Impulse current under short-circuit condition is the key factor for the structural reliability of the testing transformer. Therefore, the structural reliability analysis model of transformers was proposed based on the probability density evolution theory. Firstly, the basic principle of probability density evolution theory was introduced, and the analysis method of electromagnetic force field for windings was given considering the coupling effects of magnetic and electric fields. On the basis，the numerical analysis model of transformers structure was constructed by using the Abaqus software finite element analysis method. Taking an AGF 20 kV testing transformer as an example, the above model was validated. The longitudinal Mises stress of windings was chosen as the control variable, and the stress distribution and probability density evolution characteristics were given. Then, the structural reliability index was calculated, and the extreme mechanical response and the corresponding distribution zones of windings and iron cores were discussed. The results show that the stress of windings increases significantly under the action of short-circuit impulse current. The maximum value of windings’stress reaches 82%of the threshold, and plays the key role in structural reliability, the increase of impedance has obvious influence on the reliability of transformers.

Sandwich structures composed of PET foam core and aluminium alloy panel were taken as reserch object. In the process of fabricating sandwich structures, four types of core materials were employed. Firstly, untreated PET foam core and PET foam cores subjected to subtractive process treatment (unidirectional slotting, bidirectional slotting，and punching).Secondly, the peel resistance performance between the aluminium alloy panel and PET foam core was tested through the drum peel test, while the influence of material subtractive process on shear performance of the sandwich structures was evaluated through the pure shear test. Finally, the peel and shear failure modes, load-displacement responses, and peel and shear strengths of the structures were analysed. The results show that the peel strength between the panel and PET foam core is improved by 48.31%, 32.29%, and 16.67% respectively, compared with the untreated structure, by using bidirectional slotting, unidirectional slotting and punching processes. Although the three processing techniques cause damage to the PET foam core, they actually increase respectively the shear yield strength of the sandwich structures by 3.12%, 3.90%, and 2.92%, compared to the untreated structure.

In order to ensure the safe and stable operation of gas turbine units, and grasp the heat transfer mechanism of the ventilation system of the mainframe housing, a study on the ventilation and heat dissipation of the main engine box of gas turbine units was carried out. Based on the principle of field synergy, the internal flow field, temperature field and heat dissipation performance of key equipments in the mainframe cabinet were analysed, and an optimized scheme for adding a flow-guiding device was proposed. The results show that the volume of the high-temperature area inside the mainframe housing is 7.6%, mainly concentrated near the gas turbine shaft component, which is the main heat source inside the mainframe housing, with an average external surface temperature of 86.94 ℃. After the installation of a 50° flow-guiding device, the volume of the high-temperature area inside the mainframe housing is reduced to 5.1%, and the average external surface temperature of the gas turbine shaft is reduced to 81.98 ℃. The heat dissipation effect is significantly improved.

Coatings have extensively been used to the surfaces of critical components to enhance their service life, and the research on mechanical properties of coatings is essential for advancing this technology. TiAlN/Ti and TiN/Ti multilayer coatings were prepared on aluminum matrix composite surfaces by using the vacuum ion beam sputtering technique. The microstructure, phase composition，and mechanical properties of the coatings were characterized and analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and nanoindentor. The dimensionless function correlation between mechanical properties of material with multilayer coatings and the loading/unloading parameters of nanoindentation was derived based on dimension analysis theory, and its explicit expression was determined in conjunction with the finite element simulation method. By establishing a nanoindentation simulation model for the multilayer coating, the impact of residual compressive stress on the tensile properties of the multilayer coating was analyzed. The results indicate that residual compressive stress can enhance the yield strength of the multilayer coatings. The residual compressive stress of TiN/Ti multilayer coating is -564 MPa, increasing the yield strength by 31.25%. Similarly, the residual compressive stress of TiAlN/Ti multilayer coating is -871 MPa, resulting in a 50% increase in yield strength. An important theoretical and test basis is proposed for quantitative analysis of the factors influencing the mechanical properties of coatings.

In order to simulate the crack propagation by corrosion fatigue, a coupled peridynamics corrosion-fatigue fracture model was proposed and applied to the simulation and analysis of crack propagation in A7N01P-T4 aluminum alloy.In this model, the interaction of hydrogen and stress was used to reflect the synergy between the two mechanisms of anodic dissolution and hydrogen cracking in corrosion, and the corrosion solution step and the mechanical solution step were coupled when quantifying the fracture behavior of the material due to corrosion. Since hydrogen reduces the plasticity of the material and brittle fracture occurs, a bonded peridynamics theory suitable for simulating isotropic brittle damage was used, and the relation between near-field force and elongation was described using an intrinsic force function for quasi-brittle materials that incorporates both linear and nonlinear mechanical behavior. The feasibility of the model is verified by comparing the simulation results with the test results of A7N01P-T4 aluminum alloy in 3.5% NaCl solution, and it is found that the results are in good agreement between them.

