In this paper, the effects of doping elements（Re and Ru）content on the stability and occupancy orientation of a Ni-Al binary model nickel-based single-crystal superalloy are studied by using first-principles calculations. The results show that the total energy of the system decreases gradually with the increase of the content of Re and Ru elements, which suggests that the stability of the system is improved. The system using Ru to replace Ni has the lowest stability, while the stability of system is the best by using Re to replace Al. Therefore, Re and Ru are more inclined to replace Al, which is consistent with the previous experimental results. Meanwhile, compared to other contents of Re and Ru, when Re and Ru with the content of about 1.4% are used to replace Al, the substitution formation energy is the lowest. Furthermore, two different stacking fault modes are obtained by deleting a layer of atoms in the Ni-Al binary model. Research on these two stacking fault modes indicates that replacing Al with Re and Ru can improve the stability of the systems, and systems containing Re are more stable, which have lower substitution formation energy compared to replacing Al with Ru. However, for different stacking fault modes, when replacing Al with Re and Ru, the content of Re and Ru is different for the best of a stable system and the lowest of substitution formation energy and stacking fault energy. Replacing Al with Re results in a better stability in stacking fault systems, but the content of Re in the most stable system depends on the selected stacking fault mode.

In steel-concrete composite structures, due to the existence of certain interface slip and web shear deformation, the assumption of flat section is no longer applicable. In order to scientifically study the effects of shear deformation and interface slip on the deflection and interface slip of composite beams, this paper adopts Goodman's assumption and Timoshenko beam's double generalized displacement assumption, introduces the strain relationship of composite beams and element microsegment mechanical equilibrium, and derives the elastic bending differential equation of double inverted T-shaped steel-concrete composite beams considering shear deformation and interface slip. Then based on the equivalent spring model and the equivalent rod spring model, a theoretical calculation formula for the elastic shear stiffness of the embedded web connection is derived. By using the known deformation and constraint conditions of the composite beam, we obtain the analytical solution of deflection and slip of the simply supported composite beam under concentrated load in the span and verify it through the experimental results of four double inverted T-shaped steel-concrete composite beams with different parameters. The results show that the deflection and slip values obtained from theoretical calculations are in good agreement with the measured values, and the correctness of the theoretical calculation formula for the elastic shear stiffness of the embedded web connection is verified. In the deflection deformation of double inverted T-shaped composite beams, the deflection value caused by bending accounts for about 56% of the total deflection, the deflection value caused by interface slip accounts for about 36% of the total deflection, and the deflection value caused by shear deformation accounts for about 8% of the total deflection. This article comprehensively considers the effects of shear deformation and interface slip on the deflection and slip of composite beams, and makes a significant improvement compared to the model structure that does not consider shear deformation and interface slip.

The objective of this paper is to study the mechanical characteristics of the interface between loess and geosynthetics, in hope of providing targeted suggestions for the design of reinforced loess projects. A large-scale interface shear apparatus was used to conduct direct shear tests on the geogrid-loess interface to study the effects of the moisture content and compaction degree of loess on the shear stress-shear displacement relationships, shear strength indices, and thickness of shear band of the geogrid-loess interface. The mechanism of the effects was analyzed, and the constitutive model of the geogrid-loess interface was discussed. The test results show that as the moisture content increases（not exceeding the plastic limit）, the shear stress-shear displacement curves of the geogrid-loess interface change from softening type to hardening type. The interface cohesion and friction angle significantly decrease with the increase of the moisture content, and thus the interface shear strength decreases accordingly. The thickness of shear band increases with the moisture content. The compaction degree of loess has little influence on the shear strength of the geogrid-soil interface, but it affects the thickness of shear band significantly. The thickness of shear band increases greatly when the compaction degree reaches 90%. Hence, the compaction degree of the backfill of reinforced loess engineering should not be less than 90%. The thickness of the shear band of geogrid-loess interface decreases continuously along the shear direction, with a maximum thickness of 3 cm approximately. This indicates that the shear band between the reinforcement and soil is the thinnest at the facing column in reinforced loess retaining walls. Hence, a flexible or integral facing column is recommended to be used in reinforced loess retaining walls. The hyperbolic interface constitutive model can effectively reflect the shear behavior of the geogrid-loess interface.

