Upon charge-discharge cycling, lithium-ion batteries inevitably undergo capacity fading, which is a common and well-acknowledged phenomenon. However, the mechanisms behind this apparent performance degradation are inherently complex. In this review, the mechanical-electrochemical coupling degradation mechanisms of lithium-ion batteries in multi-scale, multi-field, and multi-process are comprehensively reviewed, starting from the particle scale to the electrode scale, with a specific focus on degradation in solid-state batteries. Furthermore, the degradation models used to describe the mechanical-electrochemical coupling degradation behavior of lithium-ion batteries are reviewed. It should be noted that due to the complexity of battery degradation mechanisms and the scarcity of externally measurable parameters, establishing degradation models is challenging, and there is still a considerable research gap. In light of this, a conceptual bidirectional degradation model that integrates physical models and data-driven models is proposed. Serving as links, internal variables with meaningful physical implications should be introduced to establish a comprehensive mapping of "mechanical behavior-internal variables-degradation behavior", to provide a novel approach for objectively and accurately describing and predicting battery degradation behavior.

Composite pressure structures refer to components made of composite materials designed to withstand pressure, such as hydrogen storage tanks for vehicles, liquid oxygen tanks, and solid rocket engines. These structures possess numerous advantages including lightweight, high strength, and excellent design flexibility, making them widely employed in aerospace, automotive, and petrochemical industries. However, under severe service conditions, the accumulation and propagation of damage in composite pressure structures can easily lead to component failure. Therefore, the development of advanced structural health monitoring technologies is crucial for enhancing their in-service safety. This paper begins by comprehensively comparing the advantages and disadvantages of monitoring methods such as ultrasonic guided waves, acoustic emission, infrared, and fiber optic gratings, focusing particularly on the methods and research progress of structural health monitoring for composite pressure structures. Subsequently, addressing the material characteristics of composite pressure structures, we discuss the application and key challenges of implanted micro/nano-material sensors in monitoring the interfacial and interlaminar properties of fiber/matrix. Finally, we explore the development progress of novel sensing technologies and artificial intelligence methods, and analyze their application prospects in the in-service safety of composite pressure structures.

In this paper we systematically introduce the research progress in compressible flow around a circular cylinder, which serves as a theoretical model for numerous engineering problems in aerodynamics, thermodynamics, and other fields. Studying the flow characteristics and influential factors of compressible flow around a cylinder is of practical significance for solving engineering problems and contributes to the theoretical development of compressible fluid mechanics. The paper summarizes recent research findings based on different ranges of inflow Mach numbers, including results in subsonic, transonic, and supersonic regimes. It covers aspects such as Mach number effects, shock wave structures, interactions between shock waves and vortices, as well as flow control methods. Finally, the paper provides an outlook on future research directions.

With the development of aerospace technology, large membrane diffraction space telescopes have gained widespread attention and research due to their advantages such as small mass and volume, high optical imaging capability, and ease of folding and unfolding. In this paper, we conduct vibration control research on a large membrane diffraction space telescope and provide a vibration control strategy based on piezoelectric actuators. Firstly, the finite element method is used to establish the dynamic model of the structure. Then, the position of the actuator is studied based on the controllability criterion. The control law is designed based on the fuzzy proportional-derivative (PD) algorithm. Finally, the effectiveness of the proposed method in this paper is verified through numerical simulation. In this paper, the corresponding relationship between the number of piezoelectric actuators and the stability time is studied through numerical simulation, and the robustness of the control law is also investigated.

In this paper, the free vibration problem of a Euler beam with multiple cracks mounted on the fractional-order viscoelastic Pasternak foundation is studied. Firstly, the fractional order derivative is introduced to establish the viscoelastic foundation model. The complex modulus of the stress-strain constitutive equation and the subgrade reaction force of the fractional-order viscoelastic Pasternak foundation are derived. Next, the cracks are modelled as massless torsional springs. The local flexibility of the crack is derived based on the relation between the energy release rate and the stress intensity factor. Further, by means of the transfer matrix method, the partial transfer matrix of each segment and the total transfer matrix of beam with multiple cracks are obtained. Finally, the linear algerbric equations of cracked Euler beam are derived based on the boundary conditions to determine the complex natural frequency and the vibration mode. As a numerical example, the Euler beam with two cracks is investigated and the complex natural frequency and the vibration mode are calculated. The curvature modes are used to analyze the effect of cracks. Besides, the effects of fractional order and viscosity coefficient of foundation as well as the location and depth of cracks on the natural frequency and vibration mode are also discussed based on the numerical results.

