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.

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.

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.

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.

Fatigue life prediction is crucial for the safety of metallic materials and structures. Machine learning (ML) models have demonstrated strong predictive capabilities in this field, but their "black-box" nature limits their reliability, trustworthiness, and application in engineering practice. Explainable Artificial Intelligence (XAI) provides key techniques to open the ML "black box". This paper aims to systematically review the current applications of XAI in the field of metal fatigue life prediction. Addressing the issue that current research applies various interpretation methods without systematic categorization, this paper proposes classifying existing methods into two main categories: "post-hoc explanations" and "interpretable by-design". This paper outlines the key techniques of these two categories and their specific application examples in fatigue life prediction, discusses the limitations of model interpretation methods and current technical challenges, and prospects for opportunities and challenges in subsequent research.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

To investigate the effects of ambient pressure and standoff distance on the bonding quality of T2/Q235 explosive welding, a three-dimensional numerical simulation of the welding process was conducted using Ansys software. Two computational approaches-the Smooth Particle Hydrodynamics-Finite Element Method (SPH-FEM) coupled algorithm and the Arbitrary Lagrangian-Eulerian (ALE) method-were employed to analyze collision velocity and collision angle under varying ambient pressures (1 atm to 0.2 atm) and stand-off distances (3 mm, 6 mm, and 9 mm). Simulation results were systematically compared with experimental data and theoretical calculations. Key findings revealed that: (1) Under decreasing ambient pressure, maximum collision velocity occurred at 1 atm for the SPH-FEM method but shifted to 0.2 atm for the ALE method, aligning more closely with experimental observations; (2) Both algorithms consistently showed larger collision angles at the 6 mm stand-off distance compared to 3 mm and 9 mm configurations, with the ALE method yielding smaller angles closer to experimental lower bounds at 3 mm stand-off under atmospheric pressure; (3) At 0.2 atm ambient pressure and 6 mm stand-off, ALE simulations demonstrated superior agreement with theoretical predictions for both collision velocity and angle. The results conclusively demonstrate that the ALE algorithm achieves higher consistency with experimental measurements and theoretical models compared to the SPH-FEM approach, validating its effectiveness for simulating T2/Q235 explosive welding dynamics.

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.

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 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.

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.

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.

Shear fracture models play a crucial role in characterizing metal fracture, with shear tensile tests serving as the fundamental method for calibrating their parameters. However, existing shear tensile experiments often achieve limited maximum strain, making it difficult to maintain a stable shear state under large strain conditions. In this study, finite element analysis was conducted using LS-DYNA to simulate four distinct shear-tensile specimens, verifying the feasibility of their constitutive model and boundary conditions. Based on the guidelines from GB/T 34487-2017, a novel shear-tensile specimen is proposed. This new design ensures minimal stress triaxiality fluctuations (within ± 0.05) and achieves an effective plastic strain of up to 10% prior to fracture.

Bubbles are one of the important factors affecting the efficiency and quality of microreactors. Understanding the mechanisms of bubble transportation in the microchannel can provide guidelines for the designation. Meanwhile, bubble motion is one of the usual bubble transportation phenomena. In this paper, systematic and parametric studies of single bubble motion characteristics are conducted using computational fluid dynamics, aiming to derive fundamental principles and uncover the underlying mechanisms. The bubble motion principle during the initial detachment from the wall is proposed: while the trajectories of a single bubble may vary, the bubble will ultimately reach an equilibrium position (with a constant distance from the wall) across all parametric cases. Furthermore, the equilibrium position of the bubble is influenced by its diameter, the driving velocity, and the properties of the surrounding solution. Reynolds number (Re) and Capillary number (Ca) are selected as two characterized parameters. Based on the bubble diameter and common solution properties, the discussion cases in the range of 0.288<Re<97.2, 0.005<Ca<0.228. The relationship between Re and Ca can be distinguished by the bubble equilibrium position Ye (the dimensionless number of the distance between the final bubbles and the wall): (1) power law when 0<Ye<0.45; (2) linear when 0.45<Ye<0.95; (3) the bubble is attached to the wall (Ye=0) when the viscous effect is negligible; (4) the bubble is positioned in the center of the microchannel (Ye=1) when the viscous effect dominates. Corresponding, the mechanism can be underlaid by the manipulation forces, including wall-induced, deformable-induced, and shear stress gradient lifting forces and viscous drag force. In conclusion, the motion of the bubble is the combined influence of the wall, inertia, viscosity and surface tension effects.

The Natural Element Method (NEM) is a meshless method based on natural neighbor interpolation. This method offers the advantages of simple shape function construction and ease of applying essential boundary conditions. Utilizing dimensional reduction techniques, a methodology for conducting lower bound limit analysis on two-dimensional elastoplastic structures has been developed through the application of NEM. In the lower-bound limit analysis, the elastic stress field is directly obtained using the NEM. The self-equilibrated stress basis vectors are derived from the elastoplastic iteration results of the NEM, and the required self-equilibrated stress field is constructed. The whole solution process of the problem is transformed into a series of sub-problems of nonlinear programming, which are solved through the complex method. Numerical examples demonstrate that the application of the Natural Element Method to lower-bound limit analysis is both feasible and effective.

