To clarify the effect of polyurethane (PU) foam filler on the failure mechanisms and energy absorption of glass fiber-reinforced polymer (GFRP) tubes, this study involved the fabrication of regular hexagonal (RH) GFRP tubes filled with PU foams of various densities (ranging from 27 to 80 kg/m3) using compression molding. Quasi-static out-of-plane and in-plane compression tests were then performed on the tubes using a universal testing machine to analyze their load-bearing and energy absorption behaviors. The results show that RH-GFRP tubes exhibit interface debonding and local wall buckling under out-of-plane compression, leading to sudden instability and loss of load-bearing capacity. This is most significant when the compression stroke reaches 70%-80%. For in-plane compression, the process can be divided into four stages: elastoplastic climb, plastic failure, stress plateau and densification. Here, the higher the density of the filled PU foam, the more it facilitates a smoother transition of the plastic failure stage and accelerates the transition from plateau to densification. Notably, RH-GFRP tubes filled with 50 kg/m3 PU foam achieve the best average crushing force, total energy absorption and specific energy absorption in both the in-plane and out-of-plane loading directions. This work provides experimental references for the application of lightweight composite materials in energy-absorbing components.

Carbon fiber reinforced polymer (CFRP), as an advanced composite material, are widely used in engineering applications. However, research on the dynamic mechanical behavior of ultrathin CFRP laminates remains relatively limited. In this study, unidirectional ultrathin prepreg and hot-pressing molding processes were employed to fabricate ultrathin CFRP laminates with a single ply thickness of only 0.1 mm. The strain rate effects on specimens with five different ply orientations—0°, 90°, 0°/90°, 45°, and ±45°—were systematically investigated. Quasi-static compression experiments indicated that the 45° ply orientation enhanced plastic behavior but reduced material strength and modulus, whereas the 90° ply orientation contributed to increased modulus and strength while reducing plastic deformation. Dynamic impact tests revealed that the 90° ply orientation improved both dynamic modulus and strength while decreasing yield strain. Although the 45° ply orientation reduced dynamic yield strength, it significantly increased the sensitivity of dynamic modulus and yield strain to strain rate. Compared with conventional CFRP laminates with a 0°/90° ply layup (ply thickness is 0.295 mm, and dynamic strength and modulus are 900 MPa and 10.12 GPa, respectively), the ultrathin CFRP composites developed in this study exhibited a 66% increase in fiber content per unit thickness; under the 0°/90° ply configuration, dynamic strength and modulus were enhanced by 123% and 926%, respectively. Based on the experimental data, a constitutive model for the ultrathin CFRP composites was established, and corresponding constitutive parameters were provided, offering a basis for predicting the mechanical behavior of CFRPs under different ply orientations and strain rates.

The dynamic crushing behavior of CFRP tubular specimens with thin-ply laminates is investigated using both experimental studies and finite element modeling. In the proposed constitutive model, rate effects are incorporated using internal damage-rate variables rather than individual strain-rate tensor components. The model is calibrated using impact-test data for CFRP and implemented in Abaqus/Explicit via a VUMAT subroutine. Simulations of tubes with various layups reproduce key experimental observations, including primary failure modes, force-displacement responses, and energy absorption. Accurate prediction of fully developed longitudinal cracks in 0 degrees tubes required extreme mesh refinement, as confirmed by sector analysis of the tube. A detailed analysis of the spatial distribution of damage modes is provided. The proposed approach demonstrates the effectiveness of the rate-dependent modeling framework for predicting the dynamic response of thin-ply composites.

Reusable landing systems are critical for sustainable space exploration, yet existing energy-absorbing materials often suffer from single-impact limitations and lack of adaptive mechanical response. Here, we present a threedimensional auxetic metamaterial (3D-AMM) lattice based on strut integration and fabricated from hyperelastic thermoplastic polyurethane (TPU). This architected metamaterial combines geometric reconfiguration, persistent global auxetic effect, and repeatable energy absorption-enabling tailored cushioning for spacecraft soft landing. Through selective laser sintering and mechanical training via quasi-static cyclic loading, we stabilize their properties and test their dynamic impact performance using a drop-hammer system. Our findings reveal that individual 3D-AMM units exhibit a well-defined dual-stress plateau response, while lattices maintain auxetic behavior throughout compression. Remarkably, cyclic tests demonstrate specific energy storage retention rates of 87.7-94.7%, exceeding conventional honeycomb and auxetic structures. Under successive low-velocity impacts, the metamaterial shows reproducible energy absorption with minimal degradation, with orthogonal configurations further enhancing stress plateau stability across loading events. These results establish a framework for designing lightweight, reusable, and intelligently reconfigurable cushioning systems, offering a promising avenue for next-generation extraterrestrial landing technologies.

