Lattice structure has attracted much attention and research due to its lightweight, high strength and efficient energy absorption properties. This research draws inspiration from biological structures and starts from their structural characteristics. Based on the gradient distribution characteristics of the vascular bundles in the bamboo stems, using the Octet-Truss Structure (OTS) as the unit cell, four gradient lattices were designed, namely the Unidirectional Transverse Gradient Lattice (UTGL), the Bidirectional Transverse Gradient Lattice (BTGL), the Unidirectional Longitudinal Gradient Lattice (ULGL), and the Bidirectional Longitudinal Gradient Lattice (BLGL) structures. Samples were fabricated from AlSi10Mg powder using Selective Laser Melting (SLM). Through numerical simulations and compression experiments, the mechanical properties and deformation mechanisms of them were systematically studied. The strain distribution of these structures was observed using Digital Image Correlation (DIC). The research results show that the ULGL and BLGL structures exhibit more stable deformation patterns compared to the UTGL and BTGL structures, with layer-by-layer collapse and no shear bands appearing. Among these four gradient lattice structures, BLGL exhibits the best Energy Absorption (EA) and Specific Energy Absorption (SEA). Subsequently, the mechanical properties of BLGL structures with different size ratios were investigated. Among them, the BLGL structure with a size ratio of 7:6:5 exhibited the best SEA. In conclusion, this study provides new ideas for the design of bionic gradient lattice structures.

Despite their potential in energy absorption, existing auxetic metamaterials face a key challenge in reconciling low initial peak load with high energy absorption efficiency. To address this issue, this paper proposes a vertex-based node-locked re-entrant honeycomb structure (VNRHs), which reinforces the re-entrant honeycomb through vertex hierarchy and realizes discretized modular design via a node-locked strategy. Two specific configurations are distinguished, namely VNRQ and VNRH, corresponding to hierarchical cell shapes of quadrilateral and hexagonal geometries, respectively. Quasi-static compression experiments were conducted to analyze the mechanical properties of the two structures and to validate the reliability of the finite element model. On this basis, the deformation modes, NPR effects, and crashworthiness of the two configurations under different structural angles and impact velocities were systematically investigated. The results show that the assembled VNRHs not only retain desirable NPR characteristics but also achieve a functional coupling of “initial buffering followed by energy absorption”. Further analysis reveals that the synergistic effect between structural self-locking and NPR significantly enhances the overall energy absorption capacity. In the application scenario of train occupant head protection, the discrete modular structure exhibits significant advantages over the integrated structure in terms of peak load and energy absorption uniformity. Specifically, the discrete structure reduces head injury criteria by 111.8% compared to the integral structure. This work provides an innovative design strategy for train head protection and broadens the application prospects for advanced protective structures.

Topology optimization (TO) of two-dimensional (2D) multi-material structures under dynamic conditions has been extensively investigated. However, Dynamic topology optimization (DTO) of three-dimensional (3D) multimaterial structures under time-varying loads remains insufficiently explored. This study presents the first systematic investigation of time-domain DTO for 3D multi-material structures subjected to time-varying loads. The proposed method develops efficient multi-material hexahedral elements, with design variables normalized using the ordered solid isotropic material with penalization (Order-SIMP) scheme. The Hilber-Hughes-Taylor-alpha (HHT alpha) method, combined with a discretize-then-differentiate adjoint sensitivity analysis, is utilized to evaluate the dynamic responses. Volume constraints are efficiently updated through the improved alternating active phase algorithm-optimality criteria (IAAPA-OC) approach to enable effective structural optimization. Moreover, the proposed method demonstrates both generality and robustness. Finally, several numerical examples with varying directions of time-varying loads, equivalent angular frequencies, material volume fractions, and objective functions are presented to thoroughly investigate the optimized topologies and numerical performance of diverse 3D cases.