Metal materials often show different mechanical behavior and fatigue characteristics in rolling direction and transverse direction. A series of uniaxial tensile tests and crack propagation tests with stress ratio R of 0.1, 0.3 and 0.5 were carried out for 6061 aluminum alloy by sampling parallel to the rolling direction (RD) and perpendicular to the rolling direction (VD). The results show that there is no obvious difference in tensile properties between RD and VD samples, whereas significant difference of 30 % in fatigue life, with the crack growth rate of RD sample higher than that of VD sample. Through SEM fracture analysis, it was found that the fringe width of RD sample was 25 % higher than that of VD sample under stable expansion zone R = 0.1, and 50 % higher under R = 0.5. Chain inclusions could be observed on the fracture surface during the unstable expansion stage, leading to accelerated crack growth. In addition, in this paper we combined Abaqus software and XFEM analysis technology to obtain the crack growth paths and lifetimes of the two samples, which are in good agreement with the test results.

Subsurface crack initiation is one of the primary damage modes for materials under rolling contact fatigue. A crystal plasticity model combined with the cohesive zone elements is used to simulate the subsurface fatigue crack initiation at original austenite grain boundaries in a high strength steel. Based on the cohesive zone model of damage initiation criterion and fatigue damage evolution law, the damage accumulation with the number of cycles was calculated utilizing the crystal plasticity model in conjunction with the USDFLD subroutine. The fatigue crack initiation in the Voronoi model is simulated, and the effect of the crystal orientation on the crack initiation is investigated. The results indicate that the crack initiation is dominated by the shear stress, and the initiation position is within the range of maximum shear stress. The simulation results are consistent with the experimental observations. The grain orientation has a significant impact on the crack initiation location.

The SiC composite cladding, composed of the monolithic SiC and the SiCf/SiC composite, has emerged as a leading structure for accident tolerant fuel cladding due to its exceptional thermodynamic properties and radiation resistance. Ensuring the structural integrity of the SiC composite cladding is crucial for reactor safety. In this study, the irradiation effects of monolithic SiC and SiCf/SiC composite were considered. Numerical simulation of the thermo-mechanical coupling behaviors of the SiC triplex composite cladding during a loss of coolant accident (LOCA) of the light water reactor after 1 146 days of safe operation was carried out. The distribution and evolution of the first principal stress of the monolithic SiC was obtained and the influencing factors were analyzed. The results show that in the early stage of LOCA, the first principal stress of the monolithic SiC increases rapidly, then slowly increases and finally decreases, with a risk of cracking. The decrease in coolant pressure is an important reason for the initial increase of stress of the monolithic SiC, while the increase in internal pressure and the damage of the SiCf/SiC composite, are the dominated reasons for the later increase of the first principal stress of the interior monolithic SiC layer. In the steady-state condition, there is a significant temperature difference along the radial direction of the cladding. The thermal stress caused by the decrease in the temperature difference in the early stage of LOCA also has a significant impact on the maximum stress of the monolithic SiC. It is feasible to reduce the failure risk of the SiC composite cladding by improving the thermal conductivity of the SiCf/SiC composite.

With the rapid development of aeroengine field, the service environment of hot end turbine blade is becoming increasing severe. In order to improve the heat bearing capacity of blade, the double-walled blade structure is proposed in the industry, which is based on the principle of "outer wall heat bearing, inner wall load bearing". In this paper, aiming at ensuring the structural strength of double-walled blade film hole, a parametric modeling is used to construct the blade shape and the outer wall hole structure, and the influences of hole design parameters on the perimeter structure strength of the cylindrical film hole, the conical expansion hole and the dustpan expansion hole are determined through simulation analysis. Then, according to the parameter input and the corresponding response, a Radial Basis Function (RBF) neural network model is constructed and further optimized through adjusting the weights and thresholds using the genetic algorithm to improve the accuracy of the surrogate model. Finally, the optimal hole designs for three film holes are obtained. Compared with the original cylindrical hole, the perimeter stress is reduced by 25.12 % and 22.54 %, respectively for the conical expansion hole and the dustpan expansion hole.

For body-centered cubic (BCC) gradient lattice structure composed of linearly variable cross-section struts, distribution of bending moments was derived. Applied to the Timoshenko beam theory, a parametric theoretical prediction model for the mechanical properties of gradient lattice structure was obtained. Using the hexahedral solid elements, the finite element models of the unit cells and the gradient lattice structure were established. Finite element analyses (FEA) were performed to verify the effectiveness of the theoretical model. For the gradient lattice structure, 3D printing technology was used to fabricate the test samples using 316L metal powders. The quasi-static compression mechanics tests were carried out, and the FEA under the same working condition was also conducted. The results verified the suitability of the Timoshenko beam model to investigate the mechanical characteristics of gradient lattice structure up to the aspect ratio of 10. Finally, the influences of varying aspect ratios, cell sizes, cell numbers, and gradient directions on the mechanical properties of gradient lattice structures were discussed. The results show that the bending moment distribution predicted by the proposed model is more accurate and with much reduced error for the bending struts with linearly variable cross-sections. Using the theoretical prediction model proposed in this paper, the relative errors of the equivalent elastic moduli of the BCC unit cells of variable cross-section and the gradient lattice structure are within 3 % for the aspect ratio range of 3.5~8.7.

