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.

Taking a 1.5 MW wind turbine tower with different initial crack lengths as the research object, vertical and horizontal earthquake loads with four earthquake intensities and three actual earthquakes were applied, respectively. The influence of vertical and horizontal earthquake loads on the strain field at the crack tip of the wind turbine tower was studied and compared. The results indicate that both under vertical and horizontal earthquake loads, the equivalen plastic strain area at the crack tip increases with the increase of earthquake intensity, but under horizontal earthquake loads, the equivalent plastic strain area at the crack tip increases more rapidly. Under earthquake intensities of Ⅵ and Ⅶ, the impact of vertical earthquake loads is greater than that of horizontal earthquake loads. As the earthquake intensity increases, the impact of horizontal earthquake loads increases sharply under earthquake intensities of Ⅷ and Ⅸ, and far exceeding the impact of vertical earthquake loads. The impact of vertical actual earthquake load on the crack tip equivalent plastic strain area is related to the magnitude and earthquake acceleration time-history curve, while the impact of horizontal actual earthquake load on the crack tip equivalent plastic strain area is related to the earthquake acceleration time-history curve.

In order to investigate the compression damage evolution of carbon fiber laminates with wrinkles and accurately predict the mechanical behavior of damage initiation and propagation, a progressive damage finite element model was proposed based on three-dimensional elastic theory by employing a spatial decomposition of damage variables method to establish the damage constitutive relation. Firstly, the maximum stress and Puck failure criteria were used to predict the intralaminar damage initiation, and the damage variables were calculated in combination with the mixed-mode damage evolution law. Secondly, based on the physical meaning of the damage variables, a spatial decomposition was carried out in the fracture plane coordinate system, and the damage constitutive relation was derived by substituting the damage stiffness matrix.Then in order to predict the interlaminar stress state and damage behavior of laminates, a cohesive zone model with a bilinear traction-separation law was adopted. Finally the corresponding Vumat subroutine was developed and implemented in Abaqus software for the numerical simulation analysis of quasi-static compression loading at 0.25 mm/min.The stress-displacement curves and damage distribution of laminates predicted by the finite element model are in good agreement with test results. The proposed calculation method is simple and direct for determining true stress, making it convenient for analyzing and identifying the damage location and damage evolution of composite laminates with wrinkles.

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.

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.

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.

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.

The relative curvature of the spur gear mesh point is one of the key geometric parameters of the tooth profile,which has a significant impact on the stress distribution and mesh stiffness of the gear. Starting from the relevant research on constant relative curvature (CRC) gears, three types of non-involute spur gear tooth profiles were constructed based on the relative curvature control strategy considering the time-varying mesh characteristics of gears, and the mesh simulation of gear pairs was implemented. The influence of relative curvature control on the maximum contact stress, maximum bending stress,and mesh stiffness of gears was analyzed. The effectiveness of the control strategy was verified. This work provides some reference for the design of spur gears based on the relative curvature control.

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.

At present, the research on supersonic civil aircraft wings mainly focuses on the low sonic boom design and supersonic drag reduction technologies. There are relatively few studies on the wing structural design. Therefore, a multi-level optimization method for the wing structural design in the preliminary design stage of supersonic civil aircrafts was proposed. It included the parametric modeling of the wing structural layout, the automatic generation of the finite element model for the structural size optimization, construction and training of a surrogate model for the deep neural network. And the optimization was solved based on the deep neural network. The analysis results show that the proposed optimization strategy could quickly design the wing structure of the supersonic civil aircraft. The deep neural network model has higher prediction accuracy than the traditional surrogate model. Thus, the proposed approach can improve the efficiency of the preliminary design for wing structure.