The gearbox of wind turbine is in the complex environment such as random wind load for a long time, and the gear contact fatigue becomes a key factor limiting the stability and reliability of wind turbine equipment. The research on the gear contact damage evolution mechanism is faced with difficulties such as complex stress states, damage anisotropy and failure modeling. Material configurational force theory can describe the effect of defect configurational change on the free energy of materials and can be used to predict the damage and failure behavior of materials. A wind turbine gear contact damage model was constructed based on this theory. The gear contact interface stress field simulation analysis was carried out for the key bearing area of gear contact, and the gear contact damage evolution process under contact load was simulated. The results show that the configurational force theory damage model can effectively simulate the contact damage phenomenon of gear and explain the pitting and spalling of gear surfaces. It has significance to predict contact fatigue life of gears accurately.

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.

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.

Dichloromethane solution was introduced as the corrosion medium by the liquid drop method.Based on the regular quadrilateral, regular hexagon and concave structures with different porosities，the effects of different corrosion cycles and areas on the porous structural mechanical properties of polylactic acid (PLA) were analyzed by comparing with the finite element simulation results.The results show that concave porous structure plate is the least affected by the corrosion cycle,while the other two structures are affected by it depending on the size of the porosity.The hexagonal structure with a porosity of 72% has the weakest corrosion defect bearing capacity, while the concave structure has the strongest bearing capacity.The regular quadrilateral structure with a porosity of 54% is most affected by the single cell corrosion.The corrosion bearing capacity of the expanded area of a single cell in a regular hexagonal structure is weaker than that of a single cell, while the corrosion bearing capacity of the expanded area of a single cell in a regular quadrilateral structure is stronger than that of a single cell.

In order to improve the traditional design concept and the lack of optimization of genetic algorithm, and promote the development and innovation of the shape optimization of truss structure, according to the basic principles of harmony search algorithm and genetic algorithm, a new hybrid genetic algorithm-harmony search genetic algorithm was proposed (the mixing of genetic algorithm and harmony search algorithm is to embed the harmony search operator after the operation of the genetic algorithm), and at the same time the cross-variation in the genetic algorithm was adaptively improved in three situations, and elitism and other improvement measures were introduced. In addition, the harmonious search algorithm is processed with mixed variables of discrete variables and continuous variables, and a truss structure shape optimization method based on the harmonic search hybrid genetic algorithm was established. In the optimization process, the two different types of design variables of node coordinates and cross-section area were considered uniformly, which solves the problem of difficulty in coupling of the two types of variables. Through the analysis of two typical examples, the results show that the harmonic search genetic algorithm (HS-GA) has efficient convergence speed and strong global ability. Compared with genetic algorithm (GA), heuristic particle swarm optimization (HPSO) and other optimization algorithms, the optimization effect is obvious, and it is a method suitable for the shape optimization of truss structure.

To address the creep issue that arises during the long-term vertical storage of solid rocket motor (SRM), a method was proposed that involved embedding a specially shaped functional combustible core model (reinforcement structure) into the propellant grain matrix without altering the basic structure of the grain. Initially, the distribution patterns of creep in the propellant grain under the coupled effect of solidification cooling and vertical self-weight were analyzed by using three-dimensional numerical simulation methods. Subsequently, the reinforcement structure was designed by using the solid isotropic material with penalization (SIMP) method for topology optimization, determining the geometric configuration of the embedded reinforcement structure. Finally, the final optimized design results were determined through comparative analysis of the anti-creep effect of the topology-optimized reinforcement structure. The research results demonstrate that the deformation stress and strain of the solid rocket motor propellant grain with the reinforcement structure are significantly reduced compared to those without the reinforcement structure, effectively suppressing the creep of the grain.

A single-degree-of-freedom mechanical collision vibration system model with nonlinear terms and unilateral new nonlinear constraints was studied.The dynamics characteristics of the p/1 periodic motion of the system under low-frequency excitation were analyzed by using the variable-step fourth-order Runge-Kutta numerical algorithm and multi-parameter co-simulation.And the frequency hysteresis characteristics of the grazing bifurcation and saddle-node bifurcation in the p/1 periodic motion were analyzed.It was found that two different motions will exist at the same time，revealing the irreversibility of the transition between adjacent periodic motions.Finally, the influence of the change of the gap on the multi-state coexistence region of the system was studied.As the gap increases, the coexistence region of partial periodic motion decreases and transits to the low-frequency region.

Metal structures are widely used in industry. Metal structures in service are prone to crack defects under tensile and compressive fatigue load.In order to realize quantitative detection of metal structures’ crack defects, a quantitative analysis method of metal structures’ weak magnetic detection based on back propagation (BP) neural network was studied. In view of the poor effect and low efficiency of BP neural network in parameter adjustment, the improved whale optimization algorithm (IWOA) based on Sine chaotic mapping was adopted to optimize the BP neural network parameter adjustment mode,giving consideration to global optimization while improving the local optimization ability, and then the optimal parameters searched by IWOA were assigned to BP neural network, improving the quality of initial network parameters.The length, width and depth of the artificial rectangular slot were quantified by inversion. The results show that the average prediction accuracy of IWOA-BP neural network is above 80%, and the prediction accuracy of depth, length and width is improved respectively by 106.72%, 9.68% and 6.86%.

In order to solve the problem of multi-source heterogeneous data fusion and improve the accuracy of reliability evaluation, a multi-source heterogeneous data fusion method based on approximate failure point was proposed by using D-S theory and the least squares method.Firstly, the probability envelope curves were obtained through constructing probability assignment for a single source of data and performing weighted fusion.A distribution fitting model based on approximate failure points was also established.Secondly, the parameter estimation value was obtained by the least squares method, and the area metric was constructed to determine the true failure distribution function，and then the reliability assessment was completed.Finally, the feasibility and effectiveness of the proposed method were verified by examples, and the accuracy was higher than that of Bayes method.

In order to construct a bone scaffold structure with good biological properties, P-type, FRD-type homogeneous multi-porous scaffolds and P&FRD gradient multi-porous scaffolds with different porosities and unit cell scales were designed based on the triply periodic minimal surface（TPMS）.The effects of unit cell types, porosities and unit cell scales on the mechanical and biological properties of TPMS multi-porous scaffolds were investigated by tests and finite element simulation.The results show that the internal pores of homogeneous and gradient multi-porous scaffolds based on TPMS have good connectivity.The mechanical properties of multi-porous scaffolds decrease with the increase of porosity, but the permeability increases with the increase of porosity.Increasing the unit cell scale can significantly improve the permeability of multi-porous scaffolds.The permeability of the gradient multi-porous scaffold is also affected by the seepage direction.The gradient multi-porous scaffolds can synthesize the performance characteristics of each homogeneous unit cell structure, and show different mechanical and biological properties in different regions of the scaffold, which is closer to the structure and biological properties of human bone.