A persistent challenge in structural mechanics lies in engineering mechanical metamaterials that seamlessly integrate programmable, multi-stage functionalities. Here, we report a hierarchical design strategy for auxetic metamaterials (AMMs) that achieves highly deterministic, sequential deformation pathways by harnessing self-similar intracellular and intercellular architectures, thereby vastly expanding the mechanical and topological design spaces. The programmed collapse mechanics of these hierarchical configurations are systematically mapped through a synergistic framework of beam-based analytical modeling, parameter-calibrated numerical simulations, and experimental validation. Our multi-tier architecture unlocks programmable multi-step structural transitions and highly discretized multi-plateau stress responses while robustly preserving the anomalous negative Poisson's ratio effect. Consequently, these multi-tier AMMs yield a remarkable enhancement of 400.1% in quasi-static specific energy absorption and an unprecedented reduction of up to 70.6% in dynamic impact peak overloads. Finally, proof-of-concept prototypes showcasing multi-objective adaptive load-bearing and state-erasable, sequential mechanical cryptography are demonstrated, showcasing the vast potential of this versatile platform for autonomous structural intelligence and physical computing. These insights establish a robust paradigm for the high-level, multi-functional programming of advanced cellular materials.

This study presents a novel cross–multiscale modeling framework for carbon fiber reinforced silicon carbide (C/SiC) composites. A systematic series of representative volume elements (RVEs) was constructed, spanning from a microscopic RVE of a single carbon fiber in a silicon carbide matrix (RVE1), to mesoscopic RVEs of a fiber bundle (RVE2) and woven fiber bundles (RVE3), and further to macroscopic single–layer and multi–layer models based on RVE3. The anisotropic mechanical behavior of the C/SiC composites was investigated through a hierarchical analysis that integrates mesoscopic mechanics theory with both periodic and non–periodic finite element simulations. The tensile and compressive properties were experimentally validated via in–situ digital image correlation (DIC) testing, providing a direct link between simulation and experiment. This integrated approach elucidates the fundamental mechanical properties and failure mechanisms of C/SiC composites across scales. The key contributions are: (1) the development of a cross–multiscale modeling and simulation methodology; (2) the multi–scale morphological characterization and analysis; and (3) the revealed tensile/compressive properties and associated failure mechanisms. The findings provide important insights for cross–scale modeling, macroscopic model equivalence, and accurate material parameter calibration in fiber–reinforced composites for aerospace applications.

RBOE is a new type of DNAN-based high-energy melt-cast mixed explosive, whose safety under thermal stimulation is significantly affected by heating conditions and venting area of the warhead. Based on the thermal decomposition reaction characteristics and combustion characteristics of each component of RBOE explosive, the cook-off calculation models of RBOE warhead before and after ignition were established. In addition, closed and vented warheads were designed, as well as fast and slow cook-off test devices. The cook-off characteristics and thermal safety venting area of RBOE warhead were extensively studied. The results showed that the closed RBOE warhead underwent deflagration reaction under both slow and fast cook-off conditions. The calculation result of the shell wall temperature before slow cook-off ignition response of the warhead was 454.06 K, with an error of +1.75% compared to the test result of 462.15 K, and the temperature rise rate calculated was in good agreement with the test. The calculated ignition time of RBOE warhead under fast cook-off was 161 s, with an error of +8.8% compared to the test result of 148 s, which verified the accuracy of cook-off model of RBOE warhead before ignition. According to the cook-off calculation model of the warhead after ignition and cook-off test of the vented warhead, it was determined that the thermal safety venting area was 1124.61 mm2 for fast cook-off and 530.66 mm2 for slow cook-off, effectively preventing the reaction of warhead above combustion. Therefore, this study provides a scientific basis for the thermal safety design and evaluation of insensitive warheads.

