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.

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.

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.

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.

Conventional composite crushing tubes exhibit limitations in energy absorption, including underutilization of axial fiber properties, high initial peak loads, and uncontrollable failure modes. In response, a novel hybrid expansion energy-absorbing tube, combining an additively manufactured continuous fiber-reinforced polymer composites (AM-CFRPCs) core tube with metal liners, is proposed and validated. The core energy absorption mechanism involves converting compression expansion loads into axial tensile loads of continuous fibers to achieve a high stress limit, while a stable, high-stress plateau is maintained through progressive fiber fracture synergistically controlled by the liners. Initially, the structural responses and energy absorption modes of bare AM-CFRPCs and the hybrid tubes were comparatively analyzed through experimental and finite element method (FEM). Subsequently, the influence of key design parameters, such as triggering mechanisms, component thickness, and material layout, on the mechanical response, energy absorption performance, and contribution of each component was thoroughly investigated. Finally, application recommendations for this novel structure in the field of rail vehicles were presented. Additionally, a sequential multiscale computational method was developed for efficient, high-fidelity prediction of AM-CFRPCs mechanical properties. Results confirm that progressive fiber fracture is the dominant energy absorption mode, and the hybrid tube achieves stable, efficient performance via synergistic reinforcement from the liners. This research provides a new paradigm for the application of AM-CFRPCs in energy absorption.

Noise and impact hazards are ubiquitous in engineering applications, creating an urgent demand for multifunctional materials capable of absorbing both acoustic and stress wave energy. However, the design of such materials presents challenges, including complex microstructure fabrication, multi-physics field coupling effects, and scalability issues. Recent advancements in decoupled design, additive manufacturing, and optimization technology have led to the development of multifunctional metamaterials. A layered multifunctional bio-inspired lattice metamaterial (MBLM) is presented in this work, drawing on inspiration from the body armor of glyptodonts and the structural features of turtle shells. The multi-layered design integrates a Helmholtz resonator with an internal micro-perforated curved plate to achieve broadband acoustic absorption in the two outer dense layers. The central layer features a hybrid BCC-Octet lattice structure, which acts as an efficient energy absorber. Experimental, numerical, and theoretical approaches were employed to systematically assess the sound absorption and impact energy performance of MBLM. The results demonstrate that MBLM achieves a stable energy absorption deformation pattern and quasi-perfect broadband sound absorption, with an average absorption coefficient exceeding 0.9 within the target frequency range of 750 Hz to 1610 Hz. Overall, this work offers an innovative approach to the design of multifunctional metamaterials.

The combination of continuous fiber-reinforced polymer composites (CFRPCs) and additive manufacturing (AM) offers a solution for the integrated manufacturing of high-performance, complex structures, but due to current process limitations, various defects exist within the parts. Most research has focused on internal pores defects and mechanical properties but lacks in-depth studies on the mechanisms of other defect forms and comprehensive quality evaluation systems. To address these gaps, this paper applied comprehensive parameter analysis, visualization techniques, rheological experiments, and mechanical experiments to systematically explore the effects of defects on the printing quality of AM-CFRPCs, focusing on shape fidelity, surface accuracy, structural integrity, and mechanical performance. Targeted improvement measures were proposed for various defects, effectively eliminating shape-related issues such as fiber slippage, fillet, first layer accumulation, and warpage, leading to a high-quality deposited surface with low roughness and waviness, as well as an internal structure with low porosity. Furthermore, a comprehensive molding quality evaluation system was established, offering a reliable framework for part quality assessment. Additionally, the variation patterns of the key-like profile cross-sections of the single path under different layer heights were summarized, and precise calculation models for path width and overlap ratio were presented. Consequently, this paper delivers detailed guidelines for enhancing molding quality to facilitate the production and evaluation of high-quality AM-CFRPCs.

Conventional anti-climbers in rail vehicles often suffer from unstable deformation and low energy absorption due to component interference. To overcome these issues, this study proposes a novel design integrating an origami-patterned outer wall with a metallic honeycomb core. The origami geometry enables controlled folding, enhancing stability and promoting coordinated energy absorption with the core. Sled impact tests under offset collision conditions were conducted, and finite element (FE) models were developed and validated. Parametric studies examined the effects of pre-folding angle and corrugation period number on performance. Results showed that a folding angle of 7.5 degrees yielded the highest energy absorption, while circumferential corrugations further improved load capacity. With the optimal configuration, initial peak crushing force (IPCF) was reduced by 18.9% and specific energy absorption (SEA) increased by 43.8% compared with a conventional straight-walled anti-climber. However, unsuitable geometric configurations led to irregular folding and performance degradation. Overall, this work demonstrates that origami-inspired geometry can effectively guide deformation, mitigate interference, and enhance energy dissipation, offering a promising strategy for railway crashworthiness.