To optimize the external piping system of an aircraft engine, a sensitivity analysis was performed on Z-pipes, a typical external component. The results indicate that both the efficiency and accuracy of the structural optimization design were significantly improved. First, the sensitivity of the natural frequency and resonant stress was analyzed based on the structural parameters of Z-pipes. Then, using the sensitivity analysis results, parameters with the highest total sensitivity index based on variance were selected for optimization. The optimal design was achieved through finite element analysis. Finally, the optimized design was validated through pipe vibration testing. This approach significantly reduced the computational effort required for optimization by eliminating less influential parameters during the sensitivity analysis. The method was proven effective in avoiding resonance and reducing resonant stress in Z-pipes, providing valuable insights for the optimization of external engine pipelines.

With the continuous advancement of composite manufacturing technology and the requirements of civil aviation for economy, the application of lightweight and high-strength composite structures in the aerospace field has gradually expanded from thin-walled secondary load-bearing structures to large-thickness, variable-section main load-bearing structures. The wide application of these complex composite structural parts has raised higher requirements for their manufacturing reliability verification. However, due to the anisotropy of the composite materials and the complexity of the shape of the aviation structure, defects such as delamination, pores, fiber waviness, and resin-rich layers are prone to occur during the manufacturing process of the main load-bearing composite structure. These microstructural anomalies significantly degrade the macro-mechanical performance of the composite components. Ultrasonic testing has become an important technology of defect detection in aerospace composite structures due to its high penetration, high sensitivity and good applicability. In this paper, we first introduce the types and characteristics of manufacturing defects in aerospace composite structures, focusing on the analysis of the causes of defects such as pores, delamination, fiber waviness and resin-rich layers and their effects on the mechanical properties of the structure. Then, the research progress of ultrasonic testing in the detection of single-type manufacturing defects and mixed-type defects in thin laminate and thick composite structures in recent years is reviewed. Subsequently, the application of artificial intelligence technology in the defect diagnosis of composite structure is discussed. Finally, the challenges faced by the current ultrasonic testing of aviation composite structures are analyzed, and the future development trend is prospected.

This paper presents an analytical form of equivalent stiffness lines on the surface of a conical lattice shell with spiral and ring ribs to obtain the lightest weight grid stiffened shell structure under prescribed mechanical constraints. The lightest weight structural parameters are obtained through parameterized finite element modeling and SVR (Support Vector Regression) method combined with NSGA-II (Non-dominated Sorting Genetic Algorithm-Ⅱ) algorithm. The results indicate that the surrogate model based on the SVR method has good reliability in predicting the critical buckling load of grid reinforced shell structures. The method of NSGA-II combined with parameterized finite element modeling can be used to effectively obtain the lightest mass parameters of the structure. Compared to the original geodesic structural design, the utilization of equal stiffness design can significantly improve the weight reduction of the structures.

The reliability of pin solder joints on vehicle-mounted power module under the combined effects of heat generated by power loss and random vibration caused by road bump was explored. Fatigue life simulations of pin solder joints under electric-thermal-solid coupling were performed using the multi-physics field finite element models. The stress distribution and fatigue damage of the random vibration response were obtained for both elevated and normal temperature conditions. Furthermore, theoretical fatigue lives were also predicted and contrasted using empirical-based Dirlik model and Miner linear cumulative damage rule. The results show that the vibration fatigue life of solder joints decreases significantly considering electric-thermal-solid coupling effect due to the decrease of local constraint rigidity and the increase of vibration stress of solder joints, nevertheless still meets the specified vibration requirement. Finally, the accuracy of analysis results and the reliability of structural design were verified through conducting the vibration failure tests under full-power heating condition.

Polylactic acid (PLA) material is widely utilized in the field of additive manufacturing. Despite numerous studies were conducted on the mechanical properties of PLA materials, most of them employed traditional contact methods, such as strain electrical measurement, which posed challenges such as inadaptability to complex environments and cumbersome operation. In this study, a non-contact optical extensometer integrating dual-rhombic prisms and digital image correlation (DIC) is used to test the tensile mechanical properties of the 3D printed PLA specimens. Through the standard uniaxial tensile tests on PLA specimens, the strain was measured and the mechanical properties such as the elastic modulus, Poisson's ratio, strength, and elongation were obtained using the optical extensometer method. Compared with the refined strain gauge method, the non-contact technique exhibits minimal measurement errors, with deviations of merely 0.12 % and 0.34 % for elastic modulus and Poisson's ratio, respectively. The experimental results show that the non-contact optical extensometer has achieved a high level of accuracy, demonstrating its huge potential for measuring material properties in complex environments.