At any time, the pace of space exploration has never stopped. In recent years, thanks to the rapid progress of space science and technology, satellites, probes, stations and other man-made equipment have been launched into space one after another, and manned space activities have become frequent. It is important to note that lightweight is still a major requirement for these equipment, as a lower launch weight allows more loads to be carried. Carbon fiber reinforced plastic (CFRP) is one of the lightweight, high strength materials commonly used in space. As a key component of spacecraft, it will inevitably experience high-speed collision events with space debris and waste recycling during operation in space, leading to more complex thermodynamic problems. In this study, a method to construct the CFRP constitutive under high strain rate impact was reported by identifying the strain rate state, generating the adiabatic temperature and modifying the (secant) stiffness matrix. In the low strain rate compression state, the initial nonlinearity caused by material defects was described by introducing the initial nonlinear modulus increasing factor. In the high strain rate impact state, the nonlinear high strain rate strengthening effect was described by introducing the dynamic strengthening factors of stress and strain based on the mechanical behavior under the reference strain rate. Based on the instantaneous temperature rise obtained from the impact adiabatic equation, the mechanical-thermal coupling effect was described by considering the influence of temperature on modulus and strength. Using incremental constitutive logic, a user-defined material subroutine was developed and feasibility verification was performed in conjunction with the experiment. This research work includes the establishment method of the constitutive of CFRP under high and low strain rate states, which provides a design reference for some extreme space collision events.

With the rapid development of related aerospace endeavors, such as near-Earth space development and deep space exploration, many ground technologies have begun to be transferred to space. This transition is not without its challenges, particularly in managing collisions during spacecraft operations, such as landing and docking. The critical need for advanced buffering, energy absorption and protective materials has sparked interest in mechanical metamaterials, which are characterized by their capability to handle multiple loading conditions and exhibit various deformation modes. Traditional single-plateau energy absorbers are proving inadequate for the diverse and unpredictable loads encountered in the harsh space environment, underscoring the necessity for mechanical metamaterials with enhanced load-bearing and deformation adaptability. This study advances the field by integrating intra-cellular multi-level gradients and inter-cellular layered gradients within a classical re-entrant configuration to develop a novel multi-plateau auxetic metamaterial. Empirical insights into the compressive mechanical behavior of both single-cell and multi-cell metamaterial configurations were obtained through quasi-static compression testing of 3D-printed samples. The results illustrate that the designed intra-cellular multi-level gradient auxetic metamaterial is not able to generate multiple load plateaus due to the unexpected fracture caused by the brittle nylon material, but multiple load peaks and the exceptional auxetic effect is realized. However, the inter-cellular layered gradient metamaterial exhibits multiple load plateaus under a complex interplay between inter- and intra-cellular deformation modes. The development of programmable multi-plateau auxetic metamaterials represents a significant step forward in addressing the multifaceted energy absorption and protection requirements of space equipment. By offering superior performance in managing multiple energy absorption scenarios and enhancing efficiency, these materials open new avenues for the development of multi-level crashworthiness and multi-functional impact resistance solutions tailored to the rigorous demands of space exploration.

This study systematically investigates the high-velocity impact response and energy absorption characteristics of carbon fiber-reinforced plastic (CFRP)—aluminum foam (AlF) hybrid composite structures, aiming to address the growing demand for lightweight yet high-performance energy-absorbing materials in aerospace and protective engineering applications. Particular emphasis is placed on elucidating the influence of key geometric and material parameters, including the aspect ratio of the columns and the relative density of the AlF core. Experimental characterization was first performed using a split Hopkinson pressure bar (SHPB) apparatus to evaluate the dynamic compressive behavior of AlF specimens with four different relative densities (i.e., 0.163, 0.245, 0.374, and 0.437). A finite element (FE) model was then developed and rigorously validated against the experimental data, demonstrating excellent agreement in terms of deformation modes and force–displacement responses. Extensive parametric studies based on the validated FE framework revealed that the proposed CFRP-AlF composite structure achieves a balance between specific energy absorption (SEA) and peak crushing force, showing a significant improvement over conventional CFRP or AlF. The confinement effect of CFRP enables AlF to undergo progressive collapse along designated orientations, thereby endowing the CFRP-AlF composite structure with superior impact resistance. These findings provide critical insight for the design of next-generation lightweight protective structures subjected to extreme dynamic loading conditions.