In the pursuit of engineering solutions capable of managing persistent hazards such as noise, vibration, and structural impacts, materials that combine sound absorption, vibration damping, and deformation resistance are crucial. Lightweight lattice metamaterials have shown potentiality for these applications. These materials offer design flexibility but typically struggle to simultaneously excel in sound absorption, vibration control, and structural load-bearing. This work introduces a hollow truncated octahedron strut-plate (HTOSP) composite lattice metamaterial, employing additive manufacturing for prototype fabrication. Comprehensive validations were conducted through numerical simulations as well as impedance tube testing, with results aligning well. Adjustments in strut diameters and plate pore sizes enable the HTOSP to achieve impressive mid-high-frequency sound absorption coefficient and half-absorption bandwidth. The structural behaviour of HTOSP under load was explored through numerical simulations and quasi-static compression testing, revealing a high, stable plateau stress and specific energy absorption that peaks and then declines with increasing hollow-strut inner diameters. Furthermore, the HTOSP effectively dampens high-frequency vibrations, achieving -62 dB elastic wave attenuation at 3173 Hz via local resonance. This multifunctional HTOSP lattice metamaterial stands out for its superior performance in sound absorption, vibration control, and mechanical strength, presenting an intriguing paradigm for the design of multifunctional acoustic-mechanical-vibration structures.

Honeycomb structures are widely used for energy-absorption subjected to in-plane and out-of-plane crushing loads. In our previous work, a self-locking honeycomb was proposed for energy absorption under out-of-plane compression, achieving an effective balance between fabrication cost and energy absorption performance in high energy absorption scenarios. However, the honeycomb energy-absorbing performance is obviously insufficient due to the degradation of self-locking stiffness for in-plane compression. To further improve the energy-absorbing performance of the honeycomb structure under in-plane loading, this paper adopts a foam-filling strategy to achieve the performance enhancement of the self-locking honeycomb structure. Firstly, the energy absorption characteristics of the self-locking structure during in-plane compression were investigated by numerical simulation. Secondly, relevant experiments were carried out to verify the accuracy of the simulation results. In addition, a theoretical model is proposed to quickly predict the structural energy absorption for in-plane compression. Finally, the effects of different compression velocities and boundary conditions on the structural energy absorption were analyzed. It is indicated that the foam-filled self-locking honeycomb structure can effectively enhance the energy-absorbing performance under out-of-plane loading, and provide effective stiffness constraints for the deformation of the bending plate inside the locking nodes to maximize the energy-absorbing efficiency. In particular, the energy-absorbing performance of the foam-filled self-locking honeycomb structure of the basic cell bending plate is closely related to the loading velocity and the boundary constraints, and the energy-absorbing efficiency can be further enhanced by setting the boundary constraints in the energy-absorbing structure design.

Multi-material additive manufacturing technology has revolutionized the fabrication of complex composite structures with unprecedented design freedom. This capability overcomes key limitations of conventional manufacturing including inefficiencies of fabricating intricate geometries. Nacre, the inner layer of mollusk shells, is composed of approximately 95 % aragonite platelets and 5 % organic matrix. The aragonite platelets are arranged in a layered configuration to provide structural rigidity, while the organic matrix fills the interplatelet spaces, imparting toughness and energy dissipation capabilities. Drawing on inspiration from natural nacreous structures and traditional masonry techniques, by combining two polymeric materials with complementary mechanical properties including one soft and one hard material. This work proposes four kinds of bioinspired multi-material brick-and-mortar composite structure (MBCS)-English bond (EB), English garden wall bond (EGWB), Flemish bond (FB), and 90 degrees rotated brick bond (90 degrees RBB)-and systematically evaluates their mechanical performance under bending and penetration loads. Through integrated experimental and simulation analysis, it is revealed that the EB configuration exhibits superior load-bearing capacity, outperforming EGWB, FB, and 90 degrees RBB by 34.5 %, 27.7 %, and 49.5 %, respectively. Three-point bending experiments confirm that lattice reinforcement substantially improves structural load-bearing performance, with the ultimate load-bearing capacity of the optimal reinforced structure being 1.59 times that of the original EB configuration. Moreover, a stress-driven graded lattice design strategy is developed to achieve enhanced structural performance. The stressdriven graded lattice design increased load-bearing capacity by 96.7 % compared to the EB structure. Finally, to fully characterize the structural penetration behavior, penetration simulations were conducted on MBCS. Results demonstrate that the EGWB brick-and-mortar structure exhibits superior penetration resistance performance under low-velocity penetration conditions. These findings collectively reveal the significant potential of bioinspired MBCS in resisting both bending and penetration loads. This work provides critical guidance and engineering insights for the advanced design of future multi-material composite structures.

