progressive damage model and cohesive force model was developed to simulate the mechanical behavior and damage evolution of the joints. Based on the Abaqus finite element software, a finite element simulation model for hybrid bonded/bolted joints woven composites was established. The damage initiation and propagation of the composite material were judged using the three-dimensional Linde criterion. The cohesive force model was used to simulate the damage failure process of the adhesive layer. On the basis of test verification of the model accuracy, the strength and damage failure process of the joints were analyzed under different tightening torques. The test and simulation results indicate that as the tightening torque increases, the extension of adhesive layer damage can be effectively suppressed.However, the shear strength of the adhesive layer in the hybrid bonded/bolted joints firstly increases and then decreases,because increasing the tightening torque can reduce the peeling stress of the adhesive layer in the joints. However, the excessive tightening torque will strengthen the stress around the adhesive layer hole, leading to a decrease in the shear srength of the adhesive layer and a decrease in the strength of the connection structure. The load-displacement curve of the numerical simulation is consistent with the test results, and the predicted adhesive layer fracture load is equivalent to the test results. At the same time, the fiber damage, matrix damage, and delamination damage on the laminated plate can also be well reflected in the numerical model, which is similar to the damage form after the connection test, verifying the effectiveness of the damage prediction model.

The eccentric installation of high-lock titanium alloy bolts (an assembly angle between the bolt head and the fastening plate) leads to premature failure, which seriously affects the safe operation of aerospace aircraft. Currently, the test research is difficult to obtain the bolt fracture process, which in turn limits the revealing of fracture mechanism. Meanwhile,test research cannot obtain the fracture strength variation value of bolts with different assembly angles. Therefore, in response to the problem of premature fracture of high-lock bolts in the eccentric installation, finite element analysis method was employed and the model was verified by test. The verified finite element model was used to visualize the fracture process of eccentric installation bolts and predict the tensile strength of eccentric installation bolts with different angles. The research results indicate that the tensile strength and fracture position of bolts with installation angles of 0° and 3° obtained from finite element analysis are consistent with the test results, which show that the finite element model has good accuracy. As the installation angle increases, both the bolt head and thread are subjected to eccentric loads, and the bending moment generated aggravates the stress concentration in these two areas. When the assembly angle is less than 3°, the stress at the thread is larger,and when the angle is over 3°, the stress on the head is greater. The finite element model successfully predicts the tensile strength of bolts with an assembly angle of 1°, 2°, and 4°. The research results effectively reveal the fracture mechanism of high-lock titanium alloy bolts under the eccentric load. Meanwhile, the simulation model can predict the tensile strength of bolts under different installation angles, and provide technical specifications for the service of eccentric bolts.

The rapid assessment method for metal fatigue performance based on the infrared thermography presents advantages such as short testing cycles, low costs, and high efficiency. However, accurately quantifying factors influencing the dissipation of energy, such as convective heat transfer and thermal radiation, proves challenging. The difficulty leads to complications in achieving the precision necessary to meet test standards in the final assessment results. A mixed-hardening constitutive model for 304 stainless steel was established and coupled with the low-cycle fatigue thermomechanical mechanism, to analyze the evolution pattern of dissipated energy caused by convective heat transfer and thermal radiation during the loading process. Furthermore, the impact of low-cycle fatigue loading frequency on the rapid assessment results of fatigue performance was explored based on the critical threshold of dissipated energy. The research indicates that during the low-cycle fatigue process of 304 stainless steel, the dissipated energy from convective heat transfer and thermal radiation constitutes over 54% of the total dissipated energy. Moreover, this proportion continuously increases with the augmentation of the convective heat transfer coefficient. Therefore, it is crucial not to neglect these factors in dissipated energy assessment calculations. With an increase in loading frequency, the peak load narrows within the region of action time. Consequently, the dissipated energy of each load cycle decreases, leading to a rapid assessment result of fatigue performance that tends to be larger than the test value.