When using auxetic honeycomb structures to create repeatable energy-absorbing components, a key challenge is selecting the appropriate unit configuration for effective functional integration. In this work, four typical honeycomb structures were prepared, and the mechanical behaviors, shape recovery effects, and energy absorption properties of three types of auxetic honeycomb structures re-entrant honeycomb (RH), arrow honeycomb (AH), and star honeycomb (SH) were compared with those of hexagonal honeycomb (HH) through quasi-static loading-unloading tests. The findings indicate that the 3D printed polyurethane (TPU) honeycomb structures demonstrate robust shape recovery, stable energy absorption, notable stress softening characteristics. The recovery behaviors can be characterized by three distinct phases, namely hyperelastic, transitional, and viscoelastic. The unit configuration significantly influences the shape recovery capability, with apparent elastic modulus and stability of the energy absorption efficiency determining the overall shape recovery capability. The loading method also affects the energy absorption and dissipation patterns in different honeycomb structures. In terms of specific energy absorption (SEA), AH has the highest rating, with RH and SH at 86 % and 50 % of the SEA of AH respectively. The number of reusable cycles is primarily dictated by the specific configuration of the unit type. In scenarios involving reusability, the energy absorption capacity of the TPU honeycomb can only reach 70 % of its original energy absorption capacity. This study may inform the application of auxetic materials in reusable energy absorbers.

Hierarchical architectures, ubiquitously observed in natural systems, have been widely adopted in advanced structural engineering applications. Drawing inspiration from the distinctive geometry of spider webs, we engineered a novel hierarchical sandwich corrugated tube (HSC). The design incorporates sinusoidal-profile corrugated tubes as core elements within hexagonal tubular matrices. The finite element (FE) models were established for aluminum alloy materials, with validation conducted through quasi-static axial compression experiments. The experimental-numerical correlation demonstrated excellent agreement, with discrepancies in specific energy absorption (SEA) and mean crushing force (MCF) metrics below 10 %, thereby verifying the model's predictive capability. Subsequent parametric investigations revealed that the second-generation HSCT configuration with convex gradient terminal features exhibited superior energy absorption (EA) characteristics. Comprehensive analysis of oblique compression behavior identified optimal EA performance at sinusoidal amplitude A= 3 mm and periodicity N = 2. Theoretical predictive models derived from simplified super-folding element principles achieved remarkable accuracy in MCF estimation, showing marginal deviations of 3.73 % (axial) and 2.18 % (oblique) from FE predictions. Through discrete multi-factor weighted optimization, the refined HSCT design demonstrated substantial performance enhancements: 11.73 % improvement in SEA and 31.45 % increase in MCF compared to baseline configurations. These findings establish a systematic biomimetic design paradigm for developing high-performance sandwich-type energy-absorbing structures.

This paper presents a low-velocity impact study on two types of structures, namely (1) planar multi-cellular auxetic structures (AUS) composed of multiple re-entrant cell structures made of unidirectional carbon fiber reinforced composite (CFRP) laminate, and (2) sandwich CFRP-AUS structures (Al/CFRP-AUS), whereby the CFRP-AUS was sandwiched by aluminium plates. The experimental results reveal the mechanical behaviors of CFRP-AUS under quasi-static compression and drop hammer impact loading, and the mechanical behavior of Al/CFRP-AUS under drop impact loading. The energy absorption of the CFRP-AUS associated with quasi-static compression is greater than that associated with drop hammer impact, which is consistent with the observed differences in failure modes. The impact energy absorption capacity of the Al/CFRP-AUS is slightly higher than that of the CFRP-AUS due to the interaction between the plates and the AUS. The corresponding finite element analysis was performed and the drop hammer impact of the multi-layered CFRP-AUS was predicted. In conclusion, the CFRP-AUS structures have good energy absorption capacity during impact loading, and the known complex mechanical behaviors of deformation, failure and contact can provide guidance for the design of energy absorption box and bumper in engineering application.

Metamaterials are a type of artificial material with microstructural features that are characterized by physical properties not found in nature. Metamaterials originated in the field of electromagnetics and have now blossomed in fields such as acoustics, mechanics and optics. Negative Poisson’s ratio (NPR) metamaterials are common mechanical metamaterials, also called auxetic metamaterials, that have a long development history and are widely known for their tension-expansion and compression-contraction deformation behavior. In this chapter, we reported the development history of mechanical metamaterials, revealed the NPR effect and deformation mechanism, and discussed the applications in three aspects. Most importantly, three kinds of new auxetic metamaterials were introduced, i.e., lightweight and high-strength auxetic metamaterials, multi-step deformation auxetic metamaterials and artificial intelligence auxetic metamaterials. For every topic, the current and future development potentials are given, especially the fabrication process of composite for lightweight and high-strength auxetic metamaterials. This content will help people understand the concept of auxetic metamaterials and continue to conduct new research based on it.

