To address the issue of characterizing static and dynamic mechanical behaviors of the surface-modified layer (SML) in 18CrNiMo7-6 alloy steel, a layered inversion method for the Johnson-Cook (J-C) constitutive model of SML was proposed. The SML was subjected to layered processing, and dynamic compression tests were conducted on cylindrical specimens with different SML thicknesses. Through progressive parameter inversion, the strain rate sensitivity coefficient C at each depth of the SML was determined. Combined with quasi-static thin plate tensile tests at different temperatures for each depth of the SML, the corresponding yield strength A, strain hardening coefficient B, strain hardening index n, and thermal softening exponent m were determined. Test results show that the SML of 18CrNiMo7-6 alloy steel exhibits significant strain hardening, strain rate strengthening, and temperature softening effects. Additionally, a correlation model between J-C constitutive parameters and dimensionless depth h/h_b (distance to SML surface/SML effective depth) was established,providing support for subsequent composite strengthening simulations.

Different parts of high-speed train bogies are usually designed with aluminum alloy materials of varying strengths, and welding is adopted to connect these different parts. When high-speed trains operate under complex road conditions, the bogies will be subjected to tensile overload, which will produce a coupled superposition effect with the strength difference of welded joints. Therefore, tensile overload tests were carried out on the welded structural components of bogies to study the fatigue crack growth behavior and intrinsic mechanism of aluminum alloy welded joints with different strengths under the action of tensile overload. The compliance method was used to measure the crack growth rate under tensile overload;the digital image correlation (DIC) technology was applied to analyze the change in the size of the plastic zone at the crack tip before and after the application of tensile overload; the scanning electron microscope (SEM) was employed to observe the fracture morphology characteristics of different aluminum alloys in the region affected by tensile overload. The crack growth behavior and intrinsic mechanism under tensile overload were explained based on the change in the size of the plastic zone at the crack tip and the corresponding fracture morphology characteristics. The results show that a single tensile overload can reduce the fatigue crack growth rate and extend the fatigue life. Further analysis indicates that during the tensile overload process, the plastic zone at the crack tip expands and the crack tip is blunted, which together lead to the reduction of the fatigue crack growth rate. The lower the material strength, the more severe the deformation at the crack tip and the more obvious the hysteresis effect under the same tensile overload. The test results of welded joints under tensile overload are consistent with those of the base metal, suggesting that the strength of the hysteresis effect depends only on the inherent strength of the material itself.

To investigate the influence of structural parameters on the yield strength and deformation behavior of truss lattice structures, face-centered cubic (FCC) porous lattices were fabricated and the mechanical responses were systematically studied. A finite element model was developed to evaluate the yield strength and failure modes of structures with varying geometric parameters. The analysis revealed a correlation between the member slenderness ratio and the transition from progressive collapse to global yielding under different loading orientations. Structures with lower slenderness ratios tend to exhibit global yielding, while those with higher slenderness ratios are prone to layer-by-layer compression failure.Furthermore, lattices supported along the face diagonals demonstrate more uniform global deformation, whereas those supported along the body diagonals are characterized by localized deformation.

Under the background of automotive lightweighting, the use of resistance spot welding to achieve effective connection of aluminum to steel structures is an unremitting pursuit. However, in actual welding production, fluctuation of working conditions occur frequently, seriously affecting the quality of weld points. Firstly, the resistance spot welding process was adopted to connect aluminum alloy and low-carbon steel plates. The influences of different inclination angles, plate gaps,and fluctuations in cooling water flow conditions on the resistance spot welding of aluminum-steel were investigated. Then,the quality of the weld points was evaluated by comparing the diameter and thickness of the nugget, the thickness of the intermetallic compound, the coach peel performance, as well as the fracture mode. The research results show that an increase in the inclination angle and the gap between the plates within a certain range, as well as a decrease in the cooling water flow within a certain range, will both reduce the quality of the weld points. Therefore, they should be avoided as much as possible in actual production. The results of this study provide a theoretical basis and practical guidance for optimizing the resistance spot welding process of aluminum to steel.

At present, the deterministic design and evaluation of high-temperature structural strength have been fully developed and formed a relatively complete system framework, laying the theoretical foundation for the design and manufacturing of numerous mechanical equipment under harsh service conditions. Considering the randomness of high-temperature structural failure and the small-sample characteristics of failure data, safety factors are usually adopted for conservative design in engineering. However, this often leads to structural redundancy and cost waste, so there is an urgent need to conduct research on design methods from determinism to uncertainty. Nevertheless, no universal and mature theoretical methods for high-temperature structural reliability or national/industrial standards have been established so far,making it difficult to effectively predict and guarantee the reliability of high-end equipment such as China's aero-engines during operation. Based on this, firstly, uncertainty analysis was elaborated. The damage-threshold interference criterion was introduced in detail, and its differences from and connections with the stress-strength interference criterion was explained.Finally, taking a certain steam turbine rotor as an example, it illustrates the engineering application of the damage-threshold interference criterion in the reliability analysis of high-temperature structures.

To enhance the assembly connection performance of adhesive structures in heavy machinery and aerospace equipment, a numerical analysis model based on the cohesive force element was developed to investigate the failure behavior of adhesive joints. The evolution of shear stress distribution in the adhesive layer during the tensile-shear failure process under different loading stages was analyzed. The variations in ultimate failure load and structural stiffness with different adhesive joint parameters were systematically studied, and tensile-shear failure tests were conducted. The results indicate that the shear stress distribution in the adhesive layer transitions from an initial U-shaped profile to an M-shaped and finally evolves into an approximately inverted U-shaped pattern as the load increases. Increasing the length or width of the adhesive layer significantly improves both the ultimate failure load and overall structural stiffness. However, increasing the adhesive layer thickness or substrate thickness exhibits a minor effect on the ultimate failure load. Notably, the structural stiffness decreases with increasing adhesive thickness but increases with higher substrate thickness.