The dynamics modeling and control of semi-passive walking of an elastic rimless wheel on an inclined plane are studied. Initially, a dynamic model of the elastic rimless wheel was constructed using the Lagrange method, based on the Spring-Loaded Inverted Pendulum (SLIP) model. Following this, a controller was devised employing the concept of feedback linearization, which, by adjusting the length of the elastic leg, reduces the walking error of the elastic rimless wheel, thereby facilitating stable periodic locomotion. Subsequently, simulation experiments based on the theoretical study were conducted to verify the effectiveness of the control strategy predicated on variable leg length under the influence of external disturbances and inherent parameter inaccuracies. The simulations also revealed that identical external perturbations exert disparate effects during the single support (ss) and double support (ds) phases, prompting an analysis of the causes behind such variations. The simulation results demonstrate that the controller designed with variable leg length is capable of ensuring the stable progression of the elastic rimless wheel along the slope. Moreover, it can effectively mitigate the external disruptions, swiftly reinstate the elastic rimless wheel to a periodic stable gait, and exhibit considerable robustness even when the elastic rimless wheel's own parameters are erroneous.

A shear force sensor is designed and manufactured using a flexible microtubule liquid metal sensor as the stress measurement element. The shear force sensor consists of an elastic PDMS (polydimethylsiloxane) member, a metal support gasket, and a flexible microtubule sensor. The working principle of the shear force sensor and the sensing mechanism of the measuring element are discussed. The shear force sensor is used to measure the shear angle of the PDMS truss members, and the measurement results are compared with the reference values measured by the gray weighted centroid method. The effects of the assemble clearance δ and the microtube arrangement distance L on the measurement accuracy are systematically analyzed. The results show that when the elastic PDMS member is used as the deformation unit, the shear force sensor can work effectively in the shear angle range of 0.004 7 rad~0.038 rad. The measurement error increases with the increase of the assemble clearance δ, and decreases with the increase of the microtubule arrangement distance L. The proposed shear force sensor has the advantages of high sensitivity and strong anti-interference ability, providing a new tool for the measurement of shear force.

Traditional creep constitutive relationship is generally developed only for one of the three stages, i.e., transient, steady-state and accelerated stages. The well known power law creep relationship is only a typical creep constitutive model for steady creep stage. In high temperature allloy structures, however, the well known three stages of creep are usually mixed up in one working cycle, and the steady-state creep stage may not be dominant and even not observable. Therefore, from the perspective of engineering application, it is necessary to develop a long term creep constitutive relationship which can be applied for actual working loadings, without the limitation of traditional creep stage distinguishments. In this paper, creep tests of high temperature alloy FGH4095 are carried out at 530 ℃, 600 ℃ and 700 ℃. From the analyses of experimental results, a modified θ-projection method has been proposed, and the detailed long-term creep constitutive relationship has been developed. This model contains 5 creep state parameters, which are dependent on both temperature and stress level. For the convenience of practical application, creep tests at several different temperatures and stress levels are conducted, from which the empirical relationships of the creep state parameters depending on the temperature and stress level have been obtained.

Conducting reliability analysis of landing gear motion mechanisms plays a crucial role in ensuring normal takeoff and landing of aircraft. To improve the efficiency of reliability analysis of landing gear motion mechanisms under imprecise probability conditions, an imprecise probability directional sampling method has been developed. First, parameterization of the established multi-body dynamics simulation model of the landing gear is conducted. Consider the case where the input variables contain interval distribution parameters, a limit state function based on the actual engineering parameters is established to form the reliability analysis model. Secondly, combining the imprecise probability random simulation method with the directional sampling method, the expressions and estimation errors of each component function are derived to form the imprecise probability directional sampling method, which improves the low computational efficiency of the current method in highly nonlinear limit state surface situations. Finally, the effectiveness of the proposed method is verified through a numerical example. The developed method was used to calculate and analyze the failure probability change curve of important components of the landing gear motion mechanism, providing new thoughts and methods for improving the reliability analysis efficiency in imprecise probability situations.

Due to the nanoscale thickness of suspended two-dimensional (2D) materials, stretching instability wrinkles are prone to be introduced during the preparation process. However, the influence of wrinkles on the indentation response of two-dimensional materials is usually ignored. In this paper, the influence of wrinkles on the bending indentation response of 2D materials is investigated through theoretical analysis, and a model for the bending indentation response of 2D materials with wrinkles is proposed. It is found that under the action of central concentrated force, the bending deflection of 2D materials with wrinkles is linearly related to the load, and the relation slope is proportional to the ratio of wrinkle amplitude to wavelength A/λ. When A/λ=0.01~0.05, the slope is 1.32~3.21 times that of the case without wrinkles. This results in a significant overestimation (up to 3.21 times) of the elastic modulus of the 2D material obtained by the bending indentation test. The mechanism of overestimating the elastic modulus of 2D materials is that the wrinkles enhance the overall flexural stiffness of 2D materials, and thus increase the slope of the indentation load displacement relationship used to fit the elastic modulus.

The cracking and damage of electrode composite active materials in lithium-ion batteries have significant negative impact on the battery's capacity and cycling performance. Choosing suitable binders and material formulations to improve the bonding strength of the active materials is crucial for the long-term cyclic use of batteries. However, measuring the fracture strength of composite active materials at the electrode scale is challenging. In this paper we propose a quantitative method for testing the fracture performance of electrode composite active materials based on the peeling experiment of porous current collector electrodes. By comparing the peeling experiments of porous and non-porous current collector electrodes, the peeling strength of the composite active materials is obtained based on different open area ratios of the current collectors. The study further verifies through experiments that the measured peeling strength of the composite active materials is independent of the geometry of the current collector openings. Finally, the peeling strength of graphite negative electrodes prepared with two commercial formulations is measured, yielding reliable results. This experimental method can measure the energy release rate of composite active materials during the stable fracture, characterizing the material's bonding strength, and is of significant importance for the preparation and numerical simulations of related electrode materials.