'A single thread cannot be spun into a cord, and a single tree cannot create a forest' - an ancient Chinese proverb highlighting the necessity of collective integration. This proverb captures the essence of fused deposition modeling (FDM) 3D printing, where multiple filaments merge into a solid structure. Diverging from this approach, we introduce lace 3D printing - an FDM-based approach that embodies the concept of 'a single thread forming a cord, a single tree becoming a forest'. Using a continuous zig-zag filament path with tunable geometry, this approach enables direct and efficient fabrication of millimeter-scale deployable metamaterials that transform from a compact to a mechanically stable cellular state under uniaxial tension. Plastic hinge formation under uniaxial stretching drives structural deployment. We investigate how printing parameters and geometries affect fabrication quality, deployment behaviours, and mechanical responses, and develop a theoretical model to predict nonlinear deformation. Introducing spatial gradients enables programmable morphing, suggesting applications in aerospace engineering and biomedical devices. Finally, the mechanical performance of the deployed metamaterials is evaluated under various loading conditions, including compression, cyclic loading, bending, and impact, highlighting their potential as cellular materials for load-bearing and energy-absorbing applications.

This study proposes a novel graded-thickness, thin-walled aluminum alloy (Al) circular tube energy-absorbing structure and conducts comprehensive parametric modeling and multi-objective optimization research. The 7050Al tube was selected for analysis of its energy absorption characteristics via numerical simulations and drop-weight impact tests. Through simulation calculations and drop hammer impact verification tests, the number and location of concertina lobes after crushing, as well as the force variation law of the structure during the crushing process, were analyzed. The results indicate that generating annular folds at the impact end can significantly enhance impact absorption and suppress structural instability. Drop-weight test results further validate the superior crashworthiness of the proposed 7050Al tube under dynamic loading conditions and confirm the accuracy of the numerical crushing model. To enable rapid and precise structural modifications, a Python-based parametric modeling framework has been developed. A fully automated parametric optimization workflow has been established within Isight to facilitate the efficient, multi-objective optimization of the structure's design. This methodology provides a robust tool for designing customizable energy-absorbing structures with tailored crashworthiness performance.

The load-bearing and deformation behaviors of structures and materials play a decisive role in their applicability. While re-entrant auxetic structures—a classic type of mechanical metamaterials—exhibit impressive mechanical properties, their functionality has traditionally been constrained by a single stress plateau under compression, limiting their multifunctional applications. In this study, we present an auxetic metamaterial with a double re-entrant configuration (DREC), engineered to achieve dual stress plateaus while preserving auxeticity, setting it apart through its simplicity and self-similarity. This metamaterial shows distinct two-phase behavior under quasi-static compressive loading, delineated as phase I and phase II. By leveraging stacking and symmetry programming of the DREC, we construct multi-cellular variants that possess additional phases, unlocking multi-step deformation characteristics driven by the formation and transformation of new configurations and showing a significant improvement in specific energy absorption over the conventional re-entrant configuration. Theoretical models, based on Euler beam and plastic hinge theories, have been developed that effectively capture the mechanical behavior of the DREC metamaterials. This work opens new avenues for engineering applications that demand adaptable and high-performance mechanical responses.

Flexible electronic metamaterials, known for their lightweight, flexibility, and stretchability, are crucial for wearable devices, biomedical monitoring, and environmental sensing. Current inverse design methods for metamaterials rely on empirical knowledge and trial-and-error, resulting in inefficiency. While Random Forest (RF) algorithms show promise in inverse design, they struggle to accurately predict the nonlinear mechanical behavior of flexible metamaterials and exhibit limited robustness. This study proposes an inverse design framework that combines the Random Sample Consensus (RANSAC) algorithm with an improved RF algorithm. The RANSAC algorithm optimizes feature selection by eliminating outliers and noisy data, thereby improving data quality. The material and structure models are inverted to derive mathematical expressions in the RF model, and the information gain approach is used to enhance the predictive ability, robustness, and interpretability. Experimental results show that this framework effectively addresses nonlinear behavior prediction and geometric parameter optimization in metamaterials. It demonstrates excellent predictive performance in inverse design for convex, concave and snap-through curves, with multiple parameters achieving R2 values close to or equal to 1. These findings enable the development of high-performance materials tailored to specific scenarios, thus advancing the application of flexible electronic metamaterials in stretchable sensors, smart materials, and biomedicine.