A novel aluminum self-locked nested chiral structure (SLKH) has been introduced to significantly enhance the energy absorption capacity of honeycomb structures. This innovative design leverages the geometrical advantages of chirality, offering a cost-effective and facile manufacturing process. A comprehensive study on the mechanical properties and energy absorption characteristics was conducted by utilizing the LS-DYNA. The multiparameter design investigation revealed that the proportional coefficient, in conjunction with the relative density, significantly influences the mechanical performance of the SLKH. Comparative analysis with integrated structures underscored the superior energy absorption and buffering capabilities of the SLKH. Furthermore, the study delved into the dynamic impact performance under quasi-static conditions, highlighting the impact of Poisson's ratio on self-locked structures. The findings provide valuable insights for the design and practical application of advanced cellular structures.

In recent decades, the search for lightweight and high-performance energy-absorbing structures and materials has made porous thin-walled structures a prominent research area due to their light weight and high energy-absorbing properties. However, due to the more intricate nonlinear interaction between the energy absorption properties and the multicellular structure topologies, it is still challenging to identify the optimal configuration effectively. Therefore, a deep-learning-based technique for predicting the energy absorption properties of thin-walled structures is presented using rib-reinforcement multi-cell tubes (RMTs) as an example. The energy absorption parameters of the thin-walled structure with varied reinforced rib configurations were derived through finite element analysis. Based on the acquired energy absorption properties, the neural network was trained and verified. The rib configuration with the optimum energy absorption performance was identified using a trained neural network. Finally, using the non-dominated sorting genetic algorithm II (NSGA-II), a thickness gradient based on multi-objective optimization of the discovered optimal configuration was carried out. The results indicate that the artificial neural network (ANN) is able to predict the energy absorption performance of RMTs with a high degree of precision, and the optimized structure effectively suppresses the peak crushing force (PCF) with a significant improvement in both the specific energy absorption (SEA) and the crushing force efficiency (CFE). In summary, the prediction capabilities of MLP in addressing difficult engineering issues are not only proven in this study, but an effective prediction tool is also offered for finding the optimal design of thin-walled structures in the future.

Wheel wear is inevitable during rail vehicle operation due to wheel-rail contact. Increased wear causes the wheel profile to deviate from the original standard profile. Accurate prediction of wheel profile evolution is crucial for monitoring wheel health and ensuring vehicle performance. In this paper, a profile evolution prediction model based on particle swarm optimization Levenberg-Marquardt back propagation (PSO-LMBP) neural network is proposed. The prediction model realizes the control of wheel profile evolution using the operation mileage and the wear position as inputs, and the wear amount as output. It is a new attempt to apply neural network model within the field of wheel profile evolution prediction. To improve accuracy, wear data are intervalized and smoothed using locally weighted regression; the LMBP neural network’s key parameters are optimized using the PSO algorithm. Comparative results show that the PSO-LMBP model achieves higher accuracy than traditional LMBP and BP models. Through applying the model to the prediction of wheel wear for vehicles with longer operation mileage and new vehicles, the long-term prediction performance and generalization performance of the model are verified. Finally, the wheel-rail contact geometry and dynamics performance of the vehicle were evaluated by establishing a wheel-rail contact model and a vehicle dynamics model using measured and predicted profiles. The simulation results show that the prediction model has high accuracy.

Gradient wall thickness design is a typical method to enhance the energy absorption efficiency of thin-walled structures. Compared with conventional uniform-thickness thin-walled structures, gradient wall structures are mostly fabricated using electrical discharge wire cutting, which significantly increases their production cost and limits their practical engineering applications. This paper proposes a novel approach to fabricate gradient energy-absorbing structures using adhesive bonded metal plate, which enables rapid fabrication while maintaining energy absorption performance. Mechanical experiments were conducted on adhesive joints to calibrate the constitutive parameters of the adhesive layer and determine the thickness of the adhesive layer and surface treatment conditions. Numerical simulations of the out-of-plane compression and crushing behavior of four adhesive-bonded rectangular tube configurations were carried out to analyze their energy absorption characteristics and structural deformation. Based on the experimentally validated model, the effects of adhesive width ratio and wall thickness of metal plate on the energy absorption for these bonded structures were investigated. Finally, a comparative analysis of the energy absorption performance between adhesive-bonded energyabsorbing structures and traditional gradient-thickness structures was conducted to verify the feasibility and effectiveness of the adhesive-bonded structures. The results indicate that increasing the adhesive width and thickness of metal plate within a certain range can significantly improve energy absorption performance. However, further increases lead to significant degradation in specific energy absorption, along with an elevated risk of adhesive layer failure at the structural ends. In addition, compared to traditional gradient thin-walled structures, the bonded structure shows improvements of 22.50 %, 19.97 %, and 6.37 % in EA, MCF, and SEA, respectively, demonstrating excellent energy absorption performance and great potential for application.