In order to investigate a structure with better mechanical properties, this paper proposes a square honeycomb lattice sandwich cylindrical shell structure, which combines metal thin-walled tubes and honeycomb structures. The mechanical behavior of the sandwich cylindrical shell structure with a square honeycomb as the core under radial compressive loads is studied by experimental and numerical methods. By comparing the results of two research methods, the accuracy of the finite element model is verified, and the deformation mode of the structure under radial compressive loads is analyzed, and the reinforcement mechanism of the structure is discussed. The results show that the rectangular honeycomb lattice sandwich cylin-drical shell structure will undergo three deformation stages:elastic stage, plastic stage and collapsibility stage under radial compression load. Compared with the simple superposition of single-layer cylindrical shells and cores, the load-bearing and energy absorption of the square honeycomb lattice sandwich cylindrical shell are greatly improved. The structure is mainly coupled and reinforced by the formation of plastic hinges and the debonding between the square honeycomb core and the inner and outer cylindrical shells.

In order to enhance the seismic performance of reinforced concrete columns, a method of embedding steel wire mesh to strengthen concrete columns was proposed. A total of six specimens including reinforced concrete column, four steel mesh-reinforced columns, and one stirrup-reinforced column were designed and poured. Constant axial pressure was applied to the specimens and horizontal quasi-static cyclic loading was carried out. The failure patterns, crack distribution, hysteretic characteristics, ductility, and energy dissipation capacity of each specimen were tested. The seismic performances of steel wire mesh-reinforced specimens and stirrup-reinforced specimens with the same equivalent stirrup ratio were compared and analyzed, and the effects of steel mesh layers and configuration height range on the seismic perform-ance of members were discussed. The research results show that the proper configuration of steel mesh can effectively restrict the formation and development of column sectional crack and“diagonal crack”, and transform the bending-shear failure mode of the specimen into bending failure mode. Therefore, compared with the reference specimen and stirrup-reinforced specimen, the wire mesh-reinforced specimen shows greater initial stiffness, better ductile deformation and cumulative energy dissipation capacity. The research results preliminarily clarify the relationship between the number of wire mesh layers, height range and ductile deformation capacity, stiffness degradation, and energy dissipation capacity of specimens, and the related results can provide reference for the design of embedded wire mesh-reinforced concrete columns.

In order to characterize the distribution law of active earth pressure with depth for a circular platform foundation pit under transient infiltrations, this study derived the slip line equation for the active earth pressure of circular platform foundation pits. The derivation was based on the strength equation of generalized effective stress for unsaturated soils and matric suction under transient infiltration conditions. Subsequently, the differential iterative method was adopted to obtain the slip line solution of active earth pressure for circular platform foundation pits under transient infiltrations. Last, the accuracy of the obtained slip line solution was verified, and an influencing factor analysis was conducted. The results indicate that the obtained slip line solution, compared with the existing solutions, can reasonably account for comprehen-sive influences of transient infiltration（time, infiltration ratio, nonlinear profiles of suction stress）, soil types（sand, silt, clay）, foundation pit model parameters（wall dip angle, wall-soil friction angle）, and the circumferential stress coefficient on the active earth pressure of foundation pits. The accuracy of the obtained slip line solution of active earth pressure under specific reduced conditions is demonstrated by comparing it with the slip line solution of circular platform foundation pits in saturated soils（when suction stress is zero）, and the limit equilibrium solution of plane retaining walls under transient infiltrations（when the radius of foundation pit tends to infinity）reported in the literature. The influence of time and infiltration ratio on the value and distribution of active earth pressure is most pronounced for foundation pits in clay, followed by foundation pits in silt. However, it is negligible for foundation pits in sand, which is caused by nonlinear profiles of suction stress for different soils. The active earth pressure of foundation pits decreases significantly with the increase of wall dip angle, wall-soil friction angle and circumferential stress coefficient, while its distribution and change with depth are closely related to soil types.

