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.

Aiming at optimizing the gear surface modification process, the influence of ion nitrogen implantation on the bending fatigue strength of carburized and quenched gears was studied.Using low-carbon alloy steel 18CrNiMo7-6 carburized and quenched gears as the matrix, nitrogen ion implantation treatment was carried out through a radio-frequency plasma-assisted ion implantation system. The root metallography, hardness gradient, residual stress distribution, and bending fatigue properties of ion-implanted gears and unimplanted gears were systematically compared. The results show that the ion nitrogen implantation process increases the root hardness from 695 HV0.1 to 780 HV0.1, an increase of 12.2%; the hardened layer depth decreases from 1.50 mm to 1.41 mm, a reduction of 6.0%; and the surface residual stress decreases from -400 MPa to -286 MPa, a reduction of 28.5%. Based on the R-S-N equation fitted by bending fatigue tests, under 99% reliability, the fatigue life of ion-implanted gears is only 12.3%-19.3% of that of the control gears, with the failure mode dominated by brittle fracture and accelerated crack propagation rate. The study indicates that although ion nitrogen implantation can delay crack initiation through surface strengthening, the excessively shallow hardened layer and reduced residual stress lead to insufficient crack propagation resistance, ultimately weakening the bending fatigue life of gears.

Shot peening process is widely used in the manufacturing process of gears and other basic components, and its own limitations limit the enhancement of the surface integrity of the workpiece. In order to further improve the surface integrity of the workplece, A combination of numerical simulation and experimental methods was utilized to study the effect of two surface composite strengthening processes, such as double shot peening and shot peening-ultrasonic rolling, on the surface integrity of 18CrNiMo7-6 carburization gear steel samples, and mainly analyzed the effect of the two composite strengthening processes on the improvement of surface integrity of the shot peened samples. The results show that the maximum value of the residual compressive stress of the double shot peening sample was 1 359.56 MPa, locates at the depth of 0.08 mm, and the maximum value of the residual compressive stress of the shot peening-ultrasonic rolling peening sample was 1 329.05 MPa,locates at the depth of 0.25 mm. Compare with the single shot peening sample, the surface roughness of the double shot peening sample and the shot peening-ultrasonic rolling sample was 29.42% and 29.42% lower than that of the single shot peening sample. Compare with the single shot peening samples，the surface roughness of the double shot peening samples and shot peening-ultrasonic tumbling peening samples decreased by 29.42% and 62.76%，respectively, the surface microhardness increased by 8.70% and 17.60%, and the standard deviation of the surface node compressive residual stress value decreased by 23.36% and 89.50%. The shot peening-ultrasonic rolling process is more effective in enhancing the surface hardness,thickness of the residual stress layer and uniformity of the residual compressive stress, as well as reducing the surface roughness of the specimens，and can effectively improve the surface integrity of the shot peened samples.

To address the issue of accuracy degradation caused by aerodynamic damping when measuring the moment of inertia of irregular specimens with large airfoil surfaces using the torsional pendulum method, a compensation approach based on drag simulation results was proposed. Initially, the mechanism of aerodynamic damping in torsional oscillations was analyzed, and a measurement model incorporating compensation through calculation of aerodynamic damping torque was established. Subsequently, the reduced frequency parameter was introduced to characterize the unsteady aerodynamic nature of the aerodynamic damping torque. By employing a quasi-steady assumption combined with equivalent linearization techniques,the unsteady time-varying aerodynamic damping torque was equivalently represented as viscous damping. Furthermore,computational fluid dynamics (CFD) simulations were conducted to obtain drag coefficients during specimen motion, from which a compensation formula based on drag coefficients was derived. Finally, validation test were designed and performed to verify the proposed method. The findings indicate that under low reduced frequency conditions (reduced frequency less than 0.01), the relative error between the equivalent aerodynamic damping ratio calculated via quasi-steady assumption and test separation values is approximately 7%. After compensating using the proposed equivalent aerodynamic damping ratio, the error between measured and theoretical moments of inertia is approximately 0.2%, demonstrating that the proposed method effectively enhances measurement accuracy for moments of inertia of irregular specimens with large airfoil surfaces.

The harsh operational environment of helicopters renders their structures highly susceptible to the initiation and propagation of hole-edge cracks around bolt holes, thereby compromising structural integrity and load-bearing capacity. To monitor hole-edge cracks in helicopter attachment lug structures, piezoelectric guided wave-based structural health monitoring(SHM) techniques are commonly employed. However, due to the difficulty in detecting small cracks at the early stages of propagation and the presence of large through-hole configurations in attachment lug structures, the accuracy of guided wave monitoring remains suboptimal. Therefore, addressing the accuracy issues in crack monitoring of attachment lug structures,this study proposes a piezoelectric guided wave array-based method for hole-edge crack detection. Firstly, damage feature information was extracted from acquired piezoelectric guided wave array signals encompassing the entire sensor network.Subsequently, a damage alarm threshold was established using a mean-value method to facilitate damage detection.Furthermore, an improved delay-and-sum imaging algorithm was developed based on the specific configuration of the attachment lug structure to optimize probability distribution and achieve precise crack localization. Finally, validation was conducted through test monitoring of crack propagation in attachment lug structures. Test outcomes demonstrate that the proposed method enables accurate alarm triggering and localization of hole-edge cracks around bolt holes, with localization errors confined within 2.01 mm, thereby confirming the efficacy and precision of the proposed approach.