Strut-and-tie model method is one of the standard methods for designing reinforcement in complex reinforced concrete structures. It is very important to construct the strut-and-tie model in complex stress regions using topology optimization. The algorithms of Solid Isotropic Microstructures with Penalization (SIMP) and Evolutionary Structural Optimization (ESO) have been widely used in such studies. These algorithms are optimized for isotropic perforated plates of unit thickness, the essence of which is to seek approximate solutions near the optimal solution. In addition, existing methods rarely consider the effect of different material tension-compression properties on the optimal topology due to the difficulties caused by the unsmooth character of the constitutive curve. A topology optimization algorithm based on a truss-like continuum with bi-modulus materials is proposed to construct the optimal topology of the strut-and-tie model. The density and orientation of the orthogonal trusses at each node are considered as the design variables. The material properties in the tension and compression regions are consistent with the tensile modulus of the reinforcement and the compression modulus of the concrete, respectively. A material substitution scheme is introduced to overcome the non-linearity caused by the bi-modulus, and a correction formula for stiffness matrix is given. The optimization is achieved through an iterative algorithm based on sensitivity information. Numerical examples show that differences in elastic modulus significantly affect the optimal topology. Compared to the density-based optimization methods, the proposed algorithm is able to accurately describe the optimal material distribution field under complex stress states, with the computational efficiency imporved by about 26 %. Besides that, more details of the material distribution can be given. The algorithm is able to improve efficiency and accuracy while giving more design details.

Tornado has the characteristics of small scope of action, short duration and high intensity of action, and is the most frequent and destructive disaster in natural disasters. Due to the danger and the randomness of occurrence of the tornado, the field data is scarce and it is difficult to obtain complete wind field in the field measurement. In view of this, a data fusion method based on neural network model is proposed to realize the fusion of wind field data from different sources. The prediction effectiveness and the generalization ability of the model are verified. On this basis, the tangential velocity field of tornado is predicted. The results show that the average error of the driven model of measured data is more than 35 % in the forecast of tornado with low swirl ratio, while the average error of the driven model with data fusion is less than 14 %, which indicates that the fusion model has better prediction accuracy. In the prediction of tornadoes with high swirl ratio, the average error of the measured data-driven model is about 28 %, while the average error of the data fusion driven model is less than 10 %, indicating that the data fusion model still maintains high precision and has good generalization when predicting high swirl ratio. In the reconstructed fusion model, the vortex core of the low vortex ratio wind field is fractured, and the wind speed in the core area of the high vortex ratio wind field is significantly increased, and the coverage of the near-surface wind speed is also increased. The model can obtain wind field data near the ground and near the vortex core center, and improve the spatial resolution of wind speed in tornado field, providing important support for the improvement of structural wind resistance in tornado environment.

In order to investigate the performance behaviour of concrete under the coupled effects of fatigue and freeze-thaw, the fatigue phase field method was used to investigate the performance evolution of concrete. The concrete aggregate model with certain area fraction and with interfacial transition zone (ITZ) was obtained by random aggregate placement algorithm. A numerical simulation of the entire process of concrete freeze-thaw fatigue cracking was conducted by introducing a thermo-mechanical coupled fatigue phase field model. The results show that during the freeze-thaw cycles, damage starts at the interface transition zone with the highest stress level at the aggregate corner. Under the condition of freeze-thaw, the damage development in the early stage of freeze-thaw is relatively slow, and the damage starts to develop rapidly in the later period. Under the condition of combined freeze-thaw cycles and fatigue, the durability of concrete is greatly reduced, and the life is only 50 % of that under pure freeze-thaw conditions. With the increase of the cycles of freeze-thaw, the concrete strength, modulus of elasticity gradually decrease, with the decrease rate gradually increasing.

This article proposes a new coupled plastic damage constitutive model, which is used to predict the damage and fracture behavior of high-strength steel under different stress states. The proposed constitutive model takes into account the influence of stress triaxiality and Lode parameter on damage. The parameter calibration can be completed only through smooth tensile and shear specimens, and the prediction of crack initiation and propagation of compact tension fracture specimens is achieved. The study found that the critical damage value of high-strength steel is a constant material property, independent of the stress state, and can be used as a fracture criterion for material crack initiation. Under this criterion, the fracture strain of the specimen can be accurately predicted. In addition, the damage and fracture are jointly affected by stress triaxiality, Lode parameter and plastic strain, resulting in differencesin the crack initiation positions of different specimens.