In this paper, the approximate Noether theorems for approximate Hamiltonian systems on time scales are investigated based on the Noether symmetry theory on time scales. Firstly, the Hamilton principle for approximate Hamiltonian systems on time scales is presented, and the corresponding approximate Hamilton canonical equations are established. Secondly, the Noether identities for approximate Hamiltonian systems on time scales are derived, and the relationship between approximate Noether symmetry and approximate conserved quantities is established. As a result, the approximate Noether theorems for these systems on time scales are obtained. Finally, an example is provided to demonstrate the application of the theoretical results.

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.

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.

Under some extreme conditions such as rapid heat transfer, it is necessary to build the non-Fourier heat conduction model considering the finite heat propagation velocity, which includes the hyperbolic heat conduction equation. Based on the modified couple-stress elasticity theory and Green-Lindsay generalized thermoelasticity theory, the governing equations of the thermal mechanical coupling theory and four dispersive waves (CP wave, CT wave, SV wave and SS wave) are obtained in this paper. Using the wave function method, the linear algebraic equations are derived based on the intact interface conditions including surface force, displacement, surface couple, micro-rotation, temperature change and heat flow so as to determine the amplitude ratio of the reflected transmission wave through the finite thickness sandwich structure relative to the incident wave. The influences of two thermal relaxation durations on the CT wave reflection transmission coefficient,as well as one couple stress parameter on the SV wave and SS wave reflection transmission coefficient are studied via investigating the incident SV wave. Finally, the accuracy of the numerical results is verified through examining the conservation of normal energy flow for each wave.

In marine environments, the corrosive effects of chloride and sulfate ions on concrete structures are significantly more severe than those of other ions. However, there remains no consensus regarding the evolution of concrete strength under their synergistic attack. This study conducted coupled chemo-mechanical experiments on concrete specimens immersed in sodium sulfate solution, sodium chloride solution, and their mixed solutions with varying concentrations. By incorporating chemical reaction equations and kinetic rate equations governing continued hydration and aggressive ion transport, a chemo-mechanical conversion methodology was employed to elucidate the competitive mechanism between chloride ingress and sulfate attack in influencing concrete strength. Furthermore, a chemo-mechanical constitutive model was developed to characterize the strength evolution of concrete subjected to coupled sulfate-chloride corrosion.

Variable-stiffness composite laminates with variable-angle layups expand the design space and enhance the mechanical properties such as buckling strength and stiffness. However, commonly used single-objective optimization methods often failed to achieve simultaneous enhancement of multiple mechanical properties. To address this issue, this paper proposed an active learning Kriging model optimization method based on the Mean Squared Error and Expected Improvement criterion for the multi-objective optimization of variable-stiffness laminates. Its effectiveness was validated through an optimization case study of variable-stiffness laminates with fiber paths represented by B-spline curves. Compared to the gradient descent-based optimization method, the Kriging model-based variable-stiffness optimization method achieved a significant improvement in computational efficiency. Finally, a multi-objective optimization framework integrating the Kriging model and a multi-objective particle swarm optimization (MOPSO) algorithm was proposed. The resulted Pareto solution set included a design with a buckling factor comparable to that of ±45° laminates but an 87 % reduction in compliance.

Segments are the lining structures outside the subway shield tunnel, and are vulnerable to various degrees of cracks due to external loads and rust expansion pressure. Segments cracking can seriously reduce the stiffness and load-bearing performance of the structure. In order to determine the distribution pattern of crack morphology inside the arch waist segment of shield tunnel under the bending load and the rust expansion pressure, the CDM-XFEM (Continuum Damage Mechanics-Extended Finite Element Methods) method was used to calculate the surface crack morphology of the arch waist segment under the bending load, and the results were verified through full-scale tests. By uniformly discretizing the steel rust layer, the irregular rust layer rust expansion pressure transformation equation of the segment was derived based on the thick-walled cylinder model. Based on this, the crack morphology inside the corroded segment under different bending loads was calculated. Research has shown that under the bending loads, the outer curved surface of the segment exhibits three curved through cracks, while the internal cracks exhibit a distribution pattern of three connected ellipses. When the bending moment of the segment increases from 220 kN·m to 320 kN·m, the transverse span of the rust expansion crack at the crack section in different areas increases by 27 %, 51 %, and 37 %, respectively, indicating that the increase in bending moment has the greatest impact on the rust expansion cracking at the middle crack section of the segment. Under the same bending moment, the shape of the rust cracking angle curve of each steel bar is basically the same, indicating that the bending load has a relatively small impact on the rust cracking angle of the segment.

Invertebrates like earthworms and slugs exhibit continuum body structures and undulatory propulsion, making them ideal references for designing worm-inspired soft robots. Developing dynamic models of such biomimetic systems is essential for guiding robot design. This study investigates axial motion in a worm-like system using a slender circular hyperelastic rod as the mechanical model. We integrate axial and radial coupling effects by incorporating the Yeoh hyperelastic strain energy, viscous friction, and internal driving forces. A sinusoidal squared strain wave drives the system to study how retrograde peristaltic waves affect its motion. The derived nonlinear continuum equations are analytically challenging. To address this, we propose a hybrid analytical-numerical method: First, geometric approximations link radial deformation to axial displacement, capturing nonlinear coupling effects. Second, peristaltic wave propagation replaces direct force calculations in simulations. Results show the model works for both small and large deformations. Through a numerical case, the correlation between average locomotion speed and waveform parameters in the axial-radial coupling model is investigated. Under constant strain energy coefficient, friction coefficient, and slenderness ratio, increasing the sinusoidal squared strain wave amplitude or decreasing the wave-width-to-body-length ratio enhances the worm-like system's average axial propulsion velocity.