Based on Reddy’s layerwise theory (RLWT) and O(1) homogenization method, a three-scale layerwise multiscale analysis method (LMAM) for composite honeycomb sandwich structures was established. The macroscopic model of composite laminates was discretized by RLWT, and the microscopic unit cell model composed of fibers and matrix was established by three-dimensional finite element method. In the numerical example, the numerical simulation of the cubic block with inclusions was carried out, and the simulation results were compared with those of the direct numerical simulation (DNS)method, which verified the correctness of the LMAM. LMAM is also used to calculate and analyze the macroscopic,mesoscopic and microscopic stress distribution of composite honeycomb sandwich structures.

Gear’s Circular plot is a result presentation method which needs to be combine with time synchronous averaging (TSA), which can clearly display gear meshing vibration waveform extracted by TSA. Aiming at the problem of parameter setting of gear’s Circular plot and lack of the quantitative index, F_i index for waveform edge recognition and Y_i index based on Hu-moments were proposed. Firstly, TSA algorithm was used to extract the gear meshing vibration signal, and the upper and lower edges of the vibration signal waveform were determined by calculating the minimum F_i index. Secondly,Circular plot of gears were drawn by the upper and lower edge parameters. Then, the Circular plot of the gear was divided into four parts, and Y_i index of the Circular plot was obtained by calculating Hu-moments of the picture after segmentation. Finally,based on the Y_i and F_i indices extracted from the gear Circular plot, a K-nearest neighbors (KNN) classifier was utilized to classify the gear vibration signals. The results show that there is a significant difference between the Y_i and F_i indices of the vibration signals of normal gears and those of abnormal gears. By combining with the KNN classifier，it is possible to distinguish between normal and abnormal gear signals，which proves the effectiveness of this method.

In order to improve the mechanical properties of three-dimensional negative Poisson ratio materials, and expand the application of negative Poisson ratio materials. A new unit cell of negative Poisson ratio structural material was proposed by introducing internal concave angles into the edges of tetrahedral porous structures, and 7 kinds of orthogonal isotropic and orthogonal anisotropic enhancement designs were carried out on it. The influence of cell geometry parameters on the dimension one equivalent elastic modulus and Poisson ratio of new and enhanced cells was studied by using the homogenized finite element method and periodic boundary conditions，and the 3D printed resin sample was used for experimental verification. Compared with the existing negative Poisson ratio unit cells, the novel unit cell can save 50% of materials while maintaining the negative Poisson ratio characteristics. The three reinforcement schemes in x-direction, y-direction and xy-direction can significantly improve the bearing-load capacity while improving the negative Poisson ratio characteristics.

To explore the penetration resistance of aluminum alloy tubes under spherical steel projectile impact, focusing on the effects of varying tube radii and wall thicknesses on ballistic limit velocity, providing a foundation for tube protection design. A finite element model of spherical steel projectile penetration into 2024-T42 aluminum alloy targets was established using Ansys/Workbench software and the Johnson-Cook material model, which was then verified. Simulations of the response characteristics of aluminum alloy tubes with different radii and wall thicknesses under normal impact of spherical steel projectiles were conducted, along with an analysis of tube deformation and damage. The study found that the penetration resistance of the upper and lower walls of aluminum alloy tubes differs, with the upper convex structure outperforming the lower concave structure. A smaller tube radius enhances the penetration resistance of the upper wall, while for tubes of the same radius,increasing the wall thickness leads to a roughly linear increase in the ballistic limit velocity of both upper and lower walls.

Elbows are an important component of oil and gas pipelines. The force state and the medium flow state are more complex than that of the straight pipe. Once the defect occurs at the elbow, the elbow pipe is more prone to fail. The high steel grade pipeline is the development trend of the long distance oil and gas pipeline construction, and it is urgent to evaluate the residual strength of the high steel grade bending pipe. Through the establishment of the finite element model, the defect size, relative position, bending radius, pipe parameters and pipe performance influence were studied on the ultimate internal pressure of the elbow, and finally the prediction formula of the bending was established. The results show that with the increase of defect length and defect depth, the ultimate internal pressure of the elbow is significantly reduced. The trench defect affects the ultimate internal pressure when the trench defect is located in the inner arch of the elbow. The bending radius, the wall thickness and the pipe material will affect the ultimate internal pressure. The error analysis shows that the prediction formula is more accurate, which can provide the basis for the residual strength evaluation of high steel grade elbows with trench defects.

The main purpose was to study the local cyclic plastic behavior of 3D printed titanium alloy notched parts. Firstly, the local stress and strain field near the 3D printed titanium alloy notch was analyzed in detail by finite element method，and the evolution of stress and strain field was deeply investigated. Then, the experimental study was carried out and the influence of the forming direction on the results was analyzed. The results show that ratcheting deformation occurs at the notch root, with the maximum ratcheting strain rate in the L₃ direction and the minimum ratcheting strain rate in the L₁ direction. The influence of the forming direction on the stress triaxiality is not too obvious. The elastic strain energy of different forming directions is almost no difference. However, the forming direction has a great influence on the plastic strain energy. With the increase of the number of cycles, the difference of plastic strain energy results for different notch radii also becomes larger.