As one of the most structurally complex and load-bearing components, the main landing gear (MLG) system experiences substantial aerodynamic loads during aircraft takeoff, landing, and retraction/extension sequences. Its aerodynamic characteristics profoundly impact the reliability of the retraction/extension mechanism and the structural fatigue life of the assembly. To accurately determine the true aerodynamic load characteristics of the MLG under varying speed and crosswind conditions, a high-fidelity numerical model of a main landing gear system from a representative civil aircraft was established using Computational Fluid Dynamics (CFD) methodology. Employing the k-ω SST turbulence model, a systematic analysis was conducted across four distinct incoming flow velocities, including superimposed crosswind conditions, investigating the surface pressure distribution, flow characteristics, and aerodynamic force variations on individual key components of the MLG. The results reveal that the MLG exhibits similar pressure distribution patterns across all tested conditions, with the leading edges of the wheels, side stays, and the frontal region of the oleo strut consistently showing characteristic high-pressure zones. Conversely, extensive flow separation on the leeward side creates significant low-pressure regions, profoundly affecting both lift and side forces. The oleo strut is identified as the primary contributor to both total aerodynamic drag and lift, whereas the wheels are the predominant generators of side force. Crosswind-induced pressure asymmetry is particularly pronounced on the left wheel; notably, the area of its negative pressure zone decreases with increasing incoming flow velocity. These findings provide a crucial theoretical basis for future landing gear structural design, aerodynamic optimization of the wheel well, and reliability analysis of retraction/extension mechanisms.

PurposeThe purpose of this article is to comprehensively investigate the load characteristics of the high-speed train bogie frame with inner axle-box and analyze the applicability of the EN 13749 standard.Design/methodology/approachThis article studies the load characteristics and the maximum load extrapolation approach for the high-speed train bogie frame with inner axle-box. The bench calibration experiments and field line measurements are carried out.FindingsThe measured variable-amplitude loads are converted to an equivalent constant-amplitude load and compared against the standard limit values, which are found to be below the specified limits. The response frequencies of the three loads show a correlation with respect to changes in velocity. The maximum load amplitude responses of both transverse damper loads and antisnaking damper loads are concentrated around 1.5 Hz. Axle-box traction link loads are primarily concentrated within the 0-50 Hz frequency range. Compared with the extrapolation results of polynomial regression, the errors of locally weighted least squares regression (LWLS) are all below 5%, validating the feasibility of this method for load extrapolation of bogie frame with inner axle-box.Originality/valueBased on axle-box traction link load data and bogie load analysis, the equations for rhombic loads and traction loads are established. Weighted least squares reflects the differences in the data used by varying the weights assigned to the fitting parameters. This work provides reasonable guidance for future research and optimization of the high-speed train bogie frame with inner axle-box.

Conventional multi-cell honeycombs excel in energy absorption but often incur high manufacturing costs. While assembling low-cost self-locking honeycombs offers a promising alternative, their crashworthiness is inherently compromised by local instability, particularly in configurations with fewer bent plates. To reconcile this trade-off between low-cost manufacturing and high energy-absorption efficiency, this study proposes a novel foam-filled self-locking honeycomb (FSLH). A comprehensive investigation combining out-of-plane compression tests and validated non-linear explicit dynamics simulations was conducted to systematically evaluate the effects of gradient foam densities, cell size, the number of bent plates, and dynamic impact velocities. The primary scientific contribution of this study lies in uncovering a scale-dependent and counter-intuitive topological coupling mechanism between the foam core and the self-locking walls. Specifically, while the specific energy absorption (SEA) of the empty structure dictates a positive correlation with the number of bent plates, the FSLH exhibits a reversed synergistic trend: reducing the number of bent plates optimally amplifies the lateral foam-wall interaction, thereby maximizing the overall SEA and fundamentally enhancing the deformation stability. Furthermore, the study evaluates the dynamic inertia responses, revealing that high-velocity impacts effectively suppress the initial peak force while generating denser progressive wrinkles. These novel findings provide a promising alternative for the design of energy-absorbing structures that are both cost-effective and highly efficient, offering new insights into the potential applications of foam-filled self-locking honeycomb structures in energy-absorption systems.

Achieving metamaterials that are simultaneously mechanically, acoustically, and thermally functional remains a central challenge in architected material design. In this research, we report a turtle shell bioinspired multifunctional lattice metamaterial (BMLM) that overcomes this limitation through topology-driven hybrid-coupling of distinct dissipation and transport pathways within a single hierarchical framework. The integration of arcuate plate-strut geometries with engineered microporosity enables coordinated mechanical energy absorption, acoustic attenuation, and convective thermal transport. Experimentally validated, the proposed architecture achieves an exceptional specific compressive energy absorption of 55.7 kJ/kg alongside broadband acoustic performance, exhibiting an average sound absorption coefficient of 0.954 and near-unity absorption (>0.9) sustained continuously from 2150 to 4250 Hz. Notably, the structure maintains acoustic stability under severe deformation; even at 40% compressive strain, absorption remains above 0.9 across a 2.1 kHz bandwidth, demonstrating deformation-resilient functionality. Moreover, the interconnected open-cell topology facilitates efficient airflow and convective thermal dissipation through its high surface-area-to-volume ratio, comparing superior to standard plate-fin heat sinks. Collectively, this work establishes a topology-driven strategy for designing bio-inspired metamaterials with robust, cross-domain performance.