Multicellular energy-absorbing structures are being designed with increasing sophistication to optimize design space utilization and load-bearing efficiency. However, their fabrication by wire electrical discharge machining or additive manufacturing is costly and limits applications. This study introduces an adhesive bonding strategy to assemble folded metal sheets into adhesive multicellular tubes (AMTs). Their axial impact resistance was evaluated through experiments and simulations, followed by analysis of bonding strategy and key geometric parameters. The results identified an optimal adhesive configuration. Parametric analysis further demonstrated that increasing the adhesive width and plate thickness within a certain range significantly improved energy absorption performance. However, excessive increases beyond this range resulted in performance degradation and a heightened risk of adhesive layer failure. Notably, under all parameter variations, the AMTs did not exhibit global collapse modes or system-level adhesive failure, confirming the reliability and applicability of the proposed bonding approach. Compared with conventional multicellular structures, the AMTs achieved a maximum improvement of 25 % in energy absorption. The proposed structure demonstrated excellent synergy between impact resistance and fabrication efficiency, highlighting its potential as a viable alternative to traditional thinwalled multicellular energy absorbers.

Traditional materials or advanced artificially engineered metamaterials are incapable of effectively addressing the simultaneous challenges of impact energy hazards and low-frequency noise. There is an urgent need for multifunctional materials that can address this multi-physics field coupling problem. Herein, a hierarchical multifunctional chiral metamaterial (HMCM) is proposed for damage-resistance and low-frequency broadband sound-absorption capabilities fabricated by means of laser powder bed fusion technology. Cavity resonators with internally extended tubes with hierarchical chiral configuration were selected as primary units. The damage-resistance performance of the HMCM was investigated systematically through experimental, numerical, and theoretical methods. Crashworthiness design and optimization on the multifunctional chiral metamaterial were implemented to explore the effect of geometrical parameters including distance ratio and wall thickness distribution on crushing resistance. It was determined that specific configurations in these parameters significantly enhance mechanism for dissipating energy of the HMCM. Furthermore, the designed metamaterial has been experimentally, numerically, and theoretically proven to possess quasi-perfect broadband sound absorption in the target range of 425 Hz to 553 Hz with an average sound absorption coefficient exceeding 0.9. Overall, this work not only offers a promising solution for designing multifunctional metamaterials but also highlights the potential of additive manufacturing techniques in the development of such sophisticated materials.

In order to improve the energy absorption efficiency of the conventional thin-walled square tube,a bionic hierarchical thin-walled square tube(BHST)was proposed by the microscopic trabecular structure of beetle wing sheaths.Based on the super folding element theory,a theoretical model of the mean crushing force of the bionic hierarchical thin-walled square tube was established.The axial energy absorption characteristics of the bionic hierarchical thin-walled square tube and the conventional multi-cell thin-walled square tube were analyzed by the nonlinear finite element method,and the influence of structural parameters on the crashworthiness of BHST4-2 structure was studied.The results show that the theoretical predictions match with the numerical simulation results,and the relative errors are all within 7％.The bionic hierarchical thin-walled square tube exhibits excellent crashworthiness.The wall thickness has a more significant effect on the crashworthiness of BHST4-2 structure than the second-order square tube edge length.The radial basis function(RBF)model and the genetic algorithm were used for the multi-objective optimization of the BHST4-2 structure,and optimal parameters of the structure were obtained.The results of the study provide new ideas for the design of thin-walled square tubes with excellent energy absorption properties.

The expansion tube plays a crucial role in the field of train collision safety protection. In this study, we combine the expansion characteristics of negative Poisson's ratio (NPR) with the deformation mechanism of the expansion tube to propose a novel design for material reconstruction: embedding NPR structures into the conventional expansion tube wall. The typical specimens of NPR tube were fabricated using additive manufacturing technology, and the experiments and numerical simulations were conducted to investigate its expansion behavior by two expansion cones with different sizes. By employing a validated numerical simulation model, the effects of cone size, expansion angle, wall thickness, and material gradient design on the mechanical response of NPR tubes were investigated. It is demonstrated that the expansion behavior and energy absorption mechanism of NPR tubes differ from that of conventional circular tube. The material of wall generates radial expansion rather than compression due to a special auxeticity characteristics subjected to circumferential tensile load. The increased normal pressure on the inner surface from the expansion cone results in the resistance reinforcement of NPR tube. The proposed expansion tube achieves higher load capacity while utilizing less material, which provides a promising approach for designing lightweight and efficient expandable tubes.