Using the "symplectic superposition" method in the Hamiltonian system and based on the theory of elastic thin plates, an analytically study was carried out for the static problem of rectangular thin plates with mixed boundary conditions of constraint on two opposite sides and middle-constraint ends-simplely-supported on the other two sides. Firstly, based on the Hamiltonian system, the symplectic geometry method was used to analytically solve the problem of classical boundary condition of simply supported edges. Then, based on this solution as the basic system, the superposition method was used to solve the case of complex mixed boundary condition of constraint on two opposite sides and middle-constraint ends-simplely-supported on the other two sides. Finally, the correctness and convergence of the proposed method were verified using the finite element numerical simulations. The method presented in this paper has both advantages of the rationality of symplectic geometry and the regularity of superposition method. During the solving process, there is no need to assume the form of the solution in advance, and the analytical solution is obtained directly from the basic equations of elasticity through strict step-by-step derivation. This method has strong generality and can be used in some rectangular plate problems that are difficult to solve analytically using the traditional methods.

During the construction and operation of tunnels, engineering challenges associated with seepage flow are consistently encountered, such as the damage of support structures or water influx. The main objective of this study is to analyze the hydraulic behavior of supported tunnels constructed in saturated ground, taking into account anisotropy of permeability and the effect of grouting/support on the seepage flow. In the determination, the coordinate transformation and the conformal mapping technique are employed to solve the governing equations, meanwhile, the points matching method is used to address the coordinate conditions of pore pressure and water flux at the rock-support interface. Finally, semi-analytical solutions of pore pressure distribution subjected to steady flow state are obtained, for the surrounding rock and the grouting/support zone. In the verification step, satisfactory agreement is achieved between the proposed analytical solutions and the numerical predictions. Then, in the parametric analyses step, the developed analytical model is applied to investigate the effect of support permeability, anisotropy of rocks' permeability, and the thickness of the grouting/support zone, etc., on the seepage flow and the pore pressure distributions of tunnels.

Chiral metamaterials can achieve unique properties different from those of conventional materials through the design of special structures. The aim of this paper is to discuss the effect of the metamaterial layers on the impact loads in water entry problem. The mechanical properties of ATH (Anti-Tetrachiral Honeycomb) were simulated by nonlinear constitutive model. The effects of the constitutive relationship on water entry process were examined. It is shown that both the plateau stress and the densification strain of the material have large influence on the load of water entry impact. When the plateau stress is high, the material properties are close to those of conventional materials. The decrease of the plateau stress and the increase of the densification strain can prolong the duration of impact loading and reduce the peak impact force applied on the material.

Increasing the outlet flow rate of an atomization nozzle can increase the liquid exit velocity, leading to smaller droplets and enhanced atomization efficiency. In order to suppress the cavitation effects and achieve a larger outlet flow rate, this paper establishes a numerical model of the internal flow field in the nozzle structure to analyze the flow field information such as velocity, liquid phase volume fraction, and turbulence kinetic energy distribution. Based on the mechanism of cavitation generation, several improvement schemes for the nozzle structure are proposed: reducing the nozzle length, adding nozzle chamfers, and decreasing wall surface roughness. These approaches can effectively reduce the cavitation effects, significantly increase the nozzle's outlet flow rate, and improve the atomization performance, providing reference for the optimization of nozzle structures.

Because of its advantages of good development foundation, short design cycle, compact structure and strong fuel adaptability, the aero-derivative gas turbine has been widely used in the field of offshore oil and gas platform, marine power and pipeline transportation, etc. For the aero-derivative gas turbine blades working in high temperature, high pressure and other harsh environments, creep is one of the main failure modes. In order to ensure the operation reliability of the blade, nickel-based alloy with strong creep resistance is usually selected as its constitutive material. The nickel-based alloy has obvious third stage of creep, occupying a relatively high proportion of its whole life. The current creep damage constitutive model is difficult to accurately characterize the failure behavior of the third stage of creep for the nickel-based alloys. In response to the above problem, a creep damage constitutive model which can reasonably describe the third stage of creep of the high temperature materials is proposed in this paper. The model is validated by comparing with the creep experimental data under different temperatures. The proposed model can provide a theoretical guideline for accurate life prediction and reliability design of the high temperature components of aero-derivative gas turbines.

In order to improve the stability and wave dissipation effect of the square box floating breakwater, in this paper we develop a combined floating breakwater and construct a two-dimensional numerical flume based on the computational fluid dynamics method with consideration of the fluid viscosity condition. Taking the combined floating breakwater as the object of study, we focus on the effects of the mooring mode and the wave parameter on the kinematic response and wave dissipation performance of the combined floating breakwater by comparing the results with those of the square box floating breakwater. In addition, the vortex distribution of the water body around the floating breakwater is analyzed to reveal the wave energy dissipation mechanism. The results show that the wave dissipation ability of the combined floating breakwater is much higher than that of the square-box floating breakwater, and it mainly attenuates waves through energy dissipation. Compared with the square box type floating breakwater, the overall motion response of the combined floating breakwater is smaller, the wave dissipation ability is stronger. The mooring method has less influence on the motion response and wave dissipation performance of the combined floating breakwater. However, when the incident wave height increases, the mooring method has a greater effect on the wave dissipation performance. The results of this study can provide a reference for the optimal design and practical engineering application of floating breakwaters.