Abstract To address the issues of traditional integrated honeycomb structures, such as complex manufacturing processes, high production costs, fixed mechanical properties, and difficulty in adapting to varying engineering demands, this paper proposes a circular self-locking honeycomb structure (CSHs) based on a node-locked strategy. The structure cleverly utilizes a spiral path to achieve nested assembly of circular elements. By adjusting the spiral radius and the number of curled layers, geometric interference between elements can be effectively eliminated, resulting in stable and reliable self-locking assembly. Through theoretical analysis and finite element simulations, the effects of the spiral radius and the number of curled layers on the crashworthiness of CSHs are systematically investigated. The results indicate that the optimal values for these parameters are R15 for the spiral radius and N0.75 for the number of curled layers, under which the specific energy absorption of the structure reaches 16.814 kJ kg −1 . With standardized elements and on-demand assembly, the structure can be shaped into square, hexagonal, or other forms as needed, achieving high energy absorption while remaining easy to fabricate and assemble. This study thus establishes a design basis for self-locking honeycomb structures in crashworthiness applications, including vehicle impact protection.

This study establishes a high-fidelity CFD model using the k-omega Shear Stress Transport (SST) turbulence model to evaluate the aerodynamic characteristics of civil aircraft nose and main landing gears across four speed conditions. The results indicate that both landing gear systems exhibit similar surface pressure distributions across different speed conditions. Furthermore, the magnitude of aerodynamic forces increases proportionally with the incoming flow velocity. Significantly, the shock struts of both landing gear systems emerge as major contributors to the overall aerodynamic drag. It is also found that aerodynamic lift remains relatively low compared to both aerodynamic drag and side forces.

Lattice structures have attracted much attention in the engineering field due to their light weight, high specific strength, and excellent energy absorption characteristics. However, traditional homogeneous designs struggle to balance load-bearing and energy absorption performance. This paper couples Orowan strengthening with gradient strengthening, and designs and manufactures four new types of lattice structures using AlSi10Mg as the material: single-layer uniform lattice (SUL), Orowan-strengthened lattice (OSL), density-gradient strengthened lattice (GSL), and Grad-Oro-strengthened lattice (G-OSL). By combining the quasi-static compression test with finite element simulation. The results show that the G-OSL structure utilizes the density gradient-induced progressive crushing mode layer by layer. In addition, the effective deflection and bypassing effect of the shear bands brought about by the Orowan strengthening mechanism have demonstrated the most outstanding comprehensive impact resistance performance. Changing the interfacial spacing will cause different degrees of damage to the unit cell by the dislocations. Further analysis of the influence of the enhanced phase spacing (2 l, 4 l, 6 l) indicates that the spacing variation does not show a clear monotonic pattern for Energy absorption (EA). Gradient strengthening causes the lattice to undergo progressive collapse, while Orowan strengthening enables the shear band to bypass the strengthened phase. It provides an effective new idea for the design of high-impact-resistant lightweight lattice structures. It has great potential for application in fields such as rail transportation, aerospace, and protective equipment.

Simultaneous enhancement of impact resistance and heat dissipation remains a critical bottleneck in the design of advanced metastructures. Drawing on inspiration from arch bridges, this work proposes a multifunctional sandwich metastructure. Two configurations "Honeycomb-Arch Lattice-Honeycomb" (HAH) and "Honeycomb-Symmetry Arch Lattice-Honeycomb" (HSAH) were developed to optimize the trade-off between structural protection and thermal efficiency. The impact resistance and heat dissipation performance of HAH and HSAH, across different arch ratios, were systematically evaluated. Assessment was performed using the Complex Proportional Assessment (COPRAS) method, based on residual velocity (v), peak crushing force (PCF), Nusselt number (Nu), friction factor (f), and pressure drop (Delta P). Configurations with a/b = 1.5 and c/d = 1.1 or 1.3 show the highest comprehensive evaluation scores (Qi). When applied to the equipment compartment floor of high-speed trains, the maximum impact stress decreased from over 500 MPa in the original corrugated structure to below 300 MPa. The v of steel sphere after impact decreased sharply. Crucially, the design also excelled in thermal management, yielding a 25%-31% reduction in equipment surface temperature. Overall, the proposed sandwich metastructure offers substantial improvements in both impact resistance and thermal management, offering a new paradigm for multifunctional design.