In response to the problems of reduced surface quality and severe twist drill wear in HR-2 hydrogen resistant steel deep small holes drilling, integrated thermal coupling finite element simulation with experimental investigations of deep small holes drilling to analyze the variations in tool wear, drilling temperature, and the quality of the machined surface during the process of machining deep small holes. The improvement effect of introducing ultrasonic vibration on poor surface quality and severe tool drilling wear was analyzed by comparing ultrasonic vibration assisted drilling (UVAD) and conventional drilling (CD). The results show that as the drilling depth increases, the heat accumulation of the tool's transverse and cutting edges significantly increases, gradually leading to problems such as coating peeling, edge passivation and chipping.Concurrently, the accumulation of cutting heat on the surface of the machined hole causes temperature rise, resulting in material coating, debris adhesion, oblique scratching and other problems on the machined surface, resulting in a deterioration of surface quality and an elevation in surface roughness. Compared to CD, the UVAD effectively reduces drilling temperature,helps to reduce tool wear and maintain cutting edge integrity, while suppressing the increase in surface roughness during machining, ultimately improving surface quality.

To address the problems of unclear internal load evolution law of the electromechanical composite transmission system for high-speed tracked vehicles and the lack of fatigue life prediction method for planetary gear bearings,a dynamic model of planetary gear bearings in the electromechanical composite transmission system was established to obtain the distribution law of contact loads on planetary gear bearings. A fatigue life prediction method based on the dynamic load characteristics of planetary gear bearings was proposed, which provides certain guiding significance for the optimization and design of the planetary mechanism in the electromechanical composite transmission system. Considering the effects of multi-row coupling effect of the electromechanical composite transmission system, gear time-varying meshing stiffness excitation,and nonlinear support stiffness excitation of planetary gear bearings, a dynamic model of the electromechanical composite transmission system was established using Simpack to obtain the load-bearing conditions of planetary gear bearings.Furthermore, a dynamic model of planetary gear bearings was established using the lumped mass method to analyze the evolution law of contact loads on planetary gear bearings. Then, a fatigue life analysis and prediction model for planetary gear bearings was established using the L-P formula to analyze the variation law of fatigue life of cylindrical roller bearings for planetary gears under different working conditions. The results show that at high rotational speeds, the centrifugal force of the planetary gear bearings during revolution has a significant impact on the contact loads and fatigue life of the planetary gear bearings. At lower rotational speeds, the service life of the planetary gear bearings in the reduction gear increases with the rotational speed. At higher rotational speeds, the service life of the planetary gear bearings in the reduction gear decreases with the increase in rotational speed. At high rotational speeds, measures such as profile modification of the rolling elements of planetary gear bearings can be taken to extend the service life according to the life requirements of the electromechanical composite transmission system.

Residual stress is the main factor affecting the machining performance and service life of brazed diamond tools. At present, in simulations, diamond is often simplified as a spherical shape, which leads to changes in the degree of structural constraint at the joint, resulting in significant differences between the calculated results and the actual situation. The evolution law and distribution characteristics of residual stress in vacuum-brazed diamonds, as well as the influence of residual stress on wear resistance, were investigated. Firstly, the geometric model of the diamond coating was optimized based on macroscopic morphology. Then, a finite element model of the stress field of vacuum brazed diamond coating was established using thermal elastoplastic mechanics, and the stress field distribution law of the diamond coating was obtained. Subsequently,residual stress measurement experiments were conducted on diamond and nickel based coatings to verify the reliability of the model. Finally, the influence of residual stress on the wear resistance of diamond coatings was explored through wear-resistant weight loss experiments. The main form of wear failure of diamond tools is diamond detachment caused by insufficient grip of the coating on diamond abrasive particles. The diamond wrapped by the brazing material layer is mainly affected by residual compressive stress, which increases the coating’s grip on the diamond. The higher residual stress inside the nickel based coating can also effectively suppress the wear-resistant failure mode of coating peeling.

Aiming at the limitations of current monitoring methods in the accuracy of early fault diagnosis for rolling mill bearings, a structural design method for intelligent rolling mill bearings based on embedded multi-source microsensors was proposed.A multi-source microsensor module integrating temperature and acceleration signals was developed, and an optimized layout structure of axial sensing leads in the bearing housing was designed, breaking through the bottleneck of sensor integration under the space constraints of traditional bearings. A mechanical performance evaluation system for the slotted structure was established, and the reliability of the intelligent structure was verified through strength check and service life calculation.The results showed that when the slotted area was 10 mm×5 mm, the maximum equivalent stress was 99.71 MPa,which had sufficient safety margin compared with the material yield limit; the maximum overall deformation of the structure was only 0.24 mm, and the local deformation was less than 0.02 mm, with the theoretical service life consistent with that of conventional bearings. The optimized intelligent bearing ensured monitoring functionality while meeting industrial application requirements in terms of structural strength and service life. The research results not only provide a high-precision monitoring method for early fault diagnosis of rolling mill bearings under extreme working conditions but also achieve an integrated"monitoring-structure" process through embedded design. Its strength check standards and service life evaluation methods can directly guide the transformation and upgrading of intelligent bearings in industrial sites, holding significant engineering value for improving the operation and maintenance efficiency of rolling production lines.