In order to ensure the industrial robot realizes the reliability goal, reliability allocation is a task to be accomplished in its manufacturing design stage. According to the characteristics of industrial robots, such as complex structure, high uncertainty, few samples, and failure correlation between component parts, a reliability allocation method for industrial robot systems based on BP neural network and Pythagorean fuzzy numbers was proposed. Using Copula function to establish a system reliability model, the failures of industrial robots were classified into three levels, the system level, the subsystem level, and the component level. By using the back propagation (BP) neural network, the system reliability,subsystem structure importance and subsystem complexity were taken as the input variables to complete the system-to-subsystem reliability allocation. The Pythagoras fuzzy number was introduced to score the influence factors of importance,environmental condition, technical level, maintainability, cost sensitivity and complexity, complete the reliability allocation from the subsystem level to the component level.The results show that the methodology achieves reliability goals and ensures reliability growth.

To study the response characteristics of the hollow extruded profile of the vehicle after the collision, the generalized incremental stress state-damage model (GISSMO) was introduced and the finite element simulation was carried out. Firstly, based on the test results of 6082-T6 aluminum alloy, the dynamic and static mechanical properties and fracture behavior under different stress states were characterized by the modified Johnson-Cook (MJC) model and DF2016 model respectively. Secondly, the parameter calibration of GISSMO was carried out based on the combination of LS-OPT soft ware and manual optimization. Then, according to the mesh size effect, the mesh size dependence correction was carried out, and the effectiveness of the model and correction were verified by comparison between the experiment and simulation. Finally, the impact simulation analysis of a hollow extruded profile on the side wall of a vehicle body was carried out, and the impact of material damage and fracture on the simulation results was compared. The results show that GISSMO can more accurately reflect the response of profiles under longitudinal impact than without considering the damage and fracture of materials.

Aiming at the problem of the weld fatigue test of the new energy vehicle subframe, a program load spectrum compilation method based on the failure dominant load was proposed. Firstly, the finite element model of the rear subframe was established, and the stress distribution under unit load was coupled with the load of each connection point. The structural stress method was used to evaluate the fatigue life of the subframe welds, and six dangerous points that were easy to fail were selected. Secondly, by comparing the load damage of each connection point, the failure dominant connection point corresponding to the weld dangerous unit was determined. Then, the failure dominant load was determined by the principal stress analysis, time domain correlation and uniaxial damage contribution at the weld, so as to reduce the dimension of the multi-axial load and reduce the difficulty of the bench test loading. Finally, a pseudo-damage matrix was output based on the failure dominant load, the characteristic working conditions and their proportions were selected to obtain the load spectrum of the fatigue accelerated test program, and the minimum number of cycles was determined according to the principle of the damage equivalence. The numerical simulation results show that the program load spectrum can reproduce the damage of dangerous points and has a high acceleration coefficient, which verifies the effectiveness of the accelerated test spectrum.

To accurately simulate the complicated load transfer pattern of the launch device under cold launch mode, the rigid-flexible coupling dynamic simulation method was adopted to analyze the dynamic response of a launch vehicle, the structural strength was also verified. The finite element flexible body was introduced and a multi-rigid-flexible-body dynamic simulation model of a launch vehicle was constructed. Accuracy of the model was verified by the actual launch test. The influence law between the vibration response and stress state of the launch vehicle and the launch angle was further analyzed. The results show that amplitudes of the transmitted load and stress inside the launcher will reduce when the launch angle is close to 90°. The modeling and analysis approaches proposed in this study can effectively support the optimal design of the launch device.

Aiming at the problems of traditional impact load identification methods, such as the requirement for a large number of sensors, high sampling frequency, and low identification accuracy, a new impact load identification method based on empirical mode decomposition (EMD) technology was proposed.The EMD technology was used to decompose the complete impact response to obtain the modal acceleration response. The impact location was quickly realized by measuring the collinearity between the uncorrected mode shape vector and the column vector of the mode shape matrix in the modal acceleration response. According to the positioning results, an optimization objective function was constructed. The time history of the impact load was fitted by using the Gaussian basis function, and the optimal fitting parameters were quickly solved by using the two-dimensional gradient descent method.Tests conducted on a cantilever plate with dimensions of 600 mm×200 mm×3 mm show that with only one accelerometer, the success rate of 36 impact positioning tests is 91.67%. The peak relative error and relative error index of the reconstruction results are less than 10% and 40%, respectively.