Particle contact friction coefficient and loading rate effects have significant influences on the shear strength of granular material system. For this purpose, the flexible biaxial compression tests are simulated by the discrete element method to investigate the macroscopic mechanical properties under different combinations of loading rates and friction coefficients. Based on the "rate-state shear strength theory", the influences of loading rates and friction coefficients on the "rotation-slip ratio" and shear strength of granular material system are further investigated. The results indicate that the rate-state shear strength theory can essentially reveal the macro micro relationship of particle material systems, and the macroscopic shear strength of granular material specimens can also be accurately described. The shear strength of granular material system increases with the increase of loading rate. However, there exists a critical loading rate below which the loading rate effect is negligible. The shear expansion of specimen is closely related to the sliding friction coefficient, and the irregularity of particle shape can significantly enhance the shear strength while maintaining a consistent shear expansion. The evolution of rotation-slip ratio in the shear band is affected by both the loading rates and the friction coefficients, with higher sensitivity to the sliding friction coefficient. Compared with the rotation-slip ratio, the "reference velocity" has an opposite trend, which increases significantly with the increase of loading rate and the decrease of friction coefficient. By establishing a quantitative relationship between the particle rotation slip ratio, the loading rate, and the generalized friction coefficient, theoretical guidance can be provided for further researches on the rate sensitive strength of granular materials.

The aero-engine blade disc works in the harsh environment of high temperature and high speed, which affect the mechanical behavior of the coating contact of the discontinuous blade-disk interfaces and the overall dynamic properties. In this paper, based on the three-dimensional elasticity theory, a contact model based on a multilayer half-space body is developed to investigate the contact responses between rough surfaces of multilayer structures. First, rough surface topography is decomposed into micro, mesoscopic and macro multi-level geometric profiles by explicit expression. Then, based on the Papkovich-Neuber potential function (P-N potential function), Fourier integral transform method and the influence coefficient method, a boundary constraint model for the multilayer contact problem is constrcuted, and is solved using a conjugate gradient algorithm. Finally, the reliability of the model is verified by comparing it with the analytical solution and the finite element results. Furthermore, a parametric study is performed to investigate the influcences of elastic modulus, Poisson's ratio and friction coefficient on the stress and displacement fields. This work provides a feasible and effective approach to study the contact response of rough interfaces of the coating systems.

The dovetail is an important connecting structure in aero-engine, and its assembly accuracy directly affects the performance and stability of the whole aircraft. However, dovetails are subjected to harsh working environments of high temperature/pressure loads and high rotation, and their assembly interfaces are subjected to elastic or plastic contact deformation, which affects the structural deviation propagation. In order to investigate the influence of the dovetail interface contact on the structural deviation propagation, firstly, in this paper we briefly introduce the tolerance analysis method of series structure based on Jacobian-Torsor model. Secondly, the interface contact mechanics analysis of asymmetric flat punch contact is realized based on the numerical solution of singular integral equation, and its equivalent torsor is constructed. On this basis, the interfacial contact deformation is incorporated into the deviation analysis by using the principle of minimum potential energy, and the partial parallel deviation propagation modeling method of dovetail considering interfacial contact is proposed. Finally, the proposed method is compared with the traditional method by taking the dovetail as an example to verify the feasibility and accuracy of the proposed method. The effect of interface contact on the deviation propagation of dovetail under different rotational speeds and wind pressures is investigated. The results demonstrate the significant effect of dovetail interface contact deformation on the deviation propagation and provide a feasible method for the deviation propagation analysis of other mechanisms.

The vibration suppression impedance control problem of space truss of space robot assembly in orbit is studied. Firstly, a system dynamics model of a single-arm space robot is established using Lagrange's method in terms of carrier attitude control. Through dynamic analysis, the Jacobian relation between the manipulator end-effector and the truss plug within the base coordinate system is derived. Based on impedance control principles, a second-order linear impedance model is established by considering the dynamic relationship between plug pose and output force. Next, a nominal PD (Proportional Derivative) controller is designed and a sliding-mode variable-structure controller is introduced to accurately compensate for the modeling uncertainties, thereby improving the force/position control accuracy. Taking into account of the inherent buffeting associated with the sliding-mode controllers as well as the fuzzy control principles, a control scheme utilizing the sliding mode surface as input and the compensation control gain as output is adopted to achieve the vibration suppression effects. This control strategy does not rely on differential signals from sliding-mode surfaces. Also, it requires less computation cost while maintaining strong robustness without complex fuzzy expert rule database. In addition, it has been proven through Lyapunov principle that this system exhibits uniform asymptotic stability. Finally, the effectiveness and suppression performance of the proposed control strategy are verified based on the analysis results of Matlab simulations.

