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 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.

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.

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.

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.

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.

During the charge and discharge processes of solid-state lithium metal batteries, the stress generated at the interface between the rough surfaces of the lithium electrode and solid-state electrolyte plays a crucial role in the formation of lithium dendrites. In this paper, a mechanical model is established by considering the electrode and electrolyte as elastic bodies. Specifically, the stress at the interface of a two-dimensional sinusoidal rough interface is investigated for isotropic linear elastic materials. Using a two-dimensional Fourier transform, the relationship between stress and displacement at the interface in the transform domain is obtained. By applying the inverse transform and incorporating boundary conditions and interface continuity conditions, an analytical solution for the interfacial stress in two dimensional conditions is derived. When the wavenumber of surface roughness in one direction of the interface is zero, the two-dimensional interfacial stress solution degrades to the one-dimensional case. Subsequently, the analytical solution is used to analyze the influences of the material parameters of the electrolyte and electrode on the magnitude of the interfacial stress.

Chiral Liquid Crystal Elastomers (CLCE), with their ability to selectively reflect specific wavelengths of light and exhibit excellent large-deformation capabilities, have gradually become a promising flexible reflective display material. Studies show that the optical coloration properties of CLCE are closely related to local strain, displaying a significant force-optical coupling effect. As a soft material, CLCE possesses viscoelastic characteristics, resulting in a time-dependent mechanical response during deformation. However, systematic research on the optical and viscoelastic coupling properties of CLCE under uniaxial and biaxial deformation conditions remains limited. In this study, using a multi-axial opto-mechanical testing platform, we systematically investigate the time-dependent characteristics of the reflection spectrum of CLCE under uniaxial and equibiaxial deformation conditions. By analyzing the spectral properties under stress relaxation and different loading rates, we propose an improved phenomenological model for CLCE based on the stretched exponential viscoelastic constitutive relationship. This model provides theoretical support and experimental insights for further optimizing the application of CLCE in smart optical devices.

Laminated beams are widely used in engineering structures due to their enhanced strength and stiffness. However, delamination, a barely visible form of damage, can occur during manufacturing or service. Accurate localization of delamination in laminated beams is essential for maintaining structural integrity. While the existing linear interface vibration model has been proposed to represent the absence of linear interface forces in the debonding region of open delamination, it fails to capture the opening-closing contact behavior of "breathing" debonding under nonlinear vibro-acoustic excitation. To address this problem, this study proposes a new nonlinear interface vibro-acoustic model, in which the nonlinear interface forces appear exclusively in the "breathing" debonding region, acting as multi-tone harmonic excitation sources to produce sideband harmonics. Moreover, this study emphasizes the use of nonlinear interface forces for the localization of delamination due to this inherent merit of localization. The nonlinear interface forces are reconstructed from nonlinear operating deflection shapes of a laminated beam. Nonlinear damage indices are established relying on nonlinear interfaces associated with multiple neighbouring sideband harmonics. The capability of the approach for localizing "breathing" debonding in laminated beams is experimentally validated through non-contact measurements using a scanning laser vibrometer. The results demonstrate that the approach is capable of predicting the occurrence of delaminations in laminated beams and accurately identifying their locations and sizes.

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.

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.

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 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.

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.

Low-frequency vibrations and noise levels are important indicators for evaluating automobile comfort. To address the issue of low-frequency vibrations and their control in automotive panel structures, we proposed a plate-type two-dimensional phononic crystal design based on the local resonance mechanism. The bandgap range of the phononic crystal was determined through the finite element method, and the mechanism of bandgap formation was analyzed. Subsequently, the transmission characteristics curve of the phononic crystal plate was calculated, and comparisons were also carried out for the vibration displacement. The results indicate that a complete bandgap appears in the plate within the frequency range from 62.48 Hz to 74.16 Hz. Within this frequency range, coupling effects between the base plate and the cylindrical resonators occur, leading to the formation of the bandgap. Elastic waves in the phononic crystal plate are successfully confined within the bandgap range. By adjusting the material and geometric parameters of the structure, the bandgap frequency range can be tuned to meet the requirements of more practical low-frequency applications. The structural design and analysis method proposed in this paper have broad application prospects in engineering fields such as low-frequency vibration reduction and noise control in automobiles.

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.

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.

To meet new detection requirements and achieve high sensitivity, microbeam-based biosensor technique faces challenges in the development of signal interpretation models. Through 3D finite element simulations of the detected quasi-static signals of microbeam under surface adsorption, we revealed an asymmetric distribution characteristic of the microbeam cross-section's warping. However, the existing theoretical models considering shear deformation cannot accurately describe this asymmetric warping. To address this issue, first, we simplified the complete adsorption of molecules as a uniformly distributed surface stress acting on the microbeam's surface and obtained the distribution pattern of warping zero point through 3D finite element simulation. Then, we employed the semi-inverse method of plane elasticity theory to determine the shear stress distribution and shear force that correspond to the asymmetric warping characteristics on the deformed cross-section. This led to an improvement in Timoshenko beam theory and the establishment of a new model to predict the detected quasi-static signals of microbeam. Finally, we validated the analytical model by comparing with experimental results and finite element simulations. The results indicate that the predictions of our improved model agree well with the relevant microbeam experiments. Moreover, within the geometric size ranges employed in the existing adsorption-microbeam static experiments (length-to-thickness ratio of 200-500, length-to-width ratio of 3-7), its prediction error for the microbeam's free-end deflection is less than 3 %, which is smaller than that of other theoretical predictions. Additionally, the shear effect and axial force effect negatively impact the microbeam's deflection, with the shear effect having a significantly greater influence than the axial force effect. This model and its conclusions provide a new perspective for interpreting the static detection signals of microbeam biosensors and developing the relevant design.