In welding, improper operation or an excessively low welding current can easily cause incomplete penetration defects. These defects significantly reduce the cross-sectional area of the weld, leading to stress concentrations that can initiate fatigue cracks and, ultimately, cause premature fatigue failure of the welded joint. To investigate the effects of different incomplete penetration defects and weld geometry parameters on the fatigue life of butt welds, this paper first verifies the validity of the structural stress method for fatigue life prediction by comparing the fatigue life of actual specimens with incomplete penetration to that of the finite element model. The effects of different incomplete penetration shapes, depths, and weld widths on fatigue life were then analyzed using the structural stress method. Finally, based on the shock absorber seat model and the bogie model, the influence of the structural location of lack-of-welding defects on the overall fatigue life of the component was quantitatively analyzed. Engineering case studies demonstrate that fatigue life prediction based on the structural stress method can be effectively applied to evaluate incomplete penetration defects in welds in practical engineering applications.

Nearly the entire fleet of high-speed electric multiple units (EMUs) at a specific depot exhibited localised wheel tread defects (LWTDs), resulting in rapid progression of high-order wheel polygonisation and significantly shortened wheel re-profiling intervals. This incident marks the first documented occurrence of its kind in high-speed EMU operations across China in the past two decades. Comprehensive field investigations and experimental studies were conducted to identify the root causes of LWTDs and investigate the influence of operating speed on the formation of LWTDs. The main findings indicate that LWTDs originate from severe impact loads generated as wheels pass over damaged insulated rail joints (IRJs) and fixed frogs on a mixed-traffic railway line serving both passenger and freight trains. Although the speed limit was reduced to 60 km/h, this measure alone was insufficient to fully mitigate LWTDs without rail defect remediation. Based on long-term vehicle vibration tracking test data, two novel diagnostic indicators for IRJs and fixed frogs are proposed, utilising axle-box impact acceleration measurements to detect damaged rails. After remediation of the defective IRJs and fixed frog nose rails, LWTDs have been substantially mitigated, with high-order roughness levels of wheel out-of-roundness returning to normal operational levels.

Energy-absorbing materials and structures have been extensively applied in fields such as railway vehicles and the automotive industry. Particularly, lattice structures have emerged as a prominent research hotspot in recent years owing to their superior energy absorption capabilities. To further enhance the design efficiency and performance prediction accuracy of these structures, this paper proposes a machine learning-based approach utilizing a Multilayer Perceptron (MLP) model to predict the energy absorption performance of lattice structures. In this study, an experimental dataset of lattice structures was initially compiled, and the MLP model was subsequently constructed based on the extracted key features. The results demonstrate that the MLP model can accurately capture the complex nonlinear mapping relationships between the input features and the energy absorption performance, exhibiting exceptional predictive accuracy. Ultimately, the findings of this research offer a novel methodology for the performance prediction of lattice structures, thereby providing a robust theoretical foundation for their future structural optimization and engineering applications.

Internal leakage through micron-scale gaps severely limits the performance of single-screw expanders (SSEs) in Organic Rankine Cycle waste heat recovery. A promising solution is dynamic sealing using a liquid film generated by the working fluid itself. This study systematically investigates such films within the complex three-dimensional flow channels of an SSE, simplified as a rectangular helical channel (RHC). A high-fidelity numerical model solving the Reynolds-Averaged Navier–Stokes equations is employed, incorporating the Volume of Fluid method for interface tracking and the standard k-ε turbulence model. The model is rigorously validated against experimental flow visualizations and pressure drop measurements. Results show that strong centrifugal forces inherent to the helical geometry drive the liquid phase to form a continuous film on the outer channel wall. Liquid mass flow rate is the key factor controlling film thickness, while gas flow rate determines circumferential uniformity. For accurate quantification, a robust interface criterion—the Liquid Film Thickness Selection Value (LFTSV) at a gas void fraction αG = 0.1 is proposed and experimentally confirmed. Classical straight-pipe correlations prove inadequate, so a new linear semi-empirical correlation linking film thickness (at θ = 540°) to the two-phase Froude number ratio is developed, offering good predictive performance. These findings advance understanding of annular flow in curved geometries and provide a practical basis for optimizing seal design and operating conditions in SSEs.