Porous metals are widely used in filtration, catalysis, adsorption and heat transfer because of their excellent mechanical properties. However, creep failure is a primary failure mode for porous metal parts experiencing the high temperature and constant stress. The research progress of the creep resistance of porous metal materials was summarized from four aspects, pore structure，edge structure, micro-defect and creep life prediction. The effects of pore structure, such as porosity, pore shape and pore diameter, on the stress index, creep resistance and deformation mechanism of porous metals were expounded. The creep resistance of the hollow and solid edge under different stress conditions was analyzed, and the effect law of edge size on the creep rate of porous metals was revealed. The effect of micro-defects on the creep mechanism of porous metals was clarified, and the constitutive model for predicting the creep life of porous metals was introduced. These studies provide scientific guidance for the long-life service and reliable operation of porous metal structures.

The calculation of bending strength for spiral bevel gears is complex, making accurate evaluation extremely challenging. Focusing on the two distinct calculation methods, B1 and B2, as outlined in the ISO 10300 standard, this study begins with the computational principles of both approaches. It compares the selection methods and numerical application principles for parameters involved in calculating root bending stress and allowable bending stress under both methods. The influence of parameter values on root bending stress calculations is analyzed for each method. Through computations on multiple design samples, the root bending stress values derived from both methods are compared. Finite element analysis is employed to validate the computational results. The findings indicate that due to differences in the types and values of correction coefficients used, there are certain discrepancies in the bending strength evaluation results obtained by the two methods. Method B1 yields a more conservative evaluation of root bending strength, with root bending stress approximately 5% lower than that calculated by Method B2. Although the ISO calculation standard accounts for load sharing among multiple teeth, it overlooks the combined effects on root bending stress, leading to deviations from finite element analysis results.Method B1 shows closer agreement with finite element results, with an error margin of about 6%.

A theoretical model of composite metal rubber (C-MR) was established on the basis of static mechanical test. A novel preparation process was used to prepare C-MR, which was subjected to static mechanical tests. The mechanical model of C-MR was established by combining the static mechanical models of wove-metal rubber (W-MR) and tangled-metal rubber (T-MR), and the effects of different knitting and winding ratios on the mechanical properties of C-MR were investigated. The comparison between the test data and the theoretical model shows that the theoretical model can predict the mechanical properties of C-MR effectively. The results show that the knitting and winding ratio has a significant effect on the mechanical properties of C-MR, and the larger the knitting and winding ratio is, the larger the stiffness and damping properties of C-MR are. The conclusion can provide a theoretical support for the preparation and application of C-MR.

Negative Poisson ratio structures are widely applied in various engineering fields due to their excellent mechanical properties. By combining the star-shaped honeycomb structure with the re-entrant structure, a novel re-entrant angle-type negative Poisson ratio honeycomb structure is proposed. Firstly, the unit cell structure was simplified and analyzed based on symmetry, and the analytical expressions for the Poisson ratio and equivalent elasticity modulus of the structure were derived using the energy method. Secondly, the vertical compressive mechanical properties of the structure were investigated using Abaqus finite element software, and the numerical simulation results were compared with the theoretical calculations to validate the accuracy of the analytical expressions. Finally, the influence of different geometric parameters of the unit cell structure on the equivalent Poisson ratio and equivalent elasticity modulus was discussed, and the equivalent mechanical properties of the structure were compared with those of conventional star-shaped honeycomb structures. The results demonstrate that the proposed structure exhibits favorable negative Poisson ratio characteristics, and its equivalent mechanical properties can be adjusted by modifying the geometric parameters. The findings provide valuable insights for the design of novel negative Poisson ratio metamaterials.

After low-velocity impact at the edge, delamination and matrix extrusion occur inside the composite laminates,which will have a serious impact on the safe use and life of the composite laminates. Therefore, it is of practical engineering significance to establish a fatigue life prediction model for low-velocity impact at the edge. The dent damage size, compressive residual strength and fatigue life of the fatigue life prediction model were obtained by low-speed impact test, compression test and compression-compression fatigue test. Based on the average stress failure criterion, the impact damage area of the laminated plate was equivalent to the corresponding aperture by combining the opening equivalent method, and the equivalent damage coefficient of different impact energy was proposed. A fatigue life prediction model considering the compressive residual strength of impact damaged laminates was established, and the prediction results were compared with the test results.The results show that the fatigue life prediction accuracy of the model is high, the error is controlled within 10%, and the model has good prediction ability.