In view of the high carbon emissions and limited land storage capacity in the eastern coastal areas of China, CO2 offshore geological storage holds significant application potential. Although the risk of CO2 leakage during offshore geological storage is extremely low, accurate assessment of CO2 diffusion in seawater under rapid leak scenarios is critical to ensure the safety of storage. Based on typical marine environment data, this study employs the Volume of Fluid (VOF) model to simulate the dynamic characteristics of CO₂ bubbles and utilizes the Euler model to simulate the diffusion characteristics of CO2 clusters in seawater, thereby completing a comprehensive simulation analysis of fluid dynamics. On this basis, a machine learning-based assessment method for subsea CO2 leakage is developed. The neural network model framework is constructed, and an inverse-problem solving model is established accordingly to analyze the morphological evolution and distribution range of CO2 leakage under different marine environmental conditions. Additionally, key parameters such as crack width and leakage velocity resulting from the leakage scenario are analyzed, enabling accurate calculation of the leakage amount. The prediction accuracy of this model can reach 95 %, demonstrating its effectiveness and applicability in addressing CO₂ leakage. This study not only offers an innovative method for rapid leakage assessment of CO2 offshore geological storage but also provides an important scientific basis and technical support for risk assessment and safety management in related fields in the future.

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.

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.

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.

Damage identification is one of the most important aspects of structural health monitoring. In order to further improve the efficiency and accuracy of damage identification, a two-stage structural damage identification method based on the improved modal strain energy index and DBO-BP (Dung Beetle Optimization-Back Propagation) neural network is proposed. Firstly, the improved normalized damage index of modal strain energy is used for the damage localization analysis of the structure. Then, taking the average change rate of the structure unit modal strain energy as the input parameter, the stiffness reduction coefficient of the damaged unit as the output parameter, and utilizing the DBO algorithm which is an improved version of the optimal latin hypercubic method, the weights and thresholds of the BP neural network are optimized to perform the structural damage quantitative analysis. The concrete slab structure and flat rigid frame structure are used as exemplary models for damage identification verification. The results show that the proposed method is accurate in damage location identification, with high calculation efficiency for the degree of damage and small identification error as low as 0.4 %, exhibiting excellent damage identification performance.

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.

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.

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.

By conducting tensile tests and numerical simulations on 304 stainless steel wire mesh/carbon fiber hybrid composite (SSWM/CFRP) laminates, the residual strength and failure modes of single hole specimens with different aperture sizes and double hole specimens with different circular hole arrangements were investigated. Digital Image Correlation (DIC) technology and Scanning Electron Microscopy (SEM) were used to observe the deformation and damage evolution characteristics of the specimens. The results indicate that the tensile stress-strain curve of SSWM/CFRP laminates with holes generally exhibits brittle failure characteristics. The residual strength of single hole specimens decreases with the increase of hole diameter, while the effective cross-sectional area of double hole specimens is affected by the arrangement of circular holes in the specimens. The DIC technology captures the maximum tensile and shear strains of a single hole specimen locally, which appear on the left and right sides of the circular hole along the diagonal direction. The constructed finite element model can effectively predict the residual strength and fracture path of the specimen, and reveal that the main failure modes of the specimen are ductile fracture of SSWM, fiber tensile damage of 0 ° fiber layer, matrix tensile damage of 90 ° fiber layer, and interlayer delamination damage.

Graphene and its related two-dimensional materials have become a hot topic in the field of nanotribology. In recent years, many significant progresses have been made in theoretical, experimental, and computational simulation studies. Due to the extremely complex nature of nanoscale friction processes, the underlying mechanisms of friction are not yet fully understood. Therefore, it is necessary to delve into the mechanisms of friction and reveal the laws of friction on the atomic-scale. In this paper, the sliding friction behavior of a diamond probe on a suspended single-layer graphene surface is studied based on molecular dynamics simulation. The dependence of the friction on the normal load and the relationship between friction and actual contact area are considered. The results show that there is a nonlinear relationship between friction force and normal load (actual contact area), which is significantly different from the friction laws of bulk materials. Specifically, the friction force gradually increases with the load in the positive load range. However, the friction force is almost unaffected by changes in the load in the negative load range. The current research findings help to understand the nanoscale friction behavior of two-dimensional materials from an atomic perspective. This research can also provide new ideas and theoretical references for the design of nanodevices and the development of nanotribology.