Large flexible appendages of flexible spacecraft are characterised by their large scale and low stiffness, resulting in vibration of large flexible appendages that can seriously affect the attitude precision of the spacecraft. Information fusion preview control is combined with fuzzy control to construct the attitude controller. According to the information fusion theory, the spacecraft's desired trajectory and system dynamics information are fused, the optimal preview control law is derived. The optimal preview control law can be easily obtained due to the information fusion control has a simple design process and low computational burden. In real engineering, the control torque generated by the actuator is limited. The fuzzy controller is employed to adjust the parameters of the control law on-line in order to satisfy the requirements of limitation. Simulation results show that the designed control strategy with high control performance can effectively suppress the vibration of the flexible appendages, and the attitude angle can reach the desired value accurately and quickly. The proposed control strategy can be served as a reference for the engineering application of large flexible spacecraft attitude control.

This paper develops a free vibration model of rectangular microplates including three material length scale parameters and two displacement field variables using the modified strain gradient theory and a refined higher-order shear deformation theory, and presented the related governing differential equations. The analytical vibration frequencies of a four-edge supported rectangular microplate were obtained via the Navier method. Combining the Gauss-Lobatto quadrature and differential quadrature rules, a four-node seventy-two-DOF differential quadrature finite element was constructed to solve the free vibration of rectangular microplates with general boundary conditions. Through typical numerical examples, the effectiveness of the present model was established, and the effects of boundary conditions, material length scale parameters, aspect ratio and length-thickness ratio on the vibration frequencies and mode shapes of rectangular microplates were revealed. The results indicate that the vibration frequencies and some mode shapes of rectangular microplates exhibit significant size effect, and its intensity is associated with the boundary conditions and geometric dimensions.

In order to determine the influence of aggregate irregularity on the mechanical properties and failure morphology of concrete, Python programs were developed to generate randomly distributed aggregate models with different sharpness in ABAQUS, and the 0-thickness cohesive element and variable-thickness solid interface transition zone（ITZ）were established respectively. First, the reliability of model was determined by changing mesh size and friction coefficient between the loading pad and concrete compared with the experiment. Then, the quality of two ITZ modeling methods was analyzed. Finally, the uniaxial compression mechanical behavior of the three-dimensional meso-concrete model was analyzed from the aspects of stress-strain curve, fracture propagation, and energy dissipation. The simulation results show that the 0 thickness cohesive ITZ and the solid thickness ITZ model can predict the compressive strength of concrete, and the stress-strain curve and failure morphology of the ITZ model with solid thickness are more consistent with the experiment. The fracture propagation of concrete is obviously affected by the shape parameters of aggregate. The interior and surface of the spherical aggregate model are penetrating cracks. The strain energy of polyhedral aggregate model is larger, and there are many micro-cracks in the concrete, the possibility being compressed and destroyed into more fragments is higher. With the increase of aggregate irregularity, the compressive strength of concrete increases slightly, but the peak strain is not affected.

The roughness of the interface between new and old concrete is one of the key factors that affect its shear performance. In this paper, the roughness of the new and old concrete interface is characterized and quantified based on fractal theory. Different fractal dimension interfaces of new and old concrete random aggregate geometric models are established using the Monte Carlo method and aggregate grading theory. By simulating the mechanical behavior of rough interfaces using zero-thickness cohesive elements locally embedded in the model, the effects of mesh size, random distribution of aggregates, fractal dimension, normal pressure, and interface material parameters on the shear performance of rough interfaces between new and old concrete are analyzed. The results show that the model's mesh size and random distribution of aggregates have no significant effect on the shear performance of the interface between new and old concrete. As the fractal dimension increases, the interface shear strength first increases and then decreases, and the fractal dimension corresponding to the maximum shear strength decreases as the normal pressure increases. Under the same fractal dimension, the shear strength increases linearly with the normal pressure. The normal pressure has a more significant impact on the interface shear strength compared to the fractal dimension. As the fractal dimension increases, cracks are more likely to propagate deeper into the old concrete area, and increasing the strength and fracture energy of the new and old interface can effectively improve the shear performance of the interface.