Interface delamination under impact load is a common failure mode in sandwich structures. In this study, short aramid fiber epoxy (SAFE) resin was introduced at the panel-core interface to enhance the interfacial toughness, and its enhancement effect on the impact resistance of sandwich panels with different core materials was systematically studied. Experimental tests and finite element simulations were conducted on carbon fiber/ aluminum honeycomb and carbon fiber/polymethacrylimide (PMI) foam sandwich panels incorporating SAFE interfacial toughening. By comparing these results with those from untoughened reference specimens, the influence of SAFE on damage resistance and damage tolerance was evaluated. The results show that SAFE enhances impact performance through different mechanisms depending on the core material. For PMI foam sandwich panels, the SAFE layer effectively suppresses impactor penetration and reduces indentation depth, thereby improving damage resistance. However, compression-after-impact (CAI) tests reveal that the intrinsic brittleness of the PMI core governs the failure process, resulting in only a marginal improvement in damage tolerance. In contrast, for aluminum-honeycomb sandwich panels, the bridge-forming capability of short aramid fibers at the interface significantly enhances damage tolerance. The residual compressive strength and energy absorption after impact were improved to a maximum of 11.13 % and 101.70 %, respectively. Overall, this work provides valuable guidance for the interfacial toughening design of sandwich panels with different core materials.

In order to address the technical challenges of detecting defects in high-speed railway wheelsets under complex conditions such as dynamic lighting, foreign object occlusion, and microscale anomalies, this paper proposes a dual-mode deep learning framework that integrates PointNet++ and Swin Transformer. This paper enhances defect recognition through cross modal feature collaboration, and combines cross modal attention (CMA) mechanism for dynamic feature alignment and geometric guidance suppression strategy for reducing occlusion noise. The experimental results showed an accuracy of 0.985, an F1 value of 0.982, and a recognition rate of 0.938 for defects smaller than 1 millimeter. Research has shown that the model maintains robust accuracy under different lighting conditions (strong/weak/reflective) and up to 40% occlusion, while optimized deployment on edge devices can achieve 23FPS with only 12M parameters. This work significantly improves the intelligence and reliability of the high-speed railway wheelset detection system.

Some traditional thin-walled structures have problems such as low energy absorption efficiency and disordered crushing patterns, which limit their application in high-performance lightweight component engineering scenarios. This study proposes a spiral biomimetic design strategy, using the elytra of beetles, natural honeycomb structures, and the shells of turtles as the basic thin-walled units. By introducing the spiral gradient arrangement mechanism of the Bouligand structure, three biomimetic spiral thin-walled structures are constructed: the spiral double-convex (BRHS), the spiral hexagonal (BHHS), and the spiral negative Poisson’s ratio (BNHS) forms. Quasi-static compression tests and finite element simulation analysis show that the mechanical response of the designed spiral bionic structure is significantly better than that of the corresponding original structure, among which BHHS-30° has the best performance with a specific energy absorption as high as 25.7 kJ/kg. Under the optimal configuration, further explore the influence laws of interlayer spiral angles (15°, 30°, 45°, 90°) and layup configurations (single/double spiral configurations) on structural performance. The research results show that, under the condition of equal relative density, by jointly regulating the helix angle and the layup configuration, the energy absorption performance and deformation mode can be simultaneously optimized, providing a new design concept for high-performance lightweight energy-absorbing structures.

Multi-cell structures are widely applied for impact resistance in engineering. The integrated hierarchical multi-cell structure exhibits excellent energy absorption performance under out-of-plane load, but it is difficult to provide soft cushioning subjected to in-plane impact. To address the common limitations of cellular materials in flexibility and their different energy absorption requirements under in-plane and out-of-plane loads, this work designed and fabricated a hierarchical square tube structure using the node-locked strategy. The in-plane and out-of-plane energy absorption performance was verified through numerical simulations and experiments. In addition, the effect of cell parameters and the type of basic elements on the energy absorption characteristics of hierarchical node-locked multi-cell structures (HNMS) was investigated. The gradient feature design of HNMS was achieved by changing the type of basic elements and different arrangement. A load prediction model for HNMS under in-plane load was established using the plastic hinge method and basic assumptions. It was indicated that the performance matching of HNMS can be realized within a relatively wide range through the parameter design and regulation of basic elements. The collaborative design for high energy absorption (SEA=11.62kJ/kg) under out-of-plane compression and in-plane buffering performance (SEA=1.34kJ/kg) has been successfully achieved via the node-locked strategy, demonstrating application potential in transportation vehicles such as high-speed trains.