Accurate measurement of the shear strength of the tile adhesive bonding layer is crucial for effectively preventing tile detachment. Initially, a conventional tensile testing machine was modified to design a shear testing device based on a single lap joint, and shear strength tests were conducted on tile adhesive bonding layers with different thicknesses. The results show that the joint failure mode is adhesive interface debonding and cracking, with no cohesive failure in the tile adhesive. The thicker the tile adhesive layer, the lower the shear strength of the bonding layer. Further numerical simulations revealed that additional bending moments occur during the shearing of the single lap joint, transforming pure shear into tensile shear action, leading to experimental errors. The thicker the tile adhesive, the larger the error caused by the additional bending moment during shearing. To eliminate the influence of additional bending moments on shear test results, an improved shear testing device was proposed. By symmetrically loading through double lap joints, the experimental errors caused by additional bending moments were effectively avoided, enhancing the accuracy of shear strength test results of the tile adhesive bonding layer.

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.

Column buckling is a critical topic in university-level Materials Mechanics courses and is widely regarded as a challenging subject to teach. In classical Materials Mechanics theory, the critical load is determined by analyzing the non-zero solution condition of the approximate equilibrium differential equation in the critical buckling state. Although this method is straightforward, it remains highly abstract and is difficult to apply to complex engineering stability problems. To enhance students' understanding of column buckling and its analytical methods, this study revisits the classical approach through the principles of virtual work and minimum potential energy. Additionally, based on the principle of minimum potential energy, the thermal buckling behavior of carbon nanotubes under a longitudinal linear temperature gradient is examined. This work aims to provide new perspectives for the teaching and research of column buckling, helping students gain a deeper comprehension of relevant concepts and methods in handling buckling problems.

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 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.

The lake-at-rest steady-state problem, which finds extensive practical applications, can be represented by shallow water equations with source terms. These equations necessitate a well-balanced approach in numerical calculations. This paper presents a well-balanced, high-order entropy stable scheme based on Targeted Essentially Non-Oscillatory (TENO) reconstruction for its low numerical dissipation. The well-balanced property of this scheme is subsequently established. The TENO reconstruction with low numerical dissipation is introduced into the TeCNO framework, appending the reconstructed numerical dissipation term to the existing entropy conservation flux to obtain high-order entropy stable numerical flux. For the source term, a discrete form corresponding to the numerical flux is adopted to achieve a numerical balance between the flux function and the source term. The high resolution and well-balanced property of the algorithm are demonstrated through multiple numerical examples. The numerical results show that the high-order entropy stable scheme, based on TENO reconstruction, offers the advantages of well-balanced property, low dissipation and high resolution. Furthermore, it effectively addresses small perturbation problem in steady-state solution.

The influence of friction coefficient and line density on the motion of continuous worm-like system is studied in this paper. Frist, based on the dynamic model and the quasi-static model describing the motion of worm-like system, the two average velocities over one period are respectively derived by employing the square strain wave. Next, through comparing these two average velocities, it is found that the dynamic model cannot be simplified as quasi-static model for small friction or large linear density conditions. Then, the condition under which the influences of these parameters on the motion of worm-like system should be considered is given on the basis of relative error principle of the average velocity. Finally, through a numerical example, the two models are compared for the displacement-time histories over ten periods. It is found that the parameters of friction coefficient and line density have significant influences on the system motion in certain conditions.

Granite often contains initial cracks, therefore its strength characteristics are greatly affected by crack propagation. Most of the existing rock strength theories do not consider crack propagation, making them difficult to effectively reflect the strength and failure characteristics of the fractured granite. In this paper, uniaxial /triaxial compression tests and Brazilian splitting tests were conducted on the intact and fractured granite samples to study the strength and failure characteristics under tensile and compression conditions. The influences of confining pressure and crack inclination angle (the angle between the crack and the cross-section plane) on the strength stiffness and failure mode of granite were analyzed, and a method for calculating the strength of the initially cracked rocks was proposed. Based on the propensities of type II friction slip fracture in intact granite and type I-II composite fracture in fractured granite, the failure conditions of intact and fractured granite were established according to fracture mechanics theory. The experimental results show that the compressive strength and stiffness of granite specimens are significantly reduced by the introduction of initial crack. The compressive strength, elastic modulus, and secant modulus decrease with the crack inclination angle, while Poisson's ratio shows opposite trend. The initial cracks will significantly reduce the tensile strength of granite, which decreases with the decrease of crack inclination angle.

The free vibration problem of non-through cracked plates on fractional-order viscoelastic foundations is studied in this paper. First, a fractional-order viscoelastic foundation model is introduced to better describe the mechanical behavior of foundation. Next, the free vibration of cracked plate with through crack under the four-edge simply-supported boundary conditions is studied. Further, the through crack situation is generalized to the non-through crack situation. Based on the relation between the energy release rate and the stress instensity factor, the additional rotation angles induced by the crack is obtained, and the compliance coefficients of the crack equivilent rotation spring are derived for both the through and non-through crack situations. Finally, the complex natural frequency are obtained according to the boundary conditions. The numerical examples are provided and the influences of the fractional order coefficient, the viscosity coefficient, crack location and crack depth on the complex natural frequency and mode shape of the cracked plate were discussed.