Understanding the geostress field in reservoirs was crucial for successful hydraulic fracturing. Current on-site stress measurement methods, limited by wellbore locations and quantities, struggled to fully capture the geostress distribution. Numerical simulation interprets the on-site stress test results and redistribute the geostress field. The variation of geostress field at the intersection of faults is complex, and the mechanism of the influence of fault interaction on geostress is still unclear. By investigating Shunbei carbonate reservoir with intersecting faults using AiFrac modeling, the geomechanical models for different types of fault intersections in reservoir areas were established, some conclusions were made. In the region far from faults, the maximum horizontal principal geostress was controlled by far-field tectonic stress. Within the faults, due to the mechanical weakening of faults, the value of maximum horizontal principal geostress was relatively low. At the ends of faults, stress concentration led to a significant increase with a symmetrical deviation. In parallel fault zones, geostress was slightly smaller near the center and slightly larger at both ends. Intersecting faults with orientations closer to parallel with the regional maximum horizontal principal geostress direction exhibited a greater reduction in internal stress, and the direction of the maximum horizontal principal geostress underwent a drastic deviation at fault boundaries. These findings supported optimizing wellbore trajectory design in reservoir reformation.

Cable structures have wide applications in engineering. Due to their high flexibility, geometric nonlinearity effects must be considered in structural analysis. The TL (Total Lagrangian) formulation and UL (Updated Lagrangian) formulation are two main computational formulations in the finite element method. They are based on different reference states of motion and differ in theoretical derivation and solving algorithms. Although both formulations are suitable for cable structure analysis, there is a relative lack of comparative analysis on the differences and applicable scenarios of the two in specific applications. In this paper, based on the energy variational principle, the expressions of tangent stiffness of cable elements under the two formulations are derived, and the differences in the iterative strategies of nonlinear equilibrium equations under each formulation are compared and analyzed. Finally, through specific examples, it is demonstrated that for the cable structure analysis involving only geometric nonlinearity, both formulations can yield consistent results. It indicates that compared to the UL formulation, the TL formulation has simpler concepts and more concise solving algorithms, showing significant advantages in the cable structure analysis involving only geometric nonlinearity.

In some experiments, it was found that applying external pressure to lithium-ion batteries during the charge and discharge process can improve the cycle performance. However, the mechanism of how pressure affects the fracture of active particles remains yet to be explored. The external forces applied to lithium-ion batteries usually transmit to the electrode particles in two ways. One is through the compressed gas and liquid in the sealed space of battery which uniformly transfer the force to the surface of active particles, the other is through the battery casing which transfers the force to the electrode material and then to the active particles via the binder. Based on the Finite-Discrete Element Method (FDEM), this paper presents a diffusion-induced fracture model under finite deformation to analyze the fracture behavior of ternary positive electrode polycrystalline particles under the influence of applied pressure during lithiation. The numerical results indicate that, for both types of force transmissions, even smaller uniformly distributed pressures cannot reduce the tensile stress at the center of the particles to a level that prevents cracking, resulting in the occurrence of a small number of central cracks. In comparison, larger uniformly distributed pressures change the maximum principal stress inside the active particles from tension into compression, thereby better preserving the integrity of the internal structure of the active particles. Moreover, increasing the magnitude of the applied pressure converts all tensile stresses induced by diffusion into compressive stresses, thereby avoiding cracks caused by tensile stress and suppressing the extension of cracks in the active particles during lithiation.

The change of water gap in fuel assembly caused by fuel assembly vibration has an important influence on the power fluctuation in the reactor. In order to study the behavior of fuel assembly vibration and water gap variation, fuel assembly vibration analysis model is established according to fuel assembly structure and its vibration characteristics, and fuel assembly vibration analysis software FAVA is developed. Firstly, the fuel assembly vibration analysis model is validated by comparing with the commercial finite element software Abaqus. Secondly, by analyzing the change of water gap caused by fuel assembly vibration, the fuel assembly vibration frequency calculated by FAVA software is compared with the core power fluctuation frequency, which shows that the core power fluctuation is mainly caused by the fuel assembly vibration. Finally, the influence of stiffness change of fuel assembly on the vibration is analyzed.

Inspired by the nervous system of biological movement, Central Pattern Generator (CPG) control theory is applied to achieve various gait patterns in legged robots, which is of great significance in bio-inspired motion control. For the gait movement control of hexapod robots, the classical Van der Pol (VDP) oscillator model is first improved by adding a time proportion function to adjust the rising and falling phases of the periodic rhythm signal, enabling the regulation of the swing and support phases of the robot's legs. Next, the improved VDP oscillator is used as a functional unit, and the coupling delay between units is employed to regulate gait patterns, constructing a novel time-delay coupled CPG controller with a unidirectional loop. Furthermore, a hexapod robot model is designed in SolidWorks, and co-simulation experiments using ADAMS and MATLAB are conducted to achieve three common gait patterns: tripod, tetrapod, and wave gaits. Finally, gait tests are performed on a physical prototype to verify the feasibility and effectiveness of the proposed time-delay coupled CPG control system.