To improve the accuracy and efficiency of load identification and structural response reconstruction, an improved Tikhonov regularization method that simultaneously considers transfer matrix error and measurement error was proposed. Firstly, the state space equation and transfer matrix were constructed through the structural dynamics model to obtain the reconstruction equation of the structural load and response. Secondly, the truncated randomized singular value decomposition method was used to calculate the approximate transfer matrix at the locations of the measurement points, while the total least squares method (TLSM) and the traditional Tikhonov regularization method were combined to identify the load,and then the unknown response was reconstructed by the transfer matrix at the locations. Finally, a numerical simulation and an experimental analysis were carried out for two-dimensional truss and simply supported beam to verify the proposed method. The results show that compared with the traditional Tikhonov regularization method, the proposed method can improve the reconstruction efficiency while guaranteeing the reconstruction accuracy.

During the gear meshing process, the driving speed plays a crucial role in evaluating mesh stiffness, a factor that many scholars often overlook along with the accompanying centrifugal effects. Based on Euler beam theory,a original computational algorithm was proposed to calculate the dynamic mesh stiffness of spur gears considering driven-speed effects by introducing centrifugal effects into the velocity field. Using the driving speed as a control parameter, the dynamic mesh stiffness in relation to driving speed was investigated, and the nonlinear relation between centrifugal effects and dynamic mesh stiffness was demonstrated. The results indicate that, under the influence of a centrifugal field, both the natural frequency and the dynamic mesh stiffness of the gears increase with rising driving speed. Additionally, materials with a high elastic modulus tend to suppress the impact of driving speed on dynamic mesh stiffness, while higher density has the opposite effect. The research results provide reference for further analysis of gear vibration and noise under centrifugal effects.

In response to challenges such as large sampling data, extended diagnosis time, and subjective fault feature selection in traditional bearing fault diagnosis, based on compressed sensing (CS) and deep multi-kernel extreme learning machine (D-MKELM) theory, a CS-DMKELM intelligent diagnosis model for rolling bearings was proposed. Firstly, sparse signals were obtained through threshold processing of transformed domain signals. A Gaussian random matrix was employed as the measurement matrix to compress the processed data. Secongly, the compressed data was used as the input signal for the D-MKELM. Particle swarm optimization (PSO) algorithm was applied to optimize critical parameters, enabling intelligent fault diagnosis. Results demonstrate that the proposed method, using only a small amount of bearing diagnostic data,automatically extracts feature information of bearings from a limited number of measurement signals through the D-MKELM.The proposed method enables rapid fault diagnosis of bearings. With a diagnostic time of 0.55 s, a final recognition accuracy of 99.29% was achieved. The proposed method reduces the diagnostic time and exhibits the high diagnostic accuracy,providing a new approach for handling massive bearing data in the fault diagnosis.

Surface texture design is an effective way to achieve small leakage, long life and highly reliable operation of mechanical end seals. To investigate the characteristics of the interface film of guide groove texture, through the design and preparation of semi-circular, herringbone and E-shaped guide groove textures, experiments and theoretical research under high-speed operation conditions were carried out, the influence of different guide groove textures on the tribological properties of end face seals was explored. The results show that the existence of the guide groove can effectively improve the bearing capacity of the interface film and improve the tribological performance. In numerical calculations, the results show that the frictional performances of face seals varied with the configuration of guide groove. The herringbone textures and E-type ones show an obvious guide-aggregation effect. When the lubricant in E-type texture after being guide-aggregation through the groove, the pressure accumulates at the textured tail barrier, and fluid in the face seal clearance cannot escape from the guide groove boundary. As a result，the low energy loss in system, and an optimal liquid film bearing capacity achieves. Under different depths, the existence of guide groove promotes the hydrodynamic pressure. With the increase in depth, the bearing capacity of the liquid film increases first and then decreases. For the E-shape texture, the optimum bearing capacity of liquid film P_av=0.527 5 MPa is obtained at h₁=10 μm. The bearing capacity of fluid film of E-shape texture has a 51.2% increase in comparison to the common grooved texture, the value of frictional torque has a 53.5% decrease. The analysis show that, the configuration of guide groove results in an accumulation of lubricant on the top of texture, which enhances the pressure convergence, thereby improving the bearing capacity of the lubricating fluid film and reducing friction（‘guide⁃aggregation effect’）. The geometric parameters of the guide groove have a significant impact on the fluid dynamic pressure in the end face sealing pair，which will influence the tribological performances of face seal. The research result provides theoretical support for the design of non-contact end face seal material surface texture in future.