The traditional Paris formula ignores the influence of various uncertain factors in the crack growth process,which leads to a big difference between the predicted crack growth process and the real crack growth process. In order to improve the prediction accuracy of fatigue crack growth, a fatigue crack growth prediction method based on the improved particle swarm optimization particle filtering (IPSO-PF) algorithm was proposed. Firstly, based on the framework of the particle filtering (PF) algorithm, the particle swarm optimization (PSO) algorithm was used to optimize some particles based on the updated observation information，keeping the state of particles with large weights unchanged, and particles with small weights tend to high likelihood region, and IPSO-PF algorithm was designed. Then，combining IPSO-PF algorithm with Paris formula, a fatigue crack growth prediction model based on Paris formula and IPSO-PF algorithm was constructed. Finally, the validity of the model was verified by using the open 2024-T351 aluminum alloy data set. The results show that compared with the traditional PF algorithm, IPSO-PF algorithm can improve the diversity of particles. The prediction error of the crack growth prediction model based on IPSO-PF algorithm is 2.6%, which is better than 9.2% based on PF algorithm.

Due to the similarity between the internal structure of wind turbine blades and plant leaves, a new type of bionic leaf vein structural distribution was proposed, along with an entire composite blade layup program based on the bionic method of applying the mid-axis morphology of plant blades to 5 MW wind turbine blades. The modal analysis and static analysis of the new bionic vein blade were performed using the fluid-solid coupling method. The results show that the first six-order of the nature frequency of the bionic blade are improved in comparison to the traditional layup blade and are difficult to resonate, as well as its torsion resistance. Under the extreme wind load of 50 m/s, the displacement of the bionic blade’s tip is significantly smaller than that of the traditional blade, and the distribution of the strain and the distribution of the shear stress are more uniform than those of the traditional layup blade, but the maximum value of shear stress rises.

The fracturing pump plunger seal pair is one of the components most prone to failure at the hydraulic end of the fracturing pump due to its long-term operation under variable load，reciprocal friction and high pressure, and acidic fracturing fluid. To study the influence of interference magnitude, medium pressure, etc. on the sealing performance of V-shaped sealing ring, the assembly process of V-shaped sealing ring was simulated by using automatic shrinkage fit, the actual fluid pressure action condition of the V-shaped sealing ring was simulated based on fluid pressure penetration, and the finite element model of V-shaped sealing ring was established. Under quasi-static and dynamic sealing, the maximum Mises stress and the variation law of contact pressure of the V-shaped sealing ring were analyzed. A two-stage differential pressure plunger seal structure was proposed, and the sealing performance analysis of the structure was carried out. The results show that the maximum contact pressure of the seals all appear in the V-shaped sealing ring near the high-pressure fluid side, and the maximum stress is mainly in the lip and shoulder of the V-shaped sealing ring in contact with the support ring and press ring,the V-shaped sealing ring is more likely to fail on the side in contact with the plunger. The use of two-stage differential pressure plunger seal can effectively reduce the Mises stress, shear stress, and friction between the V-shaped sealing ring and the plunger, which can extend the working life of the fracturing pump plunger seal and improve the reliability and economy of the fracturing operation.

Aiming at the storage life evaluation of photodetectors, a new evaluation method for multi-parameter competitive failure storage life assessment based on Monte-Carlo method was proposed. This method comprehensively considered whether the key performance parameters of the sample have deteriorated or improved trend. Firstly, the optimal degradation model with a single parameter was selected by performance degradation modeling, so that the pseudo-life of the sample with increasing degradation trend was calculated according to the failure threshold, and the pseudo-life was regarded as the right-censored data for the sample with decreasing degradation trend. Furthermore, the optimal distribution of a single performance parameter was selected based on the pseudo-life data combined with the expectation maximization(EM)algorithm, and then the competitive failure evaluation of multi-parameters was carried out by Monte-Carlo sampling method.According to the case analysis of the photodetector storage, the feasibility of this method was verified.

The bearing section of the work roll neck often suffers burnout failure due to bearing seizure, and additive manufacturing is usually used in the field to repair it. Life prediction of the repaired roll neck is the key to predict the safe service of the work roll in the field production and carry out overhaul，but there is a lack of research on the related issues. In view of the above problems, the stress analysis and multi-axis life prediction of the working roll neck bearing section of the four-high mill were carried out. Based on the SIMS model and the influence function method, the rolling force and the stress between the rolls were calculated. The moment balance equation of the roll neck end was established in the bearing section,and the bending stress model of the roll neck bearing section was established. The deformation resistance was regarded as the plastic deformation energy per unit volume to calculate the rolling torque in the deformation zone, and the torsional shear stress model of the roll neck bearing section was established. Using the first strength theory, the equivalent stress was obtained by combining the bending stress and the torsional shear stress. On the basis of proving the calculation accuracy of the model,the multi-axis fatigue model was used to predict the fatigue life of the roll neck bearing section, and compared with the service life of the actual roll in the production line. The results show that the stress calculation model of the working roll neck bearing section of the four-high mill is in line with the actual stress state of the roll neck. The error between the expected service life predicted by the theoretical model and the actual service life is less than 20%, which meets